Porous power and ground planes for reduced pcb delamination and better reliability

The subject of the invention is a power supply / ground core for a printed circuit board used, in particular, in the electronics industry.

Due to the necessity to use computers, the designers focused on increasing their reliability. Modern systems cannot tolerate the extended downtime needed to replace broken system components. If every component of a system is designed to last longer and with greater reliability, then any computer made entirely of these components will last longer and be more reliable.

This focus on component reliability has been applied to printed circuit boards (PCBs). In a computer system, most of the elements are adapted to place semiconductor elements or integrated circuits on printed circuit boards. These boards are called printed because they contain circuits or copper traces made using techniques that are essentially similar to the printing process on newsprint. The track circuits connect semiconductor elements or integrated circuits. A printed circuit board can be as simple as an insulator that has traces printed on both sides of the board and one or more components mounted on one or both sides of the board. Printed boards are usually more complex, however they are usually made of conductive metal power and ground planes and several signal planes containing circuit paths sandwiched between the insulator layers, with metal traces and contact areas on the top and bottom surfaces of the multilayer board. The tracks of the top and bottom surfaces are connected to each other and to the inner circuit layers through metallized holes (PTH).

Circuit boards made in this way have become the standard in electronics. Advances in manufacturing methods have made PCBs relatively cheap, while their simplicity makes them reliable. However, there are problems with printed circuit boards. One problem is caused by the difference in the thermal expansion coefficients (CTE) of the various materials used. A proposed solution to this problem (disclosed in EP0228017A2) is to use a plate having conductive layers made of a core made of metal wire mesh so that the thermal expansion coefficient of the plate is more closely matched with the thermal expansion coefficients of the elements mounted thereon.

However, there are other problems with printed circuit boards. One of the causes of these problems is water. The insulating layers in printed circuit boards tend to absorb water and naturally absorb relatively large amounts of water. Even if the PCB was dry during the component assembly process, it may soon absorb water from humid air or during other steps in the process. Hence, printed circuit boards contain water that freely penetrates between the insulating layers. Unfortunately, the power and ground planes, which are usually made of copper, are impermeable to water.

This lack of permeability affects the plates and can cause damage. Water collects at points between the power / ground plane and the insulating layer that covers the plane. Integrated circuits, structure support housings, or other components are soldered to the printed circuit board, typically by wave or infrared heating. A rise in temperature can cause water collected at the contact points between the power / ground planes and insulating layers to turn to steam. Turning into steam, the water increases considerably in volume and this expanded mixture of water and steam can cause the insulator to delaminate. In fact, blisters may appear on the insulator surface leading to insulator cracks, path breaks, casing cracks, hole metallization cracks and other similar detrimental effects.

To get beyond the closed surface of the insulator, the water has to diffuse through the insulator into the space with a lower concentration of water. This space with a lower concentration of water is usually on the outside of the circuit board, including the top and bottom surfaces where the layers of the sandwich structure are in contact with the air. Assuming that the air as a rule has a lower water concentration, diffusion of water through the dielectric into the atmosphere will be lengthy. However, water can cause bladder damage until it is removed from the circuit board.

Another water-induced mechanism that leads to damage in printed circuit boards is cathodic-anodic fiber growth (CAF), which occurs when circuit board short circuits increase along the glass fibers. Short circuits are created when water leaches metal ions from nearby paths to the interface between the glass fiber and the dielectric. The copper ions deposit

When biasing is applied, the deposition tends to form conductive dendrites. When this material is in solution, it is generally ionized so that it will travel towards the counter-charged metal element. Cathodes are positively charged areas while anodes are negatively charged areas. Thus, metal dendrites usually grow between two oppositely charged local cathode-anode regions. These conductive metal dendrites then cause electrical short circuits.

Water damage mechanisms have been exacerbated by the use of printed circuit boards for structure carriers. Structure carriers are devices on which microcircuits are placed before attaching them to a printed circuit board. In the past, these structure carriers were made exclusively of ceramic materials. Due to the use of ceramic materials for structure supports, the JEDEC commission, organized to publish electronic production standards, developed testing standards for structure supports which in principle assume that the base materials do not absorb water at all. Now that printed circuit boards have started to be used as structure carriers, water infiltration and the problems associated with it are becoming more and more common as there is simply more and more water in these organic materials. Structure supports which are made of organic layered materials are called layered structure supports (LCC).

The object of the invention is to provide a power supply / ground core for a printed circuit board, in which the damage caused by cathodic-anodic growth of dendrites and delamination of insulators in organic support structures, printed circuit boards and carriers are reduced.

A power / ground core for a printed circuit board comprising interconnected at least one layer of a fibrous laminate and at least one layer of a conductive metal sheet according to the invention is characterized in that the fiber laminate is an absorbent for at least one solvent, and at least one layer of the conductive metal sheet is porous to at least one solvent to reduce delamination phenomena and cathodic-anodic fiber growth.

Preferably, the conductive metal sheet comprises a metal sheet having a plurality of drilled holes to provide porosities.

Preferably, at least one layer of the conductive metal sheet is a two-layer conductive metal sheet, and at least one layer of a fibrous laminate is sandwiched between the two layers of the conductive metal sheet.

Preferably, at least one layer of a fibrous laminate comprises two layers of a fibrous laminate, and at least one layer of a conductive metal sheet is sandwiched between the two layers of a fibrous laminate.

Preferably, the conductive metal sheet comprises sintered metal.

At least one layer of the fibrous laminate is non-conductive.

At least one layer of the fibrous laminate is conductive.

Water is at least one solvent.

Preferably, the conductive material comprises metal having a plurality of openings, and the openings are spaced and sized to provide porosity.

Preferably, the holes are spaced apart by no more than 0.05 inches (0.0013 m) from each other.

Preferably, the holes are at least 0.001 inch in diameter but less than 0.010 inch (0.00025 m) in diameter.

Preferably, each opening is about 0.002 inches (0.00005 m) in diameter.

Preferably, the conductive material comprises sintered metal.

Preferably, the conductive material comprises a fibrous material woven into a structure or formed into a free paper structure.

Preferably, the fibrous material is selected from the group consisting essentially of metal coated carbon fibers, metal coated polyester, metal coated liquid crystal polymers, metal coated polyethylene, metal coated glass fibers and metal conductors.

Preferably, the at least one layer of the fibrous laminate is selected from the group consisting essentially of epoxy, bismaleimide triazine epoxy, cyanate ester, polyimide, polytetrafluoroethylene (PTFE), polytetrafluoroethylene and a fluoropolymer.

PL 196 239B1

Further, according to the invention, a printed circuit board (PCB) can be made, the printed circuit board comprising at least one signal core, each signal core comprising at least one signal layer and at least one fiber laminate layer and a power / ground core according to the first aspect.

The method of producing a printed circuit board (PCB) comprises the steps of: providing at least one power / ground plane including at least one layer of porous conductive material, creating multiple openings in at least one power / ground plane, creating a composite from at least one power / ground plane and at least one signal layer, creating in the composite many holes and creating many metallized holes in the composite, the porous conductive material being sufficiently porous with respect to the solvents to reduce cathodic-anodic fiber growth phenomena.

The preferred features of the third aspect are steps of producing features corresponding to the preferred features of the first aspect.

In accordance with embodiments of the present invention, power and ground planes are provided that are used in circuit boards and that include porous, conductive materials. The porous materials of the power and ground planes allow water and / or other solvents to pass through the power and ground planes, thereby reducing damage to printed circuit boards or printed circuit boards used as layered support structures caused by cathodic-anodic fiber growth and delamination of the insulators. Porous conductive materials can be produced using metal coated fabrics such as polyester, or structures such as carbon with graphite or glass fibers, using a mesh metal circuit instead of metal layers, using sintered metals, or by forming porous metal sheets with hole pattern. The metal mesh or structure may be made of fabric or paper structures. If the pattern of holes is produced in a sheet of metal, such a pattern of holes can be created without additional processing steps to those used using conventional methods.

Fig. 1 is a perspective view of a cross section of a power core manufactured according to a preferred embodiment of the invention, Fig. 2 is a top view of a power core manufactured according to another preferred embodiment of the invention, Fig. 3 is a cross-sectional view of the preferred power or ground planes for several embodiments of the invention, FIG. 4 is a cross-sectional view of a six-layer printed circuit board and the layers from which the six-layer printed circuit board is manufactured according to a preferred embodiment of the invention, Fig. 5 is a flowchart of a process according to a method using power or ground planes according to a preferred embodiment of the invention and Fig. 6 shows a cross-section of a six-layer printed circuit board and the layers from which the six-layer printed circuit board is made.

The preferred embodiments of the invention overcome the limitations of the prior art by providing printed circuit boards made of conductive porous materials for power and ground planes. The materials are preferably permeable to water and other solvents. The present invention relates to the production of printed circuit boards.

The starting material for the printed circuit board produced is usually a sheet of fiberglass and epoxy resin. It is often referred to as pre-impregnated material because the fiber is impregnated with resin during the pretreatment. The resin is basically the binder that binds the fiber together to form the plate. Instead of fiberglass fabric, compressed paper or other suitable materials may be used. Thus, the basis for making the board is a flat, stiff or slightly resilient dielectric material which is transformed into the final printed circuit. The starting material can be coated on both sides of the plate with a thin copper layer with good adhesion. This operation is commonly referred to as copper sheath lamination (CCL). As a result, it is possible to obtain both simple double-sided plates which have both sides covered with copper traces, and plates which may contain circuits coated with an additional dielectric, which are components of a multilayer structure.

In most cases, holes are made in these boards, usually by drilling, for the electrical connection of various electronic components. Holes are usually drilled too

Using high-speed drills, the hole locations are determined on the drawings or designs of the tiles.

In order to make an electrical connection of one side of the copper cladding through the holes with the other side, the plastic wall of the hole must be conductive. This is accomplished by a chemical process generally known in the industry as metallization, the process consisting of a relatively complicated series of filling and rinsing and an activation step that applies a thin layer of copper to the hole walls.

If the copper layer formed by the metallization process is usually too thin to form a proper electrical bridge between the two layers of the plate, copper electroplating is used to deposit a thick copper layer into the holes to create the correct copper cross-section for the current flowing. To improve the soldering properties, the plating with copper may be followed by a tin-lead coating or by tinning.

After metallization, the circuit is applied to those surfaces that require a pattern to be shaped. A circuit pattern is a circuit design that is applied to the metal surface of a drilled plate according to technical requirements or the design.

The mapping can be achieved by applying an organic photoelectric layer in the form of a dry coating. The photoelectric layer is irradiated through the mask using ultraviolet (UV) light. The mask has a shape that blocks ultraviolet rays. For the negative, areas of the photoelectric layer which are not exposed to ultraviolet rays are removed during the next developing step. Chemical etching is then applied to remove the exposed metal surface. Then the rest of the photoelectric layer is removed and only the representation in the metal is left.

Fig. 6 shows an example of a six-layer printed circuit board and the layers constituting the board. Figure 6 shows parts of a printed circuit board at different stages of production. The six-layer printed circuit board 120 is a structure formed by compressing (called laminating) two signal cores 101 and 130, one power core 111, and dielectric layers 150 and 152. The cores 101, 111, 130 are individually shaped and then compressed to form a layered printed circuit board 120. During this process, the dielectric will flow into each gap between the cores 101, 111, 130 and the dielectric layers. After the process is completed, the structure will be drilled, the epoxy, smeared on the exposed drilled copper layers, will be removed, the holes will be electroplated, and the further steps of the manufacturing process will be performed. For simplicity, Fig. 6 shows dielectric influencing regions as containing air and not dielectric regions. In addition, the electroplated holes are shown as solid metal, although generally they will be cylindrical metallized holes. The locating holes for aligning the structure with respect to the laminate and layers are also not shown.

The pre-signal core 100 includes a dielectric layer 104 sandwiched between the two copper layers 102 and 105. The signal core 100 is an untreated layered support structure. The copper layers 102 and 105 from which the copper traces will be made will become the signal carrying layers. The copper layer 102 may provide contact areas to which chips or surface mount housings will be soldered. Signal core 100 when shaped provides a signal core 101 that includes copper layers 102 and 105 formed into circuitry and metallized holes and other transition / locating holes, and a dielectric layer 104. Copper layer 102 includes two traces (not numbered) and two contact areas 107 and 103, while the copper layer 105 comprises five tracks. In addition, the copper layer 105 includes a transition region 170 in which the metallized holes will be produced after the signal core 101 is laminated into a laminar element containing metallized holes.

The feed core 111 in FIG. 6 includes a dielectric layer 114 sandwiched between the two copper layers 112 and 115. The copper layers 112 and 115 may be thicker than the copper layers 102 and 104 to provide higher current carrying capacity. The pre-feed core 110 is an untreated layered support for the structure. The copper layer 112 will become the circuit board's power plane, while the copper layer 115 will become the PCB's ground plane, or vice versa. The power core 110 is the power core once shaped

111. The feed core 111 includes shaped copper layers 112 and 115 and a dielectric layer 114. Copper layer 112 has two transition regions 182 and 179 formed, while copper layer 115 has two transition regions 184 and 180 formed.

EN 196 239B1 the power and ground planes before contacting the metallized holes that will be drilled in these locations, after the power core 111 is compressed, the holes are drilled and the metallization is done.

A complete six-layer circuit board 120 is shown. Such a circuit board 120 is commonly referred to as a six-layer circuit board because it contains six conductive layers. A six-layer printed circuit board 120 is shown after the signal cores 101 and 130, the power core 111 and the dielectric layers 150 and 152 have been compressed into a complex structure. The composite structure was drilled, the smeared epoxy was removed from the holes, and the holes were metallized. In addition, components may be attached to the complete printed circuit board 120. For example, a component 160 with J-shaped leads has been soldered to the contact areas 107 and 103 of the copper layer 102 of the signal core 101. The signal core 130 is shaped similar to the signal core 101. The signal core 130 includes copper layers 132 and 135 and a dielectric layer 134. The copper layers 132 and 135 have been formed into traces. A dielectric layer 150 has been added between the power plane (copper layer) 112 of the power core 111 and the copper layer 105 of the signal core 101, while a dielectric layer has been added between the power plane (copper layer) 115 and the power core 111 and the copper layer 132 of the signal core 130. 152. Each of the dielectric layers 150, 152 may be made of more than one dielectric layer.

Several metallized holes are shown on the printed circuit board 120. The metallized hole 109 connects the power plane of the copper layer 112 to the lead 161, to the path of the shaped copper layer 105 and to the path of the shaped copper layer 135. The transition area 180 prevents the metallized hole 109 from shorting to ground. It is worth noting that the transition region 180 should be filled with a dielectric liquid after the lamination process, which for simplicity is not shown in Fig. 6. The metallized hole 108 connects the signal paths of the copper layers 102, 105, 132, and 135. The transition regions 184 and 182 prevent the metallized hole from coming into contact with the corresponding ground plane 115 or power plane 112. The metallized hole 106 connects the ground plane 115 to the traces or contact areas of the copper layers 135, 132, and 102.

It should be noted that the electric passage openings, while allowing some water to drain, do not provide sufficient porosity for the moisture to eliminate the effects of cathode-anodic fiber growth or delamination. For example, in Fig. 6 the transition area 180 will allow some water near this area to be drained away, however the dimensions of this area 180 have been exaggerated for the sake of clarity of the drawing and in the actual layered structure carriers will be much smaller. The distance between the metallized holes and their dimensions have also been exaggerated for the sake of clarity of the drawing, and in fact the distance between the holes is much larger and their dimensions are smaller. Hence, in general, there are some locations between the ground or power plane and the metallized openings through which a small amount of vapor may diffuse, but these small areas do not provide sufficient vapor porosity to eliminate the effects of cathodic-anodic fiber growth or delamination.

The insulating or dielectric materials used in printed circuit boards absorb relatively large amounts of water. These materials absorb water when processed. They also have moderate diffusion constants on which the water displacement depends. In contrast, the ground and power planes are made of copper which is impervious to water. When water diffuses through the insulating layers, these planes are the main barriers that stop diffusion. As a result, water collects at the interface between the ground or power plane and the dielectric layers.

The preferred embodiments of the present invention overcome the limitations of the prior art by introducing ground and power planes for printed circuit boards or printed circuit boards used as layered support structures that include a conductive porous material. The incorporation of the materials into the highly porous ground and power planes allows water or other solvents to pass through them, which reduces or eliminates cathodic-anodic fiber growth and blistering from solvent expansion. Water is the main cause of fiber growth, but other solvents are known to cause delamination. In particular, trichlorethylene, methylene chloride, benzyl alcohol and propylene carbonate are solvents that can cause delamination or bubble phenomena.

PL 196 239 B1

The preferred embodiment includes a variety of conductive porous materials that may be used as power and ground planes for printed circuit boards. There are many materials available to meet the requirements of porous power and ground planes. For example, according to an embodiment of the invention, it may be an all-metal material (metal foils with a pattern of holes, powdered sintered metal, metal wire mesh, etc.) or it may have a fibrous metallized substrate to increase conductivity (metal-coated carbon fiber). metal coated fiberglass, metal coated polyester, etc.). Depending on the conductive substrate material used, different processes can be used to form both small holes for vapor diffusion and holes for electrical transition.

A brief terminology discussion is needed before continuing with the preferred embodiments. The term "pre-impregnated", introduced in the introductory part of the description, generally means glass fiber and epoxy resin and comes from the fact that the fiber is impregnated with resin during processing. The sheets of fibrous material may be called fiber composites, while sheets of fibrous material containing resin are commonly called fiber-resin composites. In the event that one or more layers are laminated to one or more power / ground planes or the power / ground plane is laminated between the sheets of pre-impregnated material, the resulting product is referred to as a "composite". For the avoidance of confusion, such a composite structure of fiber composites or fiber-resin composites will be termed "fiber laminate". The term "fibrous laminate" includes all types of pre-impregnated materials, fibrous composites, fiber-resin composites, dielectrics, insulators and other materials used in the production of printed circuit boards. Additionally, embodiments of the present invention may use the term conductive fiber laminates (such as pre-impregnated copper doped materials). It should be noted that the term fiber laminate as used herein means all kinds of thermosetting resins and thermoplastic polymers currently used in the construction of printed circuit boards, including, but not limited to, epoxy resins, bismaleimide triazine epoxy, cyanate esters, polyimides, polytetrafluoroethylene (PTFE) and other fluoropolymers, etc. ., whether they contain fiber or filler.

Porous metal power and ground planes can be made in a number of ways. The most preferred method is to make additional holes in the metal foil which is commonly used in the production of printed circuit boards. This will make the metal foil permeable to water. It is preferred that the diameter of these holes is in the range of 0.0254 to 0.25 mm (0.001 to 0.010 inch) and that the holes are spaced no more than 1.27 mm (0.050 inch) apart to provide the required porosity. water or other solvent. The most preferred diameter is 0.051 (0.002 inch) as such a diameter can be made by a common lithography technique and at the same time allows proper distribution of the feed even when the spacing between the holes is less than 1.27 (0.050 inch). Smaller holes must be made using custom processes such as laser drilling. In general, the minimum distances between openings depend on the electrical conductivity requirements of the design. While other hole sizes and spacing therebetween will increase water / solvent flow through the power and ground planes, the distances and dimensions provided will allow for proper water flow without significantly reducing the current-carrying capacity of the metal layer. Hence, the given distances and dimensions are preferred.

The dimensions and distances of the holes may also depend on when and how the holes were formed in the foil. The mapping / etching steps are the preferred steps for their production. The mapping of the power and ground planes is performed before the metal is removed from the clearance holes to which the metallized holes will not be connected. In addition, designs containing both digital and analog circuits on the same circuit board typically have separate power and ground planes. The digital circuit has one set of power and ground planes while analog components have a different set of power and ground planes. Separating these planes requires the removal of surface portions during the mapping steps.

Since the mapping is already performed during these steps, a simple modification of the process is sufficient to create holes to increase the porosity of the power and ground planes.

PL 196 239B1

For example, if photolithography is used to remove a portion of a plane, a photoelectric layer is applied to that plane. As explained earlier, the photoelectric layer is irradiated with ultraviolet through the mask to form regions of the exposed (polymerized) photoelectric layer that will then remain after the layer is developed. When the unexposed photoelectric layer is removed, the underlying copper layer is exposed. The exposed area of ​​copper is then removed during etching, while the area of ​​copper covered by the photoelectric layer is prevented from etching. In order to create an array or a large number of holes in the copper layer, the mask can be changed to one that has a plurality of opaque areas over which the pattern of holes in the laminate will be made. How to change the mask to create a hole pattern depends on the type of process used. For example, if a positive photoelectric layer is applied, the image on the mask will be the opposite of the mask used for the negative photoelectric layer. The making of patterning masks using specific photoelectric layers is well known in the art. The technique of photolithography has the advantage that it allows the formation of quite small holes.

The use of silk-screen ink to create a pattern on the surface of a layer is also well known in the art. The screen is similar to a mask in the sense that it traps paint being forced through the screen onto the layer. Hence, the image on the screen is the negative of the image that will be on the layer. In the next etching step, the paint protects the layer from the etching agent and the areas of the layer where there is no paint will be etched and the metal in these fields will be removed. If a hole pattern is required in the metal foil, an island pattern will be formed on the screen. Islets on the screen will trap paint and create holes in the paint depositing on the surface of the layer. These paint holes, after the etching operation is performed, will in turn become holes in the metal of the sandwich structure. In another stage of the process, the paint used for the etching is removed. The use of a screen to create a large number of holes has the disadvantage that they have to be larger holes, since with this method it is difficult, if not impossible, to make small holes.

Figure 1 shows a portion of a power core 200 made in accordance with a preferred embodiment of the invention. Power core 200 includes power plane 202 (copper layer), dielectric layer 204, and ground layer 205 (second copper layer). The feed core 200, before it is drilled, etc., is a conventional layered support structure, similar to the feed core 110 shown in Fig. 6. A photo-etching and etching process was performed to form the drainage hole pattern 220 and the through hole 210, 250. Clearance holes 210 and 250 act as insulation between power plane 202 or ground plane 205 and metallized holes (or locating holes). The discharge holes 220 have been arranged in parallel rows and columns. Location 260 shows where drain 220 should be in the pattern, but it was omitted because it was too close to clearance 210. While this example shows that hole 220 at location 260 has been omitted, the reason for this is that there is already some porosity provided by transition hole 210. If desired, both of the through holes 210, 250 may be made by photolithographic processes during the machining (and the locating holes may be made during the machining steps of the holes). Hence, the vent holes 220 may be formed during the same stage of the photolithography process that the through holes 210, 250 are made.

While the pattern of holes 220 has been shown as parallel rows and columns, other patterns are possible. For example, columns and rows may be staggered as shown in Fig. 2. Figure 2 shows the top surface (copper surface 202) of the power core portion 280. The columns and rows of holes 220 form parallel lines, but are staggered or alternating.

Additionally, while these examples relate to copper foil, it should be noted that this technique can also be applied to conductor planes made of other materials and material combinations such as copper / invar / copper and copper / stainless steel / copper etc.

Feed cores which have a hole pattern 220, such as feed core 200, may be used as shown in Fig. 6 with little variation in the manufacturing steps from the described small changes to the photolithography process or screen printing steps.

As noted above, other materials than copper foil may be used to provide porous power or ground planes suitable for use in circuit boards or laminated structure supports. Some of these materials may crumble during the drilling steps of printed circuit boards or laminated structure supports. For example, fibrous

When drilling, materials can be damaged much more easily than metal foils. Moreover, since the photolithography and etching techniques cannot reproduce certain porous power and ground planes, it is preferred that certain changes be made to the commonly used steps for producing printed circuit boards or layered structure support. Before presenting other materials that can be used for porous power and ground planes, the general steps involved in using and creating porous power and ground planes from porous materials will be considered.

Referring to Fig. 3, this figure shows three preferred configurations of porous power and ground planes. Each of these configurations requires slightly different processing steps to produce and use a porous power and ground plane in circuit boards / laminated structure supports. The most preferred configuration of the porous power and ground plane is shown as power / ground core 300. The power / ground core 300 comprises a porous sheet of metal 304 sandwiched between the two layers of fibrous laminate 302, 305. Two clearance holes 310 are shown with these holes drilled into the power / ground core 300 to provide an isolation gap for the metallized holes after the core has been compressed. power / ground 300 with another power / ground core and with one or more signal cores. Lamination creates a composite that will then be drilled and metallized to produce a PCB or a laminated structure support. By laminating the porous metal sheet 304 between the two layers of fibrous laminate 302, 305, the layers of fibrous laminate 302, 305 provide protection to the porous metal sheet 302, 305 during drilling and handling. The fibrous laminate layers 302, 305 can be non-conductive or conductive. In a last embodiment, the power / ground core 300 is a conductive composite. The power / ground core 300 may then be laminated between the layers of the non-conductive fibrous laminate to form a larger core, or the power / ground core 300 may be laminated along with other signal layers, power / ground cores, and non-conductive fiber laminate layers into a PCB composite.

Figure 3 also shows a second and third less preferred configuration for power and ground planes which are more susceptible to damage during drilling and handling. The power / ground core 320 includes a layer of fibrous laminate 324 sandwiched between the two layers of porous planes 322, 325. Again, the fibrous laminate layer 324 may be conductive or non-conductive. The power / ground core 320 has been drilled with through holes 330. Power / ground core 350 includes a porous plane 352. Also, power / ground core 350 has a clearance hole 360 ​​drilled. These embodiments of power / ground cores are less preferred because the porous plane is subject to potential damage during drilling and handling. However, if sufficient care is taken during handling and drilling, minimal or no damage to the porous materials that make up the power / ground planes can be achieved. Hence, it is recommended to encapsulate porous, handling and drilling damage-sensitive materials through a fibrous laminate, which reduces the potential for damage.

Each of these cores can be processed in a slightly different way. Generally, the power / ground core 300 will be laminated after an optional adhesion activation process (with a chemical formulation such as silane) of the porous plane 304. Thereafter, clearance holes 310 will be drilled in the power / ground core. Drilling is used in this step instead of photoelectric coating and etching as fiber laminates (in non-conductive or conductive configurations) typically cannot be etched. Additionally, at this stage, the passage holes 3 10 may be filled with an insulator / dielectric. The drilled power / ground core 300 may then be laminated to another power / ground core and with one or more signal cores to form a composite. The composite is then drilled, the holes are metallized and a printed circuit board or laminated structure support is formed. Optionally, the power / ground core 350 may be drilled, subjected to an adhesion activation process, and then laminated to the two sheets of fiber laminate to form the power / ground core 300. While the mechanical tapping of the power / ground core 350 is suitable for creating clearance holes and locating holes, laser drilling or other less intrusive drilling is preferred for damage-sensitive power / ground plane drilling materials.

PL 196 239B1

In general, the power / ground core 320 can be made by treating the porous layers 322, 325 with an adhesion activation process (optional), and then a sheet of fibrous laminate (conductive or non-conductive) is laminated between the two porous layers. Subsequently, clearance (or locating) holes 330 are drilled. For damage-sensitive power / ground plane materials, laser drilling or other less invasive drilling is preferred. Laser drilling has an additional advantage in this embodiment of forming two conductive porous layers with two different clearance hole patterns. Subsequently, filling of the through holes or locating holes with insulating / dielectric material can be performed. Then, the power / ground core 320 along with the other power / ground core and one or more signal planes may be laminated into a composite.

In general, power / ground core 350 may be drilled, optionally treated with a cling activation substance (such as silane or copper oxide), and laminated to two layers of fiber laminate (conductive or non-conductive) in the form of core 300. Optionally, the power / ground core 350 may be drilled, treated in an adhesion activation step, and then laminated into a composite with another power / ground core through several layers of fiber laminate and one or more signal cores. For example, to form a six-layer composite, there will be the following composite layers, starting from the top layer to the bottom layer: signal core (such as signal core 101 in Fig. 2), one or more layers of a fiber laminate, a power / ground core 352, one or more layers of a fiber laminate, and a second signal core (such as the signal core 130 in FIG. 6). To produce a PCB / structure carrier, this composite is then drilled and metallized.

As discussed previously, it is preferable that conductive materials, susceptible to drilling or handling damage, used as porous power or ground planes are fabricated on power / ground cores on which the porous conductive material is sandwiched between the two layers of fiber laminate. This method of forming power or ground cores facilitates and preserves the porous conductive material during the drilling steps. This protection reduces the amount of fibrous materials damaged by drilling. A power core, such as a power core 320 (similar to core 110 in FIG. 6) or a power core 350, may also be made, but drilling and / or handling can cause the porous material to split and crack. Additionally, the fibrous, bulk material may contaminate some manufacturing steps. By encapsulating fibrous materials and adding an insulator / dielectric to the drilled holes, the fibrous material becomes less susceptible to fouling in the subsequent process steps.

Referring to Fig. 4, there are shown several cross sections of the power and ground cores and a six-layer PCB / laminate structure support made using these cores. Figure 4 is an illustration of an example of a power core 1000, a drilled power core 1001, a ground core 1010, a drilled ground core 1011, and a six-layer circuit board / laminate structure support 1020. The feed core 1000 was formed by performing an adhesion activation process on the porous feed plane, and then laminating the plane to the two dielectric layers 1002 and 1005. The feed core was then drilled to form through holes 1082 and 1079. After the photoelectric layer mask was applied, the base core the feed core will be etched to take the form of a mapped power core (i.e., power core 111 in FIG. 6). As for some porous conductive materials used for power and ground planes or sandwich planes, etching may not be possible, drilling through holes is a preferred method. In this example, power core 1000 and 1001 is a substantially porous conductive layer sandwiched between two non-conductive fiber laminates. A ground core 1010 has been produced by performing an adhesion activation process on a porous ground plane 1012, 1015, then laminating these planes on both sides with a layer of conductive fiber laminate. Core 1010 was then drilled to create through holes 1084 and 1080. In this example, the ground core 1010 is essentially one conductive plane that consists of three conductive layers (one layer of conductive fiber laminate sandwiched between two layers of porous conductive materials). Although not shown in Fig. 4, to the core

From the power supply 1001 and the ground core 1011, a dielectric or other insulator may be added to fill the clearance holes in these cores.

In view of the conductive fiber layer 1014, a preferred method of making this layer is to add 40 volume percent copper powder to the fiber or fiber / resin layer. During lamination, the copper should be evenly distributed over the fiber layer. Other conductive fillers and other types of layer material may also be used, but this filler and layer material have the advantage of being relatively cheap and widely used in the manufacture of printed circuit boards.

To form the composite, after the cores have been drilled (and possibly an insulator added), the power core 1001 and the ground core are then pressed together, along with the shaped signal cores 101, 130 and the fiber laminate layer 1099. To create the metallized holes, the composite is drilled and subjected to metallization. After the components are mounted to the circuit board / laminated structure support, an exemplary six-layer portion 1020 is formed. The fibrous laminate layer 1099 is a non-conductive dielectric layer used to isolate the signal plane 132 from the ground core 1011, and in particular from the porous plane 1015 of the ground core 1011. The same role is played by the fiber laminate layer between the power core 1001 and the ground core 1011.

The metallized hole 1008, like the metallized hole 108 in Fig. 6, connects the lines of the signal layers 102 and 105 of the signal core 101 to the lines of the signal layers 132 and 135 of the signal core 130. The transition regions 1082 and 1084 prevent the power and ground layers from coming into contact with the metallized hole. . Although the transition regions 1082 and 1084 are shown empty, in reality they are usually filled with a dielectric: both areas have been filled with a dielectric (or other insulator) after the power or ground core has been drilled, or they will be filled with a dielectric / insulator during lamination.

The metallized hole 1009, like the metallized hole 109 in Fig. 6, connects the contact area 103 and the line on layer 135 of the signal core 130 with the power plane 1001. The transition area 1080 prevents the metallized hole 1009 from coming into contact with the ground core 1011. like the metallized hole 106 in Fig. 6, it connects the lines on the signal core layer 101 and on the signal core layers 135, 132 to the ground core 1011. In this example, the ground core 1011 includes three conductive layers (two porous planes 1012 and 1015 and one layer of conductive fiber laminate 1014) each connected to the metallized hole 1006. The transition area 1079 prevents the metallized hole 1006 from coming into contact with the feed layer 1004.

In the example in Fig. 4 it is shown that most of the layers of the sandwich structure separating the different cores are relatively thin. For example, the fiber laminate layers 1002 and 1005 are thin. This has been done for illustrative purposes only, as those skilled in the art know that more thinner or thicker layers of fibrous laminate can be used if desired. Comparing the six-layer printed circuit board / layered structure support PCB / LCC 1020 from Fig. 4 With the six-layer PCB / layered structure support 120 of FIG. 6, there are some differences except that the PCB / layered structure support PCB / LCC 1020 has separate power and ground cores. The PCB / Layered Structure Support PCB / LCC 1020 also has porous power and ground planes allowing water or other solvent to be dispersed freely through the various layers of the PCB / laminated structure support PCB / LCC 1020. Porous power and ground planes grounding devices reduce damage caused by cathodic-anodic fiber growth and delamination of insulators.

A preferred method of forming a power or ground core (such as power core 1000) including the porous conductive material of the invention is shown in Fig. 5. The method illustrated in Fig. 5 is preferably used for both power and ground cores and for joining power and ground cores into PCB or LCC composites. This method is also used in the preferred embodiments where the porous conductive material is positioned between the two layers of the fiber laminate, such as the power plane 1000. This embodiment allows better protection of the internal porous conductive material. Additionally, the fiber laminate can help seal the metal clad fibrous materials and other bulk materials, which helps keep the fiber material inside the laminate. It is especially helpful for carbon materials,

PL 196 239B1 that have the potential to contaminate PCB / LCC parts and the manufacturing process. The method starts when an additional metal layer is applied to the porous material used in step 410. The metal sheathed fibrous materials of the invention contain enough metal to provide the required current, and if more current throughput is required, step 410 will be applied to the fibers in step 410. more metal.

Additionally, if the preferred porous material of the invention has not been metallized, it can also be made at this stage. For example, if a porous carbon fiber material has been used, it may be metallized and then, in step 410, converted to a fabric. If so desired, in step 410 the fabric can be additionally doped with metal. In short, step 410 can be used both for metallizing those materials that are not metal coated and for additionally metal coating previously metallized materials. The types of preferred materials used for the grounding surfaces will be described in detail after discussing the method shown in Figure 5.

The porous material is then treated by an additional adhesion activation process or by treatment with copper oxide in step 420. Thereafter, a conductive material is introduced between the fiber laminate in step 430 to form an encapsulated porous power or ground core. Generally, a standard process for laminating porous feed and grounding material will be used. Alternatively, the porous fibrous material may be resin impregnated using the standard impregnation process in step 430. This standard impregnation process sufficiently encapsulates the fibrous material. The impregnating resin coating is then laminated to the separating sheet or rough copper foil. If a rough film is used, it can either be etched in step 437 or drilled in step 440. The divider sheet will be completely removed at step 435 prior to drilling.

Since the fiber laminate in principle cannot be etched to form the necessary clearance holes and other gaps, these are formed in the power and ground core in step 440. Generally, gaps will be created by drilling an array of clearance holes or locating holes in the laminate through the porous plane. . Both mechanical drilling and drilling using a laser or other similar hole making apparatus can be used. If a rough film has been applied to the porous material in step 435 and has not been removed in step 437, it will now be removed by etching in step 445. In this state, the gaps may be filled with pure resin, resin containing a non-conductive filler, or other appropriate insulator / dielectric in step 445. 450. The power / ground core may be incorporated into the composite, preferably by laminating or pressing into a composite wafer structure in step 460. Additional fiberglass resin flows inward and fills the drilled holes of the power plane during the laminating cycle if the holes are not filled in step 450. Then, in step 470, re-drilling may be performed to produce the holes used for the metallized holes and metallized the holes. Step 470 should be followed by a printed circuit board / laminated structure support 1020 similar to a printed circuit board / laminated structure support 1020.

The disclosed method is a preferred method for producing printed circuit boards or layered structure support containing porous power / ground planes, while the steps of the method may vary slightly depending on the configuration of the power / ground core used. For example, two layers of conductive porous material may be applied to a fiber laminate, such as the previously shown power / ground core 320 in FIG. 3. In this embodiment, the treatment steps are very similar to those shown in the method of Fig. 5. For example, the method steps 410 and 420 may be performed to add additional metal to the conductive material, respectively, and to increase adhesion. A sheet of fibrous laminate (conductive or non-conductive) can then be laminated between the two porous layers. Next, drilling is typically performed at step 440 to create clearance or locating holes. It is preferred that for power or ground plane materials that are susceptible to drilling damage, laser drilling or other less intrusive drilling is used.

Laser drilling in this embodiment of the two conductive porous layers with different clearance hole patterns has additional advantages. Filling the through holes or locating holes with insulating material may be done in step 450. Power / ground core

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320 it can then be compressed into a composite in step 460 along with another power / ground core, one or more signal planes, and non-conductive layers of the fiber laminate. The composite will then be drilled and metallized to produce a PCB / LCC board in step 470.

Additionally, a power / ground core, similar to the power / ground core 350 in FIG. 3, may be used to form a power or ground plane. In this embodiment, the manufacturing steps used to create the power or ground plane differ somewhat from the method of Fig. 5. For example, drilling in step 440 may take place before or after step 410, if performed. Thereafter, the conductive porous plane may be treated with the adhesion activation material in step 420 and laminated to the two layers of conductive or non-conductive fibrous laminate to form the core 300 of Fig. 3. In this embodiment, step 450 will generally not be necessary because during the process, the lamination holes should be filled with a fiber laminate. Optionally, a drilled porous conductive plane, similar to a power ground core 350, is subjected to a cling activation treatment in step 420 and then compressed in step 460 into a composite with another power / ground core, several fiber laminate layers, and one or more signal cores. This composite can then be drilled and metallized to form a PCB / LCC board in step 470.

As a result, the method can be applied to other configurations of printed circuit boards in relation to six-layer printed boards as shown in Fig. 4. By adapting the method processes to a specific number of layers, fewer or more of these layers can be formed. For example, referring to Fig. 4, if a four-layer printed circuit board is desired, the power core 1000 may be laminated to the outer surface 1002 with the copper layer. Thereafter, a power core 1001 can be formed by drilling. Likewise, a ground core 1010 may be bonded on the outer surface 1015 to a fiber laminate and a copper laminate. Then, by drilling, the power core 1011 can be formed. The gaps created in the drilling in the power and ground cores may be filled with an insulator. The two layers of copper laminate can then be patterned and formed into a composite along with the two power and ground cores. To create a printed circuit board, drilling and covering of the clearance holes are performed. Alternatively, drilled power core 1001 and drilled ground core 1011 may be composite formed with the layers in the following order: copper layer, optional non-conductive fiber laminate layer, power core 1001, ground core 1011, non-conductive fiber laminate layer, and copper layer. The two copper layers can then be patterned to form signal layers, and the composite can be drilled and metallized to create a four-layer PCB.

The methods of using porous materials to form porous, conductive power and ground planes have been discussed in general. These methods and materials can be related to the specific porous conductive materials discussed below. If there are no additional processing steps that are advantageous for use to form a power or ground core, these steps will be discussed in relation to the power / ground material.

Sintered metal is a preferred material suitable for use in metal power and ground planes. Sintered metal is made of metal particles that are held together by pressure and heat. The sinter metal of the feed planes can be formed by thermal pressing under pressure, high melting point and high electrical conductivity metal particles, such as copper, coated with a low melting point metal such as tin. Tin-coated copper particles fuse to form an electrically conductive but porous sheet.

This conductive sheet can be used to make a power-ground core similar to a power-ground core 300, 320, or 350. Additionally, any of the previously discussed methods of fabricating these cores and integrating them into PCB / LCC boards may be performed.

Additional preferred materials for forming porous, conductive power and ground planes can be loosely bonded to the fibrous conductive materials. These additional preferred materials include threads formed into sheets or metallized polyester structure, metallized carbon fiber structure and metallized glass fiber. The structures can then be broken down into fabrics: structured and free-flowing structures

PL 196 239B1 paper structures. Free-form paper structures are generally made of randomly oriented fibers.

For example, a preferred structural material used to form porous power and ground planes are metal threads formed into a fabric sheet or a free-form paper structure sheet. It is preferred that the threads forming the sheet are small in diameter so that the sheet is thin. It is also preferred that the thread diameter is large enough to carry the current for the intended use. Metal layers of non-woven thin wires can also be used as a material for porous power and ground planes. Additionally, the fabric sheets or sheets of free-form paper structure may also undergo a coating process to obtain better electrical interlayer bonding. This will ensure better conductivity between the individual fibers.

These conductive metal wire sheets can be used to form power / ground cores similar to power / ground cores 300, 320 or 350. Furthermore, making these cores and assembling them into PCB / LCC boards may be performed by any of the methods previously discussed.

Another metallized fibrous material suitable for use on power and ground planes in printed circuit boards is metal-coated organic fibers such as liquid crystal polymers such as VECTRAN aromatic polyamide, and other structures such as polyester, SPECTRA such as polyethylene and nylon. Aromatic polyamide and other fibers are preferred because they have a low coefficient of thermal expansion, which will be discussed below, and high thermal stability. Polyester is also a preferred fiber because it is a monofilament in the form of a woven fabric and is less prone to damage from handling. These materials can be purchased as woven fabrics or as free-form paper structures.

While some of these organic fibrous materials can be purchased as metal clad structures, organic fibrous materials suitable for use as power or ground planes can also be made using the following steps. First, the organic fibrous materials are inserted into the chamber and held in a slightly taut and / or flat position. This tension or flat orientation ensures that the metal evenly covers the exposed surfaces. Metal is then applied to the organic fibrous material. This deposition can be done in a number of ways, including electroplating, sputtering, vapor deposition, or chemical vapor deposition. If required by the process, the organic fibrous material can be inverted and more metal can be applied. For example, if sputtering is used, the metal is typically only applied to one surface of the fabric. While the fabric can be used in this way, typically more metal can be added to the other side of the fabric to increase the current carrying capacity. Alternatively, the fabric may be sputtered simultaneously on both sides using the roll-to-roll format. After sputtering or chemical vapor deposition, more metal may be added to the fabric via conventional electroplating means. The additional metal increases the possibility of carrying current through the metal-coated power and ground planes.

After forming a sheet of metallized fibers, these porous, conductive sheets can be used to form power / ground cores similar to power / ground cores 300, 320 or 350. In addition, making these cores and assembling them into PCB / LCC boards can be performed any earlier. the method discussed.

Another preferred metallized fibrous material suitable for use as a power or ground plane in circuit boards or layered structure supports is metal coated carbon fiber. Since carbon fiber can be in the form of both a woven fabric and a yarn weave, metallization of the fiber can occur in two steps. For example, metal can be applied to the fibers of the carbon fabric. Alternatively, the metal may be applied to the carbon yarn and the weave of the carbon fiber woven into a structure or fabric. Carbon fiber can be purchased already coated with metal and formed into a bundle. This bundle can then be woven into a relatively flat material. In addition, carbon fiber can be purchased as a free-form paper structure sheet.

After the sheet of metallized fiber is formed, these porous, conductive sheets of metallized carbon fiber can be used to form power / ground cores similar to 300, 320 or 350 power / ground cores. Furthermore, making these cores and combining them into PCB / LCC boards can be performed with each of the methods previously discussed.

PL 196 239 B1

Another preferred fibrous material is metallized glass fiber. Like carbon fiber, it can be purchased either as a separate fiber yarn or as a fabric sheet. The separate strands of the yarns may be metallized and then woven into a fabric, or they may be metallized sheets of woven fiber. These fibers are currently not sold with a metal coating. To form a metal-coated fiber or fabric, the previously described methods of making metal-coated fibers or fabrics may be used. In addition, fiberglass can be purchased as a free structure sheet. These sheets can be metallized using the previously discussed metal coating methods.

After the sheet of metallized fiber is formed, these porous, conductive sheets of metallized glass fiber can be used to form power / ground cores similar to power / ground cores 300, 320 or 350. In addition, making these cores and combining them into PCB / LCC boards can be carried out by each of the methods previously discussed.

It should be noted that some of the fibrous materials used in the present invention as power and ground planes have a low coefficient of thermal expansion. The low coefficient of thermal expansion of the supply and ground surfaces can lower that of the printed circuit boards or laminated structure supports. The advantage of this is that the mounted microcircuits are protected against cracking.

While copper has mainly been discussed as a metal for metallization, those skilled in the art will conclude that the techniques used for copper plating can also be used for plating with silver, gold, aluminum, tin, etc. Moreover, even when the base material for When copper is used in metallization, additional amounts of other metals may be added at certain manufacturing steps. For example, some manufacturers add small amounts of gold during the process to increase the conductivity of the primary connections.

As a result, preferred embodiments of creating porous, conductive materials can be used in circuit boards for power and ground planes. These materials should reduce common PCB problems such as delamination and cathode-anodic fiber growth caused by water and / or other solvents, and thus reduce damage to the PCBs and increase reliability of the PCBs. This is especially true for structure carriers, which must have increased resistance to moisture.

Power and ground planes are disclosed which are used in circuit boards and which contain porous, conductive materials. The use of porous materials in printed circuit boards for power and ground planes allows liquids, e.g. water and / or other solvents, penetrate the power and ground planes and thereby reduce damage to printed circuit boards (or printed circuit boards used as layered support structures) due to cathode-anodic fiber growth and delamination of insulators. Porous, conductive materials suitable for use in printed circuit boards can be formed by using organic, metal-coated fabrics (such as polyester or liquid crystalline polymers) or structures (such as made of carbon / graphite or fiberglass), using metal mesh instead of metal sheets , using sintered metal or creating porous metal sheets by forming a pattern of holes in the sheets. The structures and meshes can be woven or built freely. If a pattern of holes is formed in the metal sheet, the pattern may be made without additional steps to those performed using conventional printed circuit board manufacturing methods.