Circuit board and method for producing circuit boards

The invention relates to a printed circuit board according to the preamble of claim 1 and a method for manufacturing printed circuit boards.

In the prior art printed electric circuits are known, in which printed circuit boards are equipped with electronic components. Such circuit boards may be prepared from one or more individual layers of glass fiber-reinforced cured epoxy resin plates which switched to the formation of interconnects or copper laminated on both sides.

PCBs as such can be rigid. Furthermore, printed circuit boards, which comprise at least one rigid portion and at least a bendable or flexible region has long been known as flex-rigid circuit boards are known. Various rigid regions are hereby electrically connected by flexible regions. The material of the flexible regions is usually made of flexible plastic films (eg polyimide), which are copper-clad. The flexible portions of such rigid-flexible printed circuit boards through dynamic bending stresses with a high number of bending cycles. However, it is not necessary to always use a highly flexible material for the bending portions of the circuit board, because the board is bent only a few times during the installation and / or repair purposes.

Out <patcit id="pcit0001" dnum="DE4131935A1"><text>DE 41 31 935 A1</text></patcit> discloses a method for manufacturing a rigid-flexible printed circuit board. In this method, the rigid portion, which consists of a rigid base material is reduced by depth milling extent in thickness until the remaining material can be bent due to the reduced thickness and thus the bendable portion is formed. A disadvantage of circuit boards that are produced by this process consists in that the bendable regions can be bent only a few times with a relatively large radius. Furthermore, the flexible regions are asymmetrically on only one outside of the resulting board.

Out <patcit id="pcit0002" dnum="DE4206746C1"><text>DE 42 06 746 C1</text></patcit> discloses a method for the production of rigid-flexible printed circuit boards. In this process, a more economical thin prepreg material is used instead of an expensive flexible individual layer, which can be bent after curing. Between a rigid outer layer and the prepreg material is in the later portion of the breakout circuit board from which the bendable portion is formed, inserted an insulating film before pressing that does not adhere to copper. If in this method, the bendable portion of two or more layers is built, there is a disadvantage that the prepreg material has to be coated in a costly laminating operation with the first copper layers.

Similar to <patcit id="pcit0003" dnum="DE4206746C1"><text>DE 42 06 746 C1</text></patcit> be made by the firm. Teledyne PCBs with bendable areas under the name, "REGAL®Flex".

Out <patcit id="pcit0004" dnum="DE4003344C1"><text>DE 40 03 344 C1</text></patcit> is a generic type rigid-flexible printed circuit board is known which comprises a flexible portion and a rigid portion. A copper foil is bonded by means of an adhesive film in the form of a prepreg material with a rigid individual layer. In the later bendable portion of the circuit board, an insulation film is provided in the form of a polyimide film, which serves as a base film of the flexible region. After pressing the layers under pressure and heat the copper foil with the polyimide film and the rigid individual layer is durable and resistant to soldering temperatures associated or bonded. The bendable portion is achieved that in this area the rigid individual layer is removed by pre-formed break points. In addition, there is provided a cover in the form of a liner-piece in the flexible portion on an outer side of the copper foil, which covers the conductor tracks of copper foil. The process for producing a circuit board according to this prior art is complicated and thus expensive due to a large number of individual process steps.

<figref idrefs="f0005">Fig. 5</figref> schematically shows the layer structure of a conventional circuit board 101 before performing a hot-pressing process. Such printed circuit board 101 has a pliable sheet 104 and a rigid position 106th In the finished state, such a printed circuit board 101 has a bendable portion 102 which connects two adjoining rigid regions 103 each. Before performing a hot-pressing process between the pliable sheet 104 and the rigid layer 106 disposed a plurality of prepreg plies 105th With regard to simplified handling these prepreg plies 105 are preferably made of no-flow prepreg.

In a predetermined surface portion of the printed circuit board 101 that corresponds to a later bendable portion 102, a separate cap layer 108 and adjacent to the rigid layer 106 is a release film in the form of a Teflon film 109th During the hot-pressing process, the pliable sheet 104 and the rigid layer 106 by means of the prepregs 105 are bonded together, the arranged in the predetermined surface portion Teflon film 109 is not or only poorly adhered to the top layer 108th At the edges of the predetermined surface portion of the circuit board 101 106 112 predetermined breaking points are provided in the rigid position. This predetermined breaking points 112 facilitate after completion of the hot-pressing process, a breaking out or - disconnect the rigid layer 106 and the Teflon sheet 109 from the predetermined surface portion, so that by the bendable portion 102 of the PCB 101 results. The top layer 108 shields in the bendable section 102, the flexible layer 104 and disposed thereon interconnects o. The like. From.

A disadvantage of a conventional circuit board 101 according to <figref idrefs="f0005">Fig. 5</figref> is that adjacent to the later bendable portion 102 includes a plurality of prepregs 105 are to be arranged on the rigid layer 106 to ensure a uniform surface pressure during the hot-pressing process. A further disadvantage is that the use of a separate cover layer 108 is required, which means additional effort in handling, and increased material costs.

The invention has for its object to provide a circuit board and a method for their preparation, wherein the preparation is simplified and less expensive.

This object is achieved by a circuit board having the features of claim 1 and by a method having the features of claim 10th Advantageous further forming inventions are defined in the appended claims.

A printed circuit board according to the invention comprises at least one bendable portion having a pliable sheet, which is one or both sides with a copper coating or interconnects. The pliable sheet is at least in the bendable portion and at least one side with a covering layer, said outer layer is formed of a prepreg material.

The invention has the essential finding that the top layer, which is provided in the bendable portion on the pliable sheet for covering the copper cladding and the conductor tracks, instead of a conventional plastic film (such as polyimide) is now formed of a prepreg material. If the flexible layer is connected to at least one rigid position by means of such a prepreg material, the prepreg material is a dual function: it serves both as an adhesive between the flexible sheet and the rigid position, and also as a topcoat for the pliable sheet in the bendable portion. Accordingly, it is not necessary to provide a separate sheet or the like for providing a cover layer for the bendable portion.

A preferred embodiment of claim 2 provides that the rigid layer is omitted or removed in the bendable portion. The area of ​​the circuit board to be as desired bendable represents a predetermined surface portion of the circuit board, in which the rigid layer is removed. Thereby, the desired flexibility of the printed circuit board is achieved in its bendable portion. For ease of manufacture of the circuit board according to the invention, it is possible to remove the rigid position in the bendable portion only when previously rigid position has been linked extensively with the pliable sheet. Prefabricated knockout or predetermined breaking points in the rigid position can facilitate the removal of unbonded rigid position in the predetermined surface portion.

According to the invention, the feature is able to understand as a layer, which may consist of a single layer, a plurality of loose individual layers, or of a composite of already interconnected or bonded individual layers. In this regard it is to be understood that the pliable sheet and / or the rigid layer in the above manner can be formed. When fully completed state of the circuit board according to the invention, these layers are permanently bonded or glued together.

In an advantageous development of the invention according to claim 3, the pliable sheet at least a single layer having a thickness of 12.5 - 200 microns have. This thickness corresponds to a predetermined flexibility of the deflectable region and a concomitant strength or stability. Conveniently, the pliable sheet also made of a laminate, preferably a two-layer laminate may be made. This laminate preferably consists of two layers which are already connected to one another before another connection or gluing is carried out with the rigid position. In other words, allows for the pliable sheet a pre-assembled position, consisting of a plurality of individual layers, can be used. It is understood that the laminate for the pliable sheet also of three or more individual layers may consist, provided that flexibility is ensured for the pliable sheet in the finished state of the circuit board.

In an advantageous development of the invention according to claim 5, the cover layer has a thickness of 40-60 microns, preferably a thickness of 50 microns. Such a thickness suitable for a necessary protection of the bendable portion respectively, the copper cladding / of the conductor tracks, which are provided on the pliable sheet.

In an advantageous development of the invention according to claim 6, the prepreg material may consist of a no-flow prepreg or at least of a low-flow prepreg. The handling of such prepregs is comparatively simple and facilitates the manufacturing process for printed circuit board.

According to an alternative development of the invention according to claim 7, the prepreg material can also consist of a full-flow prepreg. Such a prepreg material is characterized by good flow properties during pressing under pressure and heat. Accordingly, it is possible to achieve with a full-flow prepreg material very uniform surface pressure in the manufacture of printed circuit board according to the invention, whereby a uniform surface quality of the finished printed circuit board is achieved.

The inventive method for producing printed circuit boards with at least one bendable portion and at least one rigid portion provides that between a pliable sheet that is provided on one or both sides with a copper coating or conductor tracks, and at least one rigid position a sheet prepreg be introduced material and in a predetermined surface portion of the circuit board release agent, adjacent to the rigid layer. Thereafter, a compression of the respective layers is performed so that it creates a permanent bond. After completion of the pressing operation, the rigid layer and the release agent are separated from the predetermined surface portion of the circuit board, so that thereby forming the bendable portion of the circuit board. In the bendable portion of the circuit board, the prepreg material is used as a cover layer for the pliable sheet.

Essential to this method is the consideration that the prepreg material fulfills a double function: it serves both as an adhesive for connecting the pliable sheet with the rigid layer, and at least in the bendable portion as a cover layer for the pliable sheet. Thus, it is not necessary to provide a separate top layer during production of the circuit board in the bendable portion of the pliable sheet, which simplifies the manufacturing process and reduces the cost.

In an advantageous embodiment of the method according to claim 11, the release agent may have a thickness of 100 - 200 microns, preferably a thickness of 140 - 160 microns have. This ensures that the rigid position, lets out cleanly separate from the predetermined surface portion of the circuit board, in which the bendable portion is to be formed without damaging the top layer in the form of prepreg material. Furthermore, this thickness of the release agent is matched to the compression of the individual layers when doing the prepreg material from flowing away laterally by the separating means.

The inventive method can be carried out in such a way that the pliable sheet and / or the rigid layer consist of a plurality of loose individual layers which are permanently connected to one another during the subsequent pressing of the plies. An important aspect here is that the superposition of the flexible sheet and the rigid layer, wherein the sheet prepreg material and the release agent can be introduced in between, and then compressing the layers takes place in a single operation, which makes the process according priced. Alternatively, the pliable sheet and / or the rigid layer consist only of a single individual layer or from a prefabricated composite of individual layers which are permanently bonded during pressing with the respective adjacent layers.

It is understood that the features mentioned above and those yet to be explained not only in the particular combination indicated but also in other combinations or alone without departing from the scope of the present invention.

The invention is shown schematically below by means of preferred embodiments in the drawings and will be described in detail with reference to the drawings. Show it:<dl id="dl0001"><dt>Fig. 1</dt><dd>a cross-sectional view of a circuit board according to the invention in-completed state with an asymmetrical structure,</dd><dt>FIG. 2</dt><dd>a side view of a plurality of layers of producing a printed circuit board <figref idrefs="f0001">Fig. 1</figref> be used,</dd><dt>Fig. 3</dt><dd>a side view of the layers of <figref idrefs="f0002">FIG. 2</figref> during a pressing operation,</dd><dt>Fig. 4</dt><dd>a cross-sectional view of another embodiment of an inventive circuit board, having a symmetrical structure, and</dd><dt>Fig. 5</dt><dd>a side view of a plurality of layers for producing a circuit board according to the prior art.</dd></dl>

<figref idrefs="f0001">Fig. 1</figref> shows a cross-sectional view of a printed circuit board according to the invention 1, wherein in the <figref idrefs="f0002">FIG. 2</figref> and <figref idrefs="f0003">3</figref> Case, steps are shown for a process for producing such a printed circuit board.

The cross-sectional view of <figref idrefs="f0001">Fig. 1</figref> makes clear that the printed circuit board 1 has a bendable portion 2, adjacent to the respective rigid regions. 3 The rigid regions 3 are here joined by the bendable portion 2 to each other electrically. The circuit board 1 comprises a pliable sheet 4, which is connected by means of a sheet prepreg material 5 with a rigid position. 6 The construction of this circuit board 1 is asymmetrical with respect to its cross section, since the rigid layer 6 to only one side of the pliable sheet 4 provided.

In a predetermined surface portion of the circuit board 1, the rigid layer 6 is removed, resulting in a recess 7 results in the circuit board. 1 This results in the bendable portion 2 of the circuit boards, since the rigid layer 6 is removed and only the pliable sheet 4 remains in communication with the prepreg material fifth The prepreg material 5 forms in the bendable portion 2 a covering layer 8, which shields the pliable sheet 4 against the recess 7 or outwardly. Thus, the prepreg material 5 simultaneously fulfills two functions, namely on the one hand adhesion of the flexible sheet 4 to the rigid layer 6, and on the other hand in the form of said cover layer 8, a shielding of the pliable sheet 4 at least in the bendable portion second

The pliable sheet 4 is formed of a suitable, thin, flexible base material such. As a multilayer laminate. An average single layer of pliable sheet 4 may be made of a polyimide film 10 having a thickness of preferably 12.5 - can have 200 microns. This polyimide film 10 is provided on both sides with a copper cladding 11th The thickness of the flexible layer 4 is suitable selected so that in the bendable section 2, the desired flexibility of the circuit board is always guaranteed 1. This base material can be used for the flexible layer 4 smaller bending radii and a higher number of bending cycles achieved than with conventional bendable areas of a circuit board, which are deeply cut.

The conductive patterns of the flexible layer 4 on its inner (ie in <figref idrefs="f0001">Fig. 1</figref> lower) copper cladding 11 are prefabricated. These conductive patterns are suitably screened in the bendable portion 2 of the outer layer 8 and electrically insulated. Accordingly, the copper cladding 11 and the conductor tracks formed thereon to be protected by the covering layer 8 against mechanical damage from the outside.

In the <figref idrefs="f0002">FIG. 2</figref> and <figref idrefs="f0003">3</figref> is a method for manufacturing the printed circuit board 1 according to <figref idrefs="f0001">Fig. 1</figref> explained. In<figref idrefs="f0002">FIG. 2</figref> the respective layers from which the printed circuit board 1 is formed, simplified and shown in particular not to scale stacked. This essentially corresponds to an arrangement of the layers in a (not shown) pressing tool. It will be appreciated that the prepreg material 5 is formed flat, so that it has substantially the same extension as the flexible sheet 4 and the rigid location 6th The prepreg material 5 is introduced prior to compression between the pliable sheet 4 and the rigid position. 6 In addition, suitable separation means, for. Example, in the form of a Teflon film 9 also introduced between the flexible sheet 4 and the rigid layer 6, the teflon sheet 9 thereby is adjacent to the rigid layer 6. Proceeding in accordance with the configuration<figref idrefs="f0002">FIG. 2</figref> a hot-pressing operation is then performed to bond the respective layers together permanently.

As an alternative to the Teflon film 9 can be used as a release agent, a gel or a flowable adhesive. This gel or flowable adhesive can, for. Example, be applied to the rigid sheet 6 by screen printing.

<figref idrefs="f0003">Fig. 3</figref> illustrates the implementation of the above-mentioned hot-pressing process for producing the circuit board first

By means of a suitable (not shown) tool to the respective outer layers of the circuit board 1, ie, the flexible layer 4 and the rigid sheet 6 pressed and pressed towards each other. As a result of the applied pressure, the prepreg material 5 is displaced to an upper surface of the teflon film 9 partially sideways. The displaced material of the prepreg material 5 fills laterally on the sections between the pliable sheet 4 and the rigid layer 6, as a result, a uniform surface pressure during pressing of the layers is achieved. The presentation of<figref idrefs="f0003">Fig. 3</figref> is also simplified to be understood, particularly with regard to a deformation of the prepreg material 5 during the pressing operation.

The Teflon film 9 fulfills the function of an isolation or separation film, thereby preventing the rigid layer 6 is bonded in the region of the Teflon film having the pliable sheet 4th After completion of the hot-pressing operation, the rigid sheet is in the predetermined surface portion of the printed circuit board 1, the bendable portion corresponding to the desired 2, 6 is removed together with the Teflon film. 9 After separating out the rigid layer 6 and the Teflon film 9 from the predetermined surface portion of the circuit board 1 is obtained in the<figref idrefs="f0001">Fig. 1</figref> Recess shown 7. As with reference to <figref idrefs="f0001">Fig. 1</figref> explained, the printed circuit board 1 in the area of ​​the recess 7 is bendable, wherein the prepreg material 5 also serves in the bendable portion 2 as a covering layer 8 for the pliable sheet 4th

When bonding the layers, the Teflon film is 9 pressed into the prepreg material 5, said prepreg material is 5 9 as explained partially displaced from an upper surface of the Teflon sheet to the side. As a consequence, the thickness of the prepreg material 5 is reduced above the teflon sheet 9 on completion of the pressing operation, such as the depiction of<figref idrefs="f0003">Fig. 3</figref> shows. After removing the rigid layer 6 and the Teflon film 9 in the bendable portion 2 is produced at the edges of the outer layer 8 is a stage, the height of this step corresponds substantially to the thickness of the Teflon film 9, which formerly in this area had been.

As an alternative to the procedure in accordance with the <figref idrefs="f0002">FIG. 2</figref> and <figref idrefs="f0003">3</figref> It is also possible to insert before the pressing of the layers 4, 6 additional prepreg plies between the flexible sheet 4 and the rigid layer 6, namely, the side of the Teflon film 9. These additional prepreg plies are in the portions of the circuit board 1 introduced that correspond to the later rigid areas, and have the same height as the Teflon film 9 substantially on. Preferably, these additional prepreg layers of no-flow prepreg what their handling considerably simplified exist. The additional prepreg plies same when pressing the layers of the height difference to the Teflon film 9, so that the teflon sheet 9 in contrast to the illustration of<figref idrefs="f0003">Fig. 3</figref> not as strong or not pushes into the prepreg material 5 in the section of the later bendable range. 2 As a result, formed on the edges of the cover layer 8 no stage when the rigid layer 6 have been removed in conjunction with the Teflon film 9 from the bendable portion second

Regarding the flexible layer 4 and / or the rigid layer 6 is to be understood that these layers can be formed in different ways. Either the layers 4, 6 are each formed by a single layer. Alternatively, the layers 4, 6 may be formed from a plurality of loose individual layers, or from a composite of previously connected individual layers. Essential for the method of producing the circuit board 1 is that the overlaying layers can be carried out of the respective layers, and then compressing the layers in a single operation, irrespective of the configuration of the respective layers. This leads to a significant ease of manufacture and thus cost savings.

The process for producing the circuit board 1 is also characterized in that the layers used for this purpose prior to insertion of the pressing tool does not have to be dried. When using loose individual layers they can be easily placed without further preparation superimposed. This reduces the cycle time in the manufacture and thus also the costs.

The prepreg material 5 may be a material with the label Isola DURAVER®-E-Cu quality 104 ML 106 in the AT05. The resin formulation of this material has a high thermal resistance and is resistant to chemicals, which reduces the risk of resin recession to a minimum. Furthermore, this material is an excessive etch-back in boreholes, which may be provided in the printed circuit board 1 is prevented, resulting in a high reliability of the via, even under cyclic loading results.

The rigid layer 6 is provided in the same manner as the pliable sheet 4 on both sides with a copper cladding 11th Alternatively, it is possible that the rigid layer 6 is provided on one side with a copper lining. By (not shown) holes in the circuit board 1 a via the copper cladding 11, which are provided on the flexible layer 4 and on the rigid layer 6 is achieved.

In <figref idrefs="f0004">Fig. 4</figref> is shown another embodiment of the printed circuit board according to the invention. 1 The same features as in the embodiment described above are in this case provided with the same reference numerals. Unlike the embodiment of<figref idrefs="f0001">Fig. 1</figref> , the embodiment according to <figref idrefs="f0004">Fig. 4</figref> a symmetrical structure in respect to their cross-section. This means that on both sides of the pliable sheet 4 a rigid location is in each case 6 is provided. The two rigid layers 6 are connected by a respective prepreg material 5 with the pliable sheet. 4 The recesses 7, which are formed in the rigid layers 6 are expediently arranged in alignment with each other, so that sets a high degree of flexibility for the bendable portion. 2

The printed circuit board 1 of the invention is characterized in that the bendable portion 2 asymmetrical (see. <figref idrefs="f0001">Fig. 1</figref>) Or symmetrical (see FIG. <figref idrefs="f0004">Fig. 4</figref>) Can be arranged in the configuration of the circuit board. 1 Compared with a conventional deep milled design a circuit board can be selected as desired for the printed circuit board 1, the bending direction. Furthermore, it is not required in the printed circuit board 1, to mill a glass fiber fabric for the bendable section so that no predetermined breaking point is formed. This results in a higher quality and reliability over a deep milled manufacturing process. Finally, has the flexible layer 4 which is explained as above from a suitable thin flexible base material, compared with deep milled conventional PCB advantage of smaller bending radii and a higher number of bending cycles.