Chip type resistor and its manufacture

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a chip type resistor having a particularly low resistance value of several mΩ to several hundred mΩ and a method for manufacturing the same.

【0002】

[Conventional technology]

Two structures are generally known as a chip type resistor having a particularly small resistance value. One is that electrode plates are welded to the left and right ends of a strip-shaped resistor with low resistivity, and insulating resin is molded on both the front and back sides of the resistor and the welded part to expose exposed parts of the electrode plate that are not resin-molded. , It is a structure that is bent toward the side surface and the bottom surface of the resin to form an external electrode. Since the mold material has both poor heat dissipation and high coefficient of thermal expansion compared to resistors, resistors molded on both the front and back sides tend to get hot when energized, and stress is applied as the temperature rises. Will be. For this reason, the resin-molded chip-type resistor is unstable because the temperature characteristics inherent in the resistor are not fully utilized and the resistance value tends to fluctuate when energized. Moreover, the mold used for the molding work is required for each different appearance specification, which is one of the causes of increasing the manufacturing cost.

【0003】

The other is that an insulating resin is interposed between a pair of electrode plates arranged at a slight distance on the left and right, and a resistor is provided on both electrode plates and the insulating resin via a film-shaped insulating layer. The structure is such that the left and right ends of the resistor and the left and right ends of both electrode plates are connected by a conductor, and a protective layer is further provided on the resistor. The resistor has poor heat dissipation on the surface coated with resin, but has an electrode plate on the back side via a thin insulating layer, and the electrode plate that occupies most of the bottom surface of the chip is inferior to the resistor. Since it has heat dissipation without heat, it has excellent heat dissipation on the back side, and as a result, it does not easily reach high temperatures. For this reason, this structure makes full use of the temperature characteristics inherent in the resistor, and the resistance value is stable when energized, but the electrode plate, which occupies most of the bottom surface, is inferior in corrosion resistance. There is a drawback that the reliability is lowered for long-term use.

【0004】

[Problems to be Solved by the Invention]

An object of the invention according to claim 1 is to provide a chip type resistor which has been made in view of the above circumstances, has high heat dissipation and corrosion resistance, and has a low manufacturing cost.

【0005】

An object of the invention according to claim 2 is to provide a chip type resistor having further improved heat dissipation in addition to the object of the invention according to claim 1.

【0006】

An object of the invention according to claim 3 is to provide a method for manufacturing a chip type resistor capable of achieving the object of the invention according to claim 1 and increasing the rate of occurrence of non-defective products.

【0007】

[Means for solving problems]

The chip-type resistor according to claim 1 is provided with terminal electrodes continuous in an L-shaped cross section on the left and right side surfaces of a rectangular ceramic substrate and the left and right edges of the bottom surface, and is non-conductive on the surface of the ceramic substrate. An adhesive layer is provided, and a conductive adhesive layer is provided on the outer surface of each terminal electrode. A metal foil having a U-shaped cross section surrounds the non-conductive adhesive layer and a pair of conductive adhesive layers, and resists the central piece of the metal foil. It is characterized in that the entire surface of the central piece is covered with a protective resin layer, and the left and right side pieces of the metal foil and the bottom surface of the terminal electrode are covered with a continuous plating layer having an L-shaped cross section.

【0008】

The outer surface of each terminal electrode is the left surface in the case of the left terminal electrode and the right surface in the case of the right terminal electrode.

【0009】

The above-mentioned chip type resistor may have a non-conductive adhesive layer provided at least on the surface of the ceramic substrate. Specifically, the chip type resistor may be provided only on the surface or continuous from the surface of the ceramic substrate to the left and right side surfaces of the terminal electrode. There is a form to be provided. However, in the latter case, it is necessary to expose a part of the side surface of each terminal electrode. This is because if it is provided over the entire side surface of each terminal electrode, there is no region where the conductive adhesive layer is provided. In addition, there is also a form in which the conductive adhesive layer is provided on the entire side surface of the terminal electrode or a part of the side surface.

【0010】

The heat of the resistor when energized is dissipated from two places, the protective resin layer and the ceramic substrate. However, in proportion to the heat dissipation of the material, the amount of heat radiation from the protective resin layer is smaller than that from the ceramic substrate. Since the heat of the resistor is transferred to the ceramic substrate via the non-conductive adhesive layer, it is desirable to use a material having excellent heat conductivity for the non-conductive adhesive layer. For example, as in the invention of claim 2, an epoxy resin-based material in which alumina powder is mixed may be used for the non-conductive adhesive layer.

【0011】

In the method for manufacturing a chip-type resistor according to claim 3, terminal electrodes are formed on the left and right side surfaces of a rectangular ceramic substrate and the left and right edges of the bottom surface, and a non-conductive adhesive layer is provided on the surface of the ceramic substrate. After providing a conductive adhesive layer on the outer surface of each terminal electrode, a metal foil having a U-shaped cross section is covered, the non-conductive adhesive layer is covered by the central piece of the metal foil, and a pair of left and right side pieces of the metal foil are used. It is characterized in that it covers the conductive adhesive layer, subsequently forms a protective resin layer over the entire surface of the central piece, and provides a plating layer on the left and right side pieces and the bottom surface of the terminal electrode.

【0012】

The manufacturing method according to claim 3 already has a non-conductive adhesive layer on the surface of the ceramic substrate and a conductive adhesive layer on the side surface of each terminal electrode when the metal foil having a U-shaped cross section is covered. However, as in the invention of claim 4, after the non-conductive adhesive layer is provided on the surface of the ceramic substrate, the conductive adhesive layer is covered with the metal foil previously adhered to the inner surfaces of the left and right side pieces, and the center of the metal foil is covered. A method of covering the non-conductive adhesive layer with a piece and covering the side surface of each terminal electrode with a pair of conductive adhesive layers may be used.

【0013】

Since the product manufactured by the above-mentioned manufacturing method uses a metal foil having a U-shaped cross section, the variation in resistance value is reduced and the non-defective rate is improved. The reason is described below. The resistance value depends on the area where the protective resin layer covers the surface of the central piece of the metal foil. Since the protective resin layer is provided over the entire surface of the central piece, theoretically, if the surface area of the central piece is constant, the resistance value becomes constant. Since the metal foil has a U-shaped cross section, the area of the central piece is constant in all products. Even if the area of the central piece is the same, the quality is slightly different, so that the resistance value is actually slightly different for each product.

【0014】

It is important for the metal foil to have a U-shaped cross section in order to improve the non-defective rate, and if the metal foil has a different shape, for example, a strip shape, the non-defective rate decreases. More specifically, when the central part of the strip is placed on the adhesive layer provided on the ceramic substrate and then the left and right ends of the strip are folded back along the left and right side surfaces of the ceramic substrate, the center of the strip corresponding to the central piece is formed. This is because the left and right lengths of the parts vary from product to product.

【0015】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the chip-type resistor according to the present invention will be described based on a manufacturing method.

【0016】

As shown in FIGS. 1 and 2, a metal leaf sheet 1 and an elongated rectangular ceramic board 2 are prepared as materials. The metal foil sheet 1 is made of Cu-Ni, Fe-Cu, Ni-Cr, etc. and has a thickness of 30 μm to 250 μm. The ceramic board 2 is provided with a large number of ceramic substrates 3 continuously along the longitudinal direction, and a groove 4 for division is interposed between the adjacent ceramic substrates 3 and 3 on the surface.

【0017】

First, by etching or pressing the metal foil sheet 1, a large number of strips 5 having a desired length and width are produced. The strip 5 is subjected to a measuring and sorting machine, and the resistance value is divided into those that fall within the predetermined tolerance and those that fall out of the predetermined tolerance. Subsequently, the strip 5 that is within the tolerance is pressed to form a metal foil 6 having a U-shaped cross section that opens downward. For convenience, each part of the metal leaf 6 is labeled as follows. Central piece 6a, left side piece 6b, right side piece 6c. The central piece 6a is a resistor.

【0018】

On the other hand, regardless of the processing of the metal foil 6, the conductive paste is screen-printed along the longitudinal direction on the left and right side surfaces of the ceramic board 2 and the left and right edges of the bottom surface, and fired to the left and right of each ceramic substrate 3. Terminal electrodes 7 having an L-shaped cross section are formed from the side surface to the left and right edges of the bottom surface. As the conductive paste, Pd-Ag, Ni, Pb-Sn or the like is used.

【0019】

Next, as shown in FIG. 3, an adhesive is applied to the surface of the ceramic board 2 to form the non-conductive adhesive layer 8. The coating area is set at the central portion in the vertical direction of each ceramic substrate 3 and is set to an area wider than that of the metal foil, and the groove 4 is exposed. Subsequently, cream solder is applied to the left and right side surfaces of each terminal electrode 7 to form the conductive adhesive layer 9, and the coated area is aligned with the non-conductive adhesive layer 8 described above. After that, the metal foil 6 is covered, the non-conductive adhesive layer 8 is covered with the central piece 6a, and the conductive adhesive layer 9 is covered with the left and right side pieces 6b and 6c. The edges of the non-conductive adhesive layer 8 are exposed before and after the central piece 6a (upper and lower in the drawing), and the edges of the conductive adhesive layer 9 are exposed before and after the left and right side pieces.

【0020】

Subsequently, the central piece 6a is pressed against the surface of the ceramic substrate 3 to be adapted to the non-conductive adhesive layer 8, heated to cure the non-conductive adhesive layer 8, and the metal foil 6 is fixed to the ceramic substrate 3. Further, by reflowing and melting the conductive adhesive layer 9 once and then cooling it, the terminal electrode 7 and the left and right side pieces 6b and 6c are firmly integrated via the conductive adhesive layer 9 to ensure continuity. It shall be. After that, a resin paste is applied to the surface of each of the ceramic substrates 3 subjected to the above treatment so as not to cover the grooves 4, and the protective resin layer 10 is formed by curing to form the entire surface of each central piece 6a and non-conductive. The front and rear edges of the adhesive layer 8 are covered with the protective resin layer 10. Next, the ceramic board 2 is folded along the groove 4 to divide the processed ceramic substrate 3 into a large number of pieces. Since the groove 4 is exposed, it is easy to divide. Finally, each ceramic substrate 3 is solder-plated or nickel-plated to form a plating layer 11 having an L-shaped cross section, and the surface of the left and right side pieces 6b and 6c and the bottom surface of the terminal electrode 7 are covered. It will be a finished product.

【0021】

The present invention is not limited to the above-described embodiment. For example, in the drawing, the protective resin layer 10 is provided so as not to cover the groove 4, but it may be provided over the entire surface of the ceramic board 2 so as to cover the groove 4. Similarly, the non-conductive adhesive layer 8 may be provided on the entire surface of the ceramic board 2, and the conductive adhesive layer 9 may be provided on the entire side surface of the terminal electrode 7.

【0022】

[Effect of the invention]

The chip-type resistor according to claim 1 has a ceramic substrate on the back surface of the resistor via a non-conductive adhesive layer, and the ceramic substrate has a characteristic of excellent corrosion resistance, which ensures reliability of long-term use. improves. Since the ceramic substrate has the characteristics of excellent heat dissipation and small thermal expansion, the resistor does not easily become hot when energized, and stress is less likely to be applied, so that the temperature characteristics inherent in the resistor are exhibited. As a result, the fluctuation of the resistance value at the time of energization becomes small and stable. In addition, since the structure is not resin-molded, a mold is not required and the manufacturing cost can be reduced.

【0023】

The chip-type resistor according to claim 2 uses an epoxy resin-based material in which alumina powder is mixed with a non-conductive adhesive layer, and alumina has excellent thermal conductivity. Therefore, the heat of the resistor is increased. Is easily transmitted to the ceramic substrate, and heat dissipation can be further improved.

【0024】

Since the product manufactured by the method for manufacturing a chip-type resistor according to claim 3 uses a metal foil having a U-shaped cross section, the area covered by the protective resin layer on the surface of the resistor is any. The products will be equal and the non-defective rate will improve.

[Simple explanation of drawings]

[Figure 1]

It is a process drawing which shows the procedure of forming a metal foil having a U-shaped cross section from a metal foil sheet.

[Figure 2]

It is a process diagram which shows the procedure of forming a terminal electrode on a ceramic board, and is the AA line sectional view of each process.

[Fig. 3]

It is a process diagram which shows the procedure of making the chip type resistor by this invention from the ceramic board which formed the terminal electrode, and the metal foil which has a U-shaped cross section, and is the AA line sectional view of each process.

[Explanation of symbols]

3 Ceramic substrate 6 metal leaf 6a Central piece (resistor) 6b Left piece 6c right side piece 7 terminal electrode 8 Non-conductive adhesive layer 9 Conductive adhesive layer 10 Protective resin layer 11 Plating layer