JPH0316799B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resistive circuit board incorporating a metal thin film electrically resistive layer. A printed circuit board with a built-in resistor generally consists of an insulating layer that also serves as a support, a metal thin film electric resistance layer bonded to the insulating layer, and a conductive metal layer such as copper foil bonded to the resistance layer. It is provided in the form of a laminate, and during the fabrication of printed resistor circuits, the insulating areas (all the layers above the insulating layer are removed) and the resistive areas (the conductive metal layer is removed) according to the pattern of the intended circuit. ), as well as conductor regions (no layers removed) are formed to form the finished product. By the way, in a circuit board incorporating a metal thin film electrical resistance layer, in order to obtain a high sheet resistance, it is necessary to make the film thin, and at the same time, it is necessary to make the film thickness uniform in order to prevent variations in resistance value. Under such a premise, conventional circuit boards with built-in resistors have the following problems and drawbacks. a. In the case of a circuit board in which a metal thin film electrical resistance layer is laminated by plating or the like on a conductive metal layer such as copper foil, and an insulating support is further bonded on top of it, in order to form the resistance layer thinly and uniformly, In this case, the surface of the underlying copper foil must be smooth without any unevenness, and therefore, sufficient bonding strength of the insulating support cannot be obtained. In particular, when forming a nickel-based resistance layer, it is known that bonding with an insulating support such as epoxy resin, polyester resin, or polyimide resin has poorer adhesive properties than directly bonding with copper foil. (b) When forming a circuit by etching, the insulating support is easily attacked by the etching solution, and as a result, the resistor layer is likely to be distorted, leading to deterioration in performance. For example, the present inventors have provided a tin-nickel alloy as a resistor layer with excellent uniform electrodeposition, smoothness, etching selectivity, and stability of alloy plating composition (Japanese Patent Publication No. 55-42510). We have provided an etching solution specifically for nickel alloys (Japanese Patent Application Laid-Open No. 55-104481).
It must be carried out at temperatures above 10°C and therefore attacks epoxy resins, etc. (c) Epoxy resins and the like that have been commonly used as insulating supports are easily distorted by thermal treatments such as solder immersion, and are therefore prone to fluctuations in resistance. d In addition, insulating supports such as epoxy resins and polyimide resins have poor thermal conductivity, and the allowable power of the sheet resistance is limited due to restrictions from heat dissipation and heat resistance. The present inventors completed the present invention as shown below as a result of intensive research in order to solve the above-mentioned technical problems and drawbacks. That is, the resistance circuit board of the present invention includes a metal thin film electrical resistance layer, a conductive metal layer electrically contacted and bonded to one side of the resistance layer, and a conductive metal layer bonded to the other side of the resistance layer. The first invention is a circuit board having an electrically insulating layer, the electrically insulating layer being composed of a composite layer made of a synthetic resin and alumina powder, and the second invention is a circuit board having an electrically insulating layer made of a composite layer made of synthetic resin and alumina powder. It is constructed from prepreg in which glass cloth is impregnated with a mixture of resin and alumina powder. Further, a detailed explanation will be given with reference to the drawings. 1st
2 and 2 are cross-sectional views of the resistance circuit board. 1st
In the figure, a conductive metal layer 1 and an electrically insulating layer 3 are bonded to both sides of a metal thin film electrically resistive layer 2. In the first invention, the electrical insulating layer 3 is composed of a composite layer of synthetic resin and alumina powder, and in the second invention, the electrical insulating layer 3 is composed of a composite layer of synthetic resin and alumina powder on glass cloth. Constructed from impregnated prepreg. In this case, by forming the electrical insulating layer 3 relatively thick, it can also be used as a support for the circuit board. Also the second
As shown in the figure, a dedicated metal support 4 may be further bonded to the electrical insulating layer 3. When forming a thick prepreg or the like, multiple sheets are stacked one on top of the other. In the present invention, epoxy resins, polyimide resins, etc. are used as synthetic resins.
It is preferable to use a mixture containing 150 to 250 parts of alumina powder per 100 parts. In order to improve heat dissipation, it is preferable that the alumina powder particles have a particle size distribution of 1 to 50 μm. As the conductive metal layer 1, for example, a copper foil having a thickness of several tens of microns and whose surface is not roughened is used. Further, as the metal thin film electrical resistance layer 2, a Sn--Ni based alloy plating layer is formed to a thickness of several hundred angstroms. The electrical insulating layer 3 has a thickness of about several millimeters when used also as a support, and has a thickness of about several tens to hundreds of microns when a metal support 4 is separately bonded. Since the gold layer support 4 also aims to improve heat dissipation, it is preferable to use an aluminum plate with good thermal conductivity, and when using an aluminum plate, it is preferable to form an alumite layer of 5 to 30 μm on the surface to improve adhesive strength and The voltage resistance is also improved.
Note that the thicknesses of the layers 1, 2, and 3 described above are only a guideline, and are not limited thereto. Next, the resistor circuit board of the present invention will be explained along with its manufacturing process. For example, a copper foil is prepared as the conductive metal layer 1, one side of which is covered with a masking sheet, and after degreasing and washing with water, the metal thin film electrical resistance layer 2 is prepared using, for example, Sn-Ni alloy, Sn-Ni- Electroplating the S alloy. Next, the masking sheet is peeled off, and a synthetic resin sheet containing alumina powder, or a prepreg made by impregnating glass cloth with a mixture of alumina powder and synthetic resin, is thermocompressed as the electrical insulating layer 3 on the resistance layer 2 side. do. If the metal support 4 is to be further bonded, it is thermocompression bonded to the electrical insulating layer 3.
The resistor circuit board thus formed is formed into a desired resistor pattern circuit by a well-known method using photoresist, etching solution, etc. Next, an example of the present invention will be shown, and a performance comparison test using a conventional example as a comparative example will be shown. Example 1 - Electrical insulating layer 3 does not contain glass cloth and metal support 4 is not used. (1) Conductive metal layer 1: 35 μm electrolytic copper foil, no roughening treatment. (2) Metal thin film electrical resistance layer 2: 200 Å Sn-Ni electroplated layer, sheet resistance 500 Ω/□. (3) Electrical insulation layer 3: 5 sheets of 0.2 mm containing 100 parts of bisphenol epoxy resin and 250 parts of alumina powder (alumina 70% by weight)
Stack them to make a thickness of 1.0 mm. Example 2 - The electrical insulating layer 3 does not contain glass cloth and uses a metal support 4. (1) Conductive metal layer 1: Same as Example 1. (2) Metal thin film electrical resistance layer 2: Same as Example 1. (3) Electrical insulation layer 3: Same as Example 1. however,
The thickness of layer 3 was 0.1 mm. (4) Metal support 4: aluminum plate, thickness 1.0
mm. Example 3 - The electrical insulating layer 3 is made of prepreg containing glass cloth, and the metal support 4 is not used. (1) Conductive metal layer 1: Same as Example 1. (2) Metal thin film electrical resistance layer 2: Same as Example 1. (3) Electrical insulation layer 3: 10 sheets of prepreg made by impregnating 0.1 mm glass cloth with a mixture of 100 parts of bisphenol epoxy resin and 150 parts of alumina powder (60% by weight of alumina) are stacked to a thickness of
1.0mm. Example 4 - The electrical insulating layer 3 is made of prepreg containing glass cloth, and the metal support 4 is used. (1) Conductive metal layer 1: Same as Example 1. (2) Metal thin film electrical resistance layer 2: Same as Example 1. (3) Electrical insulation layer 3: Same as Example 3. However, the prepreg shall be one sheet, with a thickness of 0.1mm. (4) Metal support 4: aluminum plate, thickness 1.0
mm. A conventional example in which no alumina powder is mixed, with which the above Examples 1 to 4 should be compared. Conventional Example 1 - In Example 2, alumina powder is not mixed in the electrical insulating layer 3. Conventional Example 2 - In Example 3, alumina powder is not mixed into the electrical insulating layer 3. Performance comparison tests were conducted on the following: Test 1: Adhesion test of insulating layer 3 A 180° peeling test was conducted between the metal thin film electrical resistance layer 2 and the insulating layer 3. As a result, it was revealed that each example had twice the adhesive strength of the conventional example. Test 2: Corrosion resistance of insulating layer Phosphoric acid 13.0 mo1/l, cupric phosphate 5.0×
It was immersed at 85°C using an etching solution consisting of an aqueous solution of 10 ^-3 mo1/l. As a result, each example showed markedly higher corrosion resistance than the conventional example. Test 3: Resistance change before and after immersion in solder Immersed in a jet solder tank at 260°C for 20 seconds. Assuming the resistance value before immersion as R ₀ and the resistance value after immersion as R ₁ , (R ₁
−R ₀ )/R ₀ percentage was determined. As a result, those containing alumina powder were significantly improved compared to those without alumina powder, with (R ₁ − R ₀ )/R ₀ being 1.
% or less. Test 4: Rated power The power at which the resistance change rate after 1000 hours of load time at an ambient temperature of 70° C. was determined to be 0.3% was determined per unit area of the resistor. As a result, excluding the effect of the metal support (aluminum plate), each example had a rated power more than twice that of the conventional example. The above test results are shown in Table 1. Furthermore, the present inventors investigated (a) the case where the electrical insulating layer is made of alumina and synthetic resin, and (b) the case where the electrical insulating layer is made of prepreg made of glass cloth impregnated with alumina and synthetic resin, under the same conditions. When the withstand voltage was measured, it was found that the (b) prepreg was higher. In addition, we conducted an experiment on the warping of the board due to heating using an electrically insulating layer sandwiched between an aluminum plate as a support and a copper foil as a conductive metal, and the results were also similar to the above (b).

【table】

[Table] It has become clear that the board warps less when the insulating layer made of prepreg is sandwiched. In other words, it was found that prepreg is better in terms of substrate warpage and withstand voltage. Effects of the present invention According to the first invention and the second invention having the above configurations, the following effects are achieved. The bondability between the electrically insulating layer 3 and the metal thin film electrically resistive layer 2 is significantly improved. Therefore, roll lamination processing and the like can be easily performed in its manufacture. The corrosion resistance of the electrical insulating layer 3 against etching solutions and the like is greatly improved. In other words, distortion of the thin film resistance layer during the process of forming the resistance circuit is prevented, and a high performance resistance circuit can be manufactured. Even when subjected to thermal shock such as solder immersion, distortion is sufficiently prevented and stable resistance performance can be maintained. Since heat dissipation is improved by incorporating alumina powder, it is possible to increase the allowable power for the resistor. In this case, if an aluminum plate or the like is bonded to the insulating layer 3 as the support 4, heat dissipation is further improved.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views of resistor circuit boards showing specific examples of the invention. DESCRIPTION OF SYMBOLS 1... Conductive metal layer, 2... Metal thin film electric resistance layer, 3... Electric insulating layer, 4... Metal support.

Claims (1)

[Claims] 1. A thin metal film electrical resistance layer, a conductive metal layer electrically connected to one side of the resistance layer,
A resistive circuit board having an electrically insulating layer bonded to the other side of the resistive layer, wherein the electrically insulating layer is composed of a composite layer containing a synthetic resin and alumina powder, and the blending ratio thereof is The alumina powder is 40~
A resistive circuit board characterized by being 70% by weight. 2. The resistance circuit board according to claim 1, wherein the synthetic resin of the electrical insulating layer is an epoxy resin. 3. The resistance circuit board according to claim 1, wherein the synthetic resin of the electrical insulating layer is a polyimide resin. 4. Claim 1, wherein the metal thin film electrically resistive layer is a tin-nickel alloy.
2. The resistance circuit board according to item 2, item 3, or item 3. 5. The resistance circuit board according to claim 1, 2, 3, or 4, characterized in that the electrically insulating layer is formed thickly to serve as a support for the board. 6. Claim 1, characterized in that the electrically insulating layer is bonded to a metal plate support;
The resistance circuit board according to item 2, 3, or 4. 7. The resistance circuit board according to claim 6, wherein the metal plate support is an aluminum plate. 8. The resistance circuit board according to claim 7, wherein the surface of the aluminum plate is coated with an alumite layer having a thickness of 10 to 200 μm. 9. A resistive circuit board comprising a metal thin film electrically resistive layer, a conductive metal layer electrically bonded to one side of the resistive layer, and an electrically insulating layer bonded to the other side of the resistive layer, , the electrical insulating layer is composed of a prepreg formed by impregnating glass cloth with a composite of alumina powder and synthetic resin with an alumina powder blending ratio of 40 to 70% by weight. resistor circuit board. 10. The resistance circuit board according to claim 9, wherein the synthetic resin of the electrical insulating layer is an epoxy resin. 11. The resistance circuit board according to claim 9, wherein the synthetic resin of the electrical insulating layer is a polyimide resin. 12. The resistance circuit board according to claim 9, 10 or 11, wherein the metal thin film electrical resistance layer is a tin-nickel alloy. 13 Claims 9 and 10, characterized in that a plurality of prepregs are stacked to form a thick electrically insulating layer to serve as a support for the substrate.
12. The resistance circuit board according to item 11, item 11, or item 12. 14 Claim 9, characterized in that the electrically insulating layer is bonded to a metal plate support.
The resistance circuit board according to item 1, item 10, item 11, or item 12. 15. The resistance circuit board according to claim 14, wherein the metal plate support is an aluminum plate. 16. The resistance circuit board according to claim 15, wherein the surface of the aluminum plate is coated with an alumite layer having a thickness of 10 to 200 μm. Items 17 to 20 will be deleted.