JPH0671142B2 - Method for manufacturing multilayer printed circuit board - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a high-density multilayer printed circuit board used in electronic devices and parts.

(Prior Art) As a printed circuit board capable of high-density mounting, generally, a unit in which a predetermined circuit pattern is previously formed by resist etching treatment by laminating Cu foil on both surfaces of a resin substrate such as glass epoxy resin, Those in which a conductive circuit is formed by through holes after laminating and solidifying these several sheets have been widely put into practical use. However, in this case, since the resin is a relatively thick substrate which is inferior in heat transfer property, its heat dissipation property is poor and it is practically inconvenient in many cases. In order to deal with this, a multilayer substrate using a ceramic substrate is a computer,
It is widely used in automobiles, industrial equipment, etc. However, the ceramic substrate is not limited to its size,
The cost is high and the manufacturing yield is low, which causes a high price, and there is a limit to the improvement of heat dissipation.

(Problems to be Solved by the Invention) Here, there is a wide demand for a multilayer circuit board having excellent heat dissipation characteristics and improved economical efficiency, and in order to meet this demand, it is urgently necessary to establish a new method for manufacturing a multilayer circuit board. ing.

(Means for Solving the Problems) The present invention relates to a circuit of a second layer and a third layer or more on a first layer circuit formed by an arbitrary method on a substrate such as a metal, a ceramic or a resin which has been subjected to an insulation treatment. Is a method for obtaining a multilayer circuit board by forming the above-mentioned problem without causing the above problem, which will be specifically described below with reference to FIG.

Especially when the heat dissipation is important, a metal plate of Al, Cu, Fe or the like is suitable as the base 1. First, the first layer circuits 3 and 3 ′ are formed on the substrate 1 with the first insulating layer 2 interposed therebetween. Usually, at least a part of the first insulating layer 2 is used as an adhesive, for example, 35
It is industrially advantageous to form the above-mentioned first layer circuit by laminating a Cu foil of about μ or about 18 μ and performing a resist etching process. As the first insulating layer 2, a resin such as epoxy, phenol polyamide, or polyimide is useful,
In this case, in order to improve the heat transfer and mechanical strength mentioned above, BN, A
_{l 2 O 3, TiO 2,} AlN, the ceramic powder such as ZrO ₂ 5 to 40%
Mixing is effective.

Next, through studs 4 for electrically connecting the first layer circuit and the second layer circuit are formed on the first layer circuit by using a conductive paste. The conductive paste usually contains powder such as Cu, Ag, AgPd and Au in an amount of 60 to 95% (the metal powder / metal powder + resin) and has a specific resistance of 2 to 10 ₄ mΩ / cm. As the resin component, phenol, modified phenoxy, epoxy, imide or the like is used. In addition to these components, a solvent such as butyl carbitol and various additives for the purpose of adjusting viscosity and preventing oxidation are mixed and blended. The width of the first and second layer circuits is usually about 0.1 to 0.7 mm width, and
The thickness of the insulating layer is about 0.03 in consideration of electric insulation and heat dissipation.
It is about 0.1 mm. Furthermore, the through stud has a cross section of approximately 0.3 to 1 m.
mΦ and a height of 0.03 to 0.15 mm, or a prism like this. Such minute through studs usually have to be formed at a high density of about 1 to 10 pieces / cm ^{2 in} a high-density printed circuit, and in order to reliably carry out this industrially, the screen printing method is used. Most preferably, it is done. Conductive paste screen-printed by the conventional method is about
It is heated and solidified at a temperature of 150 to 250 ° C.

Next, an insulating resin is used to form the second insulating layer 5 on the first layer circuit by using the same resin as the first insulating layer 2. In this case, it is most preferable to perform the screen printing method so as to surely form the resin in layers without damaging the through studs 4 or the like, and more than twice in order to form a resin layer having a constant thickness without defects. It is desirable to perform the screen printing separately. In particular, it is desirable that the gap portion 6 of the first layer circuit be filled with resin in advance before the step of forming the through stud. The thickness of the second insulating layer 5 may be equal to or higher than the top of the through stud 4.

Next, a Pd catalyst is deposited and formed in substantially the same shape as the second layer circuit pattern 9 described later. As this catalyst adhesion method, a Pd-containing catalyst paste is printed by a screen printing method, or a peelable resist is preliminarily printed on the entire surface and the treated portion is subjected to an etching treatment to roughen and activate the surface of the portion, and Pd A method is suitable in which Pd is adsorbed by appropriately contacting the contained solution to peel off the resist. Further, as a more industrially reliable and more efficient method, the entire surface is previously etched and the above-described Pd adsorption is performed on the entire surface, and then the second layer circuit pattern 9 and 9'is left and the other part is covered with a resist. Processing 8,8 ′
It is to be. In this case, providing a resin composition that is easily etched in advance on at least the surface layer portion of the insulating layer 5 helps improve the adhesiveness of the second layer circuit. Specifically, it is desirable to thinly screen print the adhesive layer 7 containing a small amount of rubber on the surface layer of the insulating layer such as epoxy resin.
As the rubber component, nitrile rubber, butadiene rubber, natural rubber or the like is used. The rubber component is preferentially oxidized and etched by the treatment with an etching solution using CrO ₃ or the like, so that both the effects of roughening and activation can be exhibited.

Next, this is immersed in a chemical plating solution and the second layer circuit 9, 9 '
To form. Examples of the plating metal include Cu, Ni, Ag, Au, Su and the like, but combinations thereof are also used. In particular, Cu is most practical as a conductor that is commonly used industrially, but
It is advantageous in terms of adhesiveness that Ni is plated first and then Cu is plated thereon. Various additives such as metal ions, complexing agents and reducing agents are generally added to the chemical plating solution. By such chemical plating, plating continuously occurs on the insulating layer that adsorbs Pd and on the surface of the through stud where the top is exposed. For example, in Cu plating, the reduction reaction of Cu ⁺⁺ ions with formalin is not limited to Pd, but Cu, Pd, Ag,
It is also caused by through stud conductive particles such as Au. The thickness of the second layer circuit depends on the purpose of use and conditions, but is generally 10 to 30 μm.

In the present invention as described above, in the case of forming a multi-layer circuit in the third layer or more, it can be easily carried out by repeating the steps for forming the second layer. In the figure, the catalyst attachment portion is represented by C.

(Operation) In the present invention, when a metal plate of Al, Cu, Fe or the like is used as the substrate, it is possible to exhibit a high heat dissipation property equal to or higher than that of the ceramic multilayer circuit substrate as well as the multilayer circuit of the resin substrate. Enables mounting of dense electronic components.
In addition, since the resin is particularly used for the insulating layer and the thickness can be made as thin as possible by the screen printing method, the above-mentioned obstacle of heat dissipation can be minimized. This is remarkably clear in comparison with the conventional glass epoxy-based multi-layered product. That is, in the conventional example, a large amount of voids remain in the substrate, which is a cause of remarkably lowering the electrical insulating property.
The equivalent product that can exhibit a high insulation property of 1000 mΩ or more at a thickness of 0.02 to 0.05 mm requires a thickness of 0.1 to 0.2 mm. Further, the voids may cause water or electrolyte to permeate, and the same may occur with ceramics.

Next, the above-mentioned through stud of the present invention is made of conductive paste and generally has a larger electric resistance than metal, but as described above, not only is it a short distance, but it has a large cross-sectional area as compared with the conventional through hole structure. Therefore, it can be completely ignored as the circuit resistance. Further, since the connection between the through stud and the circuit is firmly formed, it is possible to endure heat and mechanical stress for a long period of time, and high reliability can be maintained.

Example 1 Polyamide containing 15% Al ₂ O ₃ in an Al plate (thickness 1.2 mm)
Cu foil (35μ thickness) through the imide resin layer (thickness 0.04mm)
Glued. A resist treatment was carried out by a screen printing method by a conventional method, and then a first layer circuit was formed by etching with a FeCl ₃ solution. The circuit width is mainly 0.3 mm, and the land part where the through stud stands is 0.5 mm. Next, containing 85% electrolytic Cu powder with an average particle size of 7μ and 15% resol type phenolic resin,
A conductive paste containing a small amount of butyl carbinol and acetate as a solvent was used to form through studs with a diameter of 0.5 mm and a height of 0.05 mm by screen printing.
It was heated and solidified for a minute. Next, add 15% Al to the epoxy resin.
_{A second} insulating layer was provided by screen printing using an insulating paste containing ₂ O ₃ and was similarly heated and solidified. The surface of the insulating image was about 0.005 to 0.01 mm below the top of the through stud.

Then, immerse this in a 30% H ₂ SO ₄ solution at 80 ° C for 15 minutes,
Further, it was dipped in a 0.2 wt% PdCl ₂ solution for 1 minute, and then another portion was screen printed using an epoxy resin paste while leaving the shape of the second circuit. After heating and solidifying 10
% HCl solution for 1 minute, then immersed in a Cu plating bath (ELC-HS, Uemura Kogyo Co., Ltd.) at 65 ° C for 5 hours to obtain about 25μ in the unprinted area.
A thick Cu plating was formed to form a second layer circuit to obtain a highly heat conductive circuit board in which a two-layer printed circuit was provided on one surface of an Al plate.

Example 2 Without performing the above Ni plating in Example 1, directly
A similar circuit board was obtained in the same manner except that Cu plating was performed.

Example 3 In Example 1, after forming the second insulating layer, an epoxy paste containing 25% of nitrile rubber was screen printed to a thickness of about 7 μm. Then, a treatment was carried out for 5 minutes using a 65 ° C. solution of CrO ₃ 150 g / l, and thereafter, the steps after the catalyst adhesion treatment were similarly continued to obtain a similar circuit board.

Example 4 In Example 1, after forming the second insulating layer, a catalyst paste containing Pd (GP-150, Okuno Seiyaku Co., Ltd.) was screen-printed in substantially the same shape as the second circuit, and then heated. After solidification, Ni and Cu were plated in the same manner to obtain a similar circuit board.

Comparative Example A similar circuit board was obtained in the same manner as in Example 1 except that a glass epoxy board (1.0 mm thick) was used instead of the Al plate.

For each of the above example products, in accordance with MIL 107 method,
The temperature cycle with 25 ° C. was repeated 100 times, and the electric resistance of the circuit before and after that was measured. Also, in the electrode pad part (2 x 3 mm) on which the electronic component is mounted by soldering on the second circuit path.
A 1.0 Φmm Cu wire was soldered and a tensile test was performed to measure the adhesive force. Furthermore, in order to examine the heat dissipation, an IW diode was mounted and the thermal resistance was similarly measured from the temperature measurement above and below the substrate. The above results are summarized in the table below.

The results in the table are self-explanatory, and all of Examples 1 to 4 show stable sheet resistance values, that is, Examples 1 to 4 using a metal plate are about 1/3 of the glass epoxy comparative example. Stayed in heat resistance. In addition, the adhesive force of the circuit in Example 3 showed a particularly large value. Although the value in Example 2 was a little small, all were practically sufficient.

(Effect) As is clear from the above description, according to the method of the present invention,
A novel multilayer printed circuit board, which is indispensable for miniaturization and high functionality of electronic devices, can be manufactured significantly economically. As is clear from the examples, when a metal plate is used as a base, the heat dissipation becomes extremely excellent, and as a result, small parts can be mounted at high density, and further development is expected in the future. This has the effect of providing a multilayer printed circuit board that is optimal for mounting.

[Brief description of drawings]

The drawings are cross-sectional explanatory views of a circuit board according to an embodiment of the present invention. 1 ... Substrate, 2, 5 ... Insulating layer, 3, 3 ', 9, 9' ... Circuit, 4
…… Through stud, C …… Catalyst attachment part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Tani 500 Kiyotakicho, Nikko City, Tochigi Prefecture Nikko Research Institute, Furukawa Electric Co., Ltd. (56) References JP 55-158697 (JP, A) JP 50 -64767 (JP, A) JP-A-51-58667 (JP, A)

Claims (4)

[Claims] 1. When a second layer or more circuits are formed on a first layer circuit formed by an arbitrary method on a substrate to obtain a multilayer circuit board, (i) a desired portion of the first layer circuit A through stud made of a conductive paste for electrically connecting to a second layer circuit is formed on the first layer, and (ii) an insulating layer made of an insulating resin for insulating the first and second layer circuits is formed on the first layer. It is formed so that at least the through stud top is exposed on the circuit. (Iii) Next, the Pd catalyst adhesion treatment is applied to the surface of the insulating layer in the same shape as the second layer circuit pattern to be formed, (Iv) Then, a metal plating layer is formed to a desired thickness by chemical plating to form a second layer circuit.
A method for manufacturing a multilayer printed circuit board, which is formed by repeating the operation of (iv). 2. The method according to the preceding paragraph, wherein the steps (i) and (ii) are performed by a screen printing method. 3. The method according to claim 1, wherein the step (iii) is performed before depositing a Pd catalyst on the entire surface and then covering the remaining portion with a resist while leaving a surface layer in the second layer circuit pattern shape. . 4. The method according to claim 1, wherein a metal plate is used as the substrate.