JPH01259596A - Manufacture of printed wiring board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a printed wiring board.

[Conventional technology]

In recent years, in addition to the characteristics of flame retardancy, heat dissipation, electromagnetic shielding, load-bearing strength, dimensional stability such as warpage, twisting, expansion and contraction, and machinability such as bending and drawing, silicon steel sheets have been improved. The use of metal-based printed wiring boards that utilize magnetic properties is rapidly increasing. Currently, many single-sided printed wiring boards with one layer of wiring on one side of an iron plate base are used for small precision motors for VTRs, FDDs, and HDDs as metal-based printed wiring boards.

Recently, in response to demands for higher density wiring and higher density packaging, double-sided through-hole wiring boards have been put into practical use. ° Conventionally, as a method to improve the wiring density of metal-based printed wiring boards, holes are drilled in the metal plate, powder coating or electrodeposition coating is performed to form an insulating film, and then the desired thickness is formed using a known process. There is a method of manufacturing a double-sided through-hole wiring board by performing copper plating and creating a desired pattern.

[Problem to be solved by the invention]

However, in such conventional manufacturing methods, when using powder coating, there are limits to the accuracy of the finished hole diameter and control of the surface coating film thickness, making it difficult to produce high-density wiring boards. There were many. In addition, when performing electrodeposition coating, equipment costs such as electrodeposition coating equipment and waste liquid treatment are significant, and current leaks easily occur from coating pinholes, which poses many problems in terms of quality and cost. .

As a method to improve these problems, there is a method of laminating a resin-impregnated fibrous sheet on a metal plate with holes punched at predetermined positions (Japanese Patent Publication No. 5B-37720), but this method requires an expensive method. Lamination press equipment and advanced lamination technology are required, and there is a risk of blowholes occurring and leaking into the base material during through-hole copper plating. Further, the cost of drilling through-holes is high, and it is technically and cost-problematic to drill the through-holes twice concentrically with high precision, making this technique impractical.

Since double-sided through-hole wiring boards have the above-mentioned problems, attempts have been made to improve the wiring density of metal-based printed wiring boards by forming multilayer wiring on one side of the metal base instead. . However, such printed wiring boards have a problem in that the adhesion strength between the copper foil and the conductive paste is low. In other words, 1. Normally, commercially available untreated copper foil is used as the copper foil for the lowest layer wiring of multilayer wiring, so the adhesion between the conductive paste and the land made of the copper foil is poor, and commercially available conductive paste In some cases, an adhesion strength of less than 0.1 kg/mrn" can be obtained. Conductive pastes selected from the viewpoint of adhesion strength with copper foil often have low conductivity, and in such cases, In order to form an upper layer circuit with excellent conductivity, it is necessary to improve the conductivity of the upper layer circuit by performing electroless plating on the paste.

The present invention was made to solve these problems, and its main purpose is to solve the problem that even if a conductive paste with excellent conductivity is used, the adhesiveness between the paste and the copper foil at the bottom layer is insufficient. Therefore, it is an object of the present invention to provide a method for manufacturing a highly reliable, low-cost, and high-density printed wiring board.

[Means to solve the problem]

The present invention comprises: (a) a step of forming a lower layer circuit on a substrate via an insulating layer; (b) a step of laminating an insulating layer on the lower layer circuit leaving a land portion which is a connecting portion with an upper layer circuit. and (c) forming an upper layer circuit connected to the lower layer circuit at the land portion on the insulating layer using a conductive paste, the land portion being connected to the lower layer circuit using the conductive paste. The method of manufacturing a printed wiring board is characterized in that the land is previously subjected to a treatment to improve adhesion to the conductive paste.

Hereinafter, the manufacturing method of the present invention will be explained in detail along with the steps.

First, an insulating sheet is laminated on one side of the substrate. The insulating sheet may be epoxy-impregnated glass fiber, polyimide film, or the like. A copper foil of 18p, m, 35pm, or any other thickness that has been treated to improve adhesion is bonded thereon. The bonding method may be a press method, a roll method, or the like.

Note that the manufacturing method of the present invention is characterized by using a copper foil or the like that has been subjected to the above-mentioned adhesion improving treatment.

The copper foil may be treated by electrodepositing fine particles of copper and copper oxide on the surface of the copper foil. Note that the treatment only needs to be applied to at least the land portion of the copper foil where the conductive paste is laminated; for example, steel foil may be treated on one side or on both sides, or it may be treated on only the land portion. However, from the viewpoint of processing cost, single-sided and entire surface processing is preferable.

Next, the substrate (copper-clad metal plate) on which the copper foil is laminated is washed and dried, and then an etching resist film with a shape corresponding to the desired land and circuit is formed on the copper foil, and then etching is performed to remove the etching resist. The necessary parts of the copper foil are melted and removed to form the lower layer circuit. Next, remove the unnecessary etching resist film, leave the desired land area necessary for connection, and form an insulating paste film to a predetermined thickness or more, and then apply a conductive paste containing copper, silver, silver palladium, etc. A desired circuit is formed thereon using a printing method.

The resin components of the paste include, for example, resol type phenolic resin (70 wt%) and butyral resin (30 wt%).
(wt%) mixed resin.

In conventional methods, it was necessary to use a paste that had excellent adhesion to copper foil at least at the cost of sacrificing conductivity to some extent, but in the manufacturing method of the present invention, a process to improve adhesion was performed. Since copper foil is used, the adhesion to the copper foil is sufficient even if a conductive paste with a low electrical resistance value is used. Its adhesion strength is at least 1.2kg
/am'' is obtained, and the tensile strength measured by the printed wiring board standard copper foil adhesion strength measuring method is also 1.8 kg/c+w or more.

When particularly high conductivity is required for a circuit formed using a conductive paste, or when soldering to the paste is impossible, electroless plating may be performed on the paste. At this time, if a conductive paste with a copper powder content of 70% or more is used, electroless copper plating can be deposited through normal degreasing and pickling without special pretreatment such as Pd treatment, and it is also possible to deposit electroless copper plating without any special pretreatment such as Pd treatment. Electrolytic nickel plating, electroless tin plating, etc. may be used.Next, an insulating paste film is formed leaving a connection land, and then a desired circuit is formed using conductive paste. Multilayer printing can be achieved by sequentially overprinting. can.

Next, an overcoat or solder leveler finish is applied as necessary to complete the printed wiring board. The manufacturing method of the present invention does not require a drilling process that increases cost or tends to cause reliability problems, does not require any special equipment, and can be manufactured by freely selecting commercially available conductive paste as the material without special specifications. Therefore, it becomes possible to mass-produce printed wiring boards that are inexpensive, highly reliable, and satisfy the requirements for high density.

That is, by using, for example, a metal substrate as the substrate used in the method of the present invention, the problems associated with conventional metal-based printed wiring boards as described above can be solved. However, the substrate used in the method of the present invention is not limited to metal substrates, and includes, for example, ceramics, plastics,
It is also effective to use a substrate such as glass or processed paper.

〔Example〕

The present invention will be explained in more detail below with reference to Examples.

Example 1 First, 50IL was applied to one side of a 1.0 mm thick silicon steel plate 101 (Kobe Steel Shinsei S-30) with a screen adhesive 102.
Polyimide film 103 and double-sided treated copper foil 104 made by Mitsui Mining and Mining Co., Ltd. (DT wheel) were stacked, and a cellulose triacetate film was placed on the other side of the steel plate, and then hot pressed at 150°C and a pressure of 15kg/cm' for 15 minutes. After being crimped for 2 minutes, it was left in a 130°C oven for 2 hours to bond, and then left to cool to form the laminate shown in Figure 1 (A).Then, it was degreased and pickled, followed by water washing and drying. Copper foil 1
04 to form the desired pattern, dissolve and remove the unnecessary copper foil using a cupric chloride aqueous solution, dissolve the unnecessary dry film with a 1.0% sodium hydroxide aqueous solution, wash with water, and dry. Then, as shown in FIG. 1(B), the copper foil 10
After forming the desired pattern No. 4 on the copper foil 104, leaving the desired lands, an insulating film 105 as shown in FIG. A conductive paste containing copper powder manufactured by Mitsui Mining and Mining Co., Ltd. was formed into a conductive paste of 40 square meters or more, heated and solidified, washed with a 10% sulfuric acid aqueous solution, washed with water, and dried.
8 (S-5000) to form a desired circuit as shown in FIG. 1(D). Dry and solidify at 180℃ for 30 minutes, the film thickness of the circuit is 30~35 lm, and the resistance value is 3×
It was less than 10''Ω・cIB.Next, as shown in Figure 1(E), solder resist paste (Taiyo Ink Acid,
After forming the overcoat 107 using solder paste (S-40), finish with a solder leveler and place the solder 10 at the desired position.
After several days, a metal-based two-layer printed wiring board was obtained.

The bonding strength between the specially processed copper foil surface and the conductive paste was extremely excellent, and a value of around 2.0 kg/mrrf was obtained.
Even after the humidification test for too long, there was almost no change in electrical conductivity and adhesion strength.

Example 2 A pattern of copper foil 204 was formed as shown in FIGS. 2(A) and 2(B) in the same process as in Example 1.
As shown in C), an insulating film 205 of 40 g or more is formed using solder resist paste (5-22 manufactured by Taiyo Ink) by screen printing method, leaving the desired lands of the copper foil 204, and after hardening by heating, it is coated with a 10% sulfuric acid aqueous solution. Washing, rinsing,
Dry. Conductive paste containing copper powder made by Mitsui Mining & Smelting Co., Ltd.) 20
B (PC-5000) was used to form the desired circuit as shown in Figure 2 (D), and the circuit was dried and solidified at 180°C for 130 minutes.Next, it was degreased and pickled, and then placed in an electroless copper plating bath. After dipping for a period of time, a copper plating film of 3 liters as shown in FIG. 2(E) is formed. was formed on the copper paste circuit and lands. The resistance value of the circuit after copper plating is lXl0-6Ω・
cm or less.

The electroless copper plating bath composition and conditions were as follows.

Copper sulfate pentahydrate: 10g Sodium ethylenediaminetetraacetate: 30g formalin,
6mj polyethylene glycol (average molecular weight eoo): 13g Sodium hydroxide: ・Amount to reach pH 12.5 (20℃) Water:
Bath load totaling one sentence 1 drn'/bath or less at 70°C, then overcoat 208 with a solder resist film leaving desired land portions on the copper plating film 207 as shown in FIG.
The one component attachment part was finished with a solder leveler and solder 209 was applied. Copper foil 204 and conductive paste 20
The adhesion strength of the connection portion with No. 8 was measured at 20 locations, and the strength at all locations was 1.2 kg/mrn' or more, and a metal-based two-layer printed wiring board with satisfactory reliability was obtained.

Example 3 First, a 1.5+*m thick aluminum alloy plate 301 (5
052) Layer two sheets of B-stage epoxy Repreg 302 (Matsushita R1eB10.08+sm) and two sheets of single-sided adhesion improvement treated (single-sided treated) 'ii4 foil 30435 l (manufactured by Mitsui Mining & Mining Co., Ltd.) on top, with the treated side facing up, and place the aluminum A cellulose triacetate film 303 is placed on the other side of the alloy plate 301, and the film is sandwiched between the molds and heated at 175°C for 40 minutes.
0 kg/cm' for 60 minutes to obtain an aluminum base single-sided copper-clad laminate as shown in FIG. Asahi Kasei AQ2011) was crimped to form the desired lands and circuits, the unnecessary steel foil was dissolved and removed by etching, and the unnecessary dry film was removed and thoroughly washed with water.
After drying and forming the desired pattern of the copper foil 304 as shown in FIG. 3(B), solder resist paste (
Taiyo S-40) was printed, heated and solidified to form an insulating layer 305 of 40Jj, 111 or more as shown in FIG.
6 (MDP-901 manufactured by Mitsui Toatsu Chemical Co., Ltd.), a circuit as shown in Fig. 3 (D) was formed by screen printing method,
The product was baked in an oven at IEiO°C for 30 minutes, and then a solder resist 111307 was formed, leaving desired lands for parts attachment, as shown in FIG. 3(E), to produce an aluminum-based two-layer printed wiring board.

The bonding strength between the specially processed copper foil surface and the conductive paste was extremely excellent, and a value of around 2.0 kg/I1m'' was obtained.
There was almost no change in electrical conductivity and adhesion strength even after a 1000 hour humidification test.

Example 4 A photosensitive dry film (#882 manufactured by Hitachi Chemical) was bonded to the copper foil 404 side of a steel plate base DT copper foil clad laminate as shown in FIG. 4(A), which was manufactured in the same manner as in Example 1. ,
As shown in FIG. 4(B), desired lands and circuits are formed, and the second chloride t! The unnecessary portions of the copper foil were dissolved and removed using a solution consisting of 4,200 g/liter and 20 g/liter of hydrochloric acid, and then the unnecessary dry film was peeled off using a 3% aqueous sodium hydroxide solution. Next, using insulating ink based on bismaleide triazine resin, leave the land area necessary for connection and screen print the other parts as shown in Figure 4 (C).
As shown in FIG. After drying and solidification, pickling and drying were performed, and a desired circuit was formed as shown in FIG. 4(D) using conductive paste containing copper powder 40B (FL-1000-3) manufactured by Mitsui Mining and Mining.

After baking in an oven at 160° C. for 30 minutes, leaving the necessary land portions, 40 layers or more of the insulating ink layer 407 is formed in the same manner as above as shown in FIG. 4(E).
As shown in Figure (F), the copper powder-containing conductive paste 40
8 (Ft, -1000-3) to form a desired circuit. Subsequently, as shown in FIG. 4(G), an overcoat layer 403 was formed using the insulating ink, leaving desired parts such as parts mounting parts, and then immersed in the electroless copper plating bath used in Example 2 for 30 minutes. Then, as shown in FIG. 4(H), copper plating 410 is formed, and after drying, it is finished with a solder leveler, and solder 411 is formed as shown in FIG. 4(1) to form a copper plate-based three-layer printed wiring board. Manufactured.

The bonding strength between the specially processed copper foil surface and the conductive paste was very good, with a value of around 2.0 kg/+m''.10
There was almost no change in electrical conductivity and adhesion strength even after the 00 hour humidification test.

Comparative Example 1 1mm thick iron plate base copper clad laminate using ordinary copper foil (Kobe Steel KO9PRIT RIF-B100O
) was treated in the same manner as in Examples 1 and 2, and the upper layer copper powder-containing conductive paste was FL-100 manufactured by Mitsui Mining & Mining Co., Ltd.
A metal-based printed wiring board was manufactured using 0-3. The adhesion strength of the connection between the upper layer paste and the lower layer copper foil was measured, but it showed a very low value of less than 0.1 kg/m', and since the connection reliability between layers was poor, single-sided double-layer wiring was used. This was a practical problem.

〔Effect of the invention〕

As explained above, according to the manufacturing method of the present invention, the adhesion between the conductive paste and the land portion of the lowest layer circuit is sufficient, so that high reliability, low cost, and high density single-sided multilayer printed wiring can be achieved. You can get a board.

Such a single-sided multilayer printed circuit board can be widely used as a substitute for the conventional double-sided through-hole wiring board, which has had many problems.

[Brief explanation of the drawing]

Figures 1 (A) to (E), Figures 2 (A) to (F), Figures 3 (A) to (E), and Figures 4 (A) to (1) are examples 1 to 1, respectively. FIG. 7 is a partial cross-sectional view sequentially showing the state of the product in each step of Example 4. 101...Silicon steel plate, 102...Adhesive, 103
... Polyimide film, 104 ... Copper foil, 105
... insulation film, 106 ... conductive base), 107.
...Overcoat layer, 108...Solder, 201...Silicon steel plate, 202...Adhesive, 203.
...Polyimide film, 204...Copper foil, 205.
...Insulating film, 206...Conductive paste, 207...
・Copper plating film, 208... Overcoat layer, 20
9...Solder, 301...Aluminum alloy plate, 3
02... Prepreg, 303... Cellulose triacetate film, 304... Copper foil, 305... Insulating layer, 306... Conductive paste, 307... Solder resist film, 401... Silicon steel plate, 402...adhesive, 403...
...Polyimide film, 404...Copper foil, 405.
... Insulating ink layer, 406 ... Conductive paste, 407
... Insulating ink layer, 408 ... Conductive paste, 40
9... Overcoat layer, 410... Copper plating, 4
11...Solder.

Claims (1)

[Claims] 1. (a) a step of forming a lower layer circuit on the substrate via an insulating layer; (b) a step of laminating an insulating layer on the lower layer circuit leaving a land portion serving as a connecting portion with the upper layer circuit; (c) ) A method for manufacturing a printed wiring board including the step of forming an upper layer circuit connected to the lower layer circuit at the land portion on the insulating layer with a conductive paste, before the land portion is connected with the conductive paste, A method for manufacturing a printed wiring board, characterized in that the land is previously subjected to a treatment to improve adhesion to the conductive paste.