JPH07157882A - Thermosetting resin plating method - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a method for plating a thermosetting resin molded product having improved peel strength. [Structure] After electroless plating and electrolytic plating are sequentially performed on a thermosetting resin substrate, a heat treatment is performed within the temperature range of the glass transition temperature of the thermosetting resin or a temperature obtained by adding 70 ° C. to the glass transition temperature.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for plating on a thermosetting resin substrate. Specifically, in the case of forming a plating layer on the surface of a thermosetting resin, a method for improving the adhesion of the plating layer is provided. The present invention relates to a thermosetting resin plating method that can be particularly usefully applied to the production of a multilayer circuit board obtained by laminating a conductive layer made of a plating layer on the surface of an insulating layer made of a thermosetting resin.

[0002]

2. Description of the Related Art Conventionally, a method of performing chemical plating as one of means for metallizing a surface of a synthetic resin or a method of performing chemical plating and then performing electrolytic plating is known. For example, in ABS resin and polypropylene,
It is already widely used. One of the deficiencies of synthetic resin plating is that the peel strength of the metal layer is low due to the poor affinity between resin and metal. Various methods have been proposed as means for improving such defects. For example, in the case of ABS resin or the like, the butadiene component present on the surface of the resin is decomposed by chemical etching to form anchor points, or in the case of polypropylene or nylon, the surface is physically roughened. , The metal anchor effect is enhanced. However, sufficient peeling strength cannot be obtained only by the conventional anchor effect as described above. As a means for improving the peel strength, when plating with a thermoplastic resin such as nylon, the surface of the synthetic resin is chemically plated, left for several hours, and then electroplated. A method of improving the peeling strength by heating the sheet has been proposed (Japanese Patent Publication No. 1-123093). In this case, the reason why the peel strength increases, but the reason is not clear, but according to the inference by the present inventors, by plating, a stress is generated between the metal layer to be formed and the synthetic resin substrate, This promotes peeling. Therefore,
In the case of a thermoplastic resin, it is considered that the resin molecules are made to move easily by heating and the stress is relieved by fitting the synthetic resin to the metal shape.

However, in the manufacture of circuit boards, formation of conductive through holes, formation of conductive layers, etc. are generally performed on a thermosetting resin substrate by plating.
Of these, a multilayer circuit board in which a wiring pattern is laminated on a wiring pattern formed on an insulating substrate through an insulating layer made of a thermosetting resin for the purpose of increasing the circuit density or forming an electromagnetic wave shield layer. Have been developed.
Among these multilayer circuit boards, an insulating layer made of a thermosetting resin having openings for via holes is laminated on the first wiring pattern formed on the surface of the insulating board, and then chemical plating and electroplating are performed. The multi-layer circuit board in the form of forming a conductive layer has a high degree of freedom in arranging the wiring pattern, and since the multi-layer board can be obtained with extremely high precision and high wiring density, it is useful for reducing the board size and increasing the density. is there. In this case, plating on the thermosetting resin is required.

In the manufacture of the multi-layer circuit board, when the electroless plating and the electroplating are performed after the insulating layers are laminated, in order to secure the adhesion between the insulating layers, the rough surface of the insulating layers is provided. Need to be processed. In the roughening treatment, since sufficient adhesion cannot be obtained only by ordinary physical polishing such as slurry polishing, buff polishing, and scrub polishing, various chemical surface roughening treatments such as plating through-hole The roughening treatment using chromic acid, permanganate, etc., which is the desmear treatment liquid used at the time of formation, has been used in combination with the above physical polishing method.

[0005]

However, even if the above-mentioned surface roughening treatment is performed, the peeling strength of the plating layer is 0.4 to
It is about 0.7 kgf / cm, which is still insufficient especially when a fine and precise plating layer such as a wiring pattern is formed. That is, it cannot be said that it has sufficient adhesiveness as compared with a copper-clad laminated board formed by laminating and pressing a rolled copper foil that is most often used in printed circuit board production.

Further, in the plating on the surface of the thermosetting resin, since the elastic modulus of the thermosetting resin does not decrease by heating, it is considered that the effect of the heat treatment on the thermoplastic resin cannot be generally expected. .

[0007]

As a result of intensive studies to solve the above problems, the present inventors have found that after performing electroless plating and electrolytic plating on an insulating layer made of a thermosetting resin. The inventors have found that the heat treatment within a specific temperature range improves the adhesion between the plating layer and the insulating layer, and completed the present invention.

That is, the present invention provides a thermosetting resin substrate,
After sequentially performing electroless plating and electrolytic plating, the glass transition temperature of the thermosetting resin to the glass transition temperature of 70 ° C., preferably the glass transition temperature of 15 ° C. to 60 ° C. It is a method of plating a thermosetting resin, which is characterized by performing heat treatment in a range.

In the present invention, it is not clear why the heat treatment in a specific temperature range can improve the peel strength in plating the surface of the thermosetting resin. However, the present inventors have empirically found that the temperature is not lower than the glass transition temperature of the thermosetting resin, preferably not lower than 15 ° C. and not higher than the glass transition temperature of 70 ° C., preferably not higher than 60 ° C. It was found that the peel strength between the thermosetting resin and the metal layer is increased by performing the heat treatment at a temperature in the range of the temperature added by 0 ° C. or less for the time for which the object to be treated reaches a uniform temperature. That is, even if the temperature is lower than the temperature range specified in the present invention, or conversely, it is a high temperature exceeding the specific temperature range, as shown in Examples below, no improvement in peel strength is observed. I can't.

In the present specification, the thermosetting resin is a resin that forms a three-dimensional crosslinked structure after polymerization, and the resin is a general term for resins that are not softened or melted by heating. . Examples of the resin include condensation resins such as phenol resins, aniline resins, urea resins and melamine resins, epoxy resins, and polymers of compounds having two or more different polymerizable functional groups such as unsaturated polyester resins, or divinylbenzene. Compounds such as divinyltoluene, trivinylbenzene, and copolymers of these polyvinyl compounds and monovinyl compounds, which have two or more same functional groups.

The present invention will be described below by taking the multilayer circuit board shown in FIG. 1 as an example. A multilayer structure in which an insulating layer made of thermosetting resin 3 is formed on the surface of the circuit board having the first wiring pattern 2 on the surface of the insulating substrate 1, and then electroless plating and electrolytic plating are performed to stack conductive layers. It is a circuit board. Of course, the present invention is not limited to the embodiment of FIG.

The insulating substrate 1 is not particularly limited, and those having known materials and structures can be used without limitation. Typical examples are paper base material-phenolic resin laminated board, paper base material-epoxy resin laminated board, paper base material-polyester resin laminated board, glass base material-epoxy resin laminated board, paper base material-Teflon. Resin laminated substrate, glass base material-BT
(Bismaleimide-triazine) resin resin laminated substrate,
Examples thereof include a synthetic resin substrate such as a composite resin substrate, a metal-based insulating substrate obtained by insulating a metal such as aluminum, iron, and stainless with an epoxy resin or the like, or a ceramic substrate.

In the present invention, the first wiring pattern 2 is formed on the surface of the insulating substrate. The first wiring pattern is generally formed by etching a copper foil on the surface of the copper-clad laminated substrate, but a printing method using a curable conductive material typified by copper paste, silver paste, etc. Method, electroless plating, electrolytic plating, etc.
A method of forming a plating layer on an insulating substrate and etching the plating layer to form a pattern can be used without particular limitation.

In the present invention, the insulating layer 3 made of a thermosetting resin is formed on the surface of the above-mentioned first wiring pattern. The insulating layer can be formed by a method using various forms of thermosetting resin such as dry film, liquid resist, dry film / liquid resist combination, and the like. In the above method, particularly when a dry film is used, the thickness accuracy of the insulating layer is good and the front and back surfaces can be formed simultaneously, so that the insulating layer can be formed more efficiently. Further, as the thermosetting resin, phenol resin, epoxy resin, unsaturated polyester resin, melamine resin, urea resin and the like having a glass transition temperature of about 80 to 150 ° C. can be preferably used, but insulation of the insulating layer is preferable. From the viewpoint of characteristics and long-term reliability, it is desirable to use epoxy resin as the insulating resin. Further, the thermosetting resin may be a mixture of glass fiber, glass cloth, inorganic filler, other additives and the like. The above-mentioned insulating layer is a laminator using a heating roll, a screen printer, a roll coater, a curtain coater, and the like, after applying using various known coating devices,
It may be formed by drying and curing if necessary.

When forming the via hole opening 4 for ensuring electrical continuity between the first wiring pattern and the second wiring pattern, the via hole opening is formed beforehand by screen printing. Except for the above, an insulating layer is applied, or a photosensitive resin is used for the insulating layer, the insulating layer is laminated on the entire surface of the substrate, and then exposed and developed to remove the resin in the via hole opening. Etc. are used.

In the present invention, in order to improve the adhesion between the insulating layer and the second wiring pattern, the insulating layer may be roughened. The surface-roughening treatment is a normal physical polishing such as slurry polishing, buff polishing, scrub polishing,
And various chemical surface-roughening treatments, for example, surface-roughening treatment using chromic acid, permanganate, etc., which are desmear treatment liquids used in forming plated through holes. Polishing and chemical surface roughening treatment may be performed alone or in combination.

Then, the plating layer 5 is formed on the entire surface of the substrate including the insulating layer by electroless plating and electrolytic plating on the surface of the insulating layer. The material of the plating layer is
Conductive metals such as gold, silver, copper, nickel and tin are used without particular limitation, but copper is generally used because it is possible to obtain good conductivity at a relatively low cost.

The electroless plating and the electroplating are generally used methods, for example, in the case of the electroless plating, the catalyst is previously adsorbed on the substrate surface and then immersed in the electroless plating bath, or the electroplating is performed. In the case of, a method of immersing the substrate in an electrolytic plating bath and energizing it to deposit a metal,
It is used without particular limitation.

The thickness of the plated layer after each of the above plating treatments is not particularly limited, but it is usually 50 μm or less, preferably about 10 to 40 μm.

Before the formation of each plating layer, for the purpose of cleaning the surface of the insulating layer and the surface of the first wiring pattern,
Treatments such as pickling and ultrasonic cleaning may be performed.

In the present invention, it is particularly important to perform heat treatment after the plating layer is formed by electrolysis. By performing the heat treatment, the adhesion between the plating layer and the insulating layer is improved, and practically sufficient adhesion can be obtained. If the heat treatment is not performed at a temperature higher than the glass transition temperature of the resin forming the insulating layer, the effect cannot be expected. Preferably, the heat treatment may be performed at a temperature higher by 15 ° C. to 60 ° C. than the glass transition temperature. The heating time is not particularly important, and it is sufficient if the heating time is such that the entire temperature becomes uniform.
It may be performed for about 0 to 120 minutes. If the heating time exceeds 120 minutes, the adhesion of the plating layer may deteriorate due to deterioration or decomposition of the insulating layer, or blistering may occur.

Subsequently, the plated layer on the insulating layer is etched to form a second wiring pattern. As the etching method, the same method as in forming the first wiring pattern may be adopted. The above-mentioned second wiring pattern is used without particular limitation for patterns of signal lines, power lines, ground lines, electromagnetic wave shield layers, and the like.

Further, in the present invention, it is also possible to similarly laminate an insulating layer and a wiring pattern on the second wiring pattern in the same manner. However, in that case,
The heat treatment of the present invention can be collectively performed after forming the outermost plating layer. Further, the heat treatment of the present invention may be performed after etching the plated layer to form a wiring pattern.

Although the present invention has been described above with reference to FIG. 1, the present invention can be applied not only to the circuit board but also to plating on the surface of the thermosetting resin molded product.

[0025]

[Effect] According to the manufacturing method of the present invention, electroless plating and electroplating are performed on the surface of a base material of a thermosetting resin molded product to form a plating layer, and then heat treatment is performed to form a plating layer and a base material. Adhesion is improved. However, when the heat treatment is performed after the electroless plating and then the electrolytic plating is performed, the adhesion of the plating layer is not improved.

[0026]

EXAMPLES Examples will be shown below for specifically explaining the present invention, but the present invention is not limited to these examples.

Examples 1 to 4 and Comparative Examples 1 to 7 Peeling strength measurement patterns described in JIS C6481 were prepared by the following method, and the peeling strength was measured. That is, the surface of a 1.6 mm-thick glass base epoxy resin laminate obtained by removing the copper foils on both sides by etching with a cupric chloride etching solution is made of an epoxy resin having a glass transition temperature of 135 ° C. after curing. An insulating resist (trade name, “Probicoat 5000” manufactured by Nippon Paint Co., Ltd.) was applied to the entire surface by a screen printing method, dried and cured to form an insulating layer having a thickness of 20 μm. Then 320
Polishing was performed using a No. Baffle, and the surface of the insulating layer was roughened over the entire surface using a desmear solution composed of an alkaline potassium permanganate aqueous solution. Next, the surface of the substrate is electroless plated and electrolytic plated to a thickness of 20 μm.
Copper plating layer was formed. The electroless plating uses a method of depositing copper by a chemical reduction reaction using a palladium catalyst. The electrolytic plating uses a copper sulfate-containing copper electrode as an electrode to electrolyze metallic copper at a current density of 2 A / dm ^2. The method of analysis was used. Then, using a hot air drying oven, Table 1
The heat treatment was performed under the conditions shown in. After heat treatment,
Etching the plating layer, width 1.0cm, length 10.0
A peeling strength measurement pattern of cm was prepared, and the peeling strength was measured. The measurement results of the peeling strength are shown in Table 1 and FIGS. 3 and 4.

Further, regarding the sample of Example 2, 2
The operation of dipping in a solder bath at 60 ° C for 5 seconds is 1, 3, 5, 1
The peel strength was measured by repeating 0 times. The results are shown in Table 2.

Comparative Example 8 Example 1 was repeated except that the heat treatment was performed at 180 ° C. for 30 minutes after electroless plating, followed by pickling and electrolytic plating.
-2, the sample was created on the completely same conditions as Comparative Examples 1-5, and the peeling strength was measured. As a result, the peeling strength was 0.49 kgf / cm, which was almost the same as that without heat treatment (Comparative Example 1). The results are shown in Table 1.
Shown in.

Example 6 and Comparative Example 9 For measuring peel strength under the same conditions as in Example 1, except that the insulating resist was made of phenol resin having a glass transition temperature of 126 ° C. after curing. A pattern was created and evaluated. However, the heat treatment conditions after plating are
It was set to 150 ° C. for 30 minutes (Example 6) and none (Comparative Example 9). The results are shown in Table 1.

Example 7 A curable paste that gives a cured product having conductivity was prepared by the following method, and the multilayer circuit board shown in FIG. 2 was manufactured. The reference numerals in the figure are the same as those in FIG.
Represents the conductor filled in the via hole. That is, dendritic electrolytic copper powder having an average particle size of 6.8 μm, tap density of 2.99 g / cm ³ , and specific surface area of 4200 cm ² / g, and linoleic acid on the surface of the copper powder was 0.25 × 10 ⁻⁵ mmol / cm
^The ingredients were mixed in a ratio of ² and premixed in a mortar for 15 minutes under a nitrogen atmosphere. The pretreated copper powder thus obtained was used with respect to 100 parts by weight of a binder of neopentyl glycol diglycidyl ether (epoxy equivalent = 150) / novolac type phenol resin (hydroxy equivalent = 105) = 74/26 (weight ratio). 456 parts by weight, and further 2
-Ethyl-4-methylimidazole, binder 10
After adding 2.8 parts by weight to 0 parts by weight, the mixture was kneaded with a three-roll mill for 30 minutes to obtain a copper paste.

Subsequently, a 1.6 mm-thick glass-base epoxy resin copper-clad laminate is used as an insulating substrate having conductive layers on both sides, and a through hole having a diameter of 0.4 mmφ is formed by drilling. The through-hole was filled with the copper paste prepared by the above method as a curable conductive material by a screen printing method. The copper paste in an electric furnace at 80 ° C. for 60 minutes,
It was cured under the conditions of 180 ° C. for 60 minutes, and the buffs of No. 320 and No. 600 were sequentially used to grind the surface of the cured copper paste from which the cured body was projected to smooth the surface of the conductive layer containing the cured body. . Next, the surface of the substrate is electrolytically plated to a thickness of 1
A copper plating layer having a thickness of 5 μm was formed, and a water-soluble dry film resist as an etching resist was laminated on the surface of the plating layer, exposed and developed to form a resist pattern. Then, etching was performed and the etching resist was peeled off to form a first wiring pattern. Then, on the first wiring pattern, as an insulating layer,
A photosensitive insulating resist made of an epoxy resin was applied to the entire surface by a screen printing method, dried, exposed and developed to form an opening for via hole in the insulating layer, and then heat-cured. Next, the surface of the insulating layer was polished with a No. 320 buff, and then the entire surface of the insulating layer was roughened using a desmear solution composed of an alkaline potassium permanganate aqueous solution. Next, the substrate surface was subjected to electroless plating and electrolytic plating to form a copper plating layer having a thickness of 20 μm. The electrolytic plating was performed under the condition of current density of 2 A / dm ² . After forming the plating layer, the substrate was heated in a hot air drying oven at 180 ° C. for 3 days.
Heat treatment was performed for 0 minutes, and then the plating layer was etched to form a second wiring pattern.

The resistance between the second wiring patterns located on the front and back of the obtained multilayer circuit board and connected to the common through hole was measured and found to be 38 mΩ. Also, J
Thermal shock test of ISC-5012 (-65 ° C x 30 minutes ← →
50 cycles at 125 ° C for 30 minutes)
After the lapse of 0 times, no increase in the resistance between the second wiring patterns located on the front and back of the multilayer circuit board was observed, and
The adhesion between the wiring pattern and the insulating layer was good.

[0034]

[Table 1]

[0035]

[Table 2]

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a multilayer circuit board to which the method of the present invention is applied.

FIG. 2 is a cross-sectional view of a multilayer circuit board to which the method of the present invention has been applied.

FIG. 3 illustrates the evaluation results of Examples and Comparative Examples.

FIG. 4 illustrates the evaluation results of Examples and Comparative Examples.

[Explanation of symbols]

 1 Insulating Substrate 2 First Wiring Pattern 3 Insulating Layer 4 Via Hole Opening 5 Second Wiring Pattern 6 Curable Conductive Material

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H05K 3/22 Z 7511-4E 3/38 Z 7011-4E 3/46 E 6921-4E // B29K 101: 10

Claims (1)

[Claims] 1. A thermosetting resin substrate is sequentially subjected to electroless plating and electrolytic plating, and then heat treatment is performed at a glass transition temperature of the thermosetting resin or at a temperature obtained by adding 70 ° C. to the glass transition temperature. A thermosetting resin plating method characterized by the above.