JPH0828561B2 - Manufacturing method of printed wiring board - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a printed wiring board.

[0002]

2. Description of the Related Art Recently, with the spread of surface mounting, parts can be mounted on both sides of a printed wiring board.
Printed wiring boards for high-density mounting have been widely put into practical use.

In such a double-sided surface mounting type printed wiring board, various component mounting methods are adopted. For example, after soldering a chip component to the front surface of the printed wiring board by reflow, the same is applied to the back surface. As described above, solder the chip parts by reflow, then solder the electronic parts with lead wires for terminals by the reflow method, solder the chip parts on the front surface of the printed wiring board by reflow, and on the back surface A method of temporarily fixing the chip parts with an adhesive and performing flow soldering together with the insertion parts is adopted. In these methods, the printed wiring board is subjected to multiple heat treatments for soldering and curing of the adhesive, and this heating oxidizes the copper forming the conductor circuit of the printed wiring board, and the solder causes electronic It is a cause of connection failure when connecting parts.

In order to prevent such an adverse effect, for example,
A surface treatment of a printed wiring board called pre-flux treatment is performed. This method is a method of applying a pre-flux made of a rosin material or the like as a copper surface protective film after the production of a printed wiring board to achieve a rust preventive effect on a copper circuit portion. However, the preflux loses its function as a protective film due to a thermal history when heat treatment is performed multiple times by reflow soldering or the like.
There is a drawback that the solderability deteriorates and the cleaning property after soldering deteriorates.

Further, a solder coat treatment method for forming an anticorrosive film on a copper circuit portion of a printed wiring board by molten solder is also adopted. However, in this method, the mounting stability of the surface mount component is poor due to the large variation in the solder film thickness, and when the pad pitch is narrow,
There is a drawback that solder becomes excessive and solder bridges are easily generated. Further, there is a drawback that the printed wiring board is largely warped and twisted, so that it is difficult to automatically mount surface mount components, or holes are apt to be clogged due to sticking, and it is difficult to insert the components.

[0006]

In view of the problems of the prior art as described above, the present inventor has conducted earnest research to find an optimum copper circuit protection method particularly for application to a double-sided mounting printed wiring board. Came. As a result, a printed wiring board with a palladium plating film formed on a copper metal on which components should be mounted by soldering has very little deterioration in solderability due to thermal history, and a protective film Highly uniform thickness ensures good mounting stability of surface-mounted components and does not cause solder bridges. It is particularly useful as a printed wiring board for high-density mounting. Therefore, it has been found that a protective film of palladium can be easily formed even on a double-sided printed wiring board by a specific treatment method using an electroless plating method, and the present invention has been completed here.

That is, the present invention uses an electroless palladium plating solution on a copper metal of a printed wiring board having a conductor circuit made of copper metal and a solder resist pattern formed on the conductor circuit, and has a thickness of 0.01 μm to 0 μm. The present invention relates to a method for producing a printed wiring board, which comprises forming a palladium plating film having a thickness of 2 μm.

The printed wiring board obtained by the method of the present invention is a printed wiring board having a conductor circuit made of copper metal, in which a palladium plating film is formed on at least copper metal to be mounted with components by soldering. The method for manufacturing such a printed wiring board in the present invention is as follows.

In the method of the present invention, the type of the printed wiring board that can be applied is not particularly limited as long as it is a conductor circuit made of copper metal, and the base material is a substrate of various known materials, for example, a glass epoxy substrate. , Paper phenolic board,
Any paper epoxy board or the like can be adopted. There is also no limitation on the method for forming a conductor circuit on a printed wiring board, and various known methods such as panel plating, pattern plating,
A circuit formed by any of the semi-additive method, the full-additive method, the part-additive method and the like can be used. Also, there is no particular limitation on the method of mounting the components on the printed wiring board, and a single-sided board, a double-sided board,
The present invention can be applied to boards of any mounting method such as a multilayer board, but is particularly suitable for a board such as a double-sided surface mounting board that is soldered a plurality of times.

The type of electroless palladium plating solution used in the present invention is not particularly limited, and any known electroless palladium plating solution can be used. A specific example of the electroless palladium plating solution is disclosed in JP-A-62-142828.
No. 0, a) a palladium compound, b) at least one of ammonia and an amine compound, c) an organic compound containing divalent sulfur, and d) a hypophosphorous acid compound and a borohydride compound. Electroless palladium plating solution comprising an aqueous solution containing at least one kind,
At least one of a) a palladium compound, b) ammonia and an amine compound described in JP-A-268877.
Seed, c) an organic compound containing divalent sulfur, and d)
Examples thereof include an electroless palladium plating solution formed of an aqueous solution containing phosphorous acid and at least one of salts thereof.

The electroless palladium plating conditions may be the same as the usual plating conditions depending on the type of plating solution used.

The thickness of the palladium film formed on the copper metal is 0.01 μm to 0.2 μm . In the present invention,
Form a palladium film using electrolytic palladium plating solution
In case of such a very thin film thickness,
Can also effectively protect copper circuits. When the thickness of the palladium film is below 0.01 [mu] m, since solderability after heat treatment is decreased, have Na preferably when performing multiple soldering.

In the method of the present invention, the portion of the printed wiring board where the electroless palladium plating film is to be formed is
Of the conductor circuit made of copper metal, it is at least the copper metal portion to be soldered. Specifically, in the case of surface mounting, it is the pad portion, and in the case of a board having through holes, the land portion and the through hole portion. . Therefore, in the present invention, a solder resist pattern is formed on a wiring board having a conductor circuit made of copper metal, and electroless palladium plating is performed only on the exposed copper metal portion. In this case, it is usually preferable to perform soft etching according to a conventional method to remove the copper oxide layer and then perform electroless palladium plating. The soft etching may be performed according to known conditions, for example, a method of immersing in an aqueous solution of about 150 g / l of ammonium persulfate at about 30 ° C. for about 60 seconds,
A method of immersing in an aqueous solution of about 150 g / l of sodium persulfate at about 30 ° C. for about 60 seconds, and an aqueous solution containing 11% by weight of sulfuric acid and 3.8% by weight of hydrogen peroxide at about 20 ° C.
A method of soaking for about 0 seconds can be adopted. Further, in a later step, when a noble metal plating such as gold plating or rhodium plating is performed on the terminal portion, the bonding pad portion, etc., after forming a plating resist layer on these portions, electroless palladium plating is performed. You may do it.

The electroless palladium plating can be carried out directly on the copper metal using the above-mentioned plating solution, but using a catalyst solution for selectively activating copper or copper alloy, After applying the catalyst to the copper metal, electroless palladium plating is preferably carried out, whereby the time until the initial deposition of palladium plating can be significantly shortened. As such a catalyst liquid, any known liquid can be used, and examples thereof include ICP Axela (trademark: manufactured by Okuno Chemical Industries Co., Ltd.).

In the method of the present invention, another plating film, such as a Ni plating film, may be formed between the copper metal and the palladium plating film by an electroless plating method, if necessary.

By the method described above, it is possible to obtain a printed wiring board having a conductor circuit made of copper metal and having a palladium plating film on the copper metal on which components are to be mounted at least by soldering. The printed wiring board obtained by the present invention, if necessary, at an appropriate time before or after the formation of the palladium plating film, according to a conventional method, the terminal portion, the bonding pad portion, etc., gold plating, rhodium plating or other precious metal Plating can be performed. In this case, nickel plating or the like is usually used as the base plating, but the palladium coating may be directly plated with a noble metal. Further, after the palladium film is peeled off, nickel plating and noble metal plating may be performed. Further, character printing, outer shape processing, etc. may be performed according to a conventional method.

In order to mount components on the printed wiring board obtained by the present invention, any ordinary component mounting method can be adopted. For example, single-sided mounting by discrete mounting of discrete components, insertion mounting of discrete components on the surface, Various types such as double-sided mounting by surface mounting of chip parts on the back side, surface mounting of discrete parts and surface mounting of chip parts on the front side, double-sided mounting by surface mounting of chip parts, double-sided mounting by surface mounting chip parts on both sides Method can be adopted, and these may be performed according to known methods.

[0018]

The printed wiring board obtained by the present invention has a protective film for a copper circuit by a palladium plating film, and the copper circuit is effective even when it is heated a plurality of times by soldering etc. when mounting components. Protects against soldering and does not cause deterioration of solderability or deterioration of cleaning performance after soldering. Further, since the variation in the film thickness of the palladium plating film is small, the mounting stability of the surface mount component is good, and there is no occurrence of clogging of through holes or short circuit of the circuit.

The printed wiring board obtained by the method of the present invention has the excellent characteristics as described above, and in particular, the printed wiring board for high-density mounting, in which heat treatment is carried out a plurality of times by soldering, curing of an adhesive, etc. when mounting components. On the other hand, it is very useful in that it is possible to effectively prevent deterioration of solderability due to oxidation of copper metal.

[0020]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. The palladium plating solution and plating conditions used in the examples are as follows.

○ Electroless palladium plating solution Palladium chloride 0.01 mol / l Ethylenediamine 0.08 mol / l Thiodiglycolic acid 20 mg / l Sodium hypophosphite 0.06 mol / l pH 8 Liquid temperature 60 ° C. ○ None Electrolytic palladium plating solution Palladium chloride 0.01 mol / l Ethylenediamine 0.08 mol / l Thiodiglycolic acid 20 mg / l Dimethylamine borane 0.06 mol / l pH 8 Solution temperature 60 ° C. Electroless palladium plating solution Palladium chloride 0 0.01 mol / l ethylenediamine 0.08 mol / l thiodiglycolic acid 30 mg / l sodium phosphite 0.02 mol / l pH 6 liquid temperature 60 ° C.

[0022]

[Example 1] With respect to a sample in which a palladium plating film was formed on a copper plate, a change in solderability by heat treatment was examined by the following method.

A rolled copper plate (25 × 25 × 0.3 mm) is electrolytically degreased and pickled, and then a 0.1 μm palladium plating film is formed using each of the electroless palladium plating solutions, and then washed with water. And dried. Using these as samples, heat at 230 ℃ for 10 minutes, 30 minutes or 60 minutes, 25
Heating was performed at 0 ° C. for 10 minutes or 30 minutes, and the solderability before and after heating was examined. As a comparison, a sample without palladium plating was similarly tested. The measuring method is as follows. The results are shown in Table 1 below.

○ Solderability test Using a solder checker manufactured by RHESCA, the time until the acting force of the molten solder on the test piece changes from upward to downward, and the acting force in the vertical direction is balanced and becomes zero ( Second) was measured and this was taken as the zero cross time. It can be said that the smaller the zero cross time, the better the solder wettability and the better the solderability. The test conditions are as follows.

Molten solder (63 wt% tin / 37 wt%
Lead, eutectic solder) 230 ± 1 ℃ Immersion depth 12mm Immersion speed 25mm / sec Immersion time 10 seconds Sensitivity 2g Flux Tamura Kaken Co., Ltd. Solderlight MH
-820V

[0026]

[Table 1]

From the above results, it is understood that when the palladium plating film is formed, the solderability is less likely to be deteriorated by the heat treatment.

[0028]

Example 2 A rolled copper sheet was electrolytically degreased and pickled in the same manner as in Example 1, and then a catalyst solution (trademark ICP Accelerator 200 ml) was used.
/ L aqueous solution, manufactured by Okuno Chemical Industries Co., Ltd., at 30 ° C
The catalyst was applied by immersing in 30 seconds. Then, using each plating solution of electroless palladium plating solution
After forming a palladium plating film of μm, it was washed with water and dried. The deposition time of palladium plating was shorter than that in Example 1. Using these as samples, the solderability before and after the heat treatment was examined in the same manner as in Example 1. The results are shown in Table 2 below.

[0029]

[Table 2]

From the above results, it is understood that when the palladium plating film is formed, the solderability is less likely to be deteriorated by the heat treatment.

[0031]

Example 3 In the same manner as in Example 2, after applying a catalyst to a copper plate, an electroless palladium plating solution was used for 0.0
Palladium plating films having various film thicknesses between 05 and 10 μm were formed. The results of examining the solderability before and after the heat treatment in the same manner as in Example 1 are shown in Table 3 below.

[0032]

[Table 3]

From the above results, it can be seen that when a palladium plating film having a thickness of 0.01 μm or more is formed, the solderability is less deteriorated by the heat treatment.

[0034]

Example 4 The same rolled copper plate as in Example 1 was electrolytically degreased and pickled, and then a palladium plating film was formed using an electroless palladium plating solution by the following treatment methods. The soft etching was performed by immersing in a 150 g / l ammonium persulfate aqueous solution at 30 ° C. for 60 seconds.
The catalyst was applied in the same manner as in Example 2.

○ Processing method 1 Soft etching → pickling → catalyst application → palladium plating (0.1 μm) → drying ○ Processing method 2 soft etching → catalyst application → palladium plating (0.
1 μm) → drying ○ Processing method 3 electrolytic copper plating (10 μm) → catalyst application → palladium plating (0.1 μm) → drying ○ processing method 4 electrolytic copper plating (10 μm) → soft etching → catalyst application → palladium plating (0.1 μm) ) → Drying ○ Treatment method 5 catalyst application → electroless nickel plating (2 μm) → pickling → palladium plating (0.1 μm) → drying In any of the above treatment methods, the same conditions as in Example 1 were used. When a solderability test is performed after heat treatment at
The zero cross time was 1.3 to 1.8 seconds, and the solderability was good.

On the other hand, in the above treatment methods 1 to 5, when the palladium plating is not performed, all the samples have a zero cross time of 10 seconds or more after heat treatment at 230 ° C. for 30 minutes or more or 250 ° C. for 10 minutes or more, Solderability was significantly reduced.

[0037]

[Example 5] A glass epoxy copper-clad laminate was perforated,
After performing electroless copper plating and electrolytic copper plating, an etching resist layer is formed, and then etching, etching resist layer peeling, solder resist printing, character printing,
The following processing was performed on 50 100 × 170 × 16 mm copper-plated through-hole printed wiring boards for mixed mounting of double-sided surface mounting components and single-sided insertion type components obtained through the outer shape processing step.

After the printed wiring board is immersed in degreasing and pickled,
Soft etching is performed, followed by pickling, then a catalyst is applied, and a film thickness of 0.1 is obtained using an electroless palladium plating solution.
A palladium plating film of μm was formed, washed with water and dried. Soft etching and catalyst application were performed in the same manner as in Example 4.

On one surface of this printed wiring board, a solder paste was printed on a pad, surface-mounted components were mounted, and then soldering was carried out by full-heat reflow soldering, and then on the other surface, similarly. After soldering the surface mount components by reflow soldering, the insertion type components were joined by hand soldering. Good solder joints were obtained at all locations on the 50 printed wiring boards.
The defective rate was 0%.

Claims (1)

[Claims] 1. A thickness of a conductor circuit made of copper metal and a copper wiring of a printed wiring board having a solder resist pattern formed thereon, which is formed by using an electroless palladium plating solution.
A method for producing a printed wiring board, which comprises forming a palladium plating film of 0.01 μm to 0.2 μm .