JP3126417B2 - Pretreatment method of plating solution in additive method - 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 pretreating a plating solution in an additive method, which is performed before electroless plating in the production of a printed wiring board by the additive method.

[0002]

2. Description of the Related Art Conventionally, as a pretreatment method for electroless plating in the additive method, the following steps are performed. That is, first, a step of immersing the printed circuit board in an activating liquid having an acidic catalyst, and then a water washing step of performing the water washing to recover the catalyst, and then a water washing step again,
Finally, it is a new water washing process of washing with fresh water.

[0003] After passing through such a pretreatment step, electroless plating is performed. That is, electroless plating is performed by immersing the printed circuit board that has undergone the pretreatment step in a plating solution.

[0004]

However, in the above-mentioned conventional pretreatment method, an activating liquid having an acidic catalyst may remain in a through hole of a printed circuit board after the pretreatment. In this case, when the printed circuit board is immersed in the electroless plating solution, the pH of the electroless plating solution decreases. In addition, since the electroless plating solution is alkaline, there is a possibility that an acid and an alkali salt are generated between the electroless plating solution and the acidic activating solution. Therefore, there is a problem that the adhesion of the plating film to the printed circuit board is reduced.

[0005] Further, since the uncured portion of the plating resist applied to the printed board is dissolved into the electroless plating solution by the acidic activating solution, the life of the electroless plating solution is shortened, and the electroless plating solution is shortened. There has been a problem that the elongation rate of a plating film obtained by plating is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to prevent a decrease in pH of a plating solution and formation of a salt, thereby improving adhesion of a plating film. Another object of the present invention is to provide a plating solution pretreatment method in an additive method that can extend the life of a plating solution and improve the physical properties of a plating film.

[0007]

In order to achieve the above object, in the present invention, a plating resist is formed on a printed circuit board according to an additive method and then treated with an acidic catalyst activating solution as a pretreatment for performing electroless plating. In a pretreatment method of a plating solution in an additive method, comprising a step of washing the activating solution and a washing step of washing the activating solution thereafter, after the washing step, the plating solution is treated with an aqueous solution of a strong alkali at a higher temperature than the plating solution
Pretreatment method of plating solution in the additive method, characterized in that a step of a is set to its gist.

[0008]

In the pretreatment of the electroless plating, a step of applying a strong alkaline aqueous solution is provided after the water washing step, so that the acidic activating liquid remaining on the printed circuit board after the water washing step may be weakened by strong aqueous sodium hydroxide solution or the like. Neutralized by an alkaline aqueous solution. Therefore, the pH of the plating solution does not decrease, and no salt is generated by the acid and the alkali, and the adhesion of the plating film is improved.

In addition, strong alkaline water at a higher temperature than the plating solution is used.
Since the plating resist is eluted into the strong alkaline aqueous solution by treating with the solution, the elution of the plating resist into the electroless plating solution is suppressed, and as a result, the life of the electroless plating solution can be extended, and the plating can be performed. It is possible to improve the physical properties such as the elongation of the coating.

[0010]

EXAMPLES Hereinafter, examples embodying the present invention will be described.
A description will be given with reference to FIGS. In this embodiment, before performing electroless plating based on the full additive method, a pretreatment with a sodium hydroxide aqueous solution as a strong alkaline aqueous solution is performed, and then electroless copper plating is performed on a printed circuit board.

As shown in FIG. 2, an adhesive layer 2 is formed on a printed board 1, the surface of the adhesive layer 2 is roughened, and a through hole 3 is formed by drilling. A catalyst core 6 is provided on the adhesive layer 2 and in the through hole 3 by a catalyst core forming step.
On the adhesive layer 2, a plating resist 4 such as epoxy acrylate is formed in a portion other than the through hole 3 and the wiring pattern. In this state, pretreatment of electroless copper plating is performed. Thereafter, as shown in FIG. 1, a copper plating film 5 is formed on the through hole 3 and the wiring pattern portion by electroless copper plating in a usual manner.

First, the printed board 1 on which the plating resist 4 was applied was immersed in an activating solution having an acidic catalyst (accelerator 19, trade name, manufactured by Shipley Co., Ltd.).
Next, in the water washing step, water washing for collecting the acidic catalyst was performed. Subsequently, after washing with water again, washing with fresh water was performed.

Next, the printed board was immersed in a strong alkaline aqueous solution, that is, a strong alkaline pre-dip solution (sodium hydroxide concentration 20 g / l, pH 12.6, temperature 80 ° C.) for 5 minutes. This sodium hydroxide concentration is 12-40 g
/ L is preferable, and 20 to 25 g / l is more preferable. The pH is preferably in the range of 12 to 13,
The range of 2.4 to 12.6 is more preferable. The temperature is 7
The range is preferably from 0 to 90C, more preferably from 75 to 85C.

If it is larger than these ranges, the elution of the plating resist 4 becomes excessive and the printed circuit board 1 may be damaged. On the other hand, if it is smaller than these ranges, the part of the plating resist 4 that is incompletely cured, that is, the part that has not been cured due to the consumption of radicals by oxygen, will not melt.

It is desirable that the temperature and pH of the sodium hydroxide pre-dip solution are both higher than the temperature and pH of the electroless copper plating solution described later. because,
This is because the incompletely cured portion of the plating resist is eluted in the pre-dip solution and is not eluted in the electroless plating solution as much as possible.

Next, the printed board 1 pretreated as described above was subjected to electroless copper plating to form a copper plating film 5 having a thickness of about 30 μm. The plating solution used for the electroless copper plating has the following composition. That is, copper sulfate (CuSO _4.5 H ₂ O) 10 ± 1 g / l, sodium hydroxide (NaOH) 12 ± 1 g / l, formaldehyde (HCHO, 37
%) 4 ± 0.5 ml / l, disodium ethylenediaminetetraacetate (EDTA.2Na) 45 to 50 g / l, dipyridyl 2
0-30 mg / l, polyethylene glycol 70-100
mg / l, potassium cyanide 0.7 as a physical property improver
１1 g / l. Other conditions of the electroless plating are a temperature of 70 ° C. and a pH of 12.0 to 12.2.

Under these conditions, electroless plating was performed up to six turns, with one turn when the copper ions of the copper sulfate disappeared. As a result, the adhesion of the copper plating film 5 was good and the ductility of the copper plating film 5 was good up to 6 turns. The test results are shown in Table 1 below.

In Table 1, the adhesion of the copper plating film 5 is the adhesion in the through hole 3 of the printed board 1, and the printed board 1 is immersed in oil at 260.degree.
After repeating 30 seconds at 20 ° C. for 10 seconds, the presence or absence of peeling of the copper plating film 5 was examined by observing the cross section of the through hole 3. And when there is no peeling at all ◎,
When the rate of peeling was 10% or less, it was represented by ○, and when the rate of peeling exceeded 10%, it was represented by x. Further, the ductility of the copper plating film 5 was represented by a test piece in which the copper plating film 5 was formed into a strip shape, one end of which was pulled by a tensile tester, and was expressed by the extension ratio of the test piece.

In the thermal shock test, in a through-hole connection state (200 holes), immersion was performed in oil at 260 ° C. for 10 seconds, and then in oil at 20 ° C. for 20 seconds. The state of the plating film was observed.
In addition, this cooling / heating cycle was repeated five times, and the average was taken.

[0020]

[Table 1]

As described above, in this embodiment, since the immersion treatment with the pre-dip solution of sodium hydroxide was performed as a pretreatment for the electroless plating, the life of the plating solution was extended, and the through-hole was increased up to 6 turns. Copper plating film 5 in 3
And the ductility of the copper plating film 5 is sufficiently maintained.

In general, in the method of manufacturing a printed wiring board by the full additive method, since the plating solution becomes high temperature and highly alkaline, organic substances such as the plating resist 4 are easily eluted. Normally, when plating is repeated, organic matter accumulates, and the copper plating film 5 becomes hard and brittle, and its elongation decreases.

However, the use of the strong alkaline pre-dip solution can sufficiently prevent the acidic activating solution from being mixed into the electroless copper plating solution, so that the life of the plating solution can be extended to six turns. As a result, the cost for preparing the plating solution and the cost for disposing of the unnecessary plating solution can be saved.

Next, the following test was conducted for comparison with the above embodiment. That is, in the above embodiment, the step of immersion in a strong alkaline pre-dip solution was omitted in the pretreatment of electroless copper plating. Then, electroless plating was performed in the same manner as in the above example, and the adhesion and ductility of the copper plating film were evaluated in the same manner as in the above example. The results are shown in Table 2 below.

[0025]

[Table 2]

As shown in Table 2, when the number of plating turns is 5 or more, the adhesion of the copper plating film 5 is reduced, and when the number of turns is 4 or more, the ductility of the copper plating film 5 is 4 or more. % Or less, which indicates that the copper plating film 5 is brittle and its ductility is low. Therefore, only three turns can be used as compared with the case where the number of plating turns is six in the above embodiment.

As described above, in the present embodiment, since the immersion step in the strong alkaline pre-dip solution is provided after the water washing step, the activating solution having an acidic catalyst is not mixed into the electroless copper plating solution. The electroless plating solution becomes stable.
In addition, salt formation due to neutralization of the acidic activating solution and the alkaline plating solution is eliminated. Therefore, the electroless copper plating is performed smoothly and reliably, and the adhesion of the copper plating film 5 is improved.

Further, the layer of the photo-resist insufficiently on the surface of the plating resist 4, that is, the portion which has been inhibited by oxygen, dissolves in the pre-dip solution, so that the plating resist 4
Is extremely reduced. Therefore, the life of the plating solution can be prolonged, and no organic matter is mixed into the copper plating film 5, and the ductility of the copper plating film 5 increases.

The present invention is not limited to the above embodiment, but may be embodied in the following embodiments. (1) The strong alkaline aqueous solution may be a potassium hydroxide aqueous solution or the like. In that case, the concentration of the aqueous potassium hydroxide solution, p
H, temperature and the like can be set according to the above-mentioned aqueous sodium hydroxide solution. (2) In the above embodiment, the pretreatment was performed before the electroless plating was performed in accordance with the full additive method. Processing may be performed. (3) The electroless plating may be solder plating, gold plating, or the like.

[0030]

As described in detail above, according to the present invention, it is possible to improve the adhesion of the plating film by preventing a decrease in the pH of the plating solution and the generation of salts, and to prolong the life of the plating solution. And the physical properties of the plating film can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention, and is a cross-sectional view illustrating a printed board on which a copper plating film is formed by electroless plating.

FIG. 2 is a cross-sectional view of a printed circuit board showing a state before electroless plating is performed.

[Explanation of symbols]

Reference numeral 1 denotes a printed board, 3 denotes a through hole, 4 denotes a plating resist, 5 denotes a copper plating film as a plating film.

Claims (1)

(57) [Claims] 1. A step of forming a plating resist (4) on a printed circuit board (1) according to an additive method and then treating with an acidic catalyst activating solution as a pretreatment for performing electroless plating, and thereafter, activating the activating solution. A pretreatment method of the plating solution in the additive method, comprising a washing step of washing; and after the washing step , a strong alkali water at a temperature higher than the plating solution.
A pretreatment method for a plating solution in an additive method, comprising a step of treating with a solution .