JPH0613733A - Manufacture of printed wiring board - Google Patents

Abstract

PURPOSE:To devise a manufacturing method for printed wiring board capable of avoiding the deterioration in the reliability due to the decrease in copper when an electroless solder plating step is performed on a wiring pattern. CONSTITUTION:After the formation of a wiring pattern, the copper hood pad pattern part and through hole part are subjected to an electroless copper plating to a thickness which exceeds that of copper to be reduced by an electroless solder plating step, and then an electroless solder plating step is performed.

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, and more particularly, to a wiring pattern coated with a solder alloy by electroless solder plating without reducing the copper plating thickness of the through holes. The present invention relates to a method for manufacturing a printed wiring board.

[0002]

2. Description of the Related Art FIG. 6 is a flow chart showing a process of a method for manufacturing a printed wiring board in the prior art, which is developed by the same applicant and is filed in Japanese Patent Application No. 2-321183. A conventional printed circuit board in the prior art is formed by forming a wiring pattern, or after forming a wiring pattern and applying a solder resist, and then immersing it in an electroless solder plating solution to expose the exposed metal copper portion and tin ions and lead in the plating solution. It is manufactured by reacting ions to deposit a tin / lead based solder alloy on a copper pattern.

Regarding the electroless solder plating solution, for example, JP-A-1-290774 discloses an electroless solder plating solution containing tin, lead, organic sulfonic acid and thiourea as main components. . As described above, these electroless solder plating solutions can deposit a solder alloy containing tin / lead as a main component on metallic copper. Generally, in these electroless solder plating, a tin / lead ion in a plating bath reacts with metallic copper to deposit a solder alloy by the following substitution reaction. 0.74Sn ²⁺ + 0.26Pb ²⁺ + 2Cu → Sn-Pb (74at% Sn) + 2Cu ⁺ According to the above reaction formula, 1 mol of solder alloy (74at
Omic% Sn) will cause 2 moles of copper to dissolve in the plating bath. This is a solder alloy (74
This corresponds to 0.85 μm of copper for 1 μm of atomic% Sn).

[0004]

Since the electroless solder plating in the conventional method for manufacturing a printed wiring board is performed as described above, when a thick solder alloy is deposited,
For example, when a solder alloy having a thickness of 10 μm or more is deposited, the amount of decrease in copper becomes a considerable value. For example, a foot pad pattern for mounting an IC package, in particular, an IC package having a fine pitch lead such as TCP (tape carrier package) requires high dimensional accuracy. However, if the pattern width is reduced by electroless solder plating, it becomes difficult to mount these IC packages with high accuracy.

Further, it is said that the through hole of a printed wiring board lacks heat resistance fatigue reliability unless it has a copper thickness of at least 25 μm or more. FIG. 7-B shows a schematic view of a cross section of a through hole of a printed wiring board to which heat stress is applied, in comparison with a normal state (FIG. 7-A). When thermal stress is applied to the through-hole 1 having a small plating thickness, a stress due to a difference in thermal expansion coefficient between the resin portion 2 and the metal copper 3 cannot be withstood, and a crack 4 is generated in the plating in the central portion. However, φ0.6 ~
With a small-diameter through hole of 0.3 mm, it is difficult to perform copper plating to a thickness in which a reduction in copper thickness due to electroless solder plating is added. As described above, in the conventional method for manufacturing a printed wiring board by electroless solder plating, no measure is taken against the pattern width reduction and the through-hole copper thickness, so that the pattern accuracy is poor and the reliability is impaired. There was a point.

The present invention has been made in order to solve the above problems, and it is possible to prevent a decrease in reliability due to a decrease in copper that occurs when electroless solder plating is applied on a wiring pattern. It is an object of the present invention to provide a method for manufacturing a printed wiring board.

[0007]

According to the method of manufacturing a printed wiring board according to the present invention, after forming a wiring pattern,
Copper electroless copper plating with a thickness equal to or greater than the copper thickness reduced by electroless solder plating on the copper hood pad pattern portion and through hole portion, and then electroless solder plating is performed. The electroless solder plating is carried out while the substrate is stationary or in an intermittent rocking state.

[0008]

In the method for manufacturing a printed wiring board according to the present invention, the electroless copper plating is performed on the copper hood pad pattern portion and the through hole portion in advance to a thickness corresponding to the copper thickness reduced by the electroless solder plating. By performing the substitution reaction only for the electrolytic copper plating, it is possible to apparently prevent the copper loss in the copper hood pad pattern part and the through hole part, and since the electroless solder plating is performed while the substrate is stationary or in the intermittent rocking state. Since the thick film is formed on the surface pattern portion and the thin film is formed on the through hole portion, the amount of copper reduction on the inner wall of the through hole can be made smaller than that of the surface pattern.

[0009]

EXAMPLES Example 1. Embodiments of the present invention will be described below with reference to the drawings. 1 is a flow chart showing a process of a method for manufacturing a printed wiring board in Embodiment 1 of the present invention. First, on a printed wiring board on which a pattern is formed and a solder resist is applied, electroless copper plating is performed on a portion such as a copper hood pad pattern and a through hole that requires electroless solder plating. Since the electroless copper plating film required here is an electron supply source for depositing the electroless solder plating film, it is not necessary to have particularly excellent film physical properties of the electroless copper plating, and further, complete It need not be a film. Therefore, electroless copper plating with granular deposition or powdery deposition may be used. Alternatively, copper alloy plating such as a copper film containing impurities may be used.

In general, alkaline electroless copper plating using formaldehyde as a reducing agent is classified into a low temperature (15 to 25 ° C.) thin type and an intermediate temperature (35 to 55) when classified by bath temperature.
C.) high speed type and high temperature (60 to 70.degree. C.) high physical property type (for additive). The electroless copper plating solution used here is not particularly limited, and any type of electroless copper plating can be used, but from the viewpoint of completing the treatment in a short time, a medium temperature high speed type is preferable. The plating speed is about 5 μm / h for medium-temperature high-speed type and 2 for high-temperature high-physical type.
It is possible to deposit at a rate of ˜3 μm / h. An example of the composition of the medium-temperature high-speed electroless copper plating bath is shown below. CuSO ₄ : 0.06 mol HCHO: 0.20 mol NaOH: 0.22 mol EDTA: 0.12 mol Stabilizer: Trace pH: 12 to 12.5 Temperature: 60 ° C. Activation treatment before electroless copper plating treatment As degreasing (acidic degreasing liquid, 40 ° C., 5 min), soft etching (sulfuric acid / hydrogen peroxide etchant, 40 ° C., 30 sec),
Each treatment of pickling (5% sulfuric acid, 25 ° C., 1 min) was performed, and then immersed in an electroless copper plating solution. here,
Using the above electroless copper plating bath, electroless copper plating treatment was performed at 60 ° C. for 3 hours. As a result, under the above conditions, 1
A copper plating film of 4 μm was obtained.

Next, an electroless solder plating process is performed. Pickling (5 as activation treatment before electroless solder plating)
% Sulfuric acid, 25 ° C., 1 min), and then immersed in an electroless solder plating solution. The electroless solder plating solution is a plating solution containing tin (0.1M), lead (0.01M), organic sulfonic acid (0.2M), and thiourea (2M) as main components, and treated at 70 ° C for 15 minutes. went. FIG. 2 shows the relationship between the solder deposition thickness and the plating time when a solder alloy was deposited on a copper pattern of a printed wiring board using the electroless solder plating solution used in this example. From the figure, it can be seen that the solder plating thickness increases with the plating time.
As a result, under the above conditions, a solder film of about 12 μm was obtained. As described in the conventional technique, 0.85 μm of copper is dissolved in the plating bath in order to deposit 1 μm of the solder alloy. Therefore, in order to obtain a solder coating of 12 μm as described above, Although copper will be dissolved in the plating bath, in the present embodiment, as described above, 14 μ
Since a copper plating film having a thickness of m is obtained and the amount of copper reduced by the electroless solder plating can be compensated by this amount, the reduction of copper in the copper hood pad pattern and the through hole portion is prevented.

Example 2. In Example 1, the electroless copper plating process and the electroless solder plating process were performed on the substrate to which the solder resist was applied. Solder plating is possible. In this case, as shown in the flow chart of FIG. 3, surface treatment may be performed after performing electroless copper plating, solder resist may be applied, and then electroless solder plating may be performed.

Embodiment 3. Further, in each of the above examples, an alkaline electroless copper plating bath using formaldehyde as a reducing agent was used, but an acidic electroless copper plating bath using hypophosphorous acid as a reducing agent can also be used as the electroless copper plating solution. . The alkaline bath limits the types of solder resists that can be used for printed wiring boards, but the acidic bath has the advantage that ordinary solder resists can be used. An example of the composition of the acidic electroless copper plating bath is shown. CuCl _2: 0.06 molar HEEDTA: 0.074 mole _{NaH 2 PO 2 · H 2 O} : 0.34 mol pH: 5 to 7 Temperature: 60 ° C.

FIG. 4 shows, as a comparative example of this embodiment, a copper hood pad pattern dimension and a through hole when a copper wiring pad pattern and a through hole are plated with the above plating solution on a printed wiring board. The amount of decrease in hole thickness is shown. From the figure, it can be seen that the reduction amount of the copper hood pad pattern and the thickness of the copper through hole increases with the plating time. The decreasing tendency of the copper thickness in Fig. 4 and the increasing tendency of the plating thickness in Fig. 2 are correspondingly changed, and the ratio is also about 1: 1 and corresponds to the above-mentioned solder alloy and copper substitution amount. It is clear what you are doing.

Example 4. Further, in each of the above-mentioned embodiments, the state of the printed circuit board is not described, but during the electroless solder plating treatment, the printed circuit board is plated in a stationary or intermittent rocking state. The condition for intermittent rocking is 1 to 1 minute.
About 10 times of rocking, rocking speed is 0.5m / min
The following is preferable, and the swinging direction is preferably parallel to the surface of the printed circuit board.

FIG. 5 is a diagram showing the relationship between the electroless solder plating thickness and the stirring strength of the plating solution. The stirring strength shown here represents the rocking speed of the printed board which is the material to be plated. From the figure, the electroless solder plating thickness is greatly affected by the stirring strength, and up to a certain condition, in this case 2 m /
Up to min, the plating thickness increases in proportion to the stirring strength. When the stirring strength is higher than that, the effect of stirring related to the supplementation of ions is saturated, so that the plating thickness becomes constant regardless of the stirring strength. The stirrer conditions in ordinary electroless solder plating are irrespective of this stirrer strength, and plating is carried out under the condition of stirrer strength such that a constant plating thickness can be obtained.

FIG. 6 is a diagram showing the relationship between the pattern size of copper for electroless solder plating and the thickness of electroless solder plating. The electroless solder plating thickness is greatly affected by the pattern size, and the smaller the pattern size, the larger the plating thickness. This tendency is slightly different depending on the stirring strength, and the condition 2 m / m when the effect of the stirring strength shown in FIG.
Comparing the case of plating with in, it can be seen that the effect of the pattern size is more pronounced in the case of plating in a stationary state. When plated in a static state,
The plating thickness of the pattern size of 5 mm or less is approximately 2-3 times the plating thickness of the pattern size of 1 mm or more plated under the same conditions. As described above, since the plating thickness of the electroless solder plating is strongly influenced by the stirring of the plating solution and the pattern size, it is considered that the diffusion of ions is dominant. That is, it is shown that as the pattern size is smaller, ion diffusion is more likely to occur and thick plating can be easily obtained.

When the printed circuit board is plated in a static state during the electroless solder plating process, the printed circuit board surface pattern is thickly plated and the through holes are thinly plated. With the printed circuit board at rest, 70 ℃,
150μ when electroless solder plating is performed for 30 minutes
A plating thickness of about 13 μm was obtained for the surface pattern of m width, and a plating thickness of about 5 μm was obtained at the center of the through hole. This is because, as described above, the surface area of the through hole is larger than that of the printed circuit board surface pattern, and thus the effect of ion diffusion is small. Further, even if the plating solution component inside the through hole is consumed, it is difficult to newly replenish the plating solution component into the through hole because the substrate that is the material to be plated is plated in a stationary state. Is also considered to be involved.

When the printed circuit board surface pattern is thus thickly plated and the through hole is desired to be thinly plated, it is best to perform the plating in a stationary state, but the plating thickness varies depending on the distribution of the printed circuit board surface pattern. It may occur. In order to eliminate this, plating is performed on the printed circuit board in an intermittent rocking state. The plate is rocked in a direction parallel to the surface of the printed circuit board at a rocking speed of 0.5 m / min or less at a rocking frequency of about 1 to 10 times per minute, and plating is repeated in a stationary state and a rocking state. As a result, plating can be performed without causing variations in the plating thickness of the surface pattern.

According to the fourth embodiment, since the printed circuit board is plated by static or intermittent rocking during the electroless solder plating process, the printed circuit board surface pattern is thickly plated and the through holes are thinly plated. The plating could be attached. With electroless solder plating, copper with a thickness almost the same as the plating thickness is reduced, but even if a thick electroless solder plating is applied to the surface pattern, the copper loss in the through holes can be kept small, so the reliability of the printed circuit board is improved. Will not hurt. In addition, even when copper having a reduced thickness is attached in advance by electroless copper plating or the like, the thickness of the attached copper can be reduced, which is economical.

[0021]

As described above, according to the first aspect of the present invention, the step of forming the wiring pattern and the solder resist, and the electroless copper plating on the copper hood pad pattern and the through hole portion on the wiring pattern are performed. At least including a step and a step of coating the wiring pattern portion with a solder alloy containing tin / lead as a main component by electroless solder plating,

According to a second aspect of the present invention, a step of forming a wiring pattern, a step of applying electroless copper plating to a copper hood pad pattern and a through hole portion on the wiring pattern, and a solder on the wiring pattern. At least including a step of forming a resist and a step of coating a wiring pattern portion with a solder alloy containing tin / lead as a main component by electroless solder plating;

According to a third aspect of the present invention, in the first or second aspect, the electroless solder plating is performed while the printed circuit board is stationary or intermittently swung,

According to a fourth aspect of the present invention, in the first or second aspect, the electroless copper plating has a thickness equal to or greater than the copper thickness reduced by the electroless solder plating,

According to a fifth aspect of the present invention, in the first or second aspect, the electroless copper plating is performed so that the copper thickness of the wiring pattern after electroless solder plating is maintained at 25 μm. It is possible to provide a method for manufacturing a printed wiring board that can prevent a decrease in reliability due to a decrease in copper that occurs when electroless solder plating is applied on a wiring pattern.

[Brief description of drawings]

FIG. 1 is a flowchart showing a process of a method for manufacturing a printed wiring board according to a first embodiment of the present invention.

FIG. 2 is a solder deposition thickness when a solder alloy is deposited on a copper pattern of a printed wiring board using an electroless solder plating solution in the electroless solder plating step of the method for manufacturing a printed wiring board in FIG. It is a characteristic view showing the relationship between the plating time and.

FIG. 3 is a flow chart showing a process of a method for manufacturing a printed wiring board in the example of the present invention.

FIG. 4 shows a reduction amount of copper and a plating time when a solder alloy is deposited on a copper pattern of a printed wiring board not subjected to electroless copper plating by using the same electroless solder plating solution as in FIG. It is a characteristic view showing the relationship of.

FIG. 5 is a diagram showing a relationship between a plating thickness of electroless solder plating and a stirring strength of a plating solution.

FIG. 6 is a view showing a relationship between a pattern size of copper to be electrolessly solder-plated and an electroless solder-plating thickness in a state of a substrate.

FIG. 7 is a flow diagram showing a process of a method for manufacturing a printed wiring board in the prior art.

FIG. 8 is a schematic diagram showing a state in which thermal stress is applied to the through holes of the printed wiring board.

[Explanation of symbols]

 1 Through hole 2 Resin part 3 Metal copper 4 Crack

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[Procedure amendment]

[Submission date] June 25, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

Next, an electroless solder plating process is performed. Nothing
As an activation treatment before electrolytic solder plating treatment, pickling (5
% Sulfuric acid, 25 ° C, 1 min) treatment, then electroless
It was immersed in a solder plating solution. Electroless solder plating solution
(0.1M), lead (0.01M),Organic sulfonic acid
(0.2M), thiourea (2M) -based plating
The solution was treated at 70 ° C. for 15 minutes. This is shown in Figure 2.
Use the electroless solder plating solution used in the example to print
When the solder alloy is deposited on the copper pattern of the wire plate,
The relationship between the deposited thickness and the plating time is shown. Plating from the figure
It can be seen that the solder plating thickness increases with time.
As a result, under the above conditions, a solder film of about 12 μm
Was obtained. As mentioned in the prior art, solder
Copper 0.85μm is plated to deposit alloy 1μm
As it dissolves in the bath, it has a 12 μm solder crust as described above.
To obtain a film, 10.2 μm copper was dissolved in the plating bath.
As will be understood, in the present embodiment, as described above, 14 μ
m copper plating film has been obtained.
Since the thickness of copper that is reduced by the electroplating can be compensated,
Copper in the dead pad pattern and through holes
Is being prevented.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

When the printed circuit board surface pattern is thus thickly plated and the through hole is desired to be thinly plated, it is best to perform the plating in a stationary state, but the plating thickness varies depending on the distribution of the printed circuit board surface pattern. It may occur. In order to eliminate this, plating is performed on the printed circuit board in an intermittent rocking state. With 1 to 10 times of rocking per minute, the rocking speed is 0.5 m / min or less, and the plate is rocked in a direction perpendicular to the surface of the printed circuit board, and plating is repeated in a stationary state and a rocking state. As a result, plating can be performed without causing variations in the plating thickness of the surface pattern.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Morita 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation Production Technology Laboratory (72) Inventor Takashi Takahama 8-1-1 Tsukaguchihonmachi, Amagasaki Mitsubishi (72) Inventor Osamu Hayashi 8-1-1 Tsukaguchi Honcho, Amagasaki City Mitsubishi Electric Co., Ltd. (72) Inventor Shunsuke Uzaki 1-157 Miyashita, Sagamihara Mitsubishi Electric (72) Inventor Toshihide Sudo 1-157 Miyashita, Sagamihara-shi Mitsubishi Electric Co., Ltd. Sagami Manufacturing Co., Ltd.

Claims (5)

[Claims] 1. A step of forming a wiring pattern and a solder resist, a step of applying electroless copper plating to a copper hood pad pattern and a through hole portion on the wiring pattern, and a step of forming tin on the wiring pattern portion by electroless solder plating. And a step of coating a solder alloy containing lead as a main component, the method for producing a printed wiring board. 2. A step of forming a wiring pattern, a step of applying electroless copper plating to a copper hood pad pattern and a through hole portion on the wiring pattern, a step of forming a solder resist on the wiring pattern, A method for manufacturing a printed wiring board, which comprises at least a step of coating the wiring pattern portion with a solder alloy containing tin / lead as a main component by electrolytic solder plating. 3. The method for manufacturing a printed wiring board according to claim 1, wherein the electroless solder plating is performed by statically or intermittently rocking the printed circuit board. 4. The method for producing a printed wiring board according to claim 1, wherein the electroless copper plating is applied to a thickness equal to or larger than the copper thickness reduced by the electroless solder plating. 5. The printed wiring board according to claim 1, wherein the electroless copper plating is performed such that the copper thickness of the wiring pattern after electroless solder plating is maintained at 25 μm. Production method.