JPH05304350A - Printed wiring board and its production - Google Patents

Abstract

PURPOSE:To provide a printed wiring board and its production method in which it is unnecessary to displace a lead on a copper foot pad pattern when mounting an IC package and the positioning for the lead is easy. CONSTITUTION:The upper face of solder alloy film 1 on a copper foot pad pattern 3 for mounting an IC package of wiring pattern is formed as to become flat, and a lead 4a of the IC package is placed thereon and solder-jointed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board in which electroless solder plating is applied on a wiring pattern and a method for manufacturing the same, and more particularly to the shape of the upper surface of a solder plating film applied on the wiring pattern. is there.

[0002]

2. Description of the Related Art FIG. 10 is a flow chart showing a process of a method for manufacturing a printed wiring board in the prior art disclosed in Japanese Patent Application No. 2-321183 developed and filed by the same applicant. Conventional printed wiring boards in the prior art, after forming a wiring pattern, or after forming a wiring pattern and applying a solder resist, are immersed in an electroless solder plating solution and exposed to exposed metal copper portions and tin ions in the plating solution. It is manufactured by reacting lead ions to deposit a tin / lead based solder alloy on a copper pattern.

Regarding the above electroless solder plating solution, for example, Japanese Patent Application Laid-Open No. 1-290774 discloses tin,
An electroless solder plating solution containing lead, organic sulfonic acid and thiourea as main components is described. As described above, these electroless solder plating solutions can deposit a solder alloy containing tin / lead as a main component on metallic copper. In general,
In these electroless solder platings, 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 conventional electroless solder plating applied to the wiring pattern of the printed wiring board is performed as described above, the solder plating film is formed in the substitution reaction process of Cu with Sn and Pb. Since voids may occur in the inside, and the adhesion to the copper foot pad pattern deteriorates when the voids are present, the post-heat treatment process of the flowchart in FIG. 10 is performed to melt and solidify the solder plating film. , The adhesion is improved.

However, when the solder alloy film is melted and solidified in this way, the solder alloy film 1 at the time of melting as shown in FIG. 11 has a curvature radius on the upper surface 3a of the copper foot pad pattern 3 on the substrate 2 due to surface tension. Is small and the radius of curvature is large at the end portion 3b of the upper surface. Therefore, when the IC package 4 is mounted on the copper foot pad pattern 3 as shown in FIG. 12, the lead 4a depends on the roundness of the upper surface of the solder alloy film 1. May slip and be displaced, causing an electrical short circuit between adjacent pads, and the outer shape of the solder alloy film 1 becomes unclear, resulting in an IC package 4
However, there is a problem that it becomes difficult to recognize the shape of the solder alloy film 1 that is carried out during mounting, and the lead 4a cannot be positioned.

The present invention has been made in order to solve the above-mentioned problems, and when the IC package is mounted, the leads do not deviate from the copper foot pad pattern, and the leads can be easily positioned. It is intended to provide a manufacturing method thereof.

[0007]

[Means for Solving the Problems] Claim 1 according to the present invention
In the printed wiring board according to claim 1, the upper surface of the solder alloy film on the copper foot pad pattern for mounting the IC package of the wiring pattern is formed flat, and the printed wiring board according to claim 2 is the solder alloy film according to claim 1. 4. The printed wiring board according to claim 3, wherein the upper surface of the wiring pattern is formed by inclining upward from the lead tip mounting side of the mounted IC package toward the other side. The above solder alloy film is applied only to the side surface of the copper foot pad pattern, and the method for manufacturing a printed wiring board according to claim 4 is the IC of the wiring pattern.
A printed wiring board according to claim 3 is manufactured by masking the upper surface of a copper foot pad pattern for mounting a package and then forming a solder alloy film containing tin / lead as a main component by electroless solder plating. ..

[0008]

The solder alloy film formed on the copper foot pad pattern for mounting the IC package of the printed wiring board according to the present invention has a flat upper surface and is formed only on the side surface of the copper foot pad pattern. , It prevents the leads of the IC package from slipping off the copper foot pad pattern and facilitates positioning.

[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 manufacturing process of a printed wiring board in Embodiment 1 of the present invention, and FIG.
FIG. 6 is a schematic cross-sectional view showing the press working process of FIG. First,
For example, the pattern width of the copper foot pad pattern 3 is 150μ
m and a pattern-formed printed wiring board having a pattern interval of 150 μm is used, and cleaning is performed according to the flow shown in FIG.
Each process of activation-electroless solder plating cleaning / drying-post heat treatment was performed. The state of the copper foot pad pattern portion at the time of finishing the post heat treatment process is shown in FIG.
-Shown in (A). In this state, solder alloy film 1
Has an average film thickness of 13 μm and a radius of curvature R on the upper surface of 150
μm, and the radius of curvature r at the end of the upper surface is 80 μm.

Next, as shown in FIG. 2 (B), a die 5 made of a die steel material was pressed from the upper surface of the solder alloy film 1 in the direction of the arrow with a pressure of 180 kgf / cm ² for 10 seconds. The temperature of the solder alloy film 1 at this time is 140 ° C to 160 ° C. The state of the copper foot pad pattern portion after the press working process thus performed is shown in FIG. Solder alloy film 1 in this state
Has a radius of curvature R'of 350 μm, which is significantly larger than the radius of curvature R before pressing, and has a radius of curvature r ′ of 20 μm at the end of the upper face, which is significantly smaller than the radius of curvature r before pressing. Is becoming

Now, as shown in FIGS. 3- (A) and (B), the IC is formed on the solder alloy film 1 pressed as described above.
Place the leads 4a of the package 4 at a temperature of 350 ° C., 1
Soldering was performed by the pulse heating method for 5 seconds, but the radius of curvature R ′ of the upper surface of the solder alloy film 1 became extremely large, and the state was almost flat.
As shown in (C) and (D), the leads 4a did not slip from the copper foot pad pattern 3 and were not displaced, and good soldering was achieved. Further, as a result of measuring the peel strength of the solder joint, it was confirmed that the lead 4a broke before the joint broke, and good solder joint strength was obtained.

[0012] The temperature and pressure in the press working process are variously changed, and when the shape of the surface of the solder alloy film 1 is different, the same solder joining as described above is performed. Radius of curvature R '
Is 300 μm or more, and the radius of curvature r ′ at the upper end is 30
It was also confirmed that the same effect as described above is exhibited if the conditions of μm or less are satisfied. Further, since the radius of curvature at the end of the upper surface is significantly reduced, the contour of the solder alloy film 1 becomes clear and the shape can be easily recognized.
It becomes easy to position.

Embodiment 2. According to the first embodiment,
Although die steel was used as the material of the press die 5, when the temperature at the time of pressurization is 170 ° C., the solder alloy film 1 adheres to the press die 5 and becomes unusable in about 50 presses. When an alumina ceramic film having a thickness of 10 μm is formed on the surface of the die steel by a vacuum deposition method, the press die 5
Has been extended to about 500 times. It was confirmed that the same effect can be obtained by using boron nitride or silicon nitride as the ceramic material.

Example 3. Generally, an angle α is given to the tip end portion where the lead 4a of the IC package 4 is in contact with the copper foot pad pattern 3 as shown in FIG. 4 in order to improve the joining quality. The present embodiment is made by paying attention to this point. First, as the IC package 4, a lead 4a having an angle α of 6 ° was applied. Therefore, for example, for a copper foot pad pattern 3 having a pattern width of 150 μm, a pattern interval of 150 μm, and an average solder film thickness of 13 μm, a press die 5 similar to that used in the second embodiment is used and the temperature is 160 ° C. and the pressure direction θ = 6. By pressing at 180 ° with a pressure of 180 kgf / cm for 10 seconds, a solder alloy film 1 having a shape as shown in FIG. 5 was obtained.

In this state, the radius of curvature R'on the upper surface of the solder alloy coating 1 was 330 μm, and the radius of curvature r'at the edge of the upper surface was 20 μm. The leads 4a of the IC package 4 are formed on the upper surface of the solder alloy film 1 thus formed.
When the surface of the solder alloy film 1 is placed along the extending direction of the leads 4a when the soldering is carried out by mounting the above, the melted solder does not flow violently and the shape of the soldered joint is good. Therefore, the bonding strength can be obtained. It is suitable that the angle θ is 2 to 6 °.

Example 4. 6 is a diagram showing a manufacturing process of a printed wiring board in Embodiment 4 of the present invention, and FIG. 7 is a schematic sectional view showing a mask attaching process and a mask peeling process in FIG. Generally, a solder resist is applied on the pattern of a printed wiring board for the purpose of protecting the pattern and improving the insulation between the patterns. However, the solder resist cannot be applied to a minute space such as between the copper foot pad patterns 3 for mounting the IC package because the solder resist has a high liquid viscosity. Therefore, as shown in FIG. 7, the solder resist 6 does not exist between the copper foot pad patterns 3 and is a space.

First, as shown in FIG. 7- (A), a mask 5 having a thickness of 5 is formed on top of 10 copper foot pad patterns 3 having a pattern width of 150 μm and a pattern interval of 150 μm.
Apply a dry film resist of 0 μm, and
As shown in (B), electroless solder plating was performed on the side surface at a plating solution temperature of 70 ° C. for a plating time of 60 minutes to form a solder alloy film 1. Thereafter, as shown in FIG. 7- (C), the mask 7 was peeled off, and the thickness of the solder alloy film 1 was measured at 10 locations for each of the copper foot pad patterns 3 and a total of 100 locations, 2 at the thickest place
8, 1 μm, 21 in thin places, 4 μm, average 25 μm, and adjacent copper foot pad pattern 3 in all places
A good solder alloy film 1 was obtained only on the side surface of the copper foot pad pattern, as shown in FIG.

Thereafter, as shown in FIG. 9- (A), the leads 4a of the IC package 4 are directly placed on the copper foot pad pattern 3 and soldering is performed by a pulse heating method at a temperature of 350 ° C. for 15 seconds. However, when the solder alloy film 1 on the side surface is melted, the joint surface between the copper foot pad pattern 3 and the lead 4a is wetted, and good solder joint can be achieved without causing positional displacement as shown in FIG. 9- (B). I was able to. Further, as in the case of Example 1 above, as a result of measuring the peel strength of the solder joint, it was also confirmed that the lead 4a broke before the joint broke, and good solder joint strength was obtained. ..

[0019]

As described above, according to the present invention, the upper surface of the solder alloy film on the copper foot pad pattern for mounting the IC package of the wiring pattern is formed flat, and the upper surface of the solder alloy film is formed flat. I installed with
The C package is formed by inclining upward from the lead tip mounting side toward the other side, and the solder alloy film is applied only to the side surface of the copper foot pad pattern.
It is possible to provide a printed wiring board in which the leads of the C package do not deviate from the copper foot pad pattern and the positioning of the leads is easy, and a method for manufacturing the printed wiring board, which exhibits an excellent effect in practice.

[Brief description of drawings]

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

FIG. 2 is a schematic cross-sectional view showing a press working process in FIG.

FIG. 3 is a schematic cross-sectional view showing a process of soldering and mounting an IC package on a copper foot pad pattern of a printed wiring board according to Embodiment 1 of the present invention.

FIG. 4 is a diagram showing a general shape of leads of an IC package.

FIG. 5 is a schematic cross-sectional view showing the shape of a solder alloy film on a copper foot pad pattern of a printed wiring board according to Example 3 of the present invention.

FIG. 6 is a flow chart showing a manufacturing process of a printed wiring board according to Embodiment 4 of the present invention.

7 is a schematic cross-sectional view showing a mask attaching process and a mask peeling process in FIG.

FIG. 8 is a schematic cross-sectional view showing the shape of a solder alloy coating on a copper foot pad pattern of a printed wiring board according to Embodiment 4 of the present invention.

FIG. 9 is a schematic cross-sectional view showing a process of soldering and mounting an IC package on a copper foot pad pattern of a printed wiring board according to Embodiment 4 of the present invention.

FIG. 10 is a flowchart showing a manufacturing process of a conventional printed wiring board.

FIG. 11 is a schematic cross-sectional view showing the shape of a solder alloy film on a copper foot pad pattern of a conventional printed wiring board.

FIG. 12 is a schematic cross-sectional view showing a process of soldering an IC package on a copper foot pad pattern of a conventional printed wiring board.

[Explanation of symbols]

 1 Solder Alloy Film 2 Substrate 3 Copper Foot Pad Pattern 4 IC Package 4a Lead 5 Press Mold 6 Solder Resist 7 Mask

 ─────────────────────────────────────────────────── ─── 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 City Mitsubishi Electric Co., Ltd. Sagami Manufacturing Co., Ltd.

Claims (4)

[Claims] 1. A printed wiring board in which a solder alloy film containing tin / lead as a main component is formed on a wiring pattern by electroless plating, wherein the solder alloy film on the copper foot pad pattern for mounting an IC package of the wiring pattern. The printed wiring board is characterized in that the upper surface of is formed flat. 2. The upper surface of the solder alloy coating is I
The printed wiring board according to claim 1, wherein the printed wiring board is formed so as to be inclined upward from the lead tip mounting side of the C package toward the other side. 3. A printed wiring board in which a solder alloy film containing tin / lead as a main component is formed on a wiring pattern by electroless plating, wherein the solder alloy film on the copper foot pad pattern for mounting an IC package of the wiring pattern. Is a printed wiring board characterized by being provided only on the side surface of the copper foot pad pattern. 4. A solder alloy film mainly composed of tin / lead is formed by electroless solder plating after masking the upper surface of a copper foot pad pattern for mounting an IC package of a wiring pattern. The method for manufacturing a printed wiring board according to claim 3.