JPH01253294A - Printed wiring substrate and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the solder in permeability and increase its adhesive area so as to improve its solderability by a method wherein a wiring pattern of a printed wiring board is formed of a plating film mainly composed of plating particles whose diameters are 3-10mum. CONSTITUTION:A first and a second Cu plating layer, 8 and 9, are formed in lamination on a base board 2 and moreover a solder layer 10 is formed thereon for the formation of a wiring circuit section 3. A connecting circuit section 4 is structured in such a manner that the first and the second Cu plating layer, 8 and 9, are formed on an inside circumference of a through-hole 13 provided to the board 2 penetrating through it and a solder layer 10 is formed on the inner face of the through-hole 13. The second Cu plating layer 9 is formed of plating particles whose diameters are 3-10mum. Then, interfaces between the plating particles become gaps into which solder permeates easily. By these processes, the solder is improved in permeability and increased in an adhesive area, so that the solderability can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a printed wiring board in which metal wiring is patterned by plating on an insulating base substrate, and a method for manufacturing the same, and in particular to a printed wiring board formed on the inner peripheral surface of a through hole. Soldering is related to improving properties when external connection terminals and the like are soldered to a plating film or a pattern plating film on the surface of a substrate.

[Conventional technology]

In printed wiring boards, conventional methods for patterning metal wiring on a base substrate and forming a plating film on the inner peripheral surface of a through hole include, for example, the so-called additive method and subtractive method. The additive method is a method in which a plating resist film is patterned on an insulating base substrate in which through holes etc. are formed, and a wiring pattern is additionally formed by electroless plating in this state. The subtractive method is a method in which a plating resist film is patterned on a base substrate made of a copper-clad F1 layer board, electroplated, and then unnecessary portions of the underlying copper plate are removed by etching. .

[Problem that the invention seeks to solve]

By the way, when using the above printed wiring board, connect the connection terminal with the external circuit to the wiring pattern by soldering.
Alternatively, the terminals of the mounted components are inserted into the through holes of the board and the connections are made by soldering. Therefore, of course,
High soldering properties of plating films such as wiring patterns are required.

Furthermore, when soldering the through-hole portion, it is required that the solder sufficiently penetrate between the insertion terminal and the plating film on the inner surface of the through-hole. However, with the wiring patterns formed by the conventional additive method or subtractive method, the soldering performance is not necessarily satisfactory, and there is room for improvement.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional demands, the present invention aims to provide a printed wiring board and a method for manufacturing the same, which can significantly improve soldering properties.

[Means for solving problems]

In order to improve the solderability, the inventor of the present invention observed the metal structure of the wiring pattern and found that the diameter of the plating particles constituting the pattern determines the solderability. The present invention was completed based on the idea that the above object could be achieved by forming a wiring pattern while regulating the diameter of the plating particles within a predetermined range. The diameter of the plating particles referred to herein refers to the diameter of convex particles observed in a plane parallel to the substrate surface when the wiring pattern is observed from a direction perpendicular to the substrate using an electron microscope or the like.

Therefore, the specific invention of the present application provides a printed wiring board in which a wiring pattern made of a plating film is formed on a base substrate, in which most of the plating particles constituting the wiring pattern have a diameter of 3 in a plane parallel to the substrate surface. It is characterized by having a diameter of ~10 μm.

Further, a related invention of the present application is a method for manufacturing a printed wiring board, in which a base substrate is immersed in a plating solution so as to face an electrode, and electroplating is performed while the plating solution is flowing along the surface of the substrate. It is characterized in that the plated particles are made to have a diameter of 3 to 10 μm.

As mentioned above, the plating particles in the present invention refer to particles that are observed when the surface condition of the plating film constituting the wiring pattern is observed using an electron microscope, etc. The diameter of a particle is the diameter when the granular unit is viewed from a plane, but when measuring this particle size, for example, the number of particles observed in a predetermined length region of 9N is counted, and this count is used to calculate the above-mentioned predetermined number. It is calculated by dividing the length and then dividing by the current magnification.

First, in the present invention, the plating particle size is 3 to 10 μm.
The reason for this limitation is as follows.

That is, according to the inventor's experiments, particle diameters of less than 3 μm and 1
This is because it has been found that when the particle size exceeds 0 μm, the effect of improving soldering properties cannot be obtained, and that the soldering properties are improved only when the particle size is 3 to 10 μm. More preferably, the particle size is about 5 μm. good.

In order to improve soldering properties, it is considered important that the solder easily penetrates into the boundaries between the plating particles that make up the plating film, and that the adhesion area between the solder and the plating film can be increased. However, when the particle size is less than 3 μl, the surface of the plating film becomes too smooth, and there are almost no recesses for solder to penetrate at the boundaries between particles, and as a result, soldering properties cannot be improved as described above. considered to be a thing. On the other hand, when the particle size exceeds 10 μm, the number of boundaries between particles in a given area decreases accordingly.
Therefore, the solder bonding area is not sufficient, and it is considered that soldering cannot improve the properties in this case as well.

Next, in the related invention of the present application, the reason why plating is performed while the plating solution is flowing along the substrate surface is as follows.

That is, through experimental research conducted by the present inventors, it has been found that the diameter of the plating particles constituting the plating film is determined by the plating method. For example, in a plating film formed by electroplating in which a member to be plated is immersed in a stationary plating solution, the above-mentioned plating particles are hardly observed. On the other hand, in a plating film formed by electroless plating, the plating particle size is 25 μm or more.

On the other hand, when plating is performed by immersing the base substrate in a plating solution so as to face the electrodes and flowing the plating solution along the substrate surface according to the related invention method of the present application, the current density By appropriately selecting the flow rate of the plating solution, etc., a plating film having a particle size of 3 to 10 μm can be obtained.

[Effect]

In the specific invention of the present application, since the wiring pattern of the printed wiring board is formed with a plating film mainly composed of plating particles with a particle size of 3 to 10 μm, the boundaries between the plating particles become gaps through which solder can easily penetrate. Penetration is improved and the solder adhesion area is greatly increased, resulting in greatly improved soldering properties.

Furthermore, in the related invention of the present application, electroplating is performed while the plating solution is flowing along the base substrate.
By appropriately selecting the flow rate, current density, etc. of this plating solution, the plating particles of the plating film formed by this plating can be made to have a particle size of 3 to 10 μm. In this case, for example, when the flow rate of the plating solution is increased within a certain range, the diameter of the plating particles increases, and when the current density is increased within a certain range, the diameter also becomes large. As a result of being able to appropriately select the plating particle size in this way, solder permeability can be improved and soldering properties can be improved.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram for explaining a printed wiring board according to an embodiment of the present invention.

In the figure, 1 is a printed wiring board, which forms wiring circuit parts 3.3 on both the upper and lower surfaces of the base board 2, and connects the land parts 5 of both wiring circuit parts 3.3 with each other. The parts 4 are connected to each other, and the parts other than the land parts 5 are covered with a solder resist 6 made of heat-resistant resin.

The purpose of this solder resist 6 is to prevent solder from adhering to parts other than the land portions 5 when soldering external terminals and the like.

The wiring circuit section 3 is provided with first and second circuits on the base substrate 2.
It is constructed by laminating Cu plating layers 8 and 9 and further forming a solder layer 10 on the upper surface thereof. Further, the connection circuit section 4 is constructed by forming first and second Cu plating layers 8.9 on the inner peripheral surface of a through hole 13 formed through the base substrate 2, and forming a solder layer 10 on the inner surface of the first and second Cu plating layers 8.9. has been done.

3 and 4 show a plating apparatus for forming the second Cu plating layer 9 in the manufacturing process of the embodiment substrate 1. The plating particles constituting the particle size 3 of the present invention
The structure is such that it can be formed to a thickness of ~10 μm.

In FIG. 4 showing the overall configuration of the plating apparatus, the plating apparatus 24 includes a main body 25 and a supply device for supplying an acidic steel plating solution P such as copper sulfate in a plating solution tank 26 to the main body 25. It consists of 27. This supply device 27 includes a supply pump 28 and a supply side header 29 . The first one connects the discharge side headers 30. Second supply passage 31.3
2, first and second discharge passages 33 and 34, and a first discharge passage disposed in each passage. 2nd on-off valve 35.36, 1st. 2nd flow meter 37.38, 1st. It is composed of a second Hff valve 39 and 40.

In addition, as shown in FIG.
are arranged facing each other, and a holding bracket 45 for holding the plate to be plated is provided between the two electrodes. The plating electrode 44 is connected to the anode of the power source, and the holding bracket 45 is connected to the cathode. When the plate to be plated is attached to the holding bracket 45, the acid casing 43 is divided into the first and second plating chambers 46, 47 by this plate, whereby the first supply, the discharge passage 31, 33 and the second supply, The discharge passages 32 and 34 will communicate with each other.

Next, the manufacturing procedure of the printed wiring board 1 shown in FIG. 2 will be explained with reference to FIGS. 3 to 5. The method of this embodiment is located between the above-mentioned additive method and subtractive method. Therefore, it is called a semi-additive method.

■ For example, prepare the base substrate 2 by laminating and press-molding about 10 layers of epoxy resin containing glass fibers, and then applying an adhesive to improve the adhesion of copper plating, and penetrate the through holes 13 at predetermined positions. (Fig. 5(al)).

(2) After the base substrate 2 is activated as a pre-plating treatment, a first Cu plating layer 8 of 2 to 5 μm is coated on both surfaces of the base substrate 2 and the inner peripheral surface of the through hole 13 by electroless plating. (FIG. 5(bi)).

(2) A photosensitive dry film is thermocompression bonded onto the Cu plating layer 8 of the container 1, and a mask having a shape corresponding to the wiring circuit section 3 is closely attached to the film, followed by exposure and development. As a result, a plating resist substrate 18 covered with a plating resist film 15 having patterned groove openings 16 is obtained (tel in FIG. 5).
.

(2) Next, the second Cu plating layer 9 is formed on the plating resist substrate by the plating apparatus 24 on the first day. In this case, first, the plating resist substrate 18 is mounted on the holding bracket 45 inside the casing 43, the circulation pump 28 is operated, and the plating power source is turned on. Then, the plating solution P is supplied to the casing 4 from the first and second supply passages 31 and 32.
The Cu plating layer 9 is supplied into the plating resist substrate 18 and flows along both surfaces of the plating resist substrate 18 to form a second Cu plating layer 9 on the portions of the substrate 18 exposed from the pattern openings 16. Further, at this time, the opening degree of the first on-off valve 35 is set to be larger than that of the second on-off valve 36. As a result, the flow rate F1 in the first plating chamber 46 in the casing 43 becomes higher than the flow rate F2 in the second plating chamber 47, and the pressure in the first plating chamber 46 becomes higher. Therefore, a part of the plating solution flows from the first plating chamber 46 through the through hole 13 into the second plating chamber 47 (see arrow F3).
The second plating 1!9 is also reliably formed on the u plating layer 8. (Figure 5(d)).

■ And the above 1. The second Cu plating layer 8.9 is formed by electrolytic solder plating on the substrate on which the second Cu plating layer 8.9 is formed.
To form a solder 1) 10 on the Cu plating layer 9 in order to prevent the plating 1) 9 from being etched in a later process, the substrate is immersed in a stripping solution consisting of an alkaline solution. Then, the plating resist film 15 is peeled off and removed.
Furthermore, it is immersed in an etching solution. Then, the first
．． A wiring circuit section 3 consisting of a second CU plating layer 8.9 and a solder layer 10 is formed on the inner peripheral surface of the through hole 13, and a connection circuit section 4 having the same configuration as the wiring circuit section 3 is formed (
Figure 5ff)).

■ Finally, the solder layer 10 is melted to form the first and second Cu layers.
The entire substrate is heated to cover the plating layers 8 and 9.
As shown in the figure (along side), solder resist 6 is crimped and formed except for the connection land portion 5 (FIG. 5(h)). In this way, the printed wiring board 1 shown in FIG. 2 is manufactured.

FIG. 1 (tag and bl) are electron micrographs showing the state of the plating particles of the second Cu plating layer 9 in the through holes 13 of the printed wiring board 1 of this example manufactured by the method described above. Figure 8(a).

Figure 9(a) is an electron micrograph of the second Cu plated layer 9 when the second Cu plated layer 9 is formed by ordinary electroplating with the plating solution stationary.
, (bi is an electron micrograph of the first and second Cu plating layers formed successively by electroless plating.

As is clear from these photographs, the plating particles of the plating film formed by the method of this example have a particle size of 3 to 10 μm, whereas when using a static plating solution, the magnification was 1000 times (8th Figure (al), 5000x (Figure 8 (
Even in b)), hardly any plated particles were observed, and in the case of electroless plating, it was found that the plated particles were formed by large particles of 25 μm or more.

Next, an example of an experiment conducted in order to confirm the effect of improving soldering properties of a plated film according to the method of the present invention will be described.

In this experiment example, the terminal of an electronic component is inserted into the through hole.
In flow soldering in which the solder moves along the solder surface in this state, the purpose is to examine the so-called solder climbing property in which the solder rises in the gap between the inner peripheral surface of the through hole and the terminal. This solderability is determined by subjecting Cu-plated foil plated using the method of the present invention under the following conditions to a depth of 15 fins in a solder bath layer at 260°C, as shown in Figure 6, after subjecting it to a prescribed pretreatment. The test was conducted by dipping the solder layer in the same position, gently pulling it out after a certain period of time, and measuring the length A of the adhered solder layer. For comparison, a Cu-plated foil (thickness: 35 μm) plated using a static plating bath was also investigated in the same manner.

Plating conditions according to the present invention: Cu5Qn 300 g/
1. A plating bath containing 50 g/' of HtSOa = remaining pure water was maintained at 50°C, and while flowing, electroplating was performed on a stainless steel plate at a current density of 20 A/dII'', and this plating film was The above plated foil was obtained by peeling.The plated foil obtained had a tensile strength of 32 kg/
tm”, elongation 14%.

The thickness was 55 μm.

The experimental results of the soldering properties mentioned above are shown in Table 1, and in the same table,
High-speed plating shows the method of the present invention.As is clear from the same table, with the plated foil according to the method of the present invention, when no pretreatment or just wiping with trichlene, the amount of adhesion is not sufficient, but the amount of plating is not sufficient.

When pre-treated with flux, solder adhered to the entire length of the immersion length, which was significantly improved compared to the comparative example.

2 Release 1 This experiment was conducted to examine the adhesion strength when electronic components are mounted on a substrate, and as shown in Fig. The plated film and the plated film formed by the static bath were brought into contact and temporarily fixed over an area of 2 x 7 cranes, this contact part was immersed in the solder bath, and then the painter was applied at a tensile speed of 50 fiZ. The tensile load was measured when the two were separated.

In addition, for comparison, measurements were made in the same manner for the plating films formed in the above-mentioned static bath.

The results are shown in Table 2. As is clear from the table, when at least one of the plating films was formed by the method of the present invention (denoted as high speed in the table), for a separation load of 12.6 kg between the static bath plating films. is 26 to 27 kg, and it can be seen that in the plating film according to the method of the present invention, the solder sufficiently penetrates between the two plating films, and as a result, the soldering properties are greatly improved.

In the above embodiment, a printed wiring board in which a wiring pattern is formed on both sides of the base board and a through hole is formed, but the present invention can also be applied to a case where a wiring pattern is formed only on one side of the board. Of course it can be applied.

[Effects of the Invention] As described above, according to the printed wiring board according to the specified invention, since the wiring pattern is mainly composed of plating particles with a diameter of 3 to 10 μm, the solder permeability is improved and soldering becomes easier. According to the method for manufacturing a printed wiring board according to the related invention of the present application, since electroplating is performed while the plating solution is flowing, the above-mentioned plating particle size of 3 to 10 μm can be achieved. effective.

Table 1 Table 2

[Brief explanation of the drawing]

Figure 1 (81, (bl) is a micrograph showing the grain structure of the wiring pattern according to the present invention, Figure 2 is a perspective view of a printed wiring board according to an embodiment of the present invention, Figures 3 and 4 are A sectional view and an overall configuration diagram of a plating apparatus for carrying out the method of the present invention, FIG. 5+a) to FIG. Figure 7 is a block diagram for explaining the experimental method, Figure 8 is a diagram showing the structure of the experiment.
(bl, FIG. 9(δ), mountain) is a micrograph showing the grain structure of a wiring pattern formed by a conventional plating method. In the figure, 1 is a printed wiring board, 2 is a base board,
3 and 4 are wiring circuit section, connection circuit section (wiring pattern), 4
4 is an electrode, and P is a plating solution. Patent Applicant Yamaha Motor Co., Ltd. Agent Patent Attorney Tsutomu Shimo Ichi Figure 1 To ~ @xi000 10 different n Figure 1 z, um Figure 2 Figure 3 Figure 5 Figure 6 Figure 7 to Figure 8 'l+l#B Figure 9

Claims (2)

[Claims] (1) In a printed wiring board in which a wiring pattern made of a plating film is formed on a base substrate, the wiring pattern is mainly composed of plating particles having a particle diameter of 3 to 10 μm in a plane parallel to the substrate surface. A printed wiring board featuring: (2) A method for manufacturing a printed wiring board, in which a wiring pattern mainly composed of plating particles having a particle diameter of 3 to 10 μm in a plane parallel to the substrate surface is formed on a base substrate, the base substrate being used as an electrode. A method for producing a printed wiring board, characterized by electroplating the base substrate and electrodes while immersing the substrate in a plating solution so as to face the base substrate and flowing the plating solution between the base substrate and the electrodes.