JPH06177527A - Printed wiring board for surface installation - Google Patents

Abstract

PURPOSE:To provide a printed wiring board which is able to cope enough with subminiaturization and free from connection failures caused by positional deviation and-troubles such as solder bridges when a surface-mounting type part is soldered to the board. CONSTITUTION:A surface mounting printed wiring board 100 is formed through such a manner that a mask provided with an opening at a prescribed position is arranged on a surface-mounting type part mounting pad 12 on an insulating board 11, then molten solder is sprayed on the masked insulating board 11 from a nozzle installed properly distant from the insulating board 11 to form a solder layer 15 on the mounting pad 12.

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 having pads for mounting surface mounting components, and more particularly to a printed wiring board having a solder layer for surface mounting formed on the pads. is there.

[0002]

2. Description of the Related Art In recent years, along with surface mounting of electronic parts, L
Outer leads derived from the SI package have become more multi-pin and finer pitch, advanced technology is required for connection between mounted parts and printed wiring board, and mechanical and electrical connection reliability of connection part is a problem. Has become. In order to secure this connection reliability, there is a solder supply method capable of forming a solder layer having a uniform thickness with a necessary and sufficient amount for connection on a surface mounting component mounting pad on a printed wiring board. Is desired. Generally, it is said that about 100 to 200 μm is required for a QFP or the like having an outer lead pitch of about 0.5 mm and a thickness of about 0.15 mm.

The reason for this is that coplanarity (flatness of lead terminals) such as surface mount components typified by QFP using a lead frame of 42 alloy material or the like.
If it is bad, the variation of the lead terminals vertically is 100
It is often about μm. Therefore, if the solder film thickness is thin, the solder will melt when the surface mount components are mounted and heated in the reflow furnace for connection, and the solder will be sucked up to some extent by the lead terminals, and Some lead terminals do not come into contact with the solder even when they are submerged than before heating the reflow oven. The lead terminals can come into contact with the solder. Further, if the solder film thickness is about 100 to 200 μm, not only the amount of solder required between the lower surface of the lead terminal and the pad portion but also the amount of solder enough to wrap around the upper portion of the lead terminal can be supplied. A strong connection with high reliability is possible.

The outer lead pitch is 0.3 mm.
It is said that a solder layer of about 30 to 50 μm is necessary for TAB and the like whose thickness is about 35 μm. In TAB mounting, this is a method of forcibly pressing the outer leads against the pads on the printed wiring board by a thermocompression bonding jig, so there is no need to consider coplanarity, but if there is excessive solder,
Since the lead pitch is very narrow, adjacent leads may bridge due to surface tension when solder is melted, and absolute control of the amount of solder is required.

Conventionally, (1) solder leveler method, (2) plating method, (3) cream solder printing method, etc. have been adopted as a method for supplying solder to pads for mounting surface mount components on a printed wiring board. .

[0006]

[Problems to be Solved by the Invention] However, (1)
The solder leveler method of 1 has the advantage that the solder composition is easy to control, but there is a large variation in the solder film thickness,
In addition, the surface wetness of the Cu-Sn intermetallic compound deteriorates the solder wettability, and in the case of a pad having a small surface area or width, the surface shape of the solder layer becomes a curved surface. There was also a drawback that the outer lead slipped on this curved surface when it was attached and the position was displaced.

Further, the plating method (2) not only requires a long time to form a solder layer having a predetermined thickness,
In electrolytic solder plating, there are drawbacks in that there are large variations in the solder film thickness and the composition of tin and lead contained, and it is difficult to achieve fineness because a plating lead wire is required for plating. Then, in electroless solder plating, blistering occurs due to a substitution reaction, or
Since there is no choice but to rely on a substitution reaction for forming a layer, it is difficult to obtain a solder film thickness of 5 μm or more, and there is a drawback that connection failure frequently occurs due to insufficient solder.

Further, in the cream solder printing method of (3), since it is a printing method, the supply amount is affected by the unevenness of the printed wiring board around the opening of the printing plate and is non-uniform,
In printed wiring boards with a fine pad pitch, solder bridges, balls, and sagging often occur. And
There is a drawback that flux components remain in the printed solder layer. In particular, for TAB pads, the pad pitch is very small, 0.3 mm, so that an independent solder layer cannot be formed for each pad. Then, an electrically independent solder layer must be formed on each pad. That is, the formation of the electrically independent solder layer depends only on the surface tension of the molten solder, which is extremely quantitatively unstable and difficult to control.

Therefore, the present invention has been made in view of the problems in the surface mounting printed wiring board having the solder layer formed by the conventional solder supply technique as described above, and an object thereof is to achieve the object. Is to provide a printed wiring board which can sufficiently deal with finer patterns and does not have a connection defect such as a positional deviation in soldering of surface mount components or a defect such as a solder bridge.

[0010]

The present inventors have made new studies as a result of intensive studies to overcome the problems of the conventional solder supply technology as described above. In the following description, the surface mounting component mounting pad (12) on the insulating substrate (11) is provided with a solder layer (15) by solder spraying,
The printed wiring board (100) is capable of sufficiently responding to the miniaturization and has a good connection with mounted components.

That is, the printed wiring board (10) of the present invention is
0) is an opening (13) at a predetermined position on the printed wiring board.
After arranging the mask (13) having a), the molten solder is sprayed toward the masked printed wiring board from the nozzle (14) installed at an appropriate distance. The solder layer (15) having a uniform thickness and a necessary and sufficient amount for connection with the surface mount component is formed only in a necessary portion through the opening (13a) of (13).

[0012]

By adopting the above-mentioned means, the printed wiring board of the present invention is mounted on the printed wiring board through the opening (13a) of the mask (13) having an opening at a predetermined position on the printed wiring board. Pads for mounting surface mount components (1
By spraying the molten solder whose content composition of tin and lead is determined in 2) in a mist form with a high temperature carrier gas (preferably an inert gas), the surface mount component and the printed wiring board can be formed only in a necessary part. It is possible to form the solder layer (15) with a necessary and sufficient amount and a uniform thickness. The thickness of the mask (13) used is
When the mask (13) is closely attached to the printed wiring board (100), it is necessary to make it thicker than the thickness of the solder layer (15) to be formed, but when the mask (13) is not closely attached to the printed wiring board (100). The mask can be selected regardless of the thickness of the solder layer (15) to be formed.

That is, the printed wiring board (100) of the present invention.
In this case, since the solder layer (15) formed on the surface mounting component mounting pad (12) is formed by the thermal spraying method, the molten solder sprayed through the mask (13) is solidified on the pad and sequentially. By stacking the layers, an arbitrary solder layer thickness can be obtained by a simple method of changing the spraying time, and the variation in the thickness between the pads (12) can be reduced. Furthermore, since the molten solder whose solder composition is prepared in advance is sprayed as it is, the solder composition does not change during the treatment,
Unlike the plating method, it is not necessary to build a plating bath regularly.

This mask (13) is capable of fine processing corresponding to the pad (12) portion on a fine printed wiring board, has heat resistance capable of withstanding molten solder, and is convenient for removing adhered solder. Any good material,
For example, various metal masks that have undergone solder release processing such as solder resist, ceramic masks, or
A mask made of a peelable organic material is desirable.

When a metal mask or a ceramic mask is used, it is desirable that a solder resist, a fluororesin coating or the like be applied to reduce the solder adhesion. This is because the solder adhered to other than the mask opening can be easily removed and can be immediately reused as a mask.

When a mask made of an organic material is used, a portion where a solder layer is not desired to be formed on the solder resist coating on the surface of a printed wiring board manufactured by a usual process is peeled off or a solvent or The molten solder is sprayed after a mask capable of peeling is provided by an alkali peeling method or the like. The mask in this case is not special, and may be a material such as an etching resist or a plating resist generally used during the printed wiring board manufacturing process, and a liquid mask material is applied by a printing method or a spin coating method. Alternatively, it is formed by a photolithography technique after a film-shaped mask material is pressure-bonded onto a printed wiring board.

The raw material used for thermal spraying is solder (Sn).
-Pb type), for example, when the printed wiring board (100) is a material having excellent heat resistance such as ceramics, Sn-Ag type, Sn-Bi type, Sn-A type.
Any brazing material such as g-Pb can be used.
These materials are supplied in the form of alloys that do not contain flux components, and the physical changes such as melting and solidification only occur in the layer formed by thermal spraying, so there is no fluctuation or variation in composition, and there are no impurities such as flux. It is possible to obtain a high-purity bonding layer that does not contain at all in a short time.

[0018]

EXAMPLES The present invention will now be described in more detail with reference to examples. (Example 1) (1) For a surface mount having a QFP mounting pad (12) part by a general printed wiring board manufacturing process using a copper clad laminate having a glass-epoxy resin as an insulating base material (11). A printed wiring board was produced. The surface of the printed wiring board was formed by a photolithography technique by ultraviolet curing so that the pad group on each side of the pad (12) for mounting the QFP was exposed by one opening, and the film thickness was 35 μm.
m liquid solder resist coating.

(2) The QFP mounting pad (12) of the obtained printed wiring board (0.5 mm pitch, line width: 0.
3mm) only opening (13a), thickness 150μ
The stainless steel plate mask (13) of m was placed on the upper part of the printed wiring board so as not to provide a gap. (3) The solder (Sn / Pb = 63/37) was applied to the printed wiring board with the mask (13) using a gas spraying device.
Thermal spraying was performed for 0 seconds. (4) After the thermal spraying was completed, the mask (13) was removed to obtain the surface mounting printed wiring board (100) of the present invention.

This printed wiring board (100) has a QFP
It was confirmed that the solder layer (15) was formed only on the mounting pad (12) part. The obtained solder layer (1
In 5), the film thickness was about 140 μm, and the film thickness in the sprayed region was almost uniform. Further, the side surface shape of the solder layer (15) was transferred without changing the side surface shape of the mask opening (13a), and the surface shape was flat. Furthermore, when a 0.3 mm pitch QFP was chip-mounted on this printed wiring board (100) and heating was performed in a reflow furnace, it was evaluated, and it was found that there were no defective connections such as insufficient solder and solder bridge due to excessive solder. I was able to confirm that.

Example 2 (1) A printed wiring board having a TAB mounting pad portion was produced by a general manufacturing process of a printed wiring board using a copper clad laminate having a glass-polyimide resin as an insulating base material. . The surface of this printed wiring board is covered and protected by a solder resist film with a thickness of 35 μm formed by a photolithography technique by ultraviolet curing so that the pad group on each side of the TAB mounting pad is exposed at one opening. It is what

(2) A film thickness of 7 is obtained on the obtained printed wiring board.
After press-bonding an etching resist film of 0 μm, TAB is applied by photolithography technology by UV curing.
Only the mounting pad portion (0.2 mm pitch) was used as the opening portion to form a mask material. (3) Solder (Sn / Pb = 63/37) was sprayed on the masked printed wiring board for 50 seconds by an electric spraying device. (4) After completion of thermal spraying, the solder layer on the mask was forcibly removed by a water jet, and then the etching resist film was removed by an organic solvent to obtain a surface mounting printed wiring board of the present invention.

It was confirmed that a solder layer was formed only on the TAB mounting pad portion on this printed wiring board. The obtained solder layer had a film thickness of about 40 μm, and the film thickness in the sprayed region was substantially uniform. The side surface shape of the solder layer is the same as the side surface shape of the mask opening, and the surface shape is basically flat, and no connection failure due to insufficient solder or solder bridge due to excessive solder did not occur at all. Furthermore, when a 0.2 mm pitch TAB was mounted on the printed wiring board obtained as described above, the mounting was good with no mounting defects, and the connection strength of the leads did not vary, and the strength was high and suitable for practical use. It was

COMPARATIVE EXAMPLE 1 (1) Using a copper-clad laminate having a glass-epoxy resin as an insulating base material, a Q
A surface-mounted printed wiring board having a FP mounting pad portion was produced. The surface of this printed wiring board is covered and protected by a liquid solder resist film with a thickness of 35 μm formed by a photolithography technique by ultraviolet curing so that the pad group on each side of the QFP mounting pad is exposed in one opening. It has been done.

(2) QFP mounting pad portion of the obtained printed wiring board (0.5 mm pitch, line width: 0.3 mm)
A plate made of stainless steel having a thickness of 150 μm and having only the opening as the opening was used as a screen printing mask. (3) The surface of the printed wiring board for surface mounting was obtained by contact printing the cream solder on the pad portion by the screen printing method.

The thickness of the solder layer obtained on the pad portion for mounting the QFP of this printed wiring board was 100 to 150 μm, and the variation was very large. In addition, cream solder, which was bleeding from the printing plate, was confirmed between the pads. In addition, QFP for this printed wiring board
When soldering was carried out using a reflow furnace, several defective connections due to insufficient solder and solder bridges were observed, and it was not a very good printed wiring board for mounting QFP.

Comparative Example 2 (1) Using a copper-clad laminate having a glass-polyimide resin as a base material, TA was produced by a general printed wiring board manufacturing process.
A surface mounting printed wiring board having a B mounting pad portion (0.3 mm pitch) was produced. On the surface of this printed wiring board, the pad group on each side of the pad for mounting the TAB is set to 1
It is covered and protected by a 35 μm-thick solder resist film formed by a photolithography technique by ultraviolet curing so as to be exposed at one opening.

(2) A cream solder (Sn / Pb = 63/37) containing a flux component (12%) was printed one character on each pad group aligned on the printed wiring board, and then passed through a reflow oven. Then, an electrically independent solder layer was formed on each pad to obtain a surface mounting printed wiring board.

At this point, several portions where the pads were connected by molten solder were confirmed. The thickness of the solder layer is 30 μm on average, and the variation is about 5 μm.
Was about 15 μm. Furthermore, when a 0.3 mm pitch TAB was mounted on the printed wiring board obtained as described above, it was confirmed that bridges were generated at several places, and the connection strength of the leads also varied widely and was suitable for practical use. Was not.

[0030]

As described above, according to the printed wiring board of the present invention, after a mask having an opening is arranged at a predetermined position on the printed wiring board, the printed wiring board is placed on the printed wiring board through the opening of the mask. By spraying the solder onto the surface mount component mounting pad of, the solder layer with a uniform thickness is formed only in the necessary parts for the connection between the surface mount component and the printed wiring board. Since there is no variation in the solder film thickness between the two, it is possible to make a printed wiring board that is very suitable for TAB mounting on the one hand, and on the other hand, a connection that is not easily affected by the coplanarity of surface mount components such as QFP. Is possible.

[Brief description of drawings]

FIG. 1 is a sectional view of a printed wiring board of the present invention.

FIG. 2 is a process drawing showing an example of a method for manufacturing a printed wiring board of the present invention.

[Explanation of symbols]

11: Insulating substrate, 12: Pads for mounting surface mount components 15: Solder layer, 100: Printed wiring board

Claims (1)

[Claims] 1. A printed wiring board having a pad for mounting a surface mount component, wherein a sprayed solder layer is formed on the pad.