JPH0336786A - Method for mounting parts printed circuit board - Google Patents

Abstract

PURPOSE:To contrive the improvement in a mechanical and chemical addhesive strength without electrical troubles such as the short circuit between foot prints or leads caused by a solder and, etc., by a method wherein after molding a bond reinforcing structure which has an uneven shaped surface on the foot prints of a printed circuit board, the heat-pressure bonding of the foot prints and the leads of a part is effected while interposing an anisotropic conductive sheet. CONSTITUTION:On a foot print 11, uneven shapes and pin holes 12 are formed at the same time as formation of patterns such as the foot print 11. After that, an anisotropic conductive sheet 3 is stuck to the whole region of a foot print part 10 by use of an addhesive agent. Over said sheet 3, the positions of leads 21 are adjusted to those of the foot prints 11 respectively, followed by the heat-pressure bonding from the above. When the leads 21 are thus pressed against the foot prints 11 by a pressure-bonding iron, the anisotropic sheet 3 under said leads 21 are especially pressed intensely and a conductivity appears there. Accordingly, the leads 21 are electrically conducted with the foot prints 11 and also, a part of the anisotropic conductive sheet 3 enters the pin holes 12, thereby strengthening an addhesive force.

Description

[Detailed Description of the Invention] [Summary] This method relates to a method for mounting components on a printed circuit board using an anisotropic conductive sheet, which eliminates electrical troubles such as short circuits due to solder between each footprint or between each lead. The aim is to provide a method for mounting components on a printed circuit board that has sufficient mechanical and chemical adhesive strength such as impact resistance and durability. After shaping the bottom of Structure A, components are mounted by interposing an anisotropic conductive sheet between the footprint and the leads of the component and bonding them by thermocompression.
In a flexible package component where each lead is formed along the back side of a flexible lead reinforcing plate extending from the package body, a large number of pores are drilled in the portion of the lead reinforcing plate where leads are not formed, and printing is performed. An anisotropic conductive sheet was interposed between the footprint of the board and the component leads, and the components were bonded together by thermocompression.

[Industrial application field]

The present invention relates to a method for mounting components on a printed circuit board, and particularly to a method for mounting components using an anisotropic conductive sheet.

[Conventional technology]

With the demand for smaller printed circuit boards, the density of printed circuit board patterns is increasing, and the surface mounting method, which is advantageous for miniaturization, has become the mainstream method for mounting components on printed circuit boards, and the components themselves are becoming smaller. is also underway.

In advancing the miniaturization of puff cage components such as ICs, a technical issue is how far the lead spacing can be reduced. Conventionally, the leads of package components have been formed by mechanical punching, and although this method also allows the distance between the leads to be reduced to about 0.4 to 0.5 μ, it has not been possible to reduce the distance further.

However, recently, as shown in FIG. 6, a flexible lead reinforcing plate 23 with a metal thin film formed on the back side has been extended from the package body 2°, and the leads 21 have been formed by etching the metal thin film. , so-called flexible package parts 2 have come to be commercially available.

Currently, lead spacing of O1l to 0.3fi has been achieved in this type of packaged parts, and theoretically, the lead spacing can be increased to the lead spacing from the IC etc. built into the package, that is, about 80 μm. The size of the parts can be further reduced.

On the other hand, in recent years, anisotropic conductive sheets have been developed that are made by mixing fine metal powder into resin and exhibit conductivity only in the direction of pressure. It is now used for.

A method has been attempted in which the anisotropic conductive sheet is interposed between the footprint of the printed circuit board and the lead of the component, and components are mounted on the printed circuit board by thermocompression bonding.

[Problem to be solved by the invention]

When attempting to surface mount a miniaturized package component as described above (including those whose leads are formed by punching or etching) on a printed circuit board using conventional solder, the The probability that the spacing is too narrow and the footprints or the leads will be short-circuited by solder increases as the lead spacing becomes smaller.

Because of the concerns about mounting using solder, attempts have been made to apply anisotropic conductive sheets to mounting components on printed circuit boards as described above. However, with this method, the adhesive strength between the printed circuit board and the conductive sheet depends only on the performance of the adhesive used, and the adhesive strength between the conductive sheet and the leads is due to melting during thermocompression bonding of the conductive sheet. It relies only on adhesive strength and has not yet achieved sufficient impact resistance and durability.

This invention has been proposed in view of the above-mentioned conventional circumstances, and is free from electrical troubles such as short circuits due to solder between each footprint or between each lead, and has high impact resistance and
The object of the present invention is to provide a method for mounting components on a printed circuit board that has sufficient mechanical and chemical adhesive strength such as durability.

[Means to solve the problem]

This invention employs the following means to achieve the above object. That is, for example, as shown in FIGS. 1 and 2, after forming the adhesive reinforcing structure A having an uneven surface on the footprint 11 of the printed circuit board 1, the footprint 11 and the lead 21 of the component 2 are bonded together. Components are mounted by thermocompression bonding with an anisotropic conductive sheet 3 interposed between them. As the adhesive reinforcing structure A, a pinhole 12 formed in the footprint 11 or a protrusion 13 can be considered. Further, as shown in FIG. 3, the solder resist 4 around the footprint portion 10 is
The opening may be configured to be wider at the bottom than at the top.

Further, as shown in FIG. 4, the leads 21 of the lead reinforcing plate 23 of the flexible package component 2 have each lead 21 formed along the back surface of the flexible lead reinforcing plate 23 extending from the package body 21. It is also possible to provide a large number of pores 24 in the portions where the printed circuit board 1 is not formed, and to interpose an anisotropic conductive sheet 3 between the footprint 11 of the printed circuit board 1 and the component lead 2I so as to bond them by thermocompression. can. In this case, it is preferable to further apply the adhesive 25 from the upper surface of the lead reinforcing plate 23 after thermocompression bonding.

[For production]

The reinforcement structure A in which the footprint 11 has an uneven shape, that is, a pinhole 12 is formed or a protrusion 13 is formed, is embedded in the footprint 11 after the anisotropic conductive sheet 3 is crimped.
Increase the adhesive strength of both sides. Reinforcement structure A using the edge 4' of the opening of the footprint part 10 of the solder resist 4
The anisotropic conductive sheet embeds into the solder resist to increase adhesive strength. Furthermore, when a large number of pores 24 are made in the flexible lead reinforcing plate 23, the anisotropic conductive sheet 3 will be embedded in the pores 24, and the adhesive applied from above the reinforcing plate 23 will Increases the effectiveness of agents.

〔Example〕

FIG. 1 shows one embodiment of the present invention, and FIG. 1(a) is a plan view of the footprint section before component mounting;
Figure (b) is a cross-sectional view taken along line AA of the footprint portion after components are mounted. First, an uneven shape, in this case a pinhole 12, is formed on the footprint 11 at the same time as the soft print 11 and other patterns are formed. Thereafter, the anisotropic conductive sheet 3 is attached to the entire area of the footprint part 10 using an adhesive, and each lead 21 of the component and each footprint 11 are aligned and bonded by thermocompression from above.

This crimping is performed by a crimping machine that has a crimping machine, and after the crimping, the entire footprint 10 may be crimped at once, or a chip-shaped crimping machine that crimps each lead 21 onto each footprint 11 in turn may be used. It may be something.

In this way, when the leads 21 are pressed against the Fundprint 11 after crimping, the anisotropic conductive sheet 3 at the bottom of each lead 21 is pressed particularly strongly, and conductivity develops in that part, so that the leads 21 and the footprint 11 are pressed together. As the gap becomes electrically conductive, a part of the anisotropic conductive sheet 3 bites into the pinhole I2, thereby increasing the adhesive strength. In order to further increase this adhesive force, it is preferable to over-etch the bottom of the pinhole 12 so that the diameter of the bottom becomes larger as shown in FIG. 1(b).

FIG. 2 shows another embodiment of the present invention.
Figure (a) is a plan view of the footprint section before parts are installed.
Figure 2(b) shows the footprint section B-B after parts are installed.
It shows a cross-sectional view.

An uneven shape on each footprint 11, in this case protrusion 1
3 is formed. The protrusions 13 are formed by, for example, forming a pattern on the printed circuit board 1, and then forming a plating resist pattern on the soft print 11 at a portion other than the portion where the protrusions 13 are to be formed, and then partially plating the pattern. Further, the shape of the protrusion 13 may also be thinner, as shown in FIG. 2(C). In this case as well, after forming the pattern and protrusions 13, the anisotropic conductive sheet 3
is attached to the entire area of the footprint portion 10, and the adhesive 21 is thermocompression bonded thereon. At this time, the protrusions 13 sink into the anisotropic conductive sheet 3 to increase the adhesive strength. Furthermore, in this case as well, in order to further increase the adhesive strength, it is preferable that the lower part of the protrusion 13 formed by the partial plating is hollowed out by etching or the like.

FIG. 3 shows another embodiment of the present invention, and FIG. 3(a) is a plan view of the footprint section without any components mounted thereon, and FIG. 3(b) is a plan view of the footprint section with components mounted thereon. −〇 sectional view. The edge 49 of the solder resist 4 around the footprint part 10 has a structure that increases the adhesive strength between the anisotropic conductive sheet 3 and the printed circuit board 1, for example, the third edge in a plan view.
As shown in Figure (a), the edges 4' of the solder resist 4 are waved to increase the contact length between the edges 4' of the solder resist 4 and the anisotropic conductive sheet 3. In addition, in combination with this planar configuration (or a separate structure may be used), the solder resist 4 in the footprint portion 10 can be overdeveloped during development after exposure of the photosensitive material in the pattern forming process of the solder resist 4. The edges 4'' are formed with an oblique cross section so that the bottom is wider than the top.

As a result, after the lead 21 is bonded by thermocompression, the adhesive strength is increased due to the long contact distance between the conductive sheet 3 and the footprint portion 10, or because the conductive sheet 3 is dug into the bottom of the footprint portion 10.

FIG. 4 shows still another embodiment of the invention.

As shown in FIG. 5, the component to be mounted here is a so-called flexible package in which a reinforcing plate 23 is extended from the package body by 2 degrees, and leads 21 are formed on the back surface of the plate by etching. This is part 2 called . This component 2 has the advantage that the lead width can be reduced to 0.3 mm or less, and the component can be made smaller. There is a problem that the adhesive strength of the conductive sheet 3 becomes weak.

Therefore, in this example, a large number of pores 24 are provided in the part of the lead reinforcing plate 23 on the component side where the leads 21 are not formed. The component 2 according to this configuration is an anisotropic conductive sheet 3
When the anisotropic conductive sheet 3 is bonded by thermocompression to the footprint portion 10 on which the anisotropic conductive sheet 3 is pasted, the anisotropic conductive sheet 3 sinks into the pores 24 and the adhesive force between the anisotropic conductive sheet 3 and the component can be increased. By applying , you can further increase the adhesive strength.

In the configuration shown in FIG. 4 as well, in order to increase the adhesive force between the printed circuit board 1 and the anisotropic conductive sheet
It goes without saying that the configurations shown in FIG. 2, FIG. 2, or FIG. 3 may be used in combination.

〔Effect of the invention〕

As explained above, the present invention can improve component adhesion strength by using the unevenness (pinholes, protrusions) of the soft print and the structure of the edges of the solder resist around the footprint. In the package, the anisotropic conductive sheet fits into the many pores provided in the lead reinforcing plate, improving component adhesion, and by applying adhesive over the lead reinforcing plate, the adhesion can be further improved. I can do it.

[Brief explanation of drawings]

1, 2, 3, and 4 are structural diagrams showing embodiments of the present invention, FIG. 5 is a perspective view of a flexible pan cage component to which the present invention is applied, and FIG. 6 is a structural diagram showing an embodiment of the present invention. FIG. 2 is a perspective view of a flexible package component. In the diagram, 1...Printed circuit board, 2...Parts, 2°...
・Package body, 3... Anisotropic conductive sheet, 4.
... Solder resist, 10... Footprint portion, 12... Pinhole, 21... Lead, 24... Pore, A... Adhesive reinforcement structure. DESCRIPTION OF SYMBOLS 1...Edge, 1...Footprint, 3...Protrusion, 3...Lead reinforcing plate, 5...Adhesive (b) Embodiment of the present invention Figure 1 (a) Present application Embodiment of the present invention Figure 2 (a) Embodiment of the present invention Figure 3 23: Lead reinforcing plate Embodiment of the invention Figure 4 21; Lead 4 Perspective view of flexible package parts used in the present invention Perspective view of flexible package parts Figure 6

Claims (1)

[Scope of Claims] [1] After forming the footprint (11) of the printed circuit board (1) into an adhesive reinforcing structure (A) having an uneven surface, the footprint (11) and the component (2) are bonded together. Lead (2)
1) A method for mounting components on a printed circuit board, characterized in that the components are mounted by thermocompression bonding with an anisotropic conductive sheet (3) interposed between the two. [2] The adhesive reinforcement structure (A) has a footprint (11
) is a pinhole (12) formed in
The method for mounting components on a printed circuit board as described in . [3] The adhesive reinforcement structure (A) has a footprint (11
2. The method for mounting components on a printed circuit board according to claim 1, wherein the protrusion (13) is formed on the printed circuit board. [4] Adhesive reinforcement structure in which the edge (4') of the solder resist (4) is sloped so that the bottom surface of the opening is wider than the top surface of the solder resist (4) around the footprint part (10). After molding (A), the footprint (
11) and a lead (21) of a component (2), an anisotropic conductive sheet (3) is interposed between the lead (21) of the component (2), and the component is mounted by thermocompression bonding. [5] The adhesive reinforcement structure (A) further covers the edge (4) of the solder resist (4) around the footprint portion (10).
4. The method for mounting components on a printed circuit board according to claim 4, wherein the component is formed into a corrugated shape. [6] Each lead (
21) is formed into a flexible package component (
2) A large number of pores (24) are opened in the portion of the lead reinforcing plate (23) where the leads (21) are not formed, and the footprint (11) of the printed circuit board (1) and the component lead (21) are formed. A method for mounting components on a printed circuit board, characterized in that thermocompression bonding is carried out with an anisotropic conductive sheet (3) interposed between the two. [7] The method for mounting components on a printed circuit board according to claim [6], wherein an adhesive (25) is further applied from the upper surface of the lead reinforcing plate (23) after the thermocompression bonding.