JPH0451503Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention improves heat dissipation and furthermore,
This invention relates to a board for mounting electronic components, such as a plug-in package board, which has significantly improved water resistance.

[Prior art]

Conventionally, many printed wiring boards made of ceramic substrates and resin-based substrates (hereinafter referred to as resin substrates) have been used as substrates on which electronic components such as chip elements or semiconductor elements are mounted.

However, in conventional printed wiring boards, sufficient heat dissipation cannot be obtained for the heat generated by mounted electronic components, and therefore, the conventional printed wiring boards are only applied to electronic components with low power consumption, that is, low heat generation. Further, for this reason, it has been necessary to take measures such as providing heat dissipation fins for printed wiring boards on which electronic components with high power consumption are mounted.

In particular, resin substrates have extremely low thermal conductivity compared to metals, ceramics, etc., and the amount of heat generated from electronic components dissipated to the surface of the printed wiring board is extremely small. On the other hand, even ceramic substrates such as alumina are insufficient in terms of heat dissipation for mounting recent large-scale integrated circuit elements.

In order to eliminate these drawbacks, conventionally, a through hole is provided in the printed wiring board of a plug-in package, etc., and a metal plate with high thermal conductivity is fitted into the through hole, thereby transferring the heat generated from the electronic component. A substrate for mounting electronic components with high heat dissipation properties that quickly dissipates to the outside through a metal plate is being attempted (Japanese Patent Application Laid-Open No.
59-32191).

In addition, in this electronic component mounting board, after the metal plate is fitted into the through hole, the printed wiring board is printed in the electronic component recess formed by the metal plate and the through hole, and on the back side of the printed wiring board. A metal plating film is applied that continuously covers the wiring board and metal plate.

[Problem to be solved]

However, even in this attempt, water in the outside air enters the electronic component mounting recess through the bonding surface between the printed wiring board and the metal plate. When the water reaches the electronic components, there is a drawback that the reliability of the electronic components is significantly lowered and the electronic components are damaged.

This moisture infiltration is due to the following reasons.

That is, even when a metal plating film is applied to the inner surface of the electronic component mounting recess and the back surface joint between the printed wiring board and the metal plate, there is a gap of about several tens to 500 μm between the printed wiring board and the metal plate. There are always gaps.

This is because, as mentioned above, there is a dimensional error between the inner shape of the through hole drilled in the printed wiring board and the outer shape of the metal plate fitted into the through hole. This is because the two cannot be fitted together.

Furthermore, if both shapes are exactly the same, it will be extremely difficult to fit them together, and there is a high possibility that damage such as cracks will occur to the printed wiring board, which is weaker than the metal plate.

On the other hand, a metal plating film is formed by electrically depositing a thin layer of charged metal ions present in the plating film liquid on the surface of the object to be plated during the plating production process. Therefore, if the object to be plated has a void portion into which the plating solution is difficult to penetrate, the metal plating film will not be formed in the void.

Therefore, if there is a gap between the through hole of the printed wiring board and the metal plate fitted into it as described above, even if the gap is as small as several tens to 500 μm, this No metal plating film is formed in the void areas.

In reality, in the process of forming a metal plating film on both sides of the gap, that is, on each end face of the printed wiring board and the metal plate, the thickness of the metal plating film increases and the tips move toward the gap from both sides. In some cases, the metal plating film may end up covering the voids above the voids.

However, since such a coating is formed on the top of the void, pinholes are likely to be formed, and there is also a risk of moisture infiltration.

In addition, when the gap between the cavities is about 500 μm,
A very thick metal plating film must be applied. In order to do so, more metal plating film than necessary is applied to the printed wiring board and most other parts of the metal plate. As a result, there is a large disadvantage in terms of plating cost and productivity.

Furthermore, even if a metal plating film with such a large thickness is formed, it is unknown how large a gap is formed between the printed wiring board and the metal plate, and the original purpose of eliminating the gap is not achieved. Coverage may not be complete.

Therefore, in conventional substrates for mounting electronic components, the metal plating film above the voids may have pinholes or be insufficiently covered. Therefore, water enters the electronic component recess through this gap, resulting in poor water resistance.

In view of these conventional problems, the present invention aims to provide a substrate for mounting electronic components that has excellent heat dissipation properties and water resistance.

[Means for solving problems]

The present invention is constructed by bonding a metal plate for heat dissipation to a printed wiring board via an adhesive layer, and an exposed groove in which the adhesive layer is exposed is provided between the printed wiring board and the metal plate. and the exposed groove is covered with a metal plating film continuously formed between the printed wiring board, the adhesive layer, and the metal plate. It is in.

The most noteworthy feature of the present invention is that when bonding the metal plate to the printed wiring board, an adhesive layer is interposed between the two. Also,
An exposed groove exposing the adhesive layer is formed between the outer peripheral edge of the adhesive layer and the printed wiring board and metal plate.

Further, the exposed groove is covered with a metal plating film that is continuously formed between the printed wiring board, the adhesive layer, and the metal plate.

[Action and effect]

In the electronic component mounting board of the present invention, an adhesive layer is interposed between the printed wiring board and the metal plate. Therefore, there is no gap between the two, as shown in the prior art.

An exposed groove in which the adhesive layer is exposed is formed between the printed wiring board and the metal plate. (See Figures 1 to 4).

Therefore, within this exposed groove, there is no void on the surface between the printed wiring board, the adhesive layer, and the metal plate.

Therefore, the metal plating film is formed uniformly and continuously on the printed wiring board, adhesive layer, and metal plate in the exposed groove, as if on one plane, and pinholes do not occur as in the past. Not yet.

Therefore, in the electronic component mounting board according to the present invention, the metal plating film formed in the exposed groove allows the adhesive layer and the surface of the printed wiring board and metal plate connected thereto to be pinned together. It has no holes and is coated continuously and uniformly, completely preventing moisture from entering.

Further, in the present invention, since a metal plating film is also applied inside the exposed groove, heat generated by the electronic components is efficiently discharged from the printed wiring board to the metal plate through the metal plating film.

Furthermore, since the adhesive layer is interposed between the printed wiring board and the metal plate, heat dissipation is even better than in the case where there is a gap as in the past.

As is known from the above, according to the present invention, it is possible to provide a substrate for mounting electronic components with excellent heat dissipation properties and water resistance.

〔Example〕

Embodiment 1 An electronic component mounting board according to an embodiment of the present invention will be described with reference to FIG.

The electronic component mounting board of this example is formed by bonding a heat-dissipating metal plate 4 to a printed wiring board 1 via an adhesive layer 3, and connects the outer peripheral edge of the adhesive layer 3 to the printed wiring board 1 and the metal plate. An exposed groove 6 is provided between the plate 4 and the exposed surface 5 of the adhesive layer 3.

Furthermore, the inside of the exposed groove 6 is covered with a metal plating film 2 that is continuously formed between the printed wiring board 1, the adhesive layer 3, and the metal plate 4. The metal plate 4 is bonded to a deep recess formed on the back side of the printed wiring board 1 by an adhesive layer 3.

Note that a metal plating film 2 for patterning is also formed on the front surface side of the printed wiring board 1. Moreover, between the printed wiring board 1 and the metal plate 4,
An electronic component recess is formed on the front side of the printed wiring board 1.

The electronic component mounting board described above is a plug-in package board. The printed wiring board 1 is a resin board or a ceramic board.

In the electronic component mounting board of this example, since the adhesive layer 3 is interposed between the printed wiring board 1 and the metal plate 4, no void remains at the joint between the two, unlike in the conventional case.

Therefore, in the exposed groove 6, the surfaces of the printed wiring board 1, the adhesive layer 3, and the metal plate 4 also have a substantially uniform continuous surface with no voids.

Therefore, when a metal plating film is formed on these surfaces, the metal plating film will form a continuous and uniform film without pinholes on the surfaces of the printed wiring board 1, adhesive layer 3, and metal plate 4 in the exposed groove 6. Formed as a film.

Therefore, moisture intrusion into the electronic component recess is completely prevented.

Furthermore, since a continuous metal plating film is formed on the surfaces of the printed wiring board 1, adhesive layer 3, and metal plate 4, the heat generated by the electronic components in the electronic component recess is absorbed by this continuous metal plating film. It is easily released to the outside and has excellent heat dissipation.

Further, an adhesive layer 3 is interposed between the printed wiring board 1 and the metal plate 4. Therefore, compared to the conventional case where there is a gap between the two, the heat dissipation property is even better.

Example 2 As shown in FIG. 2, in this example, compared to the electronic component mounting board of Example 1, a shallow recess is provided on the back side of the printed wiring board 1, and the adhesive layer 3 is inserted into the recess. It is made by joining metal plates 4.

The rest is the same as in Example 1. In this example as well, the same effects as in Example 1 can be obtained.

Example 3 In this example, as shown in FIG. 3, in the electronic component mounting board of Example 1, an electronic component is formed between the metal plate 4 and the printed wiring board 1 on the front side of the printed wiring board 1. A metal plating film 2 is also formed inside the recess.

In this example, since the metal plating film 2 is also provided inside the electronic component recess, the water resistance is further improved. Further, the same effects as in the first embodiment can be obtained.

Example 4 In this example, as shown in FIG. 4, the electronic component mounting board of Example 1 is not provided with the electronic component recess. In the electronic component mounting board of this example, the electronic components are mounted on the printed wiring board 1.
mounted on the upper surface of the front side.

In this example as well, the same effects as in Example 1 can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the electronic component mounting board of Example 1, and FIGS. 2 to 4 are sectional views of the electronic component mounting board of Examples 2 to 4. DESCRIPTION OF SYMBOLS 1... Printed wiring board, 2... Metal plating film, 3... Adhesive layer, 4... Metal plate, 5... Exposed surface of adhesive layer, 6... Exposed groove.

Claims (1)

[Claims for Utility Model Registration] A metal plate for heat dissipation is bonded to a printed wiring board via an adhesive layer, and the adhesive layer is exposed between the printed wiring board and the metal plate. An electronic device characterized in that an exposed groove is formed, and the exposed groove is covered with a metal plating film continuously formed between the printed wiring board, the adhesive layer, and the metal plate. Board for mounting components.