JPH0555401A - Printed wiring board - Google Patents

Abstract

PURPOSE:To provide a printed wiring board which has excellent humidity-proof characteristic and heat radiating characteristic and also facilitates wire bonding process and die bonding process. CONSTITUTION:In a printed wiring board having a recess 91 for mounting electronic components and a through hole 92 on an organic resin substrate 90, the recess 91 and through hole 92 have a through hole plating layer 1 and the recess 91 has vertical wall surface formed by the counterboring process. Moreover, the outer most surface of the recess 91 is covered with gold plating layer 2.

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 excellent moisture resistance.

[0002]

2. Description of the Related Art Along with the high density mounting of electronic parts, a method of mounting electronic parts such as semiconductor elements in recesses formed by counterboring has been performed. This method is adopted for printed wiring boards used for thin parts such as watches. In a printed wiring board, an organic resin board is often used as an insulating board for forming a conductor circuit because of its light weight and ease of processing.
As the organic resin substrate, for example, a paper phenol copper clad laminated substrate, a glass epoxy copper clad laminated substrate, or the like is used.

[0003]

However, the above organic resin substrate has a high hygroscopic property, so that moisture may infiltrate into electronic components mounted on the organic resin substrate, which often impairs its electronic function. Especially, as described above, when an electronic component is mounted in the recess, moisture easily enters the electronic component from the wall surface of the recessed recess. That is, as shown in FIG. 12, when the concave portion 91 is provided in the organic resin substrate 90 of the printed wiring board 9 by the counterbore processing, the wall surface 910 and the bottom surface 911 formed by the counterbore processing have the organic resin substrate Many fibers 93 such as paper fibers and glass fibers which are cores,
It is exposed as a beard with a length of about 5 μm. This means that the wall surface 9 of the through hole 92 formed in the organic resin substrate 90 is
The same applies to 20. The through hole 92
Is a hole for inserting a conductor pin.

The exposed fiber 93 as described above
Has a small annular gap at the interface with the resin such as the phenol resin on the wall surface of the recess. And
This boundary gap extends along the periphery of the fiber 93, through the inside of the organic resin substrate 90 to the outside thereof, that is, the outside of the printed wiring board 9. Therefore, from the outside of the printed wiring board 9 through the boundary gap, the recess 91
Moisture will enter the inside. Therefore, improvement in moisture resistance against such infiltration of moisture is desired. Further, the heat generated from the electronic components mounted on the printed wiring board 9 must be released to the outside as quickly as possible. In particular, when the electronic component is mounted in the recess 91 as described above, the heat dissipation is not smooth because the periphery of the electronic component is surrounded by the wall surface of the organic resin having low heat conductivity.

On the other hand, in order to promote the heat dissipation, it may be considered that the wall surface of the recess is an inclined surface that expands upward (for example, see Japanese Patent Laid-Open No. 52-47692). However, according to such a method, the bonding distance between the conductor circuit on the substrate and the electronic component becomes long, and the bonding operation becomes difficult. Further, since the bonding wire becomes long, there is a risk that a large number of bonding wires will come into contact with each other, and the cost of the bonding wire will increase. In view of such conventional problems, the present invention intends to provide a printed wiring board excellent in moisture resistance and heat dissipation.

[0006]

According to the present invention, there is provided a printed wiring board comprising an organic resin substrate provided with a recess for mounting electronic parts and a through hole, the recess having a vertical wall surface formed by counterboring, and the recess. The bottom surface and the entire surface of the vertical wall surface and the through hole have a through hole plating layer, and the surface of the through hole plating layer of the recess is covered with a gold plating layer. The printed wiring board is characterized in that moisture that has entered the inside of the resin substrate is prevented from entering the recesses.

In the present invention, the through hole plating layer means a metal plating layer covering the inner wall of the through hole. In the present invention, the recess is coated with the same metal plating layer as the through hole plating layer. Therefore, in the present invention, the metal plating layers provided in the through holes and the recesses are collectively referred to as "through hole plating layers". Also, therefore,
The through hole plating layer is formed to have substantially the same thickness in the recess and the through hole. The thickness of the through-hole plating layer is "IPC STA" which is adopted as a standard worldwide for printed wiring boards.
NDARD "(issued in 1981, IPC-D-320
It has a relatively large thickness of usually about 10 to 50 μm, as also introduced in A., 3.5.2.3 on page 2-3 and Table 5). As the through hole plating layer, for example, a copper plating layer is used.

The recess has a vertical wall surface formed by counterboring. The outermost surface of the recess is covered with a gold plating layer for facilitating mounting of electronic components. Next, as a method for manufacturing the above-mentioned printed wiring board, for example, a through hole is formed in an organic resin substrate and a recess having a vertical wall surface for mounting an electronic component is formed by counterboring, and then the through hole and the through hole are formed. There is a method of manufacturing a printed wiring board characterized in that the surface of the recess is coated with a through-hole plating layer at the same time, then a desired conductor circuit is formed, and then the outermost surface of the recess is coated with a gold plating layer.

[0009]

In the printed wiring board according to the present invention, the through hole plating layer is formed in the recess for mounting the electronic component as in the through hole. And
The through-hole plating layer has a relatively large thickness as described above. Therefore, the wall surface of the recess is entirely covered with this thick through-hole plating layer. Therefore,
Moisture never enters the recesses through the organic resin substrate.

That is, as shown in FIG. 12 in the section of the prior art, the wall surface 910 and the bottom surface 9 of the recessed portion 91 which has been countersunk are processed.
A large number of fibers 93 such as glass fibers are exposed at 11 in the form of a mustache having a length of about 5 μm. However, in the present invention, as shown in FIG.
Are covered with the through-hole plating layer 1 having a relatively large thickness as described above. Therefore, the beard-shaped fibers 93 are buried in the through-hole plating layer 1. The same applies to the bottom surface of the recess (and so on). Therefore, as in the conventional case, the boundary gap between the fiber 93 and the resin of the organic resin substrate is
It will be blocked by the through-hole plating layer 1.
Therefore, there is no infiltration of moisture into the recess 91. In FIG. 1, reference numeral 2 is a gold plating layer that covers the outermost surface of the recess.

Further, the wall surface of the recess in the present invention is a vertical wall surface and does not spread outward. Therefore, the shortest distance can be provided between the electronic component mounted in the recess and the conductor circuit located at the peripheral edge of the opening of the recess. Therefore, the length of the bonding wire connected between the electronic component and the conductor circuit can be shortened, and the bonding operation is easy. Further, the recess has a vertical wall surface, and the shortest distance is formed between the electronic component and the vertical wall surface. Therefore, the heat generated in the electronic component is easily transmitted from the side surface to the vertical wall surface and easily dissipated to the outside through the gold plating layer and the through hole plating layer provided on the vertical wall surface. Therefore, it is also excellent in promoting heat dissipation of electronic parts.

Furthermore, since the gold plating layer is provided on the outermost surface of the recess, die bonding can be facilitated when electronic components are joined using a eutectic alloy (gold-tin brazing material). .. As described above, according to the present invention, it is possible to provide a printed wiring board which is excellent in moisture resistance and heat dissipation and is easy to perform wire bonding operation and die bonding with a eutectic alloy.

[0013]

EXAMPLE Example 1 A printed wiring board according to an example of the present invention is shown in FIG.
2 and FIG. 2. Printed wiring board 1 of this example
0, as shown in FIG. 1, is an organic resin substrate 90 provided with a recess 91 for mounting electronic components and a through hole 92.
The through hole plating layer 1 is formed on the entire surfaces of the recess 91 and the through hole 92.
Further, the recess 91 has a vertical wall surface 915 formed by counterboring. Then, on the outermost surface of the recess 91,
The gold plating layer 2 is formed. Further, in FIG. 1, reference numeral 96 is a conductor circuit.

Next, as shown in FIG. 2, the electronic component 5 such as a semiconductor element is mounted in the recess 91 of the printed wiring board constructed as described above. The electronic component 5 is
The lower surface is joined (die-bonded) to the gold plating layer 2 on the bottom surface of the recess 91 by a eutectic alloy (Au—Sn solder). A bonding wire 51 is connected between the electronic component 5 and the conductor circuit 96 on the printed wiring board. Further, the periphery of the electronic component 5, including the bonding wire 51, is covered with a sealing resin 55 such as epoxy resin. As mentioned above,
In the printed wiring board 1 of this example, the vertical wall surface 915 and the bottom surface of the recess 91 are covered with the through-hole plating layer 1 similarly to the wall surface of the through hole 92. The through-hole plating layer 1 usually has a thickness of 10 to 50 μm.
It is formed with a certain thickness.

Therefore, at the time of counter boring the recess,
The beard-shaped (about 5 μm long) fibers 93 (see FIG. 12) exposed on the vertical wall surface 915 and the bottom surface 911 are shown in FIG.
As shown in FIG. 5, the through hole plating layer 1 is buried. Therefore, moisture never enters the concave portion 91 from the outside of the substrate along the fiber 93 via the inside of the organic resin substrate 90. Further, the side wall of the recess 91 is a vertical wall surface and does not expand outward. Therefore, the distance between the electronic component 5 mounted in the recess 91 and the conductor circuit 96 is the shortest. Therefore, the length of the bonding wire connecting the two becomes the shortest, the cost is low, and the bonding operation is easy.

Further, since the concave portion 91 has the vertical wall surface 915, the shortest distance is formed between the vertical wall surface 915 and the electronic component 5. Therefore, the heat generated in the printed wiring board 5 is easily transferred from the side surface to the vertical wall surface 915,
It is easily diffused to the outside through the gold plating layer 2 and the through hole plating layer 1. Therefore, the heat dissipation of electronic parts is also excellent. Further, since the surface of the recess 91 is covered with the gold plating layer 2, die bonding using the eutectic alloy can be easily performed as described above.

Example 2 Next, a method of manufacturing the printed wiring board shown in Example 1 will be described with reference to FIGS. First, as shown in FIG. 3, an organic resin substrate 90 such as a glass epoxy copper clad laminated substrate is prepared. The organic resin substrate 90 has copper foil layers 99 on the upper and lower surfaces. Then, as shown in FIG.
In the organic resin substrate 90, a recess 91 is formed in the electronic component mounting portion by counterboring. Further, through holes 92 are formed. The recess 91 has a vertical wall surface 915. In addition, the inner wall of the recess 91 and the through hole 92
As shown in FIG. 12, the inner wall of the
Is exposed like a mustache.

Next, as shown in FIG. 5, the through holes 92 and the recesses 91 are covered with the through hole plating layer 1. Next, as shown in FIG. 6, the photosensitive resin coating 4 is attached to the surface of the organic resin substrate 90 to form a desired circuit pattern, and then etching is performed to form a conductor circuit 96 as shown in FIG. To do. Next, as shown in FIG. 8, a gold plating layer 2 is formed on the surface of the through hole plating layer 1 of the recess 91, and the printed wiring board 10 according to the present invention is manufactured. As described above, according to this example, an excellent printed wiring board as shown in Example 1 can be manufactured.

Example 3 This example is an example in which the steps of forming a circuit pattern and a conductor circuit (FIGS. 6 and 7) in the manufacturing method of Example 2 were changed. This will be described with reference to FIGS. 9 to 11. That is, in the circuit pattern forming step (FIG. 6) of the second embodiment,
As shown in FIG. 9, a negative pattern is formed by the photosensitive resin layer 45, and a circuit pattern is formed by different metal plating (not shown) such as solder, nickel, tin, or gold. Then, using the different metal plating as an etching resist, a desired conductor circuit 9 is formed by etching as shown in FIG.
6 is formed. After that, as shown in FIG.
The surface of the through-hole plating layer 1 is coated with the gold plating layer 2. As described above, according to this example, the same effect as that of the second example can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a printed wiring board according to a first embodiment.

FIG. 2 is a cross-sectional view of a printed wiring board according to the first embodiment in which electronic components are mounted.

FIG. 3 is a cross-sectional view of an organic resin substrate in the manufacturing method of Example 2.

FIG. 4 is a counterboring process diagram in the second embodiment.

FIG. 5 is a process drawing of forming a through-hole plating layer in the second embodiment.

FIG. 6 is a process diagram of a circuit pattern forming process according to the second embodiment.

FIG. 7 is a process diagram of forming a conductor circuit according to the second embodiment.

FIG. 8 is a process drawing of forming a gold plating layer in Example 2.

FIG. 9 is a process diagram of forming a negative pattern in the third embodiment.

FIG. 10 is a process diagram of forming a conductor circuit according to the third embodiment.

FIG. 11 is a process drawing of forming a gold plating layer in Example 3.

FIG. 12 is an explanatory cross-sectional view of a recessed portion and a through hole which are counterbored.

[Explanation of symbols]

 1. ． ． Through-hole plating layer, 10. ． ． Printed wiring board, 2. ． ． Gold plating layer, 5. ． ． Electronic components, 51. ． ． Bonding wire, 90. ． ． Organic resin substrate, 91. ． ． Recess, 915. ． ． Vertical wall, 92. ． ． Through holes, 93. ． ． Fiber 96. ． ． Conductor circuit,

Claims (1)

[Claims] 1. A printed wiring board comprising an organic resin substrate provided with a recess for mounting electronic parts and a through hole, wherein the recess has a vertical wall surface formed by counterboring, and a bottom surface and a vertical wall surface of the recess. All surfaces and through holes have a through hole plating layer, and the surface of the through hole plating layer in the recess is covered with a gold plating layer. The through hole plating layer and the gold plating layer are inside the organic resin substrate. A printed wiring board, characterized in that invading moisture is prevented from infiltrating into the recess.