JP2012069816A - Wiring board using aluminum composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material having superior properties, such as an appropriate thermal expansion coefficient, fast thermal conduction, and light specific gravity, as a substitute material for ceramics or metals such as aluminum and copper to achieve efficient release of heat in a smaller area, which has become important in securing usage safety and product life in using LEDs and power semiconductors.SOLUTION: A composite material based wiring board is proposed which substitutes a composite material 6 composed of carbon or silicon carbide, boron nitride, etc. and aluminum for a conventional metal consisting mainly of aluminum, thereby providing a suitable thermal expansion coefficient and further optimizing thermal transfer.

Description

  The present invention relates to a base material for a wiring board.

  Among the types of printed wiring boards, there are various restrictions due to the fact that the metal base wiring board has a slow heat transfer and a high coefficient of thermal expansion. .

The metal base wiring board has a structure in which aluminum is mainly used as a base material and a copper foil as wiring is pasted through an insulating layer. (Figure 1)
Aluminum has a thermal conductivity of about 200 W / m · K, which is not the fastest heat transfer among metals. Copper has a thermal conductivity of 390 W / m · K, which is fast, When the specific gravity is large and an LED or the like is applied as lighting, particularly when used as a lighting device such as a streetlight that requires a large area, there is a problem that the weight increases.

Furthermore, aluminum and copper have a large coefficient of thermal expansion, which causes a large difference from the coefficient of thermal expansion of LEDs and power semiconductors. For this reason, peeling, bending, warping, and the like occur due to temperature changes on the wiring board, and there is a difficulty in transferring heat well.

  Further, in the structure as shown in FIG. 1, the heat transfer resistance of the insulating layer is considered even if the insulating layer has a low thermal conductivity of 1 to 8 W / m · K and a thickness of 40 to 80 μm. Becomes dominant.

In view of the above problems, in the present invention, a carbon / aluminum composite material is adopted by replacing the base substrate with aluminum or copper.

The carbon / aluminum composite material is a composite material in which aluminum is pressed into the voids of the graphitized granular aggregate, the graphite volume ratio is 70 to 95%, and the remaining 99% or more is made of aluminum or an aluminum alloy. . It is known that this composite material has a thermal diffusivity of 2.0 to 5.0 cm ² / sec, which is much larger than that of metal, 0.8 to 1.1 cm ² / sce, and quick heat transfer. .

Further, the thermal expansion coefficient of this composite material is 6 to 7 ppm / ° C., which is compatible with 6.8 ppm / ° C. of LED and 3 to 8 ppm / ° C. of other various semiconductors. On the other hand, it is obvious that at 24 ppm / ° C. for aluminum and 17 ppm / ° C. for copper, the coefficient of thermal expansion is large, and only low output can be used.

Accordingly, the present invention has developed a wiring board having a thermal expansion coefficient that is faster in heat transfer and excellent in compatibility, using the composite material as a base material for a metal wiring board. (Figure 2)

By using the composite material, the insulating layer having a large heat transfer resistance does not become the dominant heat transfer resistance.

Furthermore, in order to form a faster heat transfer structure, a copper foil is also used to collect heat at the same time as the circuit is formed, and a structure that transfers heat directly from the collected copper foil to the composite material And the method of integrating the copper foil (FIG. 3) was also completed. At this time, since the coefficient of thermal expansion was suitable, the problem of solder cracking due to temperature change was eliminated.

In addition, in order to form a faster heat transfer structure, a method of integrating a copper foil and a composite material and further a heat sink ahead (FIG. 4) using screws instead of the solder is completed. I let you. In this case, the screw hole may be up to the composite material, or may be penetrated to reach the heat sink.

ADVANTAGE OF THE INVENTION According to this invention, the wiring board excellent in LED and the heat dissipation of a semiconductor based on a carbon aluminum composite material can be completed. This makes it possible to extend the life of high-power semiconductors and high-brightness LEDs.

An aluminum heat sink is disposed under the base material in each drawing, but is omitted.
It is a cross-sectional structure of a general metal base wiring board. In FIG. 1, the electric wiring portion is omitted for simplification. The wiring part designed for heat transfer is drawn. The base metal is changed to a composite material, and the heat transferred to the composite material portion is transferred to the heat sink contacting the lower side of the base material with a thermal conductivity of 425 W / m · K exceeding that of copper. However, although a certain effect is obtained as it is, the heat resistance caused by 1 to 8 W / m · K of the insulating layer is the heat transfer property although the organic material has a high thermal conductivity. It became an obstruction factor. The structure in which the cavity is made by partially removing the copper foil and the insulating layer from FIG. 2 is processed by a router, a drill, or laser processing. In order to connect the copper foil and the composite material, after thinly plating the composite material, solder is poured during bonding to bond the copper foil and the composite material. When the insulating layer is thin, copper plating may be performed until the surface becomes the same height as the surface copper foil. Due to these structures, it was confirmed that the heat transfer is remarkably fast because the thermal conductivity of solder is 40 to 60 W / m · K. When the insulating layer is as thin as 20 to 40 μm, copper plating is performed until it is the same height as the copper foil, so that the thermal conductivity of copper is very fast at 390 W / m · K, which may be more effective. confirmed. By making a through hole and mechanically contacting the copper foil and the composite material with a screw having a high thermal conductivity, a structure that makes the heat transfer more economical than that of FIG. 3 could be realized. In this case, it was effective to cut the female thread on the composite material and tighten the conductive material together with the conductive grease without variation.

1.4.7.13. Copper foil (18-105μm)
2.5.8.14. Insulating layer (40-200μm)
3. Base metal (aluminum / copper)
6.9.15. Base material composite 10. Solder 11. Copper plating12. Through hole 16. screw

Examples for explaining the present invention more specifically are shown below.

The graphitized powder is packed in an iron container so that the volume ratio is 85%, preheated to 700 ° C., and then impregnated with a molten JISAC4B aluminum alloy at a pressure of 90 MPa by a molten metal forging method. After cooling, a composite material having a specific gravity of 2.30 was obtained. From this, a 20 mm square plate having a thickness of 1.5 mm was obtained. Thereafter, a polyimide compounded with 40 μm of 5 wt% aluminum nitride (average particle size: 7 μm) was bonded, and a 70 μm copper foil was adhered thereon to complete a 10 W LED chip wiring board. An LED chip was placed and lighted for 100 days at a voltage of 330 mA and a voltage of 30 V, but the luminous flux remained unchanged at 1500 lm. Moreover, the temperature of LED upper part was 60 degreeC.

From a composite material similar to that of Example 1, a plate material having a thickness of 3.2 mm and an 80 mm × 40 mm was taken out, 80 μm of polyimide containing a high thermal conductive filler was bonded, and a 140 μm copper foil was pasted thereon. After the circuit of the power semiconductor substrate having an output of 167 W was formed, it was placed on an aluminum heat sink using the method of FIG. At this time, the screw reached the heat sink.
Table 1 shows the temperature at which this was compared with the case of using a copper plate of the same size instead of the composite material.
Table 1

Claims (5)

An insulating layer (hereinafter referred to as insulating material) in which alumina, boron nitride, aluminum nitride (hereinafter referred to as high thermal conductive filler) is dispersed in a thermosetting resin such as epoxy resin in a composite material of carbon and aluminum (hereinafter referred to as composite material). A structure in which a copper foil is attached via a layer) to form a wiring board. Solder is applied to the composite material by partially removing the copper foil and the insulating layer arranged to collect heat on the composite material-based wiring board, and performing nickel plating, gold plating, silver plating, or copper plating on the exposed composite material. A structure that allows attachment. A structure in which solder is poured into a metal surface that can be soldered to the composite material and connected to a copper foil on an insulating layer. A structure in which the copper foil and the insulating layer of claim 2 are removed and then copper plating is performed so that the copper foil and the insulating layer have the same height. 2. A structure in which a hole is formed in a copper foil and an insulating layer arranged so as to collect heat in the composite base wiring board of claim 1, and the surface of the copper foil and the composite material are joined with a screw having high thermal conductivity.

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