JPH06163765A - Aluminum nitride heat sink and its manufacture - Google Patents

Abstract

PURPOSE:To achieve enlargement of the current capacity of a heat sink and enhancement of the reliability of the heat sink in the heat sink wherein it is used for the mounting of a semiconductor bare chip, it is provided with conductivity between the surface and the rear and it is made of aluminum nitride and to provide the manufacturing method of the heat sink. CONSTITUTION:A heat sink is provided with an aluminum nitride heat-sink base body 10A in which through holes 12 have been made and which has been baked, with conductor parts 14A which have been filled into the through holes and which have been baked, with metallized layers 16A which have been baked and formed on both faces of the heat-sink base body and with metal-plated layers 18 which have been formed on surfaces of the metallized layers. The heat sink is manufactured in such a way that an aluminum nitride heat-sink raw body in which the through holes have been made, a conductor paste 14 filled into the through holes and a conductor paste 16 with which both faces of the heat-sink base body have been coated are baked and formed simultaneously and that the metallized layers on both faces are plated with a metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat sink made of aluminum nitride which is used for mounting a semiconductor bare chip and has conductivity between front and back surfaces.

[0002]

2. Description of the Related Art Aluminum nitride (ALN) has high thermal conductivity (5 to 10 times that of alumina) and electrical insulation and does not have the toxicity problem of beryllia. It is attracting attention as a substrate.

FIG. 2 is a sectional view showing a mounting example in which a bare chip of a power transistor 2 is integrated with this aluminum nitride substrate (hereinafter referred to as ALN substrate) 1. Here, the power transistor 2 is conventionally fixed to the substrate 1 via a heat sink (heat spreader) 3 made of copper.

That is, the silicon substrate 4 of the transistor 2
Is the collector C of the transistor 2, and the silicon substrate (semiconductor bare chip) 4 is attached to the heat sink 3 by 5
Soldered by the soldering part indicated by. The heat sink 3 is soldered to the circuit pattern 6 formed on the ALN substrate 1 by the soldering portion indicated by 7. On the other hand, the base B and the emitter E of the transistor 2 are
The lead wires 8 and 9 are connected to the circuit patterns 10 and 11 on the ALN substrate 1. The surface of the heat sink 3 used here is gold-plated or nickel-plated.

As described above, the conventional heat sink 3 is made of copper, and the coefficient of thermal expansion of this copper is about 20 × 10 ⁻⁶ / ° C., which is about 3.6 × 10 ⁻⁶ / ° C. of silicon. 4 ~
It is 5 times bigger. Therefore, particularly in the transistor 1 using the large-sized silicon substrate 4, there is a problem that the solder of the soldering portion 5 and the silicon substrate 4 are likely to be cracked due to the difference in thermal expansion coefficient between copper and silicon, and the reliability is deteriorated. there were.

Materials such as copper and tungsten which have a coefficient of thermal expansion close to that of silicon include copper and tungsten, which have a large specific gravity of about 10, which is an obstacle to weight reduction. Therefore, it is considered to use aluminum nitride (ALN) as the material of the heat sink 3. This is because this ALN has a coefficient of thermal expansion of 4.4 × 10 ⁻⁶ / ° C. on average from room temperature to 400 ° C., which is close to that of silicon. Also, the specific gravity is 3.2, which is also lightweight.

However, since this ALN is an electrical insulator, when the silicon substrate 4 which is the collector C is directly connected to the circuit pattern 6 as shown in FIG. 2, the heat sink itself may be made conductive. You will need it. Therefore, when this ALN heat sink is used, a thin film is formed on the entire surface including both sides and side edges by a vacuum deposition method or a sputtering method (thin film metallization), or a conductive paste is printed and baked to obtain a conductive thickness. A film was formed (thick film metallization). Moreover, high melting point metallization of molybdenum manganese etc. was performed.

[0008]

As described above, when a heat sink made of ALN is conventionally used, a metallization layer of a thin film or a thick film is formed on the entire outer surface of the heat sink to obtain conductivity between the upper and lower surfaces through the side edges. Was there. For this reason, the current capacity between the upper and lower surfaces is limited, which makes it difficult to apply it to a large current power transistor, and there is a problem that reliability is reduced.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is a first object of the present invention to provide an aluminum nitride heat sink capable of increasing current capacity and improving reliability. A second object is to provide a method for manufacturing this heat sink.

[0010]

According to the present invention, a first object is to provide a heat sink base made of aluminum nitride in which through holes are formed and fired, a conductor portion filled in the through holes and fired, and both sides of the heat sink base. And a metal plating layer formed on the surface of the metallized layer and an aluminum nitride heat sink.

A second object is to simultaneously form a heat sink element body of aluminum nitride having a through hole formed therein, a conductor paste filled in the through hole, and a conductor paste applied to both surfaces of the heat sink element body. After firing
This is achieved by a method for manufacturing an aluminum nitride heat sink characterized by applying metal plating to both metallized layers.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing processing steps of a manufacturing method according to the present invention. In FIG. 1A, reference numeral 10 is a green sheet of aluminum nitride (ALN). The green sheet 10 has a thickness and size substantially corresponding to the heat sink 3 described in FIG.

As shown in FIG. 1B, the green sheet 10 has a plurality of through holes, that is, through holes 12, to form a heat sink body 10A. The green sheet with the through holes 12, that is, the heat sink body 10A has the conductor paste 1 in the through holes 12.
4 and filled with conductor paste 16 on both upper and lower surfaces thereof.
Is applied to form a green sheet 10B shown in FIG. For the conductor pastes 14 and 16, it is desirable to use a paste containing particles of molybdenum / manganese or tungsten having a coefficient of thermal expansion close to that of aluminum nitride.

When the same material is used for the conductor pastes 14 and 16, the conductor pastes 14 and 16 are simultaneously formed on the through hole 12 and the upper and lower surfaces by using the squeeze method or the screen printing method on the heat sink body 10A. Can be supplied. The conductor pastes 14 and 16 may be separately supplied as pastes of different materials.

In this way, the green sheet 1 having the through holes 12 and the conductor pastes 14 and 16 provided on both sides thereof.
OB is put into a firing furnace (not shown) and fired.
As a result, as shown in FIG. 1D, the conductor pastes 16 and 16 on both upper and lower surfaces become metallized layers 16A and 16A,
The conductor paste 14 in the through hole 12 is a conductor portion 14A for electrically connecting these metallized layers 16A, 16A.
Becomes Further, the heat sink body 10A is fired to become a heat sink base body 10C. This heat sink 10
A may be formed by laminating a plurality of sheets to adjust the thickness.

After firing in this way, the metallized layer 1
Metal plating layers 18, 18 such as gold or nickel plating are formed as finish plating on the surfaces of 6A, 16A by electrolytic plating or electroless plating.

As a result, a fired aluminum nitride heat sink substrate 10C, a conductor portion 14A filled in the through holes 12 and fired, metallized layers 16A and 16A fired on both sides, and metal plating layers 18 and 18. A heat sink 3A having the above is formed (see FIG. 1E).
Although it is desirable to provide a large number of through holes 12 because the current density of the conductor portion 14A becomes small, the present invention also includes a single through hole 12.

[0018]

According to the first aspect of the present invention, the conductor portion filled in the through hole of the heat sink substrate and fired provides conductivity between the metallized layer and the metal plated layer on both sides of the conductor portion. Since a current is passed through the conductors here, the current capacity can be easily increased by increasing the number of conductors.
Further, even if the heat sink substrate becomes thick, the conductivity is surely obtained and the reliability is high. According to the invention of claim 2, the method for manufacturing the heat sink can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of the present invention.

FIG. 2 is a diagram showing an application example of a heat sink.

[Explanation of symbols]

 3A heatsink 10 green sheet 10A heatsink body 10C heatsink substrate 12 through holes 14, 16 conductor paste 14A conductive part 16A, metallization layer 18 metal plating layer

Claims (2)

[Claims] 1. A heat sink base made of aluminum nitride in which through holes are formed and fired, a conductor portion filled in the through holes and fired, a metallized layer fired on both sides of the heat sink base, and this metallized layer. An aluminum nitride heat sink having a metal plating layer formed on the surface of the aluminum nitride heat sink. 2. A heat sink element body of aluminum nitride having a through hole formed therein, a conductor paste filled in the through hole, and a conductor paste applied to both sides of the heat sink element are co-fired, and then both sides 2. A method for manufacturing an aluminum nitride heat sink, which comprises subjecting the metallized layer of 1. to metal plating.