JPH04230063A - Multilayer heat sink - Google Patents

Abstract

PURPOSE:To obtain a multilayer heat sink by a highly reliable soldering and to make possible a combination of a low-thermal expansion material and a high-heat conductive material by a method wherein a heat sink is formed of two kinds or more of metals or alloys and a heat sink material is bonded to the heat sink by soldering. CONSTITUTION:A plate 12 made of Cu of a high heat conductivity is soldered to a plate 11 made of Mo of a low thermal expansion coefficient using a silver solder 8 paste consisting of a compositional ratio of 45% of Ag, 15% of Cu, 16% of Zn and 24% of Cd, for example, to manufacture a multilayer heat sink 1. A power element 2 is placed on the sink 1, a ceramic substrate 3 is arranged on the opposite side to this element 2 and a fin 4 is arranged on the side of the substrate 3 which opposes to the sink 1. A heat dissipation grease 5 is mode to interpose between the substrate 3 and the film 4 and the sink 1 is bonded to the element 2 and the substrate 3 with solders 6.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat sink for power devices, and more particularly to a multilayer heat sink with improved joint reliability and heat dissipation.

0002

[Prior Art] Conventionally, as heat sink materials, Cu and Cu alloys have been used from the standpoint of heat dissipation, and Mo and W have been used from the standpoint of solder joint reliability. It is bonded between Al2O3 ceramic substrates.

[0003]Cu has a high thermal conductivity and excellent heat dissipation properties, but its coefficient of thermal expansion is 3 to 30% lower than that of Si or Al2O3.
When a high-power element that is four times larger is mounted, distortion caused by the difference in thermal expansion accelerates the deterioration of the solder bonding material. On the other hand, Mo and W have a relatively low coefficient of thermal expansion and are excellent materials for delaying solder deterioration, but because of their low thermal conductivity, they are inferior to the case where Cu is used in terms of heat dissipation. Therefore, by combining both, a heat sink suitable for power devices can be expected.

[0004] Proposals for combining Cu with Mo or W include a method in which Mo or W is molded together with a resin, the resin is removed to make it porous, and then Cu is impregnated. There is a way to do this (commonly).

[0005]

[Problems to be Solved by the Invention] In the prior art, impregnating low thermal expansion metal with Cu involves a complicated process and increases costs, and the cladding method requires difficult pressure welding conditions, making it impossible to achieve highly reliable bonding. In particular, since Mo and W are formed into a plate shape by rolling from a sintered ingot, it is difficult to obtain a long material, and furthermore, the presence of strong oxides makes cladding with different metals extremely difficult.

[0006]

[Means for Solving the Problems] The present invention has been made to solve the above problems, and proposes a multilayer heat sink made by soldering at least two or more types of metals. For example, in the combination of Mo and Cu, 200 to 3
Ni plating is applied to each 00 mm square plate material, and the plates are brazed together in a vacuum or an oxygen-free atmosphere. Afterwards,
By cutting and molding, a small piece in which Mo and Cu are bonded is obtained. In addition, when placing more emphasis on heat dissipation, Cu-
By using three layers of Mo-Cu and changing the thickness of each layer, various multilayer heat sinks can be obtained. Here, Ni plating is applied to ensure the reliability of the soldered joint and to improve the solderability when soldering to a power element or Al2O3. Soldering onto Cu has a problem with heat resistance, and direct soldering onto Mo is not possible.

From the above, the gist of the present invention is to provide a multilayer heat sink made by brazing at least two or more metals or alloys,
Metals or alloys containing at least one species of Mo and W, and Fe-Ni
and the other is a multilayer heat sink made of copper or copper alloy.

[0008]

[Operations and Effects] According to the present invention, a highly reliable multilayer heat sink by soldering can be obtained. Furthermore, by combining low thermal expansion materials and high thermal conductivity materials, it is possible to manufacture multilayer heat sinks depending on the application. That is, Mo and W
By combining Cu and Cu and appropriately selecting the thickness of each, a multilayer heat sink that takes advantage of the characteristics of both can be obtained. Furthermore, since the Fe-Ni alloy has a different coefficient of thermal expansion depending on the Ni content, it is possible to combine plates with different Ni contents to produce a composite material whose thermal expansion coefficient gradually changes in the thickness direction.

[0009]

[Embodiment] The present invention will be explained below based on one embodiment.

(Example 1) In FIG. 1, 1 indicates a Cu plate 12 with high thermal conductivity and a Mo plate 11 with a low coefficient of thermal expansion.
and Ag45%-Cu15%-Zn16%-Cd24%
2 is a power element placed on the multilayer heat sink 1, and 3 is a ceramic element placed on the opposite side of the heat sink 1 from the power element 2. On the board,
Reference numeral 4 denotes a fin disposed on the side of the ceramic substrate 3 opposite to the multilayer heat sink 1. 5 is heat dissipation grease interposed between the ceramic substrate 3 and the fins 4;
is a solder that joins the multilayer heat sink 1 to the power element 2 and the ceramic substrate 3.

[0011] To explain more specifically, the length is 200 mm.
×Width 200mm × thickness 0.3mm Mo plate 11 and length 2
00mm x width 200mm x thickness 0.2mm Cu plate 12
were plated with Ni, Ag45%-Cu15%-Z
Silver solder 8 paste consisting of 16% N-24% Cd was printed on one side. Here, Ni plating was performed by a general electroplating method using a Watts bath, and the plating thickness was 5 μm. Also, Mo board 11
Since adhesion cannot be obtained with Ni plating, adhesion is ensured by heat treatment in a N2-H2 mixed gas flow after Ni plating.

[0012] The Cu plate 12 and the Mo plate 11 were stacked on top of each other with their silver solder surfaces aligned, and they were held in a vacuum heat treatment furnace at 700°C for 30 minutes to braze them. Subsequently, the brazing material 1 was cut with a diamond grindstone into a shape of 7 mm x 7 mm, and mounted as shown in FIG. 1.

(Example 2) FIG. 2 shows Mo having a low coefficient of thermal expansion.
It is a diagram showing a heat sink with a three-layer structure in which Cu plates 12 and 13 with higher thermal conductivity are joined by soldering to the top and bottom of a plate 11, and the other configurations are substantially the same as in Example 1. This is example 2.

[0014] To explain more specifically, the length is 200 mm.
×Width 200mm × thickness 0.3mm Mo plate 11 and length 2
00mm x width 200mm x thickness 0.3mm Cu plate 12
and 13 were each plated with Ni, with Ag45%
Silver solder 8 paste consisting of -Cu15%-Zn16%-Cd24% was printed on one side of the Cu plates 12 and 13, and on both sides of the Mo plate 11. Here, Ni plating was performed by a general electroplating method using a Watts bath, and the plating thickness was 5 μm. Further, since Ni plating on the Mo plate 11 does not provide good adhesion, the Mo plate 11 is heat-treated in a N2-H2 mixed air flow after Ni plating to ensure adhesion.

[0015] Mo plate 11 is further placed on Cu plate 12.
2 and held in a vacuum heat treatment furnace at 700°C for 30 minutes to perform soldering. Subsequently, it was processed into a disk with a diameter of 10 mm using a wire cutting method. Thereafter, when the thermal conductivity was measured by a laser flash method, an excellent thermal conductivity of 187 [W/m·K] was obtained. The thermal conductivity of Cu and pure Mo is 3
98 [W/mK] and 138 [W/m·K].

(Example 3) C created in the same manner as in Example 2
The u-Mo-Cu brazing material was cut with a diamond grindstone into a shape of 7 mm x 7 mm. Also, the thickness is 0.
A small piece of 7 mm x 7 mm was cut out from a 5 mm Mo board, and Ni plating was applied to 5 μm to prepare a comparative material.

As shown in FIG. 3, these multilayer heat sinks 1 are assembled into a laminated structure assuming ideal heat dissipation, and the power element 2 and the ceramic substrate 3 are sandwiched and bonded with solder 6, and the ceramic substrate 3 is coated with heat dissipation grease 5. via A
It was brought into contact with fins 4 made by L. Further, the power element 2 was caused to generate heat, and the temperature rise at that time was measured using a thermocouple at the temperature measurement point 7.

FIG. 4 is a diagram showing the temperature rise when the calorific value is 5 W, 15 W, and 25 W. While the comparative material Mo(1b) exhibits a thermal resistance of 1 K/W, the Cu- Mo
-Cu brazing material (1a) improves heat dissipation to 0.75 K/W.

[0017]

[Brief explanation of the drawing]

FIG. 1 is a side view of a semiconductor device using a heat sink with a two-layer structure of the present invention in which a Cu plate and a Mo plate are joined by soldering.

FIG. 2 is a side view of a semiconductor device using a three-layer heat sink of the present invention in which a Cu plate, a Mo plate, and a Cu plate are bonded together by soldering.

FIG. 3 is a diagram of a laminated structure for thermal resistance measurement of a heat sink in Example 2.

FIG. 4 is a diagram showing thermal resistance (temperature rise with heat generation amount) of the present invention and a conventional heat sink.

[Explanation of symbols]

1 Heat sink 11 Mo board 12 Cu board 13 Cu board 2 Power element 3 Ceramic substrate 4 Fin 5 Heat dissipation grease 6 Solder 7 Temperature measurement point 8 Brazing filler metal

Claims (3)

[Claims] 1. A multilayer heat sink in which a power element is mounted via a heat sink, characterized in that the heat sink is formed of at least two kinds of metals or alloys, and the heat sink materials are joined by soldering. . [Claim 2] At least one side of the heat sink is made of Mo.
, W metals or alloys, and Fe--Ni alloys. [Claim 3] At least one side of the heat sink is made of Mo.
, W, or an Fe-Ni alloy, and the other is made of one or more of Cu and a Cu alloy.