JPS60155600A - Heat sink for electronic device - Google Patents

Abstract

PURPOSE:The titled heat sink, obtained by coating the surface of an Ib type synthetic diamond crystal with a specific metal, and coating the resultant film with a specific different metal. CONSTITUTION:A heat sink for electronic devices obtained by coating the surface of an Ib type synthetic diamond crystal wth one or more metals of Ti, Cr, Hf, Zr and Ta, and coating the resultant film with one or many layers of one or more metals of Au, Pt, Ag, Ni and Sn. The Ib type synthetic diamond single crystal has a definite face orientation and is surrounded by faces, and therefore is easily worked and capable of supplying the heat sink at a low cost. The peeling of a coating film and deterioration in heat resistance can be prevented by coating the surface thereof with Ti by ion plating, etc. The coating of an alloy film of gold and tin on the outermost layer of the coating film improves the yield in bonding of the diamond heat sink to both a semiconductor device and a substrate, and labor of soldering is saved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) As is known, diamond is a material with the highest thermal conductivity and has a wide range of industrial uses.

However, in the case of natural rough diamonds, their thermal conductivity varies significantly depending on the amount of nitrogen they contain. The higher the amount of nitrogen content, the lower the thermal conductivity, and the value is 24W/℃, ・Cm~6W/℃ depending on the amount of nitrogen content at room temperature.
It changes by about ℃・σ. Among these diamonds, diamonds with a nitrogen content of 1 PPM or less are selected and referred to as Type 1a (those containing even more nitrogen are referred to as Type Ia). this[
Most LA type diamonds are 20W/'C.
It exhibits a high thermal conductivity of σ or higher, and is used as a heat sink for heat dissipation in electronic devices such as semiconductor lasers, diodes, and microwave oscillation elements that generate high heat. In particular, semiconductor lasers have become more powerful in recent years, and are now being used as heat sinks in new fields such as laser printers and optical memory displays, and the demand for them is extremely large.

The present invention relates to a diamond heat sink used in this electronics device. In particular, this invention relates to a metal coating film applied to bond a semiconductor element and a diamond heat sink, and a substrate and a diamond heat sink.

(Prior art and its problems) However, naturally produced λ-type diamonds are produced in small quantities and are extremely expensive. It is often limited to heat sinks for microwave diodes.

Furthermore, even with the same LA type diamond rough, the thermal conductivity changes depending on the nitrogen content, so it has the disadvantage of lacking stability. It is also well known that diamond is the hardest substance. For this reason, processing is extremely difficult.

Diamond has significantly different wear characteristics depending on its crystal plane (see Figure 1'). If you polish the (110) surface (6), you can get good results, but if you accidentally polish the (111) surface (1),
The diamond becomes almost uncuttable.

For this reason, correctly determining the surface orientation of rough diamonds is an essential condition for processing diamonds.

Most natural gemstones are dodecahedrons, consisting of 110 faces (3).
Alternatively, it is composed of an octahedron consisting of 111 faces (1), but in many cases the edges at the boundaries between faces are fused, and finding the face orientation requires skill and often leads to mistakes. Note that (2) in FIG. 1 is (100 planes).

The next problem in making a diamond heat sink is that since the diamond surface is used as an electrode in an electronic device, a gold coating must be applied to the surface. The technology involved is difficult, and sufficient surface strength cannot be obtained over all the heat sinks, resulting in poor yields. If diamond alone is used, the adhesion strength with diamond is low, and devices, lead wires, etc. cannot be bonded together. Usually, a metal that easily reacts with oxygen, such as Ti or Cr, is first coated using a method such as vapor deposition or sputtering, and then gold or platinum and gold is coated on top using the same method and used as a heat sink. many. In this case, the surface treatment and coating conditions when coating Ti, Cr, etc. are difficult, and sufficient adhesion strength cannot be obtained between the diamond and the coating film, resulting in the coating film peeling off when the lead wire is glued. There are things. Furthermore, if the adhesion strength is low, it will cause an increase in thermal resistance.

A semiconductor device is bonded to one surface of the diamond heat sink produced by the method described above, and a substrate is bonded to the other surface. In this case, gold-tin solder is often used. When adhering to a semiconductor device or substrate using gold-tin solder, the solder and the coated gold tend to become alloyed and form droplets.

This phenomenon causes the following inconveniences.

■ The coating film is cut at the edge of the diamond, eliminating electrical continuity between the semiconductor device and the substrate.

It attaches to the OP type element and the N type element to electrically short-circuit them.

For a θ light-emitting element, the light-emitting portion may be partially or completely covered by droplet-shaped gold-tin alloy.

(Structure of the Invention) The present invention solves the above-mentioned problems by providing a diamond heat sink that has stable high thermal conductivity and is easy to process by using artificially synthesized diamond.

That is, the heat sink for electronic devices of the present invention uses Ib type synthetic diamond crystal, coats the surface of the diamond with one or more metals selected from titanium, chromium, hafnium, zirconium, and tantalum, and further coats the surface of the diamond with one or more of the following metals: gold, platinum, silver, nickel,
It is characterized by being coated with one layer or multiple layers of one or more metals among tin.

Furthermore, in the above, the coating with one or more of the metals titanium, chromium, hafnium, zirconium, and tantalum is a method in which the diamond is coated with a metal film with strong adhesion by using an ion-blating method. It is.

In addition, in the present invention, instead of coating the outermost layer with a metal such as gold as in the past, the outermost layer is coated with a gold-tin alloy in advance, thereby eliminating the trouble of soldering the semiconductor element and the heat sink and the board and the heat sink. Instead, it prevents the gold-tin alloy from turning into droplets and having an adverse effect on semiconductor devices.

The present invention will be explained in detail below.

■About the invention using type Ib diamond crystals in heat sinks Naturally produced diamonds are divided into type IIa (nitrogen content of 2 PPm or less) and type Ia (nitrogen content of 2 PPm or more) depending on the nitrogen content. Among these, the thermal conductivity of type (1) varies at room temperature, but it has a high amount of existing material of 20 W/°C α, making it ideal as a material for heat sinks, but it is produced in extremely small quantities and is expensive. Ja type diamond has a thermal conductivity of 5 to 14 W'/℃
・Variation across a wide range of countries, most of them are 6~9W/
Indicates the value in °C. Synthetic diamond ('Ib type)
exhibits an extremely high thermal conductivity of 20 W/°C, and is inexpensive with little variation. Furthermore, it has the advantage of being easy to process, and by using the b-type diamond crystal, an inexpensive heat sink can be provided.

Now, when processing diamond heat sinks compared to natural rough stones, there were the following drawbacks.

■The surface orientation is not well determined, and the polished surface (the surface that can be polished well)
may be mistaken.

■Diamond surfaces have many curved surfaces and require a lot of machining allowance and time.

In the present invention, by using an artificially synthesized diamond with clear crystal planes (see FIG. 1), the orientation of the diamond crystal plane can be easily determined and there is no possibility of erroneously identifying the polished plane. Furthermore, since the crystal plane is flat, there is an advantage that machining allowance is small.

＠ Regarding the invention of coating Ib type diamond heat sinks with metals such as titanium and chromium by ion blating Even if type Ib rough stones, which have the excellent advantages mentioned above, are used, if the adhesion strength of the metal coating film is low, semiconductor devices or substrates may be damaged. When soldering a heat sink, the diamond surface and metal film often separate, making it unusable. Another disadvantage is that thermal resistance increases and heat dissipation becomes poor.

Conventionally, when coating a diamond surface with a metal such as titanium or chromium, a vapor deposition method or a sputtering method has been used. However, the metal film produced by the same method had insufficient adhesive strength, and the adhesive yield was low due to peeling of the metal film and increased thermal resistance. In particular, the following precautions were required when coating a metal film using the above method.

■' Thoroughly clean the surface of the diamond to be coated with acid or alkali.

■' Thoroughly degrease the diamond surface using an organic solvent.

■'When co-coating, it is necessary to maintain the diamond surface temperature at a high temperature.

07 In order to make the film thickness uniform on the surface and sides, it is necessary to rotate the table or jig that holds the diamond.

In the present invention, unlike the conventional vapor deposition method and sputtering method, the Ib
This improves the adhesive strength between the molded diamond and metals such as titanium and chrome.

In the case of ion blating, titanium, chromium, etc. are vaporized using an electron beam gun, and the ionization rate of the metal is further increased using an ionization electrode. Furthermore, by applying a high voltage between the diamond and the stand or jig that holds it, it is possible to firmly coat the diamond surface with metals such as titanium and chrome.

In this case, as mentioned above, the ion blating method considerably reduces the effort required to take precautions (1) to (2) when coating the diamond surface with titanium, chromium, etc. using the conventional method.

○ Regarding the invention in which the outermost layer of the coating film is formed with a gold-tin alloy film, even if Hbb diamond single crystal is coated with a strong metal film of titanium, chromium, etc. on the diamond surface by ion blasting, the outermost layer of the coating film will not be coated with gold or platinum as in the past. If a coating of gold or the like is applied on the film, the following problems will occur. That is, when a diamond heat sink, a semiconductor device, and a substrate are bonded together using gold-tin solder, the gold in the coating film and the solder become alloyed and form droplets. For this reason, the coating film is cut at the edge of the diamond, and electrical continuity between the semiconductor device and the substrate is lost.

■“It adheres to the P-type element and N-type element, causing an electrical short circuit and making them inoperable.

■“For a light-emitting element, the light-emitting part may be partially or completely covered by gold-tin alloy in the form of droplets.

is likely to occur.

In the present invention, this drawback is improved by coating the outermost layer of the coating film with a gold-tin alloy in advance.

By uniformly coating the outermost layer of the coating film with a gold-tin alloy in advance as in the present invention, adhesion between a semiconductor device or a substrate and a heat sink becomes extremely easy. The bonding method is to raise the entire heat sink to around the melting point of the gold-tin alloy, and then press-bond the substrate or semiconductor device. In this case, since the gold-tin alloy melts uniformly, it does not form into droplets as in the conventional case. Therefore, the above-mentioned drawbacks of the conventional method are eliminated, and the bonding yield is significantly improved.The outermost layer can be coated with a gold-tin alloy by vapor deposition, sputtering, or ion-blating. Almost the same effect was obtained.Also, there was no significant difference in the effect of the present invention whether the method involved coating by evaporating a pre-alloyed metal or the method of simultaneously evaporating gold and tin and alloying them during the coating process.

(Effects of the Invention) As described above, by using the (1)bb synthetic diamond single crystal, it has become possible to create a heat sink that has a high thermal conductivity equivalent to that of the naturally produced (2)λ type and with less variation.

In addition, since the bb single crystal has a clear plane orientation and is surrounded by a plane, it is easy to process, and an inexpensive heat sink with little processing loss can be provided.

In addition, by coating the surface of a diamond heat sink using Hb-type packed crystals with metals such as titanium and chromium using ion blating, it is possible to create a film with strong adhesive strength, which prevents peeling of the coating film and heat. A decrease in resistance can now be prevented.

Furthermore, by coating the outermost layer of the coating film with a gold-tin alloy film, not only the bonding yield between the semiconductor device and the substrate and the diamond heat sink was improved, but also the trouble of soldering became unnecessary.

(Example) Examples will be described below to help understand the present invention.

Example-1 Using an ultra-high pressure generator, 6. A 0.45 carat synthetic diamond type Ib single crystal was prepared under OGP pressure and the temperature was maintained at 145D°C for 5D hours.

This rough stone is polished to 2 mm x 2 mm x
When the thermal conductivity was measured with a size of 2, it was 19.1W/℃
・cm (at 45°C). In addition, the nitrogen content was estimated from the infrared absorption coefficient and was 57 PPm (sample N
o, -L).

The thermal conductivity of a natural ■-shaped diamond single crystal processed into the shape of 2111111 x 2 rra x 2 was measured to be 18.5 W/'C·cm (at 45°C). The nitrogen content estimated from the infrared absorption coefficient is 1PP.
m (sample No. -2).

Natural IA type diamond single crystal 2 mm x 2 m
8.4 when processed into the shape of m x 2 cylinder and measured the thermal conductivity
W/'C·cm (at 45°C). The nitrogen content was estimated from the infrared absorption coefficient and was 1700PPm (
Sample No.-3).

A portion of the above-mentioned samples Nos. 1 to 3 was processed several times into the shape shown in FIG. 2, and Ti was coated with 600A0. A diamond heat sink was created by coating Au with a thickness of 1.5μ. Furthermore, as shown in FIG. 6, the semiconductor laser element was soldered to a diamond and gold-plated Cu substrate, lead wires were attached, and a laser output test was conducted. The surfaces of the element and heat sink were subjected to body treatment, and the element surface temperature was measured using an infrared measuring device. The test results are shown in Table 1 below.

As shown in Table 1, the measured values of the thermal conductivity of the raw stones are the same for the old type and the Ib type. Furthermore, even when used as a heat sink, there is no difference in heat dissipation characteristics between the la type and the Ib type, indicating that they are excellent heat sinks.

Table 1 Rice (at 45° C.) Example 2 Synthetic diamond type Ib was prepared in the same manner as in Example 1, and 600 pieces were processed into the shape shown in FIG.

100 of them were deposited using a vapor deposition method such as Ti (600A”), A
A u(1,5μ) film was coated on the diamond surface (sample No.-1).

In addition, 100 of the remaining samples were sputtered.
-1 was coated with the same membrane. Furthermore, the remaining 10
Sample No. 0 was coated with the same film as sample No. 1 by ion blating, and the following adhesive strength test was conducted. The test results are shown in Table 2.

Table 2 (Note) The number of samples is 100 each.

(1) Beer test A test in which a tape with strong adhesive strength is adhered to the heat sink surface, and the adhesion strength is determined by whether or not the coating film peels off all at once when the tape is peeled off. (2) Lead wire bonding test on the heat sink After 10 thermal cycles from room temperature to 450°C, a lead wire is thermocompression bonded to the surface using an indenter heated to 250°C and subjected to ultrasonic waves.

At that time, the adhesion strength was determined by whether or not the coating film peeled off.As can be seen from Table 2, the film produced by the ion-blating method is a film with extremely high adhesive strength.

Example 3 Synthetic diamond type Ib was prepared in the same manner as in Example 1, and 200 pieces were processed into the shape shown in FIG.

100 of them were coated with Ti (6QQA) and Pt (600A0) using the ion blating method, and then coated with 2 μm of Au (1 μm for trial use).
It was coated with Au. Furthermore, Au-8
It was coated with 1μ of n-alloy. (Sample No. -2)
.

Using the diamond heat sink of sample NQ, -1, the third
As shown in the figure, the semiconductor laser and the substrate were bonded using Au-5n solder. After attaching the lead wires, we applied power and tested the laser output. Among them, those that did not output laser light were called output defects, and those that did not output 9 mW or more even when a forward current of 75 mA was applied were called element defects, and the details of the defects were classified. Further, the diamond heat sink of sample No. -2 was heated to 280° C. for a short time to bond the substrate and the semiconductor element. As with sample No. 1, a laser output test was conducted with the lead wires attached as shown in FIG. The results are shown in Table 3.

As can be seen from Tables 3 and 6, the adhesion yield was significantly improved by using the diamond heat sink according to the present invention (sample N[1-2).

[Brief explanation of the drawing]

FIG. 1 is a perspective view illustrating a typical shape of a type Ib synthetic diamond single crystal. FIG. 2 is a perspective view illustrating the shape of the heat sink. FIG. 6 is a perspective view of a package in which a diamond heat sink is bonded on a substrate, a semiconductor element is bonded thereon, lead wires are connected, and a laser beam can be emitted. (1)...(111 pages), (2)...(100 pages)
, (3)... (110 planes), (4)... diamond heat sink, (5)...
Semiconductor element (laser element), (6)... base, (7
)... Lead wire, (8)... Laser light, (9)...
・Lead wire connection terminal Fig. 1 Fig. 2 O Fig. 3

Claims (1)

[Claims] b (1) Using # type synthetic diamond rough, the surface of the diamond is coated with one or more metals selected from titanium, chromium, hafnium, zirconium, and tantalum, and further coated on top of the diamond surface. gold, platinum, silver, nickel,
A heat sink for an electronic filter device characterized by being coated with one or more metals selected from tin in one layer or in multiple layers. (2) The heat sink for an electronics device according to claim (1), wherein the coating of one or more metals selected from titanium, chromium, hafnium, zirconium, and tantalum is an ion-blating coating. (3) The outermost layer or multilayer coating of one or more metals selected from gold, platinum, silver, nickel, and tin is a coating of a gold-tin alloy.
1) A heat sink for electronic devices as described in item 1).