JPH0497581A - Heat sink of semiconductor device - Google Patents

Abstract

PURPOSE:To realize semiconductor layer chip mounting configuration where the length of a wire is 0.3mm by removing the difference in the levels of the faces, which are connected by the bonding wire, of a semiconductor laser chip and a heat sink. CONSTITUTION:A semiconductor chip 2 is fused together to a heat sink l, and the p-type electrode 21 of the semiconductor chip is coupled with the metallic film 12, which is formed on the surface of the part projecting from the surface where the semiconductor chip is fused together, by a bonding wire 31. The difference in the levels of the p-type electrode face 21 of the semiconductor layer chip and the face 12 coupled by the bonding wire 31 are removed, therefore the length of the wire can be made 0.3mm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a heat sink for fusing a semiconductor laser.

[Conventional technology]

It has already been a long time since semiconductor lasers have been put into practical use as light sources for optical fiber communications. In particular, distributed feedback semiconductor lasers, which oscillate in a single-axis mode, are used as light sources for trunk optical fiber communications.
-1aser diode (DFB laser) has been put into practical use in recent years, and
Research and development is being conducted on semiconductor lasers that operate at ~2 Gbps.

[Problem to be solved by the invention]

When attempting to operate a semiconductor laser at the high speeds mentioned above, it is not only necessary that the semiconductor laser chip itself has a sufficiently fast response speed, but also requires some restrictions on the method of mounting the chip. . The main thing is to reduce reactance and capacitance as much as possible when the semiconductor laser is viewed from the signal feeding side.

Semiconductor laser chips exhibit characteristics due to temperature rise due to self-heating.
Since reliability is greatly affected, semiconductor lasers, especially for communications, are used with a semiconductor laser chip fused to a heat sink.

As the material for the heat sink, one is selected that has high thermal conductivity and a coefficient of linear expansion close to that of the semiconductor material constituting the semiconductor laser chip. FIG. 4 shows a perspective view of a semiconductor laser mounted in a so-called chip-on-carrier format. The semiconductor laser chip 2 is fused to the heat sink 1 using solder, and a metal film button on the heat sink is electrically connected between the semiconductor laser chip's electrode [r21 and the metal block 5 and with the other electrode of the semiconductor laser chip. 11 and the metal film button 51 on the insulator are connected by bonding wires 31 and 32, respectively.

Since semiconductor lasers for communications are normally used with a grounded anode, the example in Fig. 4 uses n
The wiring is arranged such that the metal block 5 becomes an anode in a type substrate and an upside-up mount configuration. In such a structure, the bonding wire actance is the main cause of speed deterioration. There is also a report that in order to obtain good response characteristics in the region of 5 Gbps or more, the total wire length needs to be 0.5 mm or less when using 30 μm wires for boat fishing. In order to shorten the length of the bonding wire in the configuration shown in the example shown in FIG. 4, the metal film button 51 on the insulator must be brought closer to the semiconductor laser chip 2. - On the other hand, in order to efficiently transfer the heat from the semiconductor laser chip to the metal blocks, the heat sink itself needs to be larger than the semiconductor laser chip to some extent (for example, the fusion surface of the semiconductor laser chip is
．． In the case of 3mm square, it is about 0.6mm square).

In addition, since wire bonding cannot be performed in the area 13 where the solder that fuses the semiconductor laser chip has spread, there is a limit to how much the length of one of the bonding wires 32 can be shortened, and the total wire length exceeds 1 mm. .

To improve this, consider a configuration in which the metal block is abolished and the heat sink itself is mounted directly on the board. FIG. 3 is a perspective view showing one example. The p-side pole 21 of the semiconductor laser chip is coupled by a bonding wire 31 to a metal thin film 12 separated by a groove 15 from a portion electrically connected to the n-type electrode of the semiconductor laser chip. Bonding from heat sink to board 31
．． As for 32, there is no need to worry about stress unlike in the case of a semiconductor laser chip, so a ribbon lead with sufficiently low reactance can be used. When bonding from a semiconductor laser chip to a heat sink, due to the level difference between the two, in general NTC bonding, the wire length must be kept at 0.5 mm or less due to the size and shape of the capillary, the elasticity of the wire, the level difference on the bonding surface, etc. On the contrary, if you bond the semiconductor laser chip from the heat sink, you can shorten the wire length slightly, but the electrode 21 of the semiconductor laser chip is several Gb.
In order to operate in a region of ps or more, pad electrodes are used, and it is difficult to provide sufficient strength against bonding wire post-implantation.

[Means to solve the problem]

A heat sink for fusing a semiconductor laser chip according to the present invention is characterized in that a surface of the heat sink that is bonded to an electrode of the semiconductor laser chip by wire bonding protrudes from a surface for fusing the semiconductor laser chip. do.

[Example 1] Next, an example of the present invention will be described. FIG. 1 is a perspective view of a semiconductor laser mounted on a heat sink, which is an embodiment of the present invention. The semiconductor laser chip 2 is fused to the beat sink 1, and the p-type electrode 21 of the semiconductor laser chip is connected to the metal thin 11112 and bonding wire 3 formed on the surface of the portion protruding from the surface to which the semiconductor laser chip is fused.
They are connected by 1. There is no step difference between the p-type electrode surface 21 of the semiconductor laser chip and the surface 12 connected thereto by the bonding wire 31, so that the length of the bonding wire can be reduced to 0.3 mm or less.

[Embodiment 2] FIG. 2 is a perspective view of a semiconductor laser mounted on a heat sink, which is another embodiment of the present invention. Thin metal M11 on the heat sink connected to the n-side electrode of the semiconductor laser chip, and pat pole 21 of the semiconductor laser chip
The metal thin film 12 formed on the surface of the portion protruding from the surface 13 to which the semiconductor laser chip is fused and bonded by the bonding wire 31 is connected to the heat sink side surface 111, respectively.
112 to the bottom surface, each connected to strip lines 41 and 42 on the board. In this example, the length of the bonding wire connecting the semiconductor laser chip and the heat sink is shortened, and wire/lead bonding between the heat sink and the board is no longer required.
This embodiment has the advantage that it is possible to realize an even smaller reactance than the first embodiment.

〔Effect of the invention〕

By eliminating the level difference between the surfaces connected by the bonding wire of the semiconductor laser chip and the heat sink, a semiconductor laser mounting configuration with a bonding wire length of 0.3 mm has been realized, and the device can be driven satisfactorily in a region exceeding 5 Gbps. did it.

[Brief explanation of drawings]

1 and 2 are perspective views of a semiconductor laser mounted on a heat sink according to an embodiment of the present invention, and FIGS. 3 and 4 are perspective views of a semiconductor laser mounted on a conventional heat sink.

Claims (1)

[Claims] In the heat sink that fuses the semiconductor laser chip,
A heat sink for a semiconductor laser chip, wherein a surface of the heat sink that is bonded to an electrode of the semiconductor laser chip by wire bonding protrudes from a surface that fuses the semiconductor laser chip.