JPH03106089A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To elongate a semiconductor laser element in service life even if it is assembled in an UPSIDE-DOWN mode by a method wherein Ag containing epoxy resin conductive paste of specific thickness is used as a bonding material. CONSTITUTION:A sub-mount 11 is provided onto a heat sink 10 of a Cu stem, and a metal layer 12 is formed on the sub-mount 11, and a conductive paste layer 13 of Ag containing epoxy resin is applied as thick as prescribed onto the whole face or the required part of the metal layer 12 through a method such as a screen printing or a stamping method. That is, an Ag containing epoxy resin conductive paste layer having a thickness of 0.5-3mum is used as a bonding material for bonding a semiconductor laser element 1 to the heat sink 10 provided with the sub-mount 11 in an UP-SIDE-DOWN mode. Therefore, if the thickness of the conductive paste is set in a range of 0.5-3mum, the semiconductor laser element 1 is free of the influence of inner stress caused by the conductive paste when it is in operation after bonded. By this setup, the semiconductor laser element has a life span equivalent to that when it is bonded with solder, a net time required for bonding is 1/6 of that of solder bonding, and optical shielding caused by the squeeze-out of resin hardly occurs, so that a semiconductor laser element can be efficiently assembled high in yield.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses a heat sink having a submount to
Regarding a semiconductor laser device mounted on an lP-SIDE-DOWN. [Prior Art] In order to cause a semiconductor laser device to oscillate continuously for a long period of time at room temperature, it is necessary to efficiently dissipate the heat generated in the active layer of the device and lower the operating temperature. An UP-SIDE-DOWN assembly method was adopted in which the main surface side closest to the main surface is joined to a heat sink (heat dissipation body), thereby dissipating heat from the active layer. At this time, a semiconductor laser element whose substrate is made of GaAs or the like and C
Since heat sinks such as U heat sinks have significantly different thermal expansion coefficients, when they are directly soldered together, strong stress is applied to the active layer during the solidification process after melting the solder, creating a transition network called a dark line, which causes the oscillation threshold current to increase. increases and eventually oscillation becomes impossible. Therefore, as a countermeasure to this problem, it is necessary to bond the semiconductor laser element to the heat sink using a soft solder such as In, or to interpose a submount such as Sin Mo, which has a small difference in thermal expansion coefficient from the GaAs substrate, and then mount a submount such as AuSn alloy on top of it. One of the methods used is to apply a few micrometers of hard solder layer and melt it to bond the semiconductor laser element to the heat sink. [Problems to be Solved by the Invention] When assembling a semiconductor laser device as described above, in such a light emitting device, it is necessary to accurately position the light emitting point with respect to the reference plane of the stem that serves as a heat sink. It is necessary to determine extremely high positional accuracy. Therefore, when performing solder bonding as described above, even after placing the semiconductor laser chip in the optimal position on the solder layer,
The tip must be pressurized and fixed to prevent the chip from shifting due to melted solder and flowing. Therefore, when bonding the chip of a semiconductor laser element, the chip is positioned with high precision and placed on the solder surface of the stem, and then the chimney is fixed to the stem under pressure from above, and the solder is heated and melted. A series of processes are required, including cooling and solidifying after bonding, and the time required to bond one chip is 10 seconds for positioning and 50 seconds for soldering, so it takes a total of 60 seconds. In this way, most of the time required for bonding a semiconductor laser chip is soldering time, which leads to poor assembly efficiency and problems with mass production. Therefore, it is desirable to shorten this time from the point of view of cost reduction. Another problem is that because solder is used, there is a high possibility that the solder will swell during bonding and block the active region, thus interfering with laser emission. On the other hand, in UP-SIDE-DOWII assembled elements such as light emitting diodes, ICs, and photodiodes, which are bonded to the heat sink on the active layer side rather than on the substrate side, a conductive paste such as epoxy resin containing Ag is used. High-speed bonding with a bonding time of 1 to 2 seconds is possible, but active fiI is not suitable for semiconductor laser devices.
Since the area is located far from the heat sink, it is not desirable in terms of heat dissipation effect. However, until now, UP
When a semiconductor laser chip was bonded to a heat sink using the -SIDE-DOWli method, the life of the semiconductor laser chip could not be expected, even though a submount was used. This is because the coefficient of thermal expansion of the resin component after the paste has hardened is significantly larger than that of the chip compared to the case of solder, and even if a slight temperature change occurs during operation of the semiconductor laser element, a large stress will be generated due to the difference in these coefficients of thermal expansion. It seems to work. The present invention has been made in view of the above points, and its purpose is to perform UP-SI[l! ! -An object of the present invention is to provide a semiconductor laser device that can maintain a long life even when assembled using the DOInN method. [Means for Solving the Problems] In order to solve the above problems, the present invention provides a method for mounting a semiconductor laser element on a heat sink having a submount.
! -0.5 to 3 as a material for bonding to DOWN
It uses conductive paste of Ag-containing epoxy resin with a thickness of n. [Function] Because the present invention is constructed as described above, the semiconductor laser element after bonding is not affected by internal stress during operation due to the conductive paste at a thickness within this range, and is equivalent to the conventional one. Moreover, since the conductive paste is used, the time required for bonding can be reduced to 176 times compared to the case of using conventional solder. [Example] The present invention will be implemented below. Let's explain based on an example. FIG. 1 is a schematic sectional view showing the main structure of a semiconductor laser device after assembly according to the present invention. In FIG. 1, the chip of the semiconductor laser device includes a semiconductor crystal substrate 2, an active region 114 having an active region 3 shaped by crystal or elongation on this substrate 2, and each necessary crystal elongation layer. First clad layer 5, second clad layer 6. It consists of a contact layer 7 and two electrode metals 8 and 9 formed by vapor deposition or plating. A submount 11 of Sl is bonded to the heat sink IO of a Cu stem for dissipating heat from the top of the chimp using solder or conductive paste, and a metal lwl2 of TtNi-Au is formed on the submount 11 by vapor deposition or the like. There is. In the present invention, a conductive paste layer 13 of epoxy I4 resin containing Ag having a predetermined thickness is applied to the surface of this metal layer 12, and the chip top and submount 11 are bonded together. Next, we will describe the procedure for obtaining such a joint structure. First, a submount 11 is formed on the heat sink 10 of the Cu stem, a metal layer 12 is formed on this submount 1l, and the metal FI 1 is formed.
An Ag-containing epoxy resin conductive paste layer 13 is applied to the entire surface or necessary portions of 2 to a predetermined thickness using a method such as screen printing or stamping. Thereafter, the chip is positioned UP-SIDE-DOWN, placed in a predetermined position so as to overlap the conductive paste layer 13 coated on the metal layer 12, and the whole is pressurized. At this time,
It is preferable to place the heat sink 10 on a heat plate (not shown) so that the submount 11 is heated to about 100°C. Then, the entire body is heated for 20 minutes using a tunnel furnace or constant temperature bath.
0℃, 40 seconds tree! Perform n conversion. Conductive paste layer 13
During curing, there is almost no change in the paste volume, so there is no need to apply pressure, and the accuracy of the light emitting point can be maintained when positioning on the chip. Regarding the net time required for die bonding, the resin curing time can be ignored since many pieces are processed at the same time, and the time required for positioning the typhoon soil is
It only takes seconds. 1/1/2 of the time traditionally required for this process
6 would be fine. Next, the thickness of the ag-containing epoxy resin conductive paste layer 13 was set to 0.1 μm. 0.5 Jlll 1 its. 2
n+ 3 items 4-15n, lQ4, 10 pieces of each thickness were fabricated using the above procedure to fabricate a semiconductor laser device having the structure shown in FIG. 1 with the chip top bonded to the submount 11, and the bonding In addition to examining the intensity, AgP. C. (
A lifespan test was conducted on the Automatic Power Control (Automatic Power Control) operation, and the results are shown in Table 1. 1st
The paste thickness in the table is the average value of each 10 pieces. Element life is expressed as mean failure time. For comparison, a conventional bonding structure using AuSn alloy solder is also shown.

From Table 1 Table 1 Conductive paste layer 1 of Ag-containing epoxy resin
It can be seen that the same results as the conventional method using AuSn solder can be obtained when the thickness of No. 3 is between 0.5 and 3 μm. The thickness of the conductive paste layer 13 is 0. When In is the thinnest, sufficient bonding strength cannot be obtained, and as the thickness becomes thicker than 3n, the lifetime of the semiconductor laser device decreases rapidly. The reason for this is that when the conductive paste layer 13 is thin, the internal stress generated by thermal expansion with respect to the laser chip due to temperature rise can be ignored, but as the thickness increases, the internal stress becomes more noticeable. This is because it directly acts on the active layer 4 on the laser beam. Therefore, the conductive paste layer 13 of Ag-containing epoxy resin used in the present invention
The optimal thickness is 0.5 to 3 nm. As described above, the present invention uses a thin conductive paste instead of solder to improve bonding efficiency, eliminate the disadvantages caused by solder, and provide semiconductor laser elements with the same life characteristics as conventional ones. ．． [Effects of the Invention] Conventionally, solder was used as the material for mounting the semiconductor laser element on the heat sink, which caused various problems such as poor bonding efficiency and solder protrusion. As shown above, instead of solder, the thickness is 0.5 ~
Because it uses a conductive paste of 3n Ag-containing epoxy resin, it has the same life characteristics as solder joints, and the net time required for joining is only 176 cm.
Since there is no light blocking due to resin protruding, it is possible to assemble with high yield and high efficiency.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view showing the main parts of the semiconductor laser device of the present invention, which has a structure mounted on a heat sink.

Claims (1)

[Claims] 1) A semiconductor laser device in which the electrode surface on the side closer to the active layer is bonded UP-SIDE-DOWN to a heat sink having a submount, and the bonding material is 0.5 to
A semiconductor laser device characterized by using a conductive paste of Ag-containing epoxy resin having a thickness of 3 μm.