Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-11-30
2004-03-02
Lee, Eddie (Department: 2815)
Coherent light generators
Particular active media
Semiconductor
C372S043010
Reexamination Certificate
active
06700911
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to semiconductor laser devices, and in particular, to a semiconductor laser chip mounting structure and fabricating method and an optical pickup employing the device.
Prior art semiconductor laser devices are shown in FIG.
6
through
FIG. 9
, and the die bonding process of one prior art semiconductor laser device fabricating method is shown in
FIGS. 10A and 10B
.
In the prior art semiconductor laser device of
FIG. 6
, a semiconductor laser chip
50
is placed in a specified position of a header portion
51
a
located at an end of a stem
51
via a metal brazing material (solder or the like)
52
. The semiconductor laser chip
50
is bonded by the metal brazing material
52
in the place where the chip is to be die-bonded. Therefore, in the bonding stage, the semiconductor laser chip
50
is required to be fixed by a bonding collet (not shown) or the like so that the chip does not move. In
FIG. 6
, an emission light optical axis
55
of the semiconductor laser device is an axis that connects a main radiation side light emission point
53
with a monitor side light emission point
54
.
There are the preceding references of, for example, Japanese Patent Laid-Open Publication No. SHO 63-138794 and Japanese Patent Laid-Open Publication No. HEI 5-291696, each of which employs a metal brazing material (gold-tin alloy solder or the like) and pays attention to the size of the semiconductor laser chip and the size of a protruding portion (or a header portion) of a mount. These devices are now described with reference to FIG.
7
and FIG.
8
.
Referring to
FIG. 7
, a prior art semiconductor laser device
60
is obtained by forming a mount
63
by mesa-etching silicon, die bonding a semiconductor laser element
61
whose active layer
62
faces the mount side to a protruding portion of the mount
63
by means of a gold-tin alloy solder
64
and bonding a gold wire
66
to a semiconductor laser element
61
. A heat radiating plate
65
is provided underneath the mount
63
.
As shown in
FIG. 7
, the semiconductor laser element
61
and the mount
63
are not put in contact with each other in the peripheral portion of the semiconductor laser element
61
. Therefore, the gold-tin alloy solder
64
that oozes out of the upper surface of the protruding portion of the mount
63
in the die bonding stage of the semiconductor laser element
61
stays around the protruding portion of the mount
63
and does not rise on the side surfaces of the semiconductor laser element
61
.
FIG. 8
shows a sectional view of another prior art semiconductor laser device
70
. The semiconductor laser device
70
is provided with a laser chip
71
and a heat sink
72
. The heat sink
72
is provided with a protruding portion
80
that has a trapezoidal cross-section shape, and the upper surface of the protruding portion
80
is slightly smaller than the lower surface of the laser chip
71
and has a flat mounting surface
72
a
. The laser chip
71
is mounted on the upper surface of the protruding portion
80
, i.e., the mounting surface
72
a
via a brazing material
73
.
Fabrication of this semiconductor laser device
70
includes the steps of coating a low-melting-point brazing material (Indium (In), for example)
73
on the upper surface of the protruding portion
80
, performing melting with heat (temperature of 300° C.) and cooling and mounting the laser chip
71
on the protruding portion
80
.
As described above, the laser chip
71
is directly die-bonded (direct bonding system) to the protruding portion
80
of the heat sink
72
by means of the brazing material
73
with interposition of no sub-mount. Therefore, the semiconductor laser device can be fabricated at low cost. The brazing material
73
pushed out of the mounting surface
72
a
of the heat sink
72
by the laser chip
71
creeps on the surfaces of the protruding portion
80
when melted with heat and does not rise on the side surfaces of the laser chip
71
. Therefore, even when a cap layer
75
is made thin to put a light-emitting section
74
close to the heat sink
72
, a laser beam L can be prevented from being diffusively reflected or partially hampered by the brazing material
73
, and the radiation characteristic can be improved.
In recent years, there is a demand for improving the productivity of the semiconductor laser device fabricating method through value engineering (VE) or the like by an increase in mounting efficiency, a reduction in the number of processes and mechanization. From this standpoint, the conventional semiconductor laser devices have had the problems that much time is necessary for the heating and cooling cycles of the metal brazing material (gold-tin alloy solder or a low-melting-point brazing material In) and that the material cost of the metal brazing material is high.
As a measure for improvement, there is the semiconductor laser device shown in FIG.
9
. In
FIG. 9
are shown a semiconductor laser chip
50
, a stem
51
, a header portion
51
a
of the stem, a main radiation side light emission point
53
, a monitor side light emission point
54
and a semiconductor laser device emission light optical axis
55
that connects the main radiation side light emission point with the monitor side light emission point. In the semiconductor laser device shown in
FIG. 9
, the semiconductor laser chip
50
is die-bonded by means of a conductive die bonding paste
56
employed in place of the metal brazing material
52
. If the conductive die bonding paste
56
is employed, then the material cost is inexpensive, and the heating and curing of the paste can be performed after the die bonding. Therefore, if the die bonding paste
56
is employed, then there is no need for heating and cooling the semiconductor laser device in the bonding place or by means of a bonding apparatus. This enables the reduction in time of the die bonding process and the reduction in the occupation time of the bonding place (or the bonding apparatus). The die-bonded semiconductor laser device is moved to another place and subjected to the heating and cooling processes.
FIGS. 10A and 10B
show the die bonding process of the aforementioned prior art semiconductor laser device fabricating method. In
FIG. 10A
, a specified trace quantity of conductive die bonding paste
56
is ejected from a needle tip
57
of a syringe needle of a dispenser, and the needle tip
57
of the syringe needle is moved in a downward direction
58
A. The conductive die bonding paste
56
is coated in a specified position of the header portion
51
a
of the stem
51
by the descent of the syringe needle, and thereafter, the needle tip
57
of the syringe needle is moved in an upward direction
58
B to put the syringe needle apart as shown in FIG.
10
B. Subsequently, the semiconductor laser chip
50
is placed on the coated conductive die bonding paste
56
.
The semiconductor laser chip
50
has a size of about 0.2 mm square, and the light emission point is located at a height of about 0.05 mm from the lower surface of the semiconductor laser chip
50
. On the other hand, the needle tip
57
of the syringe needle has a diameter of about 0.3 mm. The needle tip
57
of the syringe needle should preferably be small. However, in order to reliably coat a specified quantity of conductive die bonding paste
56
, the needle tip size cannot be set smaller than a diameter of about 0.3 mm.
Therefore, due to the fact that the syringe needle tip
57
has the size of a diameter of about 0.3 mm and the fact that the semiconductor laser chip
50
has the size of about 0.2 mm square, the conductive die bonding paste
56
is coated in an area broader than that of the semiconductor laser chip
50
.
However, in the aforementioned prior art semiconductor laser device, the conductive die bonding paste
56
discharged from the lower surface of the semiconductor laser chip
50
has a thickness of up to about 0.05 mm in relation to the viscosity of the conductive die bonding paste. On the other hand, the light emission point of the semic
Hamaoka Osamu
Horiguchi Takeshi
Kohashi Ikuo
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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