Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Including adhesive bonding step
Reexamination Certificate
2002-11-15
2004-01-13
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Including adhesive bonding step
C438S026000, C438S119000, C438S121000, C438S125000
Reexamination Certificate
active
06677184
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to semiconductor laser apparatuses and a method of producing them and more particularly, to a semiconductor laser apparatus having a semiconductor laser chip die-bonded to a bonding surface with a conductive die-bonding paste and a method of producing it.
As disclosed in Japanese Patent Application Laid-Open No. 6-37403, in conventional semiconductor laser apparatuses, a semiconductor laser chip is die-bonded to a predetermined position of a bonding surface, such as of a lead frame, a stem, or a sub-mount disposed on the stem, through a metal soldering material such as In, Pb/Sn (solder), Au/Sn or the like.
FIG. 5
shows a first conventional semiconductor laser apparatus in a state that a semiconductor laser chip
50
is bonded in a predetermined position of a die-bonding surface
51
a
of a sub-mount
51
with a metal soldering material
52
. The metal soldering material
52
is a solid at the room temperature, and is deposited to the bonding surface in the predetermined bonding position by evaporation or the like. After the semiconductor laser chip
50
is placed on the metal soldering material
52
, the metal soldering material
52
is heated to 150° C. or higher to melt. At this time, the semiconductor laser chip
50
is immobilized with a bonding collet or the like (not shown) Finally, the metal soldering material
52
is cooled to harden or set. Thus, the semiconductor laser chip
50
is die-bonded to the predetermined position of the die-bonding surface
51
a
. In
FIG. 5
, reference numeral
53
denotes a main-discharge-side light-emitting point of the semiconductor laser chip
50
, reference numeral
54
denotes a monitoring sub-discharge-side light-emitting point of the semiconductor laser chip
50
, and reference numeral
55
denotes an emission light axis of the semiconductor laser chip
50
connecting the main-discharge-side light-emitting point and the sub-discharge-side light-emitting point to each other.
In the method of producing the first conventional semiconductor laser apparatus shown in
FIG. 5
, the melting point of the metal soldering material
52
is high. Thus, the heating/cooling cycle takes much time and thus it takes long to produce the semiconductor laser apparatus. Further, the hardened metal soldering material
52
is thinner than 0.01 mm. Thus, if this semiconductor laser apparatus is adopted for an optical pick-up using a three-beam scheme which is a dominant tracking control method, the following problem occurs. Of the three beams which have returned from an optical disk, one auxiliary beam is regularly reflected off a discharge surface of the semiconductor laser chip
50
back to the optical disk, and is then incident on a signal detection photodiode to generate noise.
As a measure of overcoming the problem that it takes long to make the semiconductor laser apparatus, there is proposed a method (hereinafter referred to as second conventional art) of making a semiconductor laser apparatus. In the method, the semiconductor laser chip is die-bonded to a bonding surface with a conductive die-bonding paste (conductive adhesive agent) instead of the metal soldering material. The conductive die-bonding paste contains resin and a conductive filler such as silver flakes. It is possible to lower the hardening temperature of the conductive die-bonding paste to about 100° C., depending on the resin of the paste. Accordingly, the heating/cooling cycle becomes short. Thus it is possible to reduce the time required to produce the semiconductor laser apparatus.
FIG. 6
shows a semiconductor laser apparatus formed by die-bonding a semiconductor laser chip to a die-bonding surface with a conductive die-bonding paste. In
FIG. 6
, parts similar to or same as the parts shown in
FIG. 5
are denoted by the same reference numerals as in FIG.
5
. Reference numeral
56
denotes a conductive die-bonding paste.
In the method of producing the semiconductor laser apparatus according to the second conventional art, when the proportion of the conductive filler is increased to reduce the electric resistance of the conductive die-bonding paste
56
, the viscosity of the conductive die-bonding paste
56
becomes high. Consequently, when a semiconductor laser chip
50
is placed on the conductive die-bonding paste
56
, the conductive die-bonding paste
56
swells and adheres to the end surfaces and side surfaces of the semiconductor laser chip
50
, and blocks a main-discharge-side light-emitting point
53
and/or a monitoring sub-light-emitting point
54
. This will be concretely described below with reference to
FIGS. 7A and 7B
.
Referring to
FIG. 7A
, a predetermined slight amount of the conductive die-bonding paste
56
, which has been discharged from a dispenser (not shown), is on a tip of a syringe needle
57
. With a downward movement of the tip of the syringe needle
57
in a descending direction
58
A, the conductive die-bonding paste
56
is placed in a predetermined position of a die-bonding surface
51
a
of a sub-mount
51
. Then, with the tip of the syringe needle
57
moved in an ascending direction
58
B as shown in
FIG. 7B
, the conductive die-bonding paste
56
is applied to a predetermined part of the die-bonding surface
51
a
of the sub-mount
51
.
Then, as shown in
FIG. 6
, the semiconductor laser chip
50
is placed on the conductive die-bonding paste
56
applied to the die-bonding surface
51
a
of the sub-mount
51
. The size of the lower surface of the semiconductor laser chip
50
is about 0.2 mm×0.2 mm, and the light-emitting point is located at about 0.05 mm from the lower surface of the semiconductor laser chip
50
. That is, the light-emitting point is at a level higher than the semiconductor laser chip mounting surface
51
a
by about 0.05 mm. On the other hand, from the viewpoint of reliably applying the conductive die-bonding paste
56
to the die-bonding surface
51
a
, it is impossible to make the diameter of the tip of the syringe needle
57
smaller than about 0.3 mm. Consequently, the application area of the conductive die-bonding paste
56
is wider than the size (area of the lower surface) of the semiconductor laser chip
50
, and the thickness of the conductive die-bonding paste
56
frequently exceeds 0.05 mm. Accordingly, as shown in
FIG. 6
, the conductive die-bonding paste
56
swells along the end surfaces and side surfaces of the semiconductor laser chip
50
mounted thereon. The end surfaces have the main discharge-side light-emitting point
53
and the monitoring light-emitting point
54
, respectively. Thus, if the conductive die-bonding paste
56
is heated and cooled to harden in the above state, it follows that the conductive die-bonding paste
56
blocks the main-discharge-side light-emitting point
53
and the monitoring light-emitting point
54
.
SUMMARY OF THE INVENTION
The present invention has been made to solve the problems. Therefore, it is an object of the present invention to provide a semiconductor laser apparatus which hardly generates noise even when it is used for a pick-up using a three-beam scheme.
It is another object of the present invention to provide a method of producing a semiconductor laser apparatus which method prevents a conductive die-bonding paste, if used, from blocking a main discharge-side light-emitting point and a monitoring light-emitting point of a semiconductor chip as mounted.
According to an aspect of the invention, there is provided a semiconductor laser apparatus having a semiconductor laser chip bonded to a bonding surface with a conductive die-bonding paste, the semiconductor laser chip having a light-emitting point at each of opposed end surfaces thereof,
wherein a highest position at which the conductive die-bonding paste adheres to the end surfaces of the semiconductor laser chip is at a height of more than 0.01 mm from the bonding surface, but is below the light-emitting point of the semiconductor laser chip.
The semiconductor laser apparatus with the above arrangement does not cause noise even i
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