Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With housing or contact structure
Reexamination Certificate
2003-03-26
2004-08-31
Lebentritt, Michael (Department: 2824)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With housing or contact structure
C257S079000, C257S082000, C257S693000, C257S694000
Reexamination Certificate
active
06784464
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device including two semiconductor laser elements and a wire bonding method for the device.
Conventionally, there has been a semiconductor laser device in which one semiconductor laser element and a monitoring use photodiode (hereinafter referred to as a monitoring PD) for monitoring an output of the semiconductor laser element are arranged on a metallic stem. However, in order to read information from a recorded medium such as a CD (compact disc) and a DVD (digital versatile disk), there is needed a semiconductor laser device that emits two kinds of laser light of different wave lengths by means of two semiconductor laser elements.
Accordingly, there can be considered a semiconductor laser device as shown in
FIG. 12
where two semiconductor laser elements and a monitoring PD for monitoring the output of the semiconductor laser element are arranged.
FIG. 12
shows a perspective view of the inside of this semiconductor laser device with its cap removed. It is to be noted that this semiconductor laser device is shown for facilitating the explanation of this invention and is not the prior art.
As shown in
FIG. 12
, this semiconductor laser device includes a metallic stem
200
having an eyelet
201
and a heat radiation base
202
which are integrally formed. Lead pins
221
through
223
are mounted on the eyelet
201
of the stem
200
so that one end penetrates the eyelet
201
of the stem
200
, and one end of a lead pin
224
is electrically connected as a common electrode to the eyelet
201
. The lead pins
221
through
223
are fixed to the eyelet
201
with a low melting point glass and electrically insulated with respect to the stem
200
. The eyelet
201
has an outer diameter of 5.6 mm, and the lead pins
221
through
224
constructed of a columnar metal having a diameter of 0.4 mm are arranged at regular intervals of 90 degrees in a circle of a diameter of 2 mm.
A silicon sub-mount (hereinafter referred to as an Si sub-mount)
260
is die-bonded to the heat radiation base
202
formed integrally with the eyelet
201
with a conductive paste (not shown). Two semiconductor laser elements
231
and
232
are die-bonded onto the silicon sub-mount
260
with a brazing material (not shown) made of an Au—Sn alloy. The die bonding surface of the Si sub-mount
260
is covered with a metal, providing a common electrode of the semiconductor laser elements
231
and
232
. The common electrode on the surface of the Si sub-mount
260
is connected to the heat radiation base
202
via metal wires
252
and
254
, respectively. On the other hand, upper electrodes of the semiconductor laser elements
231
and
232
are connected to the lead pins
221
and
222
via metal wires
251
and
253
, respectively. A monitoring PD
240
is die-bonded to a recess
201
b
formed on the eyelet
201
of the stem
200
with a conductive paste (not shown), and an upper electrode of the monitoring PD
240
is connected to an end surface
223
a
of the lead pin
223
via a metal wire
255
.
The two semiconductor laser elements
231
and
232
are provided particularly by a combination of an InGaAlP based semiconductor laser element
231
that emits red laser light (having a wavelength of 630 nm to 680 nm) and an AlGaAs based semiconductor laser element
232
that emits infrared laser light (having a wavelength of 760 nm to 850 nm).
It is required to die-bond the semiconductor laser elements
231
and
232
onto the Si sub-mount
260
by using a brazing material (Au—Sn alloy, for example) whose melting point is sufficiently higher than a temperature of 80° C., which is the upper limit of the normal use temperature range so as not to move the relative positions of the light emitting points of the two semiconductor laser elements
231
and
232
in operation. If the semiconductor laser elements
231
and
232
are die-bonded directly to the metallic heat radiation base
202
, then there is the problem that an intense stress is applied to the semiconductor laser elements
231
and
232
due to a difference in the linear expansion coefficient of the metal and the semiconductor, consequently destroying and deteriorating the crystal. Therefore, it is indispensable to perform the die bonding to the Si sub-mount
260
.
The semiconductor laser device having two semiconductor laser elements shown in
FIG. 12
has the problem of complicated structure, and the processes of die-bonding the monitoring PD
240
and the Si sub-mount
260
increase cost.
Accordingly, it can be considered to simplify the fabricating processes by forming a monitoring PD on the surface of the Si sub-mount and eliminating the die bonding process of the monitoring PD. If the above-mentioned structure is adopted, then the electrode surface of the monitoring PD becomes parallel to the electrode surfaces of the two semiconductor laser elements and the electrode surface formed on the surface of the Si sub-mount. The wire bonding cannot easily be performed unless the surfaces of the electrodes of the semiconductor laser elements and the monitoring PD and the surfaces of the lead pins to which metal wires are to be bonded are parallel to one another when connecting the electrodes of these semiconductor laser elements and the monitoring PD with the lead pins by way of metal wires. This will be described below on the basis of the semiconductor laser device of the construction shown in
FIG. 12
(monitoring PD is assumed to be formed on the surface of the Si sub-mount).
In this semiconductor laser device, the two semiconductor laser elements
231
and
232
are connected to the lead pins
221
and
222
, respectively, located on both sides. Accordingly, there is only the lead pin
223
that is located on the upper side in FIG.
12
and is able to be connected to the electrode of the monitoring PD formed on the surface of the Si sub-mount. In this case, there is the problem that almost no surface parallel to the electrode of the monitoring PD to be formed on the Si sub-mount
260
exists since the tip of the lead pin
223
is not protruding from a surface
201
a of the eyelet
201
. As a method for solving this problem, it can also be considered to provide a recess around the lead pin
223
on the eyelet
201
to expose the lead pin
223
and perform die-bonding to the outer peripheral surface of the cylindrical lead pin
223
. However, such a recess may penetrate the eyelet
201
to disable the sealing of the inside with a cap (not shown), which would cause a problem that the semiconductor laser elements easily deteriorate.
When wire-bonding the end surface
223
a
of the lead pin
223
to the electrode of the monitoring PD formed on the Si sub-mount
260
, the end surface
223
a
of the lead pin
223
and the electrode surface of the monitoring PD are perpendicular to each other, and therefore, it has been difficult to connect the surfaces together by the conventional wire bonding method. The reason for the above will be described below with reference to FIG.
13
through
FIG. 19
, which show the wire bonding processes of the semiconductor laser device of FIG.
12
.
First of all, the wire bonding method for connecting the electrode surface of the monitoring PD
240
of the semiconductor laser device
200
shown in
FIG. 12
with the end surface
223
a
of the lead pin
223
by way of a metal wire will be described with reference to FIG.
13
through FIG.
18
.
As shown in
FIG. 13
, a bonding head
70
has a capillary
71
attached to the tip of a capillary holder
72
and a wire clamp
73
, and the capillary
71
and the wire clamp
73
move in such a manner as an integrated body. The capillary
71
has a tip diameter of about 200 &mgr;m and operates to guide a metal wire
50
kept linear. A gold wire having a diameter of 25 &mgr;m is used as this metal wire
50
, and a ball
50
a
is formed by arc discharge or the like at the tip of the metal wire
50
that protrudes from the tip of the capillary
71
.
Next, the bonding head
70
is moved down as shown in
Ichikawa Hideki
Okanishi Mamoru
Santo Terumitsu
Yoshida Toshihiko
Lebentritt Michael
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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