Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With provision for cooling the housing or its contents
Reexamination Certificate
2001-05-03
2002-12-03
Elms, Richard (Department: 2824)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With provision for cooling the housing or its contents
C257S621000, C257S680000, C257S433000, C257S448000, C257S708000, C257S698000
Reexamination Certificate
active
06489677
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an optical semiconductor device package, and more particularly, to an optical semiconductor device package which permits a cooling device for cooling an optical semiconductor device to be appropriately solder-joined thereto and an optical semiconductor device module having a package of this kind.
2. Related Art
In an optical communication system, optical semiconductor device modules are employed, which comprise a package and an optical semiconductor device accommodated therein for receiving and/or transmitting an optical signal. Although the optical semiconductor device constituting such a module is requested to produce a high power, it generates heat and is raised in temperature when operated at a high power level, so that its operation may become unstable. A similar problem can occur if the optical semiconductor device module is employed under high temperature circumstances. Thus, the optical semiconductor device module is generally provided with a cooling device for cooling the optical semiconductor device, thereby stabilizing the operation of the optical semiconductor device.
As this kind of optical semiconductor device module, a transmitter module shown in
FIG. 1
is known. This transmitter module comprises, as shown in
FIGS. 1 and 2
, an optical semiconductor device package comprised of a metal bottom plate
1
and a metal frame
2
joined to an upper periphery of the bottom plate. The metal bottom plate
1
is ordinarily made of a Cu-W alloy and has a surface thereof plated with Au. The metal bottom plate
1
forms a package housing in conjunction with the metal frame
2
and a seal ring
3
joined to an upper face of the metal frame. The package housing accommodates therein module components such as an optical semiconductor device and a cooling device. The metal frame
2
has a right wall to which a hollow cylindrical window frame
5
is joined, and an optical fiber
20
is drawn out to the outside through a glass or sapphire window joined to the window frame
5
.
In the illustrated optical semiconductor device module, a Peltier device
10
serving as the cooling device is solder-joined to an upper face of the metal bottom plate
1
in a state it is disposed in a recess
1
a
formed on that face, and a base which is excellent in heat and electric conductivity is solder-joined to the upper face or cooling face
10
a
of the Peltier device
10
. Furthermore, module components such as laser diode carrier
12
, photodiode carrier
13
, first lens
14
, optical isolator
15
are solder-joined to the base
11
, with these elements aligned with one another. Then, a laser diode (LD)
16
and a thermistor (not shown) for monitoring the temperature of the LD are solder-joined to the LD carrier
12
, and a photodiode (PD)
17
for monitoring an LD light signal is solder-joined to the PD carrier
13
. A second lens
19
is disposed inside the window frame
9
. Leads
18
are supported by electrical signal input/output sections
7
of a ceramic material which are joined to notches formed in front and rear walls of the metal frame
2
, respectively.
After the module components are received in the package housing, lead terminals of the LD
16
and respective one ends of the leads
18
are electrically connected to each other by means of wires, not shown, to thereby make it possible to transfer electric signals between the LD
16
and external devices through the leads
18
.
Finally, a metal lid
4
is seal-welded to the metal frame
2
through the seal ring
3
, whereby the fabrication of the optical semiconductor device module is completed. The metal lid
4
may be directly seal-welded to the metal frame
2
without using the seal ring
3
.
The Peltier device
10
comprises, for instance, two insulating layers and P-type and N-type thermoelectric conversion devices that are alternatively arranged between the insulating layers and electrically connected in series with one another. The two insulating layers have functions of generating and absorbing heat at their surfaces, respectively, when a DC voltage is applied to the thermoelectric conversion devices. Outputs from the thermistor and the PD are employed for temperature control and constant optical-output control in the optical semiconductor device module, respectively.
With the optical semiconductor device module having the above construction, heat generated by the LD
16
is transferred to the cooling face
10
a
of the Peltier device
10
through the LD carrier
12
and the base
11
and then dissipated to the outside through the heat generating face
10
b
of the Peltier device
10
and the metal bottom plate
1
serving as a heat sink, if the Peltier device
10
is appropriately solder-welded to the metal bottom plate
1
, thereby preventing the LD
16
from becoming excessively high in temperature. However, an improper soldered joint may be formed between the metal bottom plate
1
and the Peltier device
10
for the following reasons.
In conventional solder joining processes, the cooling device such as a Peltier device
10
is placed on a solder foil of 20 to 50 &mgr;m thick disposed on the metal bottom plate
1
, and then the solder foil is heated to melt while pressing the Peltier device
10
by means of a weight, not shown, placed thereon. As the solder foil is heated and raised in temperature, the plated Au on the surface of the metal bottom plate
1
diffuses into the solder foil, so that the melting point of the Au diffusion part of the solder foil becomes high. The high melting point part cannot melt during the process of solder-joining the metal bottom plate
1
and the Peltier device
10
, and hinders the spread and wetting of molten solder between the opposite faces of the metal bottom plate
1
and the Peltier device
10
to thereby form air spaces or voids therebetween. As a result, unmelted parts of the solder foil and voids remain between the metal bottom plate
1
and the Peltier device
10
after completion of the solder joining process.
Since the adhesion between the metal bottom plate
1
and the Peltier device
10
is lowered by the unmelted parts and the voids, there occurs a deterioration in heat transfer between the metal bottom plate
1
and the heat generating face
10
b
of the Peltier device
10
whose cooling face
10
a
receives heat generated by the LD
16
. Thus, the Peltier device
10
cannot fully dissipate heat and is deteriorated in its cooling ability, so that the LD
16
is raised in temperature and becomes unstable in operation. If unmelted solder or a void is present between the metal bottom plate
1
and the Peltier device
10
, the Peltier device
10
and the LD
16
are inclined relative to the metal bottom plate
1
so that the optical axis of the LD
16
goes out of alignment, causing improper optical signal transmission in the optical semiconductor device module.
To prevent the solder foil from increasing in melting point attributable to diffusion of Au thereinto, if a countermeasure such as to increase the thickness of the solder foil, i.e., the solder joint layer between the metal bottom plate
1
and the Peltier device
10
is taken, a tilt of the Peltier device
10
relative to the metal bottom plate
1
is liable to become large, and if another countermeasure such as to decrease an amount of Sn in the solder foil is taken, the adhesion between the metal bottom plate
1
and the Peltier device
10
is lowered since the melting point of the solder foil excessively decreases at parts other than Au diffusion parts of the solder foil. Thus, these countermeasures are not useful to attain an improved solder joint between the metal bottom plate and the Peltier device in the optical semiconductor device module and at the same time reduce the tilt of the Peltier device relative to the metal bottom plate.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical semiconductor device package permitting a cooling device for cooling an optical semiconductor device to be properly sol
Kimura Toshio
Okada Takahiro
Elms Richard
Menz Douglas M
The Furukawa Electric Co. Ltd.
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