Multichip module

Details Multichip module Multichip module

2000-01-14

2002-08-27

Lee, Eddie (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

Incoherent light emitter structure

With housing or contact structure

C257S082000, C257S083000, C257S084000, C257S115000

Reexamination Certificate

active

06441404

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a multichip module provided with a light-emitting device such as an LED (light-emitting diode) or LD (laser diode) and an integrated circuit and designed for use in an electronic appliance or the like that exchanges data by infrared communication such as a PC (personal computer), PDA (personal digital assistant), DSC (digital still camera), or DVC (digital video cassette recorder).
BACKGROUND ART
A conventional multichip module provided with an LED and an LSI (large-scale integration) will be described. In
FIG. 7
, at (a) is shown a schematic view of a conventional multichip module provided with an LED
12
and an LSI
13
, and at (b) is shown an equivalent circuit diagram thereof The LED
12
, when a voltage is applied thereto, emits near-visible light such as infrared rays.
The LSI
13
is a monolithic integrated circuit having a circuit formed only on one side of a wafer. In the circuit diagram shown at (b) in
FIG. 7
, the monolithic LSI
13
is represented by a frame of broken lines. Within the frame of broken lines, only an output transistor, among other components incorporated in the monolithic LSI
13
, is shown. This output transistor is an NPN-type bipolar transistor having a high driving capacity, and is inserted between the LED
12
and a reference potential. Here, the monolithic LSI
13
serves to control the amount of light emitted from the LED
12
by controlling the current flowing through the LED
12
.
A metal lead frame
19
is constituted of island portions
14
a
and
14
b
for bonding chips such as the LED
12
and lead terminal portions
16
for external connection. Here, as shown at (b) in
FIG. 7
, neither of the cathode and the anode of the LED
12
is connected to a reference potential or a supplied voltage, and therefore the potential of the substrate thereof cannot be made equal to the potential of the substrate of the monolithic LSI
13
. Thus, the LED
12
cannot be mounted on the same island portion as the monolithic LSI
13
, and this is the reason that, as shown at (a) in
FIG. 7
, they are mounted on separate island portions
14
a
and
14
b.
The LED
12
and the monolithic LSI
13
are together sealed in a package
15
made of resin. In the circuit diagram shown at (b) in
FIG. 7
, reference numeral
17
represents a current limiting resistor that is either mounted externally via the lead terminal portions
16
of the lead frame or formed within the LSI
3
.
When this multichip module
11
having the above-described structure is energized, the LED
12
emits light and simultaneously generates heat. This heat is first absorbed by the island portion
14
a
, which has a low heat resistance, and is then dissipated into air through the package
15
.
In this multichip module
11
having the above-described structure, the monolithic LSI
13
is larger than the LED
12
, and accordingly the island portion
14
b
for the monolithic LSI
13
is so formed as to be larger than the island portion
14
a
for the LED
12
. Since the island portions
14
a
and
14
b
need to be formed within the package
15
having a limited size, it is inevitably impossible to secure a sufficiently large area for the island portion
14
a
for the LED
12
.
As described above, the island portion
14
a
for the LED
12
first absorbs the heat of the LED
12
and then dissipates the heat into air through the package
15
. However, the island portion
14
a
, which is thus smaller than is desired, cannot absorb sufficiently the heat of the LED
12
, and accordingly the multichip module offers an unduly low package power (power dissipation capacity); that is, the LED
12
offers an unduly low heat capacity. This requires that the current flowing through the LED
12
be limited so as to restrict the amount of heat generated, and thus the amount of light emitted.
To achieve satisfactory dissipation of the heat of the LED
12
, it is possible to form, for example, a heat dissipation fin on the island portion
14
a
.
FIG. 8
is a schematic view of a multichip module as is realized by additionally forming heat dissipation fins
18
a
and
18
b
in the multichip module
11
described above. The heat dissipation fins
18
a
and
18
b
are formed integrally with the island portion
14
a
, with parts thereof protruding from the package
15
. The heat dissipation fin
18
a
dissipates heat into air, and the heat dissipation fin
18
b
, which is so formed as to make contact with the printed circuit board (not shown) on which the multichip module
11
is mounted, dissipates heat through this printed circuit board.
Instead of providing heat dissipation fins
18
a
and
18
b
, it is also possible to make the package
15
itself larger so as to enlarge the island portion
14
a
for the LED
12
and thereby increase the heat capacity of the island portion
14
a.
However, forming a heat dissipation fin
18
a
or
18
b
or enlarging the package
15
inevitably makes the multichip module as a whole larger. This imposes extra limitations on the above-mentioned printed circuit board, or hinders miniaturization of electric appliances in which the multichip module is incorporated.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a compact multichip module that offers a higher package power and that allows a satisfactorily large amount of light to be emitted from a light-emitting device.
To achieve the above object, according to the present invention, a multichip module is provided with: a light-emitting device having an anode electrode or a cathode electrode thereof connected to a supplied voltage or a reference voltage; a control circuit, having a substrate of an opposite conductivity type to the substrate of the light-emitting device, for controlling the electric current that is passed through the light-emitting device; a lead frame including an island on which both the light-emitting device and the control circuit are mounted; and a package for sealing the light-emitting device and the control circuit. In this structure, the heat that the light-emitting device generates as it emits light is absorbed by the lead frame, and is then dissipated therefrom into air through the package.


REFERENCES:
patent: 5990499 (1999-11-01), Kuhlmann et al.
patent: 6169295 (2001-01-01), Koo
patent: 60-240171 (1985-11-01), None
patent: 402105472 (1990-04-01), None
patent: 6-69413 (1994-03-01), None
patent: 406125116 (1994-05-01), None
patent: 8-18003 (1996-01-01), None
patent: 411260985 (1999-09-01), None

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