Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
2000-03-14
2002-11-05
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C257S666000, C257S670000, C257S671000, C257S672000
Reexamination Certificate
active
06476471
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to microelectronic devices and, more particularly, to the housing of microelectronic devices.
2. Description of the Related Art
Microelectronic devices are typically housed to provide protection from environmental factors (e.g., moisture, dust and other contaminants) and yet provide operational access to the devices. A variety of microelectronic-device housings have been disclosed (e.g., see U.S. Pat. Nos. 5,021,864, 5,122,858, 5,389,577, 5,929,514 and 5,969,414) and an exemplary housing is illustrated by the conventional microelectronic-device assembly
20
of
FIGS. 1 and 2
.
The assembly
20
includes a microelectronic device
22
, bonding wires
24
and a lead frame
26
that defines a tie bar
28
that is coupled to a paddle
30
by tie-bar supports
31
. The lead frame also defines a plurality of elongate leads
32
that each have an inner end
33
directed towards the microelectronic device
22
and an outer end
34
that couples to the tie bar
28
.
The microelectronic device
22
has a back face
35
and a front or circuit face
36
that includes a plurality of bonding pads
38
. The bonding pads are generally located proximate to the perimeter of the circuit face
36
and are connected to various microelements within the microelectronic device
22
to thus provide operational access to the microelectronic device.
The back face
35
has a back-face area and the front circuit face
36
has a circuit-face area that typically equals the back-face area. In contrast, the paddle
30
has a paddle area that generally exceeds the back-face area to thereby facilitate carrying the back face
35
on the paddle
30
(accordingly, portions of the paddle
30
are typically visible all about the perimeter of the microelectronic device
22
). The back face
34
is generally secured to the paddle with an adhesive
40
(e.g., an epoxy adhesive or tape) or with solder.
Each of the bonding wires
24
is coupled to a respective one of the bonding pads
38
and a respective one of the inner lead ends
33
. The bonding wires permit the bonding pads to be accessed from the outer lead ends
34
.
As shown in
FIG. 2
, a plastic overmold
48
is typically formed to encapsulate the microelectronic device
22
, the bonding wires
24
, the paddle
30
and the inner ends
33
of the leads
32
. After this encapsulation, the tie bar (
28
in
FIG. 1
) and its tie-bar supports (
31
in
FIG. 1
) are removed so that only the outer ends
34
extend from the overmold
48
for operational access of the microelectronic device
22
.
The lead frame
26
is typically formed from a conductive metal (e.g., a nickel-iron or a copper-based alloy), the bonding wires are typically aluminum or gold, the overmold
48
is generally a thermosetting material (e.g., epoxy, silicone, or urethane) and exemplary dimensions of the bonding pads are 100×100 &mgr;m.
Although it may take on other forms, the microelectronic device
22
is typically a semiconductor die that contains a large number of microelements organized in an integrated circuit and, accordingly, the back face
35
is generally a semiconductor substrate. The integrated-circuit microelements are often microelectronic elements (e.g., transistors, resistors, capacitors and interconnection traces) but they may also be micromachined mechanical elements that include movable members (e.g., the vibrating members of a gyroscope or the acceleration-responsive mass of an accelerometer).
Microelectronic elements may also include movable members (e.g., the arm of a microswitch or microrelay) and, in addition, the performance of some microelectronic elements (e.g., thin film resistors) may be sensitive to pressure. Operation of other exemplary microelements may be degraded by outgassing of constituents from various assembly parts (e.g., the overmold).
When these sensitive microelements are positioned proximate to an area of the front circuit face
36
, it is desirable to exclude extraneous elements (i.e., elements that restrict or degrade operation) from this sensitive area. Although a thin cover coat (e.g., a polyimide) is conventionally applied to the front circuit face
36
before the microelectronic device
22
is encapsulated in the overmold
48
, such coatings fail to provide the desired exclusion.
SUMMARY OF THE INVENTION
The present invention is directed to microelectronic-device assemblies and methods that enhance operation of microelectronic devices because they exclude extraneous elements from sensitive device areas.
The invention is particularly suited for a device that has a sensitive area on a device face that carries a plurality of bonding pads. In an embodiment, a paddle is provided that has an area less than that of the device face and it is spaced from the face and positioned to cover the sensitive area and expose the pads. A plastic ring is arranged to surround the sensitive area and abut the face and the paddle.
A lead frame preferably forms the paddle and a plurality of elongate leads. Each of the leads has an inner end and an outer end and each of a plurality of bonding wires is coupled between a respective one of the pads and a respective one of the inner ends.
An overmold is arranged to encapsulate the die, the paddle, the ring and the inner lead ends and expose the outer lead ends to provide operational access to the microelectronic device. A void is thus defined within the ring and between the device face and the paddle and, accordingly, extraneous elements are excluded from this void. When the plastic ring includes an electrically-conductive filler, it and the paddle provide an electrical and magnetic shield for the device face.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.
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patent: 5021864 (1991-06-01), Kelley et al.
patent: 5122858 (1992-06-01), Mahulikar et al.
patent: 5352852 (1994-10-01), Chun
patent: 5389577 (1995-02-01), McClure
patent: 5687474 (1997-11-01), Hamzehdoost
patent: 5693573 (1997-12-01), Choi
patent: 5849608 (1998-12-01), Abe
patent: 5929514 (1999-07-01), Yalamanchili
patent: 5969414 (1999-10-01), Parthasarathi
patent: 6064576 (2000-05-01), Edwards
patent: 6204454 (2001-03-01), Gotoh
patent: 6239487 (2001-05-01), Park et al.
patent: 6255741 (2001-07-01), Yoshihara et al.
patent: 405315510 (1993-11-01), None
Analog Devices Inc.
Chaudhuri Olik
Ha Nathan W.
Koppel, Jacobs Patrick & Heybl
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