Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Assembly of plural semiconductive substrates each possessing...
Reexamination Certificate
2000-06-30
2001-04-10
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Assembly of plural semiconductive substrates each possessing...
C438S119000, C438S124000, C438S126000, C438S127000, C438S014000, C438S015000, C438S107000, C438S110000, C438S113000, C438S025000, C438S026000, C438S051000, C438S055000, C438S064000
Reexamination Certificate
active
06214644
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to a method of fabricating a micromachine package.
2. Description of the Related Art
Micromachine sensing elements (hereinafter micromachine elements) are well known. A micromachine element typically includes a miniature moveable structure, such as a bridge, cantilevered beam, suspended mass, membrane or capacitive element, which is supported over a cavity formed in a silicon wafer. Since the operation of the micromachine element depends upon the moveability of the miniature moveable structure, it is critical that the package, which includes the micromachine element, does not contact the miniature moveable structure in any manner.
FIG. 1
is a cross-sectional view of a structure
8
during the formation of a plurality of micromachine packages in accordance with the prior art. As shown in
FIG. 1
, a silicon wafer
10
included a plurality of micromachine chips
12
. Micromachine chips
12
included micromachine areas
14
on a front surface
10
F of wafer
10
. Micromachine areas
14
included the miniature moveable structure of the micromachine element. Micromachine chips
12
further included bond pads
16
on front surface
10
F of wafer
10
. Bond pads
16
were connected to the internal circuitry of micromachine chips
12
.
Micromachine chips
12
were often integrally connected together in an array. Each of micromachine chips
12
in the array was delineated by a singulation street
20
, which was located between adjacent micromachine chips
12
.
A lid
30
was positioned above wafer
10
. Lid
30
included a plurality of caps
42
integrally connected to one another. Each cap
42
included a micromachine cavity
32
. Each micromachine cavity
32
was positioned over a corresponding micromachine area
14
. Generally, micromachine cavities
32
were wider than micromachine areas
14
.
Each cap
42
further included a bond pad cavity
34
. Each bond pad cavity
34
was positioned over a corresponding set of bond pads
16
on a micromachine chip
12
. Generally, bond pad cavities
34
were wider than bond pads
16
, and were at least as deep as bond pads
16
were tall.
FIG. 2A
is a cross-sectional view of structure
8
of
FIG. 1
at a further stage in fabrication in accordance with the prior art. As shown in
FIG. 2A
, lid
30
was attached to wafer
10
. Micromachine cavities
32
were positioned above corresponding micromachine areas
14
. Further, bond pad cavities
34
were positioned above corresponding sets of bond pads
16
.
FIG. 2B
is a cross-sectional view of structure
8
of
FIG. 2A
at a further stage of fabrication in accordance with the prior art. Referring to
FIG. 2B
, a series of shallow cuts were made to remove a portion of each cap
42
to expose bond pads
16
. Micromachine chips
12
were electrically tested by connecting test probes to bond pads
16
. If testing of a micromachine chip
12
indicated that the micromachine chip
12
was defective, the micromachine chip
12
and/or corresponding cap
42
was marked. For example, micromachine chip
12
A was marked as being defective. Wafer
10
was then singulated along singulation streets
20
. Micromachine chips
12
which were marked as defective were discarded.
Disadvantageously, a cap
42
was attached to a micromachine chip
12
even if the micromachine chip
12
was defective. The cap
42
and defective micromachine chip
12
were discarded. However, since a cap
42
was attached to the defective micromachine chip
12
, the cost associated with the defective micromachine chip
12
was increased compared to the cost associated with the defective micromachine chip
12
alone. This increased the cost of fabricating each batch of micromachine packages. This, in turn, increased the average total cost of fabricating each individual micromachine package, which passed testing.
After singulation of wafer
10
, each good micromachine chip
12
with cap
42
was further packaged.
FIG. 3
is a cross-sectional view of a single micromachine package
40
in accordance with the prior art. As shown in
FIG. 3
, micromachine chip
12
and cap
42
were attached to a substrate
52
. Bond pads
16
were electrically connected to traces
44
by bond wires
46
. To prevent accumulation of static charge on cap
42
, which would render micromachine chip
12
inoperable, cap
42
was electrically connected to a ground trace
48
by a bond wire
50
. Ground trace
48
was grounded during use. Although effective at prevent accumulation of static charge on cap
42
, grounding cap
42
by electrically connecting cap
42
to ground through bond wire
50
and ground trace
48
was relatively labor intensive and complex which increased the cost of fabricating package
40
.
SUMMARY OF THE INVENTION
In accordance with the present invention, a micromachine package includes a micromachine chip mounted as a flip chip to a substrate. The micromachine chip includes a micromachine area and bond pads formed on a front surface of the micromachine chip. The substrate includes traces formed on an upper surface of the substrate. The bond pads are coupled to the traces by bumps, e.g., formed of solder.
Advantageously, the micromachine package is sealed with a package body formed from a cured limited flow liquid encapsulant to protect the micromachine area from the ambient environment. More particularly, the micromachine chip, the package body and the substrate define a cavity, and the micromachine area is located within the cavity.
Recall that in the prior art, the cap was mounted over the micromachine area. Advantageously, by mounting the micromachine chip as a flip chip to the substrate in accordance with the present invention, the requirement for the cap utilized in the prior art is eliminated. By eliminating the cap, the materials and labor associated with manufacturing and installing the cap are also eliminated. Further, since the requirement for the cap is eliminated, the requirement for grounding the cap is also eliminated.
In one embodiment, the limited flow liquid encapsulant is applied in an edge fill configuration for situations requiring a thinner package. In an edge fill configuration, the limited flow liquid encapsulant contacts sides of the micromachine chip.
In another embodiment, a partial overfill configuration is used for those situations having less restriction on total component height. In a partial overfill configuration, the limited flow liquid encapsulant contacts sides of the micromachine chip and extends over at least a portion of a back surface of the micromachine chip.
In yet another embodiment, a full overfill configuration is provided for those situations having little or no restriction on total component height. In a full overfill configuration, the limited flow liquid encapsulant contacts sides of the micromachine chip and extends over and covers the entire back surface of the micromachine chip.
External connectivity configurations, such as a ball grid array (BGA), leadless chip carrier (LCC), or land grid array (LGA) configurations, are provided which are contemplated to be implemented in combination or separate from the embodiments previously described.
Also in accordance with the present invention, a method of fabricating a flip chip micromachine package includes attaching a micromachine chip as a flip chip to a substrate. The micromachine chip has a micromachine area on a front surface of the micromachine chip. The method further includes dispensing a limited flow material, e.g., liquid encapsulant, around the micromachine chip. The limited flow material is cured to form a package body. The micromachine chip, the package body, and the substrate define a cavity, the micromachine area being located within the cavity.
Advantageously, only a micromachine chip which has been tested and found to operate correctly is attached to the substrate. In this manner, waste of the substrate is avoided and labor associated with attaching
Amkor Technology Inc.
Gunnison, McKay & Hodgson LLP
Hodgson Serge J.
Niebling John F.
Zarneke David A.
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