Coating apparatus – Work surface shields – masks or protectors – Work-attached
Reexamination Certificate
1999-05-25
2001-05-01
Edwards, Laura (Department: 1734)
Coating apparatus
Work surface shields, masks or protectors
Work-attached
C427S282000
Reexamination Certificate
active
06224674
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of Japanese Patent Application Nos. 10-150456, filed May 29, 1998, and 10-239263, filed Aug. 8, 1998, the disclosures of which are expressly incorporated by reference herein in their entireties.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mask conveniently used for seal coating of a semiconductor element and a method of fabricating a sealed type semiconductor device using the mask.
2. Discussion of Background Information
A semiconductor device is fabricated with a semiconductor element mounted on a wiring board. The semiconductor element is electrically connected to the wiring board with bonding wire or with bumps formed on the semiconductor. After connection to the wiring board, the semiconductor element is sealed with a sealing material.
In the sealing process, as shown in FIG.
11
(
a
) a semiconductor element
2
is mounted on a wiring board
1
. The semiconductor element
2
is electrically connected to a circuit (not shown) of the wiring board
1
by bonding wires W. After this connection, a coating mask
3
′, with an opening
31
′ located at the mounting position of semiconductor element
2
on wiring board
1
, is overlaid on wiring board
1
such that semiconductor element
2
is located inside opening
31
′. A sealing material
4
, supplied in advance on the mask
3
′, is then forced in with a squeegee
5
, whereby sealing material
4
is coated as a pattern on the front surface of wiring board
1
through mask opening
31
′.
FIG.
11
(
b
) shows a semiconductor device obtained after removing mask
3
′ from wiring board
1
. When mask
3
′ is removed from wiring board
1
, the sealing material
4
, which has a viscosity, attaches to the inner peripheral surface
311
′ of opening
31
′ as shown in FIG.
12
(
a
). Under this condition, mask
3
′ is removed. The sealing material
4
develops a stringiness. The stringy sealing material
4
curls onto the back suite of mask
3
′ as shown in FIG.
12
(
b
). This curled portion
41
is pressed and forms a pattern on the surface of the wiring board
1
as shown in FIG.
12
(
c
) the next time when mask
3
′ is used. The amount of this curled portion
41
is variable according to the position of the back peripheral edge of opening
31
′, and therefore the spread
42
on the front surface of the wiring board assumes an irregular pattern as shown in FIG.
12
(
d
).
For the purpose of preventing this phenomenon, Japanese Patent document 6-95594 discloses a mask
3
″ formed with an annular protrusion
32
″ in linear contact along the whole periphery of the edge of the back of an opening
31
″ as shown in FIG.
13
.
Also, Japanese Patent document 3-181142 discloses a space portion
33
″ formed outside of the annular protrusion
32
″ for cutting off the sealing material as shown in FIG.
14
. Specifically, by forming space portion
33
″ on the back of the mask, the sealing material is prevented from curling around to the outside of annular protrusion
32
″.
FIG.
16
(
a
) shows the method disclosed in Japanese Patent document 6-95594. When mask
3
″ is removed from wiring board
1
after sealing, the sealing material
4
remains attached in drips at the forward end of the annular protrusion
32
″. Thus, when mask
3
″ is set on a new wiring board
1
at the next coating session, the sealing material
4
in drips is pressed against new wiring board
1
and spreads over the surface of wiring board
1
as shown in FIG.
16
(
b
). The size of the drips, however, is varied from one point to another of the annular protrusion (in the case where the annular protrusion is in the form of a rectangular frame, for example, the drips on the side portions are thicker than those at the corners). Therefore, the spread described above is inconsistent and irregular, and not uniform. In other words, a sediment deposit appearance develops. If the sealing material is forced in and the mask
3
″ is removed from wiring board
1
under this condition, the foot of the sealing material thus forced in extends over the entire irregular spread that has already expanded over the front surface of the wiring board, with the result that the foot of the sealing layer assumes an irregular jagged form and cannot be finished in an attractive manner. The recent trend of semiconductor elements is toward a higher density package, and the sealing area is strictly defined. An irregular jagged foot of the sealing layer, therefore, is liable to cause a conduction failure. For this reason, it is desirable that the drips at the forward end of the annular protrusion are prevented from spreading over the surface of the wiring board.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a seal coating mask for a semiconductor element and method of use thereof that substantially obviates one or more of the problems arising from the limitations and disadvantages of the related art.
It is an object of the present invention to provide a semiconductor seal coating mask and a method of use thereof, by which the sealed area is contained definitely within the design range at the time of coat sealing.
Accordingly, one aspect of the present invention is directed to a seal coating mask for a semiconductor element that includes an opening located at a position where a semiconductor element is mounted on a wiring board where an annular protrusion is formed along the whole periphery of the opening. A clearance of about 0.01 to 0.5 mm is formed between at least a part of the whole periphery of the annular protrusion and the front surface of the wiring board. A space portion is formed on the back of the seal coating mask for cutting off sealing material outside of the annular protrusion. The coating mask is used to forcibly coat a material for sealing the semiconductor element in the front surface of the wiring board.
According to another aspect of the present invention, the space portion communicates with the exterior of the seal coating mask. The space portion is not coated with the sealing material.
According to yet another aspect of the present invention, the annular protrusion is a protruded rectangular frame having the clearance at each opposed corners thereof.
In a further aspect of the present invention, the annular protrusion is formed with the clearance along the whole periphery thereof.
According to another aspect of the present invention, the annular protrusion is formed of resin.
According to still another aspect of the present invention, a leak passage extends from the space portion to the exterior of the seal coating mask.
In a further aspect of the present invention, the leak portion extends from the center of the space portion.
According to another aspect of the present invention, the leak portion extends from an edge of the space portion.
According to still another aspect of the present invention, the annular protrusion is formed of a thin eaves-shaped plate about 0.05 to 0.5 mm thick.
In a further aspect of the present invention, the forward end of the eaves are curled in.
According to another aspect of the present invention, the invention includes a method of fabricating a semiconductor device using the seal coating mask from above. The method includes mounting the semiconductor element on the wiring board. The coating mask is overlayed on the wiring board such that the semiconductor element is located inside the opening. A squeegee is used to forcibly coat sealing material onto the front surface of the wiring board through the coating mask opening in order to seal the semiconductor element onto the wiring board. The mask is then released from the wiring board.
According to yet another aspect of the present invention, a method of fabricating a semiconductor device includes reducing an ambience pressure after overlaying and restoring the ambience pressure to the atmosph
Fukui Taro
Hino Hirohisa
Kitamura Kenji
Edwards Laura
Greenblum & Bernstein P.L.C.
Matsushita Electric & Works Ltd.
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