Active solid-state devices (e.g. – transistors – solid-state diode – Encapsulated
Reexamination Certificate
1997-10-09
2001-01-09
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Encapsulated
C257S723000, C257S730000
Reexamination Certificate
active
06172424
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority of prior Japanese Patent Application No. H. 8-269989 filed on Oct. 11, 1996, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating a resin sealing type semiconductor device and a die assembly for fabricating the resin sealing type semiconductor device.
2. Description of Related Art
As shown by
FIG. 18
, in respect of a molded IC, that is, a resin sealing type semiconductor device which is sealed by a transfer molding process using a molding resin, when there is an element
43
which cannot be sealed by the resin block
40
, the element
43
is arranged at a hollow portion
41
of the molded resin block
40
. A lead frame
42
exposed to the hollow portion
41
and the element
43
are connected through wire bonding.
In that case, the following drawbacks may generally occur by which wire bonding may not be favorably carried out.
(A) Burrs of the molding resin adhere onto the exposed lead frame
42
after forming the molded resin block
40
by which wire bonding cannot favorably be performed.
(B) A die for forming the molded resin block
40
is brought into direct contact with the lead frame
42
during a molding operation. Therefore, a release agent adhered to the die is transferred to the lead frame
42
by which wire bonding cannot favorably be performed.
(C) The lead frame
42
is harmed since the die is brought into direct contact with the lead frame
42
in the molding operation by which excellent wire bonding cannot be performed.
In order to resolve the drawbacks as described above, the following techniques have been known.
(A) Favorable wire bonding regions are secured on the lead frame
42
by removing the burrs of the molding resin on the lead frame
42
and cleaning the release agent thereon after the molding operation as disclosed in, for example, Japanese Patent Application Laid-Open No. 6-85222.
(B) A protective film is previously formed at the wire bonding region on the lead frame
42
and the protective film is removed by etching after the molding operation thereby securing the excellent wire bonding region on the lead frame
42
as disclosed in, for example, Japanese Patent Application Laid-Open No. 6-302744.
However, when such a method is used, addition of steps is needed which gives rise to an increase in cost.
SUMMARY OF THE INVENTION
Hence, it is an object of the present invention to secure an excellent wire bonding region on a lead frame without causing an increase in fabricating cost due to the addition of steps or the like.
According to the present invention, a lead frame is clamped by a die in a state where the die is in non-contact with the lead frame in a wire bonding region of a lead frame and the wire bonding region is separated from a space to be injected with molding resin. Under this state, the molding resin is injected into the space formed in the die assembly.
Therefore, the excellent wire bonding region can be secured on the lead frame without removing burrs of the molding resin, cleaning a release agent, or forming and removing a protective film at the wire bonding region on the lead frame after a molding operation. As a result, because there is no need of addition of steps for securing the excellent wire bonding region, an increase in fabricating cost can be avoided.
It is preferable that a contact portion of the die which makes contact with the lead frame in a region for forming the hollow portion is formed to project toward the lead frame side more than contact portions of the die contacting with the lead frame in regions other than the region for forming the hollow portion. In this case, the contact portion of the die which makes contact with the lead frame in the region for forming the hollow portion is applied with pressing force by the length of projection. Therefore, the region for forming the hollow portion can favorably be sealed by the contact portion of the die.
If a film for promoting a sealing performance between the contact portion and the lead frame is formed on the surface of the lead frame, the sealing performance can be promoted by the amount of squashing the film.
When the film for promoting the sealing performance is constituted by a plated layer, the film for promoting the sealing performance can be also used as an under film utilized in carrying out wire bonding.
To clamping the lead frame by the die in a state where the die is in non-contact with the lead frame in the wire bonding region of the lead frame, a die having a recess portion or a through hole which opens to the wire bonding region on the lead frame can be used.
When a surface of the contact portion of the die contacting with the lead frame in the region for forming the hollow portion is processed into a smoothed flat surface, the sealing performance between the contact portion and the lead frame is enhanced.
The die has a first die and a second die which sandwich a lead frame. In this case, it is preferable that the first die has a projection for forming a hollow portion that is in contact with the surface of the lead frame and the second die also has a projection that is in contact with the rear surface of the lead frame at least in a wire bonding region on the lead frame. According to this structure, the sealing performance at the contact portion of the first die around the recess portion or the through hole in the first die is preferably promoted.
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patent: 4554126 (1985-11-01), Sera
patent: 4697203 (1987-09-01), Sakai et al.
patent: 5264393 (1993-11-01), Tamura et al.
patent: 5328552 (1994-07-01), Benzoni
patent: 5424249 (1995-06-01), Ishibashi
patent: 5523608 (1996-06-01), Kitaoka et al.
patent: 5594282 (1997-01-01), Otsuki
patent: 0 322 122 (1989-06-01), None
patent: 2103917 (1972-03-01), None
patent: 61-271859 (1986-12-01), None
patent: 3-1560 (1991-01-01), None
Kato Yukihiro
Kinouchi Kan
Kuroda Michitake
Nomura Hiroshi
Denso Corporation
Pillsbury Madison & Sutro LLP
Potter Roy
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