Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – Of specified material other than copper
Reexamination Certificate
2000-12-07
2003-07-15
Zimmerman, John J. (Department: 1775)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
Of specified material other than copper
C257S787000, C029S856000, C029S883000
Reexamination Certificate
active
06593643
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a semiconductor device lead frame, a process of production of the same, a semiconductor device using the lead frame, and a process of production of the same.
BACKGROUND ART
A semiconductor device lead frame used in a resin sealing type semiconductor device is made using, other than an iron-nickel-based alloy (representatively Fe-42% Ni alloy), a copper-based material made of copper or a copper alloy.
In the case of a lead frame using this copper-based material, in order to flatten the surface and improve adhesion of a silver or other precious metal plating film to be formed later, generally, a copper strike plating film is formed on the surface of the material, then the above precious metal plating film for improving die bonding and wire bonding is formed on a die pad and on wire bonding portions of inner leads.
When using a copper-based material, due to exposure to a high temperature of about 150° C. to 350° C. in the step of mounting a semiconductor chip on the lead frame to assemble a semiconductor device, there is a problem that an oxide film of copper is apt to be formed and therefore the adhesion between the sealing resin and the lead frame body made of the copper alloy material will be hindered.
Particularly, when the material is a copper alloy, if exposed to a high temperature, oxidation progresses from the surface of the material to the inside of the material due to oxygen, a segregation layer is formed by the additional element of the copper alloy (layer due to the oxide of the additional element) at an interface between the formed oxide film of copper and the copper alloy material, and the oxide film of the copper ends up being peeled off together with this segregation layer. This is caused by the large difference in density between the copper oxide film and segregation layer and the copper alloy material and therefore mismatching or incoherency at the interface. As a result, when the semiconductor device is finally completed, a problem arises in the adhesion with the sealing resin.
In order to solve this problem, Japanese Examined Patent Publication (Kokoku) No. 5-19820 proposes a semiconductor device lead frame comprised of a lead frame material made of copper or a copper alloy on which is formed a copper-zinc alloy plating film serving as an under plating of the precious metal plating (silver plating).
In the above proposed lead frame, the zinc of the copper-zinc plating film acts as a barrier against diffusion of the oxygen from the outside and suppress the formation of the segregation layer, whereby a semiconductor device lead frame excellent in adhesion with the sealing resin is obtained.
The above proposed lead frame, however, suffered from the following problems (1) to (4):
(1) When plating a precious metal (plating silver as a representative case) on a copper-zinc alloy plating film in a later step, the zinc of the copper-zinc alloy plating film leaches into the precious metal plating solution and contaminates it, so the precious metal plating film becomes irregular or uneven and, in addition, the adhesion of the precious metal plating film is lowered.
(2) When plating a precious metal (plating silver) on the wire bonding portions, an unnecessary silver plating film is formed up to an inner lead side or back side. When peeling off this unnecessary silver plating film, the zinc of the copper-zinc alloy plating film leaches into the peeling solution, so not only is the original barrier function of the copper-zinc alloy plating film degraded, but also patch-like irregularities or unevenness are formed at the surface left after the peeling and the appearance is remarkably degraded.
(3) In the step of assembling the semiconductor device, an external solder plating film is formed on the outer leads after sealing by the resin. This external solder plating is directly formed on the lead frame material exposed by removal of the copper-zinc alloy plating film. If any of the copper-zinc alloy plating film remains on the surface of the material after the step of removing it, patch-like irregularities or unevenness will form at the solder plating film and the appearance will be degraded and, at the same time, the adhesion of the solder plating film will be lowered.
(4) Without a precious metal plating, outer leads cannot satisfy the requirements of corrosion resistance and moisture resistance if there is any zinc, which is highly corrodible, at the surface. The surface ends up degrading before the step of mounting the semiconductor chip to assemble the semiconductor device. Therefore, this lead frame is not practical.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a semiconductor device lead frame excellent in an adhesion with a sealing resin, free from contamination of a precious metal plating solution (particularly a silver plating solution), having a good appearance of the precious metal plating film, excellent in corrosion resistance and moisture resistance, and having a good appearance and adhesion of an outer lead solder plating film, a process of production of the same, a semiconductor device using the lead frame, and a process of production of the same.
To attain the above object, according to a first aspect of the present invention, there is provided a semiconductor device lead frame made of copper or a copper alloy and used for a resin sealing type semiconductor device, comprising:
a lead frame body made of copper or a copper alloy,
a double-layer under plating film formed on the lead frame body and consisting of a lower layer made of zinc or a copper-zinc alloy and an upper layer made of copper having a thickness of 0.02 to 0.4 &mgr;m, and
a precious metal plating film formed on at least a wire bonding portion of an inner lead of the copper upper layer of the under plating film.
According to a second aspect of the present invention, there is provided a semiconductor device lead frame made of copper or a copper alloy and used for a resin sealing type semiconductor device, comprising:
a lead frame body made of copper or a copper alloy,
a double-layer under plating film formed on the lead frame body and consisting of a lower layer made of one type of metal selected from silver, tin, iron, cadmium, a copper-nickel alloy, and copper-cadmium and an upper layer made of copper, and
a precious metal plating film formed on at least a wire bonding portion of an inner lead of the copper upper layer of the under plating film.
In the past, due to the heat treatment when mounting a semiconductor chip on a lead frame made of copper or a copper alloy in the step of assembling the semiconductor device, an oxide film was formed at the interface between the copper under plating film and the lead frame material, so the adhesion between the sealing resin and the lead frame was lowered.
In the first aspect of the present invention, provision is made of a double-layer under plating film consisting of a lower layer made of zinc or a copper-zinc alloy and an upper layer made of copper having a thickness of 0.02 to 0.4 &mgr;m.
By setting the thickness of the copper upper layer provided on the zinc or the copper-zinc alloy lower layer to at least 0.02 &mgr;m, formation of an oxide film at the interface between the under plating film and the lead frame material can be prevented. Namely, in the heat treatment when mounting the semiconductor chip, the copper plating film at the surface layer is oxidized, but after the zinc or the copper-zinc alloy plating film is oxidized, oxygen will no longer reach the copper alloy material of the lead frame body, oxidation of the material will be greatly suppressed, and, as a result, no segregation layer of the additional element of the alloy (layer of the oxide of the alloy element) will be formed, so that the peeling of the oxide film and the interface of the material can be prevented.
Further, the zinc or the copper-zinc alloy plating film of the lower layer is covered by the copper plating film of the upper layer and therefore is not exposed. Due to this, the following e
Sato Harunobu
Seki Kazumitsu
Yoshie Takashi
Paul & Paul
Shinko Electric Industries Co. Ltd.
Zimmerman John J.
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