Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor
Reexamination Certificate
1998-10-06
2001-02-06
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
C438S614000, C438S107000, C438S108000, C438S613000, C438S653000, C438S678000
Reexamination Certificate
active
06184061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device such as a flip chip, a BGA (Ball Glid Array), an CSP (Chip Scale Package), or the like, an electrode of the semiconductor device, and a method of manufacturing the electrode.
2. Description of the Related Art
A flip chip, a BGA, an CSP and so on are conventionally known as semiconductor devices which can satisfy a demand to increase the number of pins of the device. Such a semiconductor device has, for example, an electrode structure called a “solder bump structure” manufactured by electroless plating (for example, see JP-A-8-306816, and JP-A-1-185920).
FIG. 8
is a sectional view illustrating an electrode structure of a flip chip which is an example of a conventional electrode structure. This electrode has a pad
50
formed of metal such as aluminum (Al) or the like. The pad
50
is formed on a chip substrate
51
, and on the surface thereof, with an electroless barrier metal film
52
for protecting the pad
50
.
The electroless barrier metal film
52
has a double-layer structure constituted by an electroless diffusion prevention film
52
a
for preventing Al which is a material of the pad
50
from diffusing, and an electroless oxidation prevention film
52
b
for preventing the surface of the pad
50
and the electroless diffusion prevention film
52
a
from being oxidized. For example, an Ni—P film is used for the electroless diffusion prevention film
52
a.
On the other hand, for example, an electroless Au film is used as the electroless oxidation prevention film
52
b.
The flip chip is mounted onto a circuit board in such a manner that a solder bump
53
is attached to the surface of the electroless barrier metal film
52
, and then the solder bump
53
is melted on the wiring pattern. The reference numeral
54
represents a passivation film for preventing the pad
50
from being oxidized.
However, in the electrode with the above-mentioned solder bump
53
attached thereto, a columnar intermetallic compound layer
60
was formed in the solder bump
53
so as to erect on the surface of the electroless barrier metal film
52
as shown in FIG.
9
A. Therefore, there was a problem that the solder bump
53
was apt to defectively break when force F was applied to the solder bump
53
from the outside, as shown in FIG.
9
B.
More specifically, the electroless Au film
52
b
melts into the solder bump
53
when the solder bump
53
is attached to the electroless barrier metal film
52
. As a result, the solder bump
53
comes into contact with the surface of the electroless Ni—P film
52
a.
On the other hand, generally, the electroless Ni—P film
52
a
is microcrystalline or amorphous because of eutectoid of reducer elements P in a reducer used for electroless plating. As a result, Ni in the surface of the electroless Ni—P film
52
a
enters the solder bump
53
. Ni entering the solder bump
53
performs a chemical reaction with Sn in the solder bump
53
. Consequently, an intermetallic compound layer
60
of Ni
3
Sn
4
is produced in the solder bump
53
.
On the other hand, when Ni is released from the electroless Ni—P film
52
a,
the content of the reducer elements P in the electroless Ni—P film
52
a
increases in the vicinity of the surface thereof (for example, increases from 9.5 wt % to 17 wt %). As a result, an amorphous layer containing the reducer elements P at high concentration (P-rich amorphous layer) is formed in the electroless Ni—P film
52
a
in the vicinity of the surface thereof. Because of existence of this P-rich amorphous layer, the growth of the above-mentioned intermetallic compound layer
60
is blocked in a direction h along the surface of the electroless Ni—P film
52
a.
Consequently, the produced intermetallic compound layer
60
grows in its height-wise direction v.
In such a manner, the intermetallic compound layer
60
grows in its height-wise direction v. Therefore, for example as shown in
FIG. 9A
, the intermetallic compound layer
60
is formed in the form of a column in the solder bump
53
. In this case, the bonding area between the intermetallic compound layer
60
and the electroless Ni—P film
52
a
is very small, and the height of the intermetallic compound layer
60
is comparatively high, for example, 1 (&mgr;m) or more. Further, an P-rich amorphous layer is formed in the electroless Ni—P film
52
a
in the vicinity of the surface thereof.
Therefore, a bonding force between the solder bump
53
and the electroless Ni—P film
52
a
is very small. Accordingly, when a force F is applied to the solder bump
53
from the outside during the work of soldering by melting the solder bump
53
, the intermetallic compound layer
60
itself is broken, or defective breaking is produced between the intermetallic compound layer
60
and the P-rich amorphous layer as shown in FIG.
9
B. Therefore, an electrode cannot be attached to the wiring pattern. After all, the device often becomes a rejected product.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electrode of a semiconductor device and a method of manufacturing the electrode, in which defective breaking of a solder bump (solder ball) can be prevented when a semiconductor device is manufactured by an electroless film formation process such as electroless plating.
It is another object of the present invention to provide a semiconductor device having the above-mentioned electrode so that the reliability thereof is improved.
In order to achieve the above problem, according to an aspect of the present invention, provided is an electrode of a semiconductor device comprising: a pad; an electroless diffusion prevention film formed on a surface of the pad for preventing material of the pad from diffusing; a solder precoat film formed on a surface of the electroless diffusion prevention film, and having a thickness not larger than a predetermined value, for preventing a solder bump or a solder ball from defective breaking; and a predetermined intermetallic compound layer formed in the solder precoat film in the vicinity of a boundary surface between the solder precoat film and the electroless diffusion prevention film, the intermetallic compound layer having a bonded surface bonded substantially to the whole of the surface of the electroless diffusion prevention film. The solder precoat film is necessary to have a thickness so that an intermetallic compound layer having a bonded surface bonded substantially to the whole of the surface of said electroless diffusion prevention film, is formed in said solder precoat film in the vicinity of a boundary surface between said solder precoat film and said electroless diffusion prevention film.
According to another aspect of the present invention, provided is an electrode of a semiconductor device comprising: a pad; an electroless diffusion prevention film formed on a surface of the pad for preventing material of the pad from diffusing; a solder bump of a solder ball formed on a surface of the electroless diffusion prevention film; and a predetermined intermetallic compound layer formed in the solder bump of the solder ball in the vicinity of a boundary surface between the solder bump or the solder ball and the electroless diffusion prevention film, the intermetallic compound layer having a bonded surface bonded substantially to the whole of the surface of the electroless diffusion prevention film.
According to a further aspect of the present invention, provided is a semiconductor device comprising a wiring pattern electrically connected to electronic parts; and electrodes defined above and electrically connected to the electronic parts through the wiring pattern.
According to a further aspect of the present invention, provided is a method of manufacturing an electrode of a semiconductor device comprising the steps of: forming an electroless barrier metal film, as a pad protection film, on a surface of a pad; and forming a solder precoat layer on a surface of the electroless barrier metal film so as to have
Tomita Yoshihiro
Wu Qiang
Anya Igwe U.
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
Smith Matthew
LandOfFree
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