Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified configuration
Reexamination Certificate
2000-03-21
2001-09-04
Flynn, Nathan (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified configuration
C257S772000, C257S775000
Reexamination Certificate
active
06285083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure for mounting a semiconductor device to a mounting substrate, such as a printed circuit board, and a semiconductor device itself.
2. Description of the Related Art
A basic concept of a prior art structure for mounting a semiconductor device to a printed circuit board will be described below with reference to FIG.
4
.
First, a general structure of a semiconductor device
10
and a printed circuit board
12
will be explained.
An electrode
14
is formed to be exposed on a surface of the semiconductor device
10
.
A metallic bump
16
is attached in advance on a surface of the electrode
14
. The metallic bump
16
is made of eutectic solder to have a generally spherical or columnar shape.
A pad
18
is formed on a surface area of the printed circuit board
12
to which the semiconductor device
10
is mounted at a position corresponding to that of the electrode
14
formed on the semiconductor device
10
.
Next, the structure for mounting the semiconductor device
10
(onto the printed circuit board
12
) will be explained.
The semiconductor device
10
is placed on the mounting area of the printed circuit board
12
so that the respective metallic bumps
16
attached to the respective electrodes
14
of the semiconductor device
10
are located on the corresponding pads
18
of the printed circuit board
12
.
While maintaining this positional relationship, heat is applied to melt the metallic bumps
16
of eutectic solder.
Thus, the semiconductor device
10
is mounted onto the printed circuit board
12
.
In the above-mentioned prior art structure for mounting the semiconductor device, the spherical or columnar metallic bumps
16
of eutectic solder are molten to flow over the entirety of the pads
12
on the printed circuit board
12
side. Thereby, the metallic bump
16
collapses in shape as shown in
FIG. 4
to reduce the height H.
Particularly, when a semiconductor device is small in size, such as indicated at the reference numeral
10
shown in
FIG. 5
wherein an insulating protective film
30
is formed on a passivation film
28
through which electrode terminals
26
of aluminum are exposed and circuit patterns
32
electrically connected to the electrode terminals
26
are formed on the protective film
30
and wherein electrodes
14
(of a columnar shape in
FIG. 5
) are formed on the circuit patterns
32
which are embedded in a mold resin
36
to solely expose tip ends of the respective electrodes
14
to which metallic bumps
16
are attached, or one, as shown in
FIG. 6
wherein metallic bumps
16
are directly attached to electrodes
14
formed on an active device surface of a semiconductor chip
24
, it is necessary to minimize a diameter of the metallic bump
16
because the arrangement pitch of the electrodes
14
is small. As an example, when a spherical metallic bump
16
of approximately 0.45 mm diameter is formed, a height thereof after being molten will be in a range from approximately 0.3 to 0.32 mm.
However, it has been found that, in a connection-reliability estimation test wherein the semiconductor device
10
is subjected to a heat shock while being mounted to the printed circuit board
12
there is a tendency in that, the higher the height of the metallic bump
16
after being mounted to the printed circuit board
12
, the better the test result. Accordingly, it is desirable to maintain the height of the metallic bump
16
as large as possible to realize the high reliability.
Also, when the semiconductor device is subjected to heat shock, fatigue (for example, cracking) may occur in the vicinity of an end of the metallic bump
16
on the semiconductor device
10
side or an end thereof on the printed circuit board
12
side to cause a failure of connection. Accordingly, it is favorable to increase the strength of the end region having a low strength to realize high reliability.
Particularly, since the original height of the metallic bump
16
is low in the semiconductor device
10
shown in
FIG. 5
or
6
, it is most important to maintain the original height as much as possible to facilitate the connection reliability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a structure for mounting a semiconductor device to a printed circuit board and a semiconductor device itself capable of further stabilizing the connection between the semiconductor device and the printed circuit board.
Another object of the present invention is to solve the above-mentioned problems in the prior art.
According to the present invention, there is provided a mounting structure for mounting a semiconductor device having an electrode on a mounting substrate having a conductive pad, the structure comprising: a metallic bump electrically connecting the electrode of the semiconductor device to the conductive pad; a first eutectic solder for soldering between the metallic bump and the electrode of the semiconductor device; a second eutectic solder for soldering between the metallic bump and the conductive pad of the substrate;
a melting point of the metallic bump being higher than those of the first and second eutectic solders and a resistance to fatigue of the first eutectic solder is different from that of the second eutectic solder.
According to the present invention as defined above, since the metallic bump is made of metallic material having a melting point higher than those of first and second eutectic solders, the metallic bump is not molten when the semiconductor device is heated during the mounting thereof to maintain the original height. Thereby, a favorable result can be obtained in the connection-reliability estimation test wherein the semiconductor device is subjected to heat shock while being mounted to the printed circuit board. Also, for connecting either one of the end portion of the metallic bump on the semiconductor device side or that on the printed circuit board side, where it is thought fatigue such as cracking is liable to occur when exposed to heat shock, eutectic solder having a higher resistance to fatigue is used, compared to one used for connecting the other end portion, so that a durability to heat shock is facilitated as a whole to result in a high reliability.
An example of the eutectic solder having a higher resistance to fatigue is composed mainly of Sn component and Pb component and also composed of at least two of Ag component, In component, Sb component and Cu component, for example, composed an Sn component of 63% by mass, a Pb component of 14.3% by mass, an In component of 1% by mass, an Sb component of 0.7% by mass and an Ag component of 1% by mass.
The other examples of the eutectic solder having a higher resistance to fatigue are shown in Table I below: (1) two metals (from among Ag, In and Sb) added to Sn and Pb; (2) three metals (Ag, In and Sb) added to Sn and Pb; and (3) four metals (Ag, In, Sb and Cu) added to Sn and Pb.
TABLE I
(% by mass)
Sn
Pb
Ag
In
Sb
Cu
Two metals added
63
bal.
1.0
1.0
0
0
″
63
bal.
1.0
0
0.7
0
″
63
bal.
0
1.0
0.7
0
″
63
bal.
1.0
0
1.0
0
Three metals added
63
bal.
1.0
1.0
0.7
0
Four metals added
63
bal.
1.0
1.0
1.0
0.1
An example of the material for the metallic bump is a high-melting point solder, Cu or Ni, having a melting point higher than that of the eutectic solder.
According to an embodiment of a semiconductor device of the present invention, wherein the insulating protective film is formed on the surface of the semiconductor chip on which the electrode terminals are formed and the circuit patterns electrically connected to the electrode terminals are formed on the insulating protective film and wherein the metallic bumps are attached to the electrodes formed on the circuit patterns, the eutectic solder used between the metallic bump and the electrode is composed of an Sn component of 63% by mass, a Pb component of 34.3% by mass, an In component of 1% by mass and an Ag component of 1% by mass to have a high resistance to fatigue, and the metallic bump is made of a
Imai Kazunari
Watanabe Shoji
Flynn Nathan
Forde Remmon R.
Pennie & Edmonds LLP
Shinko Electric Industries Co. Ltd.
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