Dynamic magnetic information storage or retrieval – Head mounting – For shifting head between tracks
Reexamination Certificate
2000-02-04
2002-11-05
Letscher, George J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head mounting
For shifting head between tracks
C439S083000
Reexamination Certificate
active
06477016
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to junction assemblies for use in magnetic head devices and the like, in which bonding pads provided on substrates, and bumps provided on wiring members and composed of copper or the like are bonded to each other by soldering. More particularly, the present invention relates to a junction assembly of a bonding pad having an Au film formed on the surface thereof.
2. Description of the Related Art
FIG. 10
is a cross-sectional view showing a conventional bonding pad, and
FIG. 11
is a cross-sectional view showing a copper bump being soldered to the bonding pad.
The bonding pad
2
shown in
FIG. 10
is formed by sequentially depositing a Cu film
2
a
, an Ni film
2
b
, and an Au film
2
c
on a base film la constituting a flexible substrate
1
. Wettability in soldering is decreased when the Cu film
2
a
is oxidized; however, by forming the Ni film
2
b
, oxidation of the Cu film
2
a
can be prevented and the decrease in the wettability can be avoided. In addition, by forming the Au film
2
c
on the surface of the Ni film
2
b
, the wettability of the bonding pad to the solder can be further improved.
In the flexible substrate
1
, a conductive pattern composed of a Cu film is formed on the base film
1
a
, and a part of the Cu film constituting the conductive pattern is used as the Cu film
2
a
of the bonding pad
2
a
. The surface of the conductive pattern, except for the bonding pad
2
, is covered by an insulating layer, such as a resist.
A wiring member
3
shown in
FIG. 11
has a conductive pattern
3
b
composed of copper foil formed between resin films
3
a
and
3
a
. A copper bump
3
c
protruding from gaps between the resin films
3
a
and
3
a
through an opening provided in one resin film
3
a
, is provided. The surface of the copper bump
3
c
is covered by a solder layer.
By contacting the copper bump
3
c
covered by the solder layer at the surface thereof with the bonding pad
2
and heating the wiring member
3
and the flexible substrate
1
having the bonding pad
2
formed thereon, which are sandwiched between a heater and a holding plate for heating, the solder on the surface of the copper bump
3
c
is melted. A solder junction portion
4
bonding the bonding pad
2
and the copper bump
3
c
is thus formed.
However, the conventional junction assembly has a problem in that bonding strength of the soldering junction
4
is not satisfactory.
The bonding strength of the soldering junction
4
can be measured by observing a position at which the wiring member
3
and the flexible substrate
1
separate when the wiring member
3
is pulled upward and the flexible substrate
1
is pulled downward.
When the bonding strength of the soldering junction
4
is low, the wiring member
3
and the flexible substrate
1
are separated by breakage at the position
5
indicated by a dashed line, such as the interior of the soldering junction
4
as shown in FIG.
11
. That is, the separation occurs due to the breakage of the soldering junction
4
. In contrast, when the bonding strength of the soldering junction
4
is high, the copper bump
3
c
is separated from the resin film
3
a
. When a plurality of samples in which the flexible substrates
1
and the wiring members
3
are bonded are pulled upward and downward, respectively, the bonding strength of the soldering junction
4
can be numerically represented. The numerical valve is calculated by comparing the samples which are separated by breakage at position
5
indicated by the dashed line in the interiors of the soldering junctions
4
to the total number of samples.
According to research conducted by the inventors, it was understood that the reason for insufficient bonding strength of the soldering junction
4
could be explained as follows. Since the Au of the Au film
2
c
melts into the solder when the thickness E
1
at the soldering junction
4
is too great, compounds of Au and Sn generate. When compounds of Au and Sn are formed in the soldering junction
4
, the compounds precipitate in the solder or on the surface thereof, and cracks in the solder readily occur.
In soldering junctions
4
of conventional bonding pads
2
, the observed Au content is approximately 14 percent by weight and the, amounts of the compounds of Au and Sn in the soldering junction
4
are larger. As a result, cracks in the solder tend to readily occur. Consequently, the ratio of samples in which the soldering junctions
4
are broken at the position
5
indicated by the dashed line to the total samples reaches 5 percent.
Furthermore, in the conventional junction assembly, the thickness E
1
of the Au film
2
c
at the surface of the bonding pad
2
, as shown in
FIG. 10
, is so large that Au melts into the solder at the junction boundary between the soldering junction
4
and the bonding pad
2
. As a result spread H
1
of a solder fillet at the soldering junction
4
is suppressed. Consequently, separation at the boundary between the soldering junction
4
and the bonding pad
2
readily occurs.
The junction assembly of the bonding pad and the copper bump are used in, for example, a magnetic head device, as shown in FIG.
9
.
The magnetic head is provided with a load beam
31
in which a base portion is a fixing edge
31
a
and a front portion is a supporting edge
31
b
, a flexure
32
provided at the supporting edge
31
b
of the load beam
31
, a magnetic head body
34
mounted on the flexure
32
, and a flexible substrate
33
laminated on the flexure
32
.
A bonding pad
35
is formed at one edge of the flexible substrate
33
.
A copper bump
37
covered by a solder layer and formed at a wiring member
36
extending from the body side of the magnetic head device is brought into contact with the bonding pad
35
and is sandwiched between a heater and a holding plate, so that a soldering junction
4
similar to that shown in
FIG. 3
is formed.
In magnetic head devices and the like, since mechanical vibration is frequently generated and mechanical force is frequently applied to soldering junctions, the possibility of the generation of connection failure during use is high when a junction assembly of the conventional bonding pad and the copper bump are used.
SUMMARY OF THE INVENTION
In order to solve the problems in the conventional art described above, objects of the present invention are to provide a junction assembly of a bonding pad and a bump, which can prevent decrease in bonding strength of a soldering junction, and to provide a magnetic head device utilizing the junction assembly. In the present invention, the amount of Au in the bonding pad precipitated in the soldering junction can be suppressed, and the dimension of a spread of a solder fillet at the soldering junction can be increased.
A junction assembly according to the present invention comprises a substrate having a conductive pattern and a bonding pad formed thereon, the bonding pad being electrically connected with the conductive pattern and being provided with an Au film on the surface thereof, and a wiring member having a conductive pattern and a bump formed thereon. The bump is electrically connected with the conductive pattern, in which the bonding pad and the bump are bonded to each other by soldering. In the junction assembly described above, in a state in which the bonding pad is bonded to the bump, the thickness of the Au film is determined so that the Au content is not more than 9 percent by weight in a soldering junction between the bonding pad and the bump.
When the thickness of the Au film on the surface of the bonding pad is appropriately determined, the Au content in the soldering junction, which was conventionally approximately 14 percent by weight, can be decreased, the precipitated amounts of compounds of Au and Sn in the solder or on the surface thereof can be decreased, and a cracking of the solder becomes unlikely. In addition, when the Au film is thinned, a phenomenon of Au which melts into the soldering junction at the boundary thereof with the bondin
Naito Koichi
Yamaguchi Ooki
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Letscher George J.
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