Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2002-04-12
2003-11-11
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S615000, C428S618000, C257S781000, C257S784000
Reexamination Certificate
active
06645606
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of Japanese Patent Application No. 2001-171497 filed on Jun. 6, 2001 and No. 2002-9817 filed on Jan. 18, 2002, the contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to an electrical device having bonding pads that is bonded with metal wiring and a manufacturing method thereof.
BACKGROUND OF THE INVENTION
An electrical device such as the device shown in
FIGS. 11A
,
11
B includes a substrate
10
, which is made of ceramics or the like. Pads
22
for connecting to electrical parts or for bonding with wiring are formed on a first surface
11
and a second surface
12
. The pads
22
include W (tungsten) layers
22
a
as base layers and Cu (cupper) plating layers
22
b
thereon. Regarding the pads
22
on the second surface
12
, resistors
72
constructed by thick layers are formed through Cu thick layers
70
. Further, a passivating glass
74
and a passivating resin
76
are respectively formed to cover the resistors
72
, the Cu thick layers
70
and the pads
22
.
Next, as shown in
FIG. 11B
, IC tips
30
,
55
and other electrical parts
40
such as capacitors or the like are connected to the pads
22
formed on the first surface
11
by using solder
41
,
51
and a conductive adhesive
31
. Thereafter, the pads
22
are electrically connected to the IC tips
30
,
55
via Au wiring
60
or Al wiring
61
.
However, in the above-mentioned method, the heat used to melt the solder
41
,
51
or for hardening the conductive adhesive
31
oxidizes the exposed Cu plating layers
22
b
of the pads
22
that are formed on the first surface
11
. Therefore, a bonding force between the wiring
60
,
61
and the Cu plating layers
22
b
decreases.
Alternatively, JP-A-2000-58745 discloses that Ni plating layer and Au plating layer are deposited on Cu conductive wiring in this order on a resin board. In this construction, oxidization of the Cu conductive wiring can be prevented. Further,Cu diffusion from the Cu conductive wiring to the Au plating layer decreases.
However, though the Cu in the Cu conductive wiring is a flexible material, it is possible that ultrasonic waves can be more easily transmitted during wire bonding because Ni is solid material. In addition, in the above-mentioned Cu—Ni—Au construction, a battery effect occurs between the Ni plating layer and the Au plating layer due to water in a humid environment. Therefore, corrosion by products such as NiOH or the like are generated, thereby possibly separating the bonding wiring from the pad.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electrical device having a metal pad bonded with metal wiring that is capable of obviating the above problem.
It is another object of the present invention to provide a metal pad that is capable of repressing separation of the metal wiring.
If a two-layer plating structure having a Cu plating layer and Au plating layer directly thereon is used as a pad, it is able to prevent the Cu plating layer from oxidizing because of the Au plating layer. Further, corrosion by products that would be generated between the Ni plating layer and the Au plating layer are not generated because the Ni plating layer is not used.
Accordingly, in this invention, a substrate has a first surface and a second surface. A plurality of pads is formed on the first surface. Further, each pad has a Cu plating layer and an Au plating layer that is directly formed on the Cu plating layer.
However, when the Al wiring is used as metal wiring, a Kirkendall void is generated between the Au plating and the Al wiring under a high temperature environment, thereby also separating the bonding wiring from the pad.
It is considered that the Kirkendall void is generated because a diffusion speed of Au under high temperature is much faster than that of the other metal materials, for example, Al, Cu. Namely, Au deficient portions are generated in the Au plating layer, thereby forming the Kirkendall void. Incidentally, regarding the three-layer construction having the Cu conductive wiring, the Ni plating layer and Au plating layer, the Kirkendall void is hard to generate because Au cannot diffuse due to a barrier layer of Ni plating.
Accordingly, in this present invention, the thickness of the Au plating layer that is bonded with the Al wiring is less than 0.5 &mgr;m.
Further, in case that the Al wiring is used as metal wiring, it possible that the wiring bonding separates from the pad if the Au plating layer is too thin.
Accordingly, the thickness of the Au plating layer that is bonded with the Au wiring is 0.05 &mgr;m or more.
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patent: 4517252 (1985-05-01), Hugh
patent: 4840302 (1989-06-01), Gardner et al.
patent: 5647942 (1997-07-01), Haji
patent: 5829124 (1998-11-01), Kresge et al.
patent: 5897336 (1999-04-01), Brouillette et al.
patent: 6020048 (2000-02-01), Oka et al.
patent: 6335104 (2002-01-01), Sambucetti et al.
patent: 6435398 (2002-08-01), Hartfield et al.
patent: A-63-73697 (1988-04-01), None
patent: A-2-260550 (1990-10-01), None
patent: A-8-340019 (1996-12-01), None
patent: A-10-294394 (1998-11-01), None
patent: A-11-64139 (1999-03-01), None
patent: A-2000-58745 (2000-02-01), None
patent: A-2000-208548 (2000-07-01), None
Asai Yasutomi
Maeda Yukihiro
Nagasaka Takashi
Nakano Tetsuo
Denso Corporation
Lam Cathy
Posz & Bethards, PLC
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