Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-12-17
2003-11-04
Karlsen, Ernest (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S754090
Reexamination Certificate
active
06642731
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a probe structure for testing a device-under-test (DUT), such as a semiconductor device, by a burn-in test or the like, and also to a method of manufacturing the probe structure. It is to be noted throughout the instant specification that the probe structure is electrically contacted with a contact object, such as an electrode pad or a circuit pattern, which is formed on the DUT and which may be simply called an electrode.
2. Description of the Related Art
In a conventional probe structure, a hemispherically projecting bump contact is formed as a contact point for contacting with the electrode formed on the DUT, such as a semiconductor device.
As a bump contact having the conventional bump structure, it is known in the art that fine projections are intentionally formed on a surface of the bump contact so as to improve reliability of contact with the electrode (for example, Japanese Unexamined Patent Publication (A) No. H06-27141, namely, 27141/1994). By forming fine projections on the surface of the bump contact, the contact area of the bump contact with the electrode becomes large and this enables a reliable contact with the electrode. Even when an oxide film is formed on the surface of the contact object, namely, the electrode, the fine projections can break the oxide film, and give a stable contact resistance.
Another probe structure has been disclosed in Japanese Unexamined Patent Publication (A) No. H09-133711 (133711/1997) and has a structure similar to that shown in FIG.
1
. Specifically, a bump contact
2
illustrated in
FIG. 1
is protruded from one side or one principal surface of an insulating substrate
1
. The bump contact
2
is electrically connected through a conductive portion
4
to an electrode
3
which is operable as a part of an electric circuit provided on the other side, namely, another principal surface of the insulating substrate. The bump contact
2
has a basic shape portion
2
a
(an inside layer), of nickel, and an intermediate layer of plated gold on a surface of the basic shape portion
2
a
. In addition, a surface layer
2
c
and fine projections
2
d
each of which is formed by rhodium are deposited on the surface of this intermediate layer. The surface layer
2
c
and the fine projections
2
d
may preferably be formed by the same material (rhodium) deposited by plating. The fine projections
2
d
are formed by controlling plating current so as to be locally protruded from the surface layer
2
c
. With this structure, the surface layer
2
c
and the fine projections
2
d
are combined together to form an integrated material structure without a boundary between them. As a result, the above-mentioned publication reports that fine projections are obtained which hardly come off and which are practically kept constant in configuration.
However, no disclosure is made at all in the above-referenced publications about sizes and surface roughness of the fine projections formed on the surface of the conventional bump contact. From this fact, it is difficult from the publications to know about appropriate ranges for the surface roughness specified by Rmax and Ra, a ratio of Rmax/Ra, and about a projection pitch or spacing, the projection shape including the thickness, the projection density and other configuration of projections. As a result, forming conditions are liable to fall outside of an acceptable range and to give rise to undesirable shapes of the projections. Since the forming method itself of projections makes it difficult to avoid a variation of the projection shape, the projection shape often falls outside the acceptable range. A projection shape formed outside the acceptable range results in inconveniences, such as breakaway of projections and a variation of contact resistance.
Alternatively, a method is also disclosed in Japanese Unexamined Patent Publication (A) No. H09-133711 (133711/1997) to manufacture a bump contact. The bump contact actually manufactured by the method is disadvantageous in that adhesion of the surface layer
2
c
and the projections
2
d
is weak and the projection shape or configuration is variable. This is also similar to the case where no intermediate layer
2
b
of plated gold is interposed between the surface layer
2
c
of rhodium and the projections
2
d
of rhodium and, as a result, the surface layer
2
c
and the projections
2
d
are formed directly on the surface of the basic shape portion
2
a.
Practically, it is confirmed that the surface layer
2
c
and the projections
2
d
of rhodium in the bump contact manufactured by the method disclosed in the aforementioned Publication have easily peeled off in a tape peeling test. This shows a low adhesion of the projections.
In the bump contact prepared by the method described in the above-publication, as projections become high, they become thinner in some cases. This easily comes off the bump surface through repetition of contact between the bump contact and the contact object, and this brings about a variation in contact resistance.
Heretofore, it is difficult to deposit the fine projections always to a constant height (a constant surface roughness) and to keep a variation of surface roughness and a projection density invariable. This sometimes results in a variation of the contact resistance between different bumps. If the contact resistance is varied among bumps, inconvenience is liable to occur on transmitting electric signals between the probe structure and the DUT. This makes it difficult to obtain accurate and reliable measurement results due to the variation of the contact resistance among the bumps. Very high contact resistance makes it difficult to transmit and receive electric signals between the probe structure and the DUT.
As a result of searching for causes of the above circumstances, it has been ascertained that presence of an inert layer under the projecting portions brings about a poor adhesion of the projecting portions, and that presence of the inert layer gives rise to a variation of the projection shape. It has also been found out that a change in current density during plating adversely affects stability of current density and also deforms the projection shape.
Provision of an intermediate layer of gold or the like under the projecting portion has been also found to lead to a poorer adhesion of the projecting portion. Provision of such an intermediate layer has a problem of a more complicated manufacturing process.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a probe structure which is capable of making a configuration or shape of projections uniform within a predetermined range and which therefore has excellent properties.
It is another object of the present invention to provide a method of manufacturing a probe structure which has projections with a comparatively uniform configuration.
Another object of the invention is to provide a probe structure which has projections of a good adhesion, excellent bump contacts in strength and which rarely causes breakage to occur even after repetition of contact. The probe structure can keep contact resistance substantially constant among individual bump contacts and is easy to manufacture.
The probe structure and the manufacturing method thereof of the invention have the following configurations.
Configuration 1
A probe structure which comprises an insulating substrate having first and second principal surfaces, a bump contact protruded from the first principal surface, and an electrode electrically connected to the bump contact and operable as a part of an electrical circuit formed on the second principal surface and/or an inner side of the insulating substrate, wherein the bump contact has a surface roughness which is specified by Rmax within a range from 0.01 to 0.8 &mgr;m, Ra within a range from 0.001 to 0.4 &mgr;m, and a ratio of Rmax/Ra within a range from 2 to 10.
Configuration 2
A probe structure according to configuration 1, wherein the bump contact has, on
Hoya Corporation
Karlsen Ernest
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