Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-01-11
2002-02-05
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S754090, C439S072000
Reexamination Certificate
active
06344753
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a test socket capable of continuously and stably measuring the electric characteristics of an electronic device or semiconductor package, as well as to a method of forming contact terminals, i.e. contacts or contact pins for measurement purposes, of the test socket.
2. Background Art
There will be described a method of establishing electrical contact between contact terminals (contacts) of a conventional test socket (a socket provided for measurement purpose) and external connection terminals of an integrated circuit (IC) or a semiconductor package, by reference to an example of a surface-mounted IC, e.g., a quad flat package (QFP).
FIG. 10
is a perspective view showing an IC
10
to be measured and a test socket
60
having a plurality of contact terminals (contacts)
20
. Contact terminals
20
of the test socket
60
are embedded in a housing
30
formed from an insulating member. External connection terminals
50
of the IC
10
are brought into pressing contact with contact planes
21
of the respective contact terminals
20
.
FIGS. 11A and 11B
are enlarged cross-sectional views showing contact between one of the external connection terminals
50
and the contact plane
21
of the corresponding contact terminal
20
.
FIG. 11A
is an enlarged view showing the contact plane
21
of the contact terminal
20
and a contact plane
51
of the external connection terminal
50
, and
FIG. 11B
shows contact when the contact plane
51
is brought into pressing contact with the contact plane
21
.
An oxide insulation film
52
(hereinafter referred to as an “oxide film,” as needed) is present on the surface of the external connection terminal
50
of the IC
10
and possesses high electrical resistance. In order to ensure superior electrical contact, the contact surface
51
to be electrically connected must be brought into contact with the contact plane
21
by means of fracturing the oxide film
52
. The external connection terminals
50
are further pressed to a certain degree while remaining in contact with the respective contact terminals
20
, thus deflecting the contact terminals
20
. As a result, relative slippage arises between the contact plane
21
of the contact terminal
20
and the contact plane
51
of the external connection terminal
50
, thus removing the oxide film
52
and bringing the contact plane
51
into electrical contact with the contact plane
21
.
Contact established by the foregoing conventional contact terminals (or contacts) suffers the following problem.
In association with fracture of the oxide film
52
of the external connection terminal
50
, which results from relative slippage between the contact plane
21
of the contact terminal
20
and the contact plane
51
of the external connection terminal
50
, a member
54
constituting the external connection terminal
50
(solder plating in this case) coagulates onto the contact surface
21
of the contact terminal
20
. Greater relative slippage contributes to fracture of the oxide film
52
and enlargement of the contact area, thus effectively establishing superior electrical contact. However, the greater relative slippage also results in an increase in the amount of solder coagulating onto the contact plane
21
. In most cases, the substance to coagulate corresponds to metal which oxidizes, such as solder. Through repetition of oxidation of the surface of the contact plane and deposition of the substance on the surface of the contact plane, contact resistance is increased, thereby preventing good electrical contact. More specifically, although relatively new contact terminals
20
establish good electrical contact, contact resistance is gradually increased with the number of times the contact terminals
20
are brought into contact with the contact planes of the external contact terminals
50
for measurement, thus rendering electrical contact difficult to achieve and shortening the life of the contact terminal
20
.
Secondly, if superior electrical contact is not achieved, a non-defective IC may be determined to be defective, and the non-defective IC may be discarded.
Thirdly, if the percentage of ICs determined to be defective through erroneous determination exceeds a certain specified percentage, the group of ICs determined to be defective through erroneous determination is again subjected to determination, thus unnecessarily consuming time or incurring unnecessary costs.
Fourthly, the external connection terminals of the most current ICs tend to be arranged at narrower pitches. In association with this tendency, a contact failure is caused when foreign matter generated by an IC; for example, resin burrs or glass fillers contained in resin, is present between the contact terminal and the external connection terminal.
Japanese Patent Application Laid-Open No. Sho-58-199545 describes a measure for avoiding such a contact failure; i.e., a contact terminal whose tip end is formed into a plurality of sharp projections so as to establish contact by avoiding generation of foreign matter. However, since the projections of the contact terminal are sharp, the projections damage the external terminals, thus causing appearance or packaging failures.
SUMMARY OF THE INVENTION
The present invention has been conceived to solve the drawbacks of the conventional test socket, and the object of the present invention is to ensure stable contact between the external terminals of an electronic device and contact terminals of a test socket, thus realizing stable, continuous contact.
According to one aspect of the present invention, a test socket comprises contact terminals which are brought into electrical contact with external connection terminals of an electronic device or a semiconductor package, and each of the contact terminal has a plurality of protuberances and a plurality of recesses. The plurality of protuberances are formed from smooth curved surfaces in the portion of the contact terminals which contacts the corresponding external connection terminal, and the plurality of recesses are formed from smooth, curved surfaces adjacent to the respective protuberances.
According to another aspect of the present invention, a test socket comprises a plurality of contact terminals, and each of the contact terminals includes one or more contact projections provided on the surface thereof for contacting the external connection terminals of the electronic device or semiconductor package. The tip end of each of the contact projections being formed to assume a substantially spherical surface having a radius of curvature of 0.03 to 0.3 mm. Further, each of the contact projections has a plurality of minute protuberances and a plurality of minute recesses provided on the substantially spherical surface thereof formed from smooth curved surfaces.
According to still another aspect of the present invention, in a method of forming contact terminals of the test socket as stated above, the portion of each contact terminal, which contacts an external connection terminal of the electronic device or the semiconductor package, is machined to a desired surface roughness through electric-discharge machining. Then, the thus-roughened portion is plated with electrolytic nickel. Further, the thus nickel plated portion is plated with gold.
Other and further objects, features and advantages of the invention will appear more fully from the following description.
REFERENCES:
patent: 5170117 (1992-12-01), Chio
patent: 5230632 (1993-07-01), Baumberger et al.
patent: 5699612 (1997-12-01), Inoue et al.
patent: 5936418 (1999-08-01), Ideta et al.
patent: 6208155 (2001-03-01), Barabi et al.
patent: 58-199545 (1983-11-01), None
patent: 8-306749 (1996-11-01), None
Kaneko Keiko
Maekawa Shigeki
Takada Shigeru
Tokumo Yasushi
McDermott & Will & Emery
Metjahic Safet
Nguyen Vincent Q.
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