Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1998-11-23
2001-10-09
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
Reexamination Certificate
active
06300771
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an electrical inspection device for detecting a latent defect and, more particularly, to an electrical inspection device for effectively detecting a latent defect in a printed circuit board etc. The present invention also relates to a method for electrically inspecting a printed circuit board etc. against such a failure.
(b) Description of the Related Art
In general, a printed circuit board may have an open-circuit failure in an interconnect or a short-circuit failure between interconnects caused by fabrication steps such as mounting a semiconductor chip on the printed circuit board, which necessitates an electrical inspection of the printed circuit board to confirm the absence of these defects.
The printed circuit board generally has defects such as a pseudo ON-state (or a latent open-circuit failure: a defect in an apparent normal ON-state that results in an open-circuit failure upon application of only a small mechanical, thermal or electrical stress) or a pseudo insulated state (a defect in an apparent normal insulated state that results in a short-circuit failure upon application of only a small mechanical, thermal or electrical stress) in a printed circuit board. In the text to follow, both the failures are referred to as “loose contacts”.
A conventional electrical inspection of a printed circuit board is executed by using an electrical inspection device such as shown in FIG.
1
.
The conventional electrical inspection device
40
includes a test block
41
having a current source
411
for generating a specified constant current and a measurement block
412
for allowing the constant current, supplied from the current generator section
411
, to impress upon an interconnect
21
between subject terminals
22
a
and
22
b
by using probes
23
a
and
23
b
so as to detect the resistance component involved between the terminals
22
a
and
22
b
after measuring the voltage between the terminals
22
a
and
22
b
. The inspection device also has a comparator block
42
for detecting a ON or OFF state of the interconnect
21
in the printed circuit board based on the measured resistance component of the interconnect
21
.
JP-A-60(1985)-102707 proposes a method for detecting a loose contact in a thin film interconnect, by applying a moderate pulse voltage having a specific pulse width and detecting a defect from the disturbance in the measured current wave.
In the conventional electrical inspection method, the loose contact cannot be effectively detected in a printed circuit board even when the loose contact resides in the interconnect.
Especially in the electrical inspection method proposed in JP-A-60-102707, there is a problem in that it is difficult to determine what kind of disturbance in the current wave falls within a defect to be detected as a loose contact.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electrical inspection device for use in a printed circuit board which is capable of effectively detecting a loose contact in the printed circuit board. It is another object of the present invention to provide a method for electrical inspection of a printed circuit board.
The present invention provides an electrical inspection device for inspecting a defect in an electric circuit comprising a pulse generator for generating a pulse train including a plurality of current pulses each having a specified current, a measurement block for impressing the pulse train between a pair of subject terminals and measuring a voltage appearing across the pair of subject terminals for each of the current pulses, a variation detector for detecting variation of resistance appearing between the pair of subject terminals based on the current of current pulses and the voltage measured for each current pulse, and a comparator block for comparing the variation against a threshold.
The present invention provides a method for electrically inspecting a defect in an electric circuit comprising the steps of impressing between a pair of subject terminals a pulse train including a plurality of current pulses each having a specified current, measuring a voltage appearing across the pair of subject terminals for each of the current pulses, detecting variation of resistance appearing between the pair of subject terminals based on the current of current pulse and the voltage measured for each current pulse, and comparing the variation against a threshold to detect a defect in the circuit.
In accordance with the present invention, a loose contact can be effectively detected which provides a significant variation in the resistance measured for each current pulse between the subject terminals.
REFERENCES:
patent: 5453696 (1995-09-01), Becker et al.
patent: 5502395 (1996-03-01), Allen
patent: 5525909 (1996-06-01), McCollum
patent: 60-102707 (1985-06-01), None
patent: 62-211568 (1987-09-01), None
patent: 7-146327 (1995-06-01), None
patent: 9-230002 (1997-09-01), None
Kerveros J
McGuireWoods LLP
Metjahic Safet
NEC Corporation
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