Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-05-23
2004-11-30
Deb, Anjan (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S658000
Reexamination Certificate
active
06825673
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus and method for inspecting electrical continuity of a circuit board, for example, having a fine wiring pattern. The present invention also relates to a jig for use in such an inspection.
BACKGROUND ART
As a system for inspecting a circuit board, there have been known a pin-contact system and a non-contact system. As shown in
FIG. 1
, the pin-contact system is configured to inspect electrical continuity between both ends of a conductive pattern as an inspection object by bringing two pin probes directly into contact with the ends, respectively, and applying a current to one of the pin probes so as to determine a resistance value of the conductive pattern from a detected voltage at the other pin probe.
This pin-contact system has an advantage of a high signal-to-noise (SN) ratio because of the pin probes contacted directly with the conductive pattern.
On the other hand, in case of inspecting a fine-pitch board, it is fundamentally difficult to set up the pin probes only to a conductive pattern as an inspection object, and it is increasingly hard to secure an adequate positioning for bringing the pin probes into contact with the aimed pattern. Due to the necessity for keeping in the contact state, it is also difficult to maintain the initial accuracy of the pin probes themselves, resulting in undesirably increased running cost arising from replacements of the pin probes.
As shown in
FIG. 2
, the other non-contact/contact combined system is configured to apply an inspection signal including an alternating current (AC) component with making one pin probe contact directly with one end of a conductive pattern as an inspection object (or through a capacitive coupling in a non-contact manner) and detect the inspection signal through a capacitive coupling at the other end.
The non-contact/contact combined system allows at least one of the pin probes not to be contacted with a pattern wire or the conductive pattern. This provides a relatively wide acceptable range of positioning accuracy for the pin probe, which makes it possible to use the pin probe commonly for a plurality of pattern wires, and thereby to reduce the number of pin probes. Furthermore, since the pin prove is free from any wear, the combined system is effective for a board with a fine wiring pattern.
However, the non-contact/contact combined system has a small value of coupling capacitance and a high impedance (from several M&OHgr; to several G&OHgr;). Thus, this system cannot detect any defective portion having a resistance ranging from about 10&OHgr; to about 100&OHgr;.
As a result, due to the property including high impedance despite having many advantages, the non-contact/contact combined system has been actually implemented only for a board with an extremely narrow pitch not to allow pin probes to be adequately set up thereon. Thus, the required high accuracy in the pin probes and a jig thereof has been an obstacle in the effort to facilitate the cost reduction in the non-contact/contact combined system.
It is therefore an object of the present invention to provide a continuity inspection apparatus capable of inspecting any electrical conductivity not only under a high resistance but also under a low resistance by making a capacitance provided in the non-contact system generate a resonance in oscillations of a circuit formed on a board to reduce the impedance of the circuit.
DISCLOSURE OF THE INVENTION
According to the present invention, an electrode is disposed close to one of ends of a pattern as an inspection object to form a capacitance C between the end and the electrode, and an inductive element L is connected to the capacitance C. An inspection signal (frequency f) including an AC component is applied to the other end of the pattern wire through a pin probe.
When the impedance of a resonance circuit is reduced by appropriately adjusting the value L, or when the value L is adjusted, for example, so as to satisfy the following formula (1),
2
f·L
=(1/2)
f·C
(1)
the following formula is derived from the formula (1).
L
=(1/4
2
)×
f
2
×C
(2)
In other words, the impedance of the circuit can be zero by adjusting the value L in the formula (2), and then an output voltage V exhibits a maximum value. Given that V
R
is the output voltage V in case of using a reference circuit board (i.e. a circuit board in which no disconnection has been verified) and applying a resonance frequency f
R
thereto, the output voltage V
x
in case of using an actual circuit board as an inspection object would indicate a larger value because the circuit is expected to come close to a resonance state.
As one example, when the value of the coupling capacitance is 10 fF, the relationship between the working frequency f
R
and the inductive element L which can cooperatively generate the resonance state is shown as follows,
when f
R
=10 kHz, L=25.3 kH, or
when f
R
=10 MHz, L=25 mH, or
when f
R
=50 MHz, L=1 mH, or
when f
R
=100 MHz, L=250 mH.
A parameter for controlling resonance includes the frequency f of the input inspection signal, the coupling capacitance C, and the inductance L of the inductive element. For example, when the electrode has a fixed size and the measuring is carried out with keeping the distance between the electrode and the pattern constant, the capacitance C would be, for example, about 15 fF. Then, by adjusting the value of the inductive element L in the range of about 250 mH to about 1 mH, and providing an AC signal source having a frequency ranging from about 50 MHz to about 100 MHz, the impedance can be substantially zero.
Based on the above knowledge, according to a first aspect of the present invention, there is provided a continuity inspection apparatus for inspecting electrical continuity between first and second terminals of a pattern wire formed on a board, comprising:
capacitive coupling means to be capacitively coupled with the first terminal in a non-contact manner to provide a coupling capacitance therebetween;
an inductive element connected to the capacitive coupling means to form a resonance circuit in conjunction with the capacitance yielded by the capacitive coupling means;
a first lead wire connected to the inductive element;
probe means connected to a second lead wire and to be contacted with the second terminal;
signal inputting means for inputting an inspection signal including an AC component into one of the first and second lead wires; and
signal detecting means for detecting an output of the inspection signal at the other of the first and second lead wires.
The arrangement of the inductive element may be variously modified. Thus, according to a second aspect of the present invention, there is provided a continuity inspection apparatus for inspecting electrical continuity between first and second terminals of a pattern wire formed on a board, comprising:
probe means to be directly contacted with the first terminal;
an inductive element connected to the probe means;
a first lead wire connected to the inductive element;
capacitive coupling means connected to a second lead wire and to be capacitively coupled with the second terminal in a non-contact manner to provide a coupling capacitance therebetween;
signal inputting means for inputting an inspection signal including an AC component into one of the first and second lead wires; and
signal detecting means for detecting an output of the inspection signal at the other of the first and second lead wires.
The coupling capacitance may be formed at both the first and second terminals. Thus, according to a third aspect of the present invention, there is provided a continuity inspection apparatus for inspecting electrical continuity between first and second terminals of a pattern wire formed on a board, comprising:
first capacitive coupling means to be capacitively coupled with the first terminal in a non-contact manner to provide a coupling capacitance therebetween;
an inductive element connecte
Benson Walter
Deb Anjan
OHT Inc.
Westerman Hattori Daniels & Adrian LLP
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