Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2001-01-22
2002-04-16
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S095000
Reexamination Certificate
active
06373258
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an inspection probe used for inspecting a board in a non-contact manner, and an inspection method and apparatus using this probe. A target board is represented by a board printed with conductive patterns at a small pitch and includes e.g., a flexible board (a “flexible board” includes an LSI package which is not mounted with IC chip and is to be mounted therewith, and will be referred to simply as a “circuit board” hereinafter). More particularly, the present invention relates to a non-contact board inspection probe and an inspection method and apparatus, all of which are suitable for inspecting local patterns on a board for disconnections and the like.
The board inspection probe and the inspection method and apparatus of the present invention are effective in inspecting a so-called bare circuit board on which no circuit elements such as IC packages are mounted yet although conductive patterns having a small pitch are printed thereon.
In conventional board inspection, if a board on which conductive patterns having a small pitch are printed has a large pitch on the electrode side, as shown in
FIG. 1
, probes can be brought into contact with the electrode groups (two or more electrode groups) of the board to energize the board (power is supplied from one electrode group, and the inspection result is detected on the other electrode group).
A recent highly-integrated circuit board, however, has small pitches in not only conductive patterns, but also electrodes. This makes it difficult to accurately bring probes into contact with the electrodes having a small pitch. An inspection for determining defectiveness
ondefectiveness (particularly, the presence/absence of a disconnection) of such a board having patterns (conductive paths) with a small pitch has often relied on visual observation or the like.
In recent years, the conductive patterns of a board (inspection target board) have a higher density (smaller pitch) along with decreases in size and weight of electronic devices. The decrease in pitch tends to cause disconnections in conductive patterns. A strong demand has therefore arisen for board inspection meeting this tendency. Demands for improving workability and reliability and decreasing the cost have become important.
In inspection for a board having patterns with a small pitch, in addition to a problem posed by the difficulty in accurate positioning of probes on electrodes, another problem is posed by an increase in the number of measuring points. More specifically, in such a board, when the wiring density of conductive patterns increases (i.e., when the pitch becomes small), the number of input and output points (the number of measuring points) increases. Even if contact probing is possible, it is technically difficult to maintain stable contact precision and contact properties. In addition, as the test conditions are becoming stricter than before, complicated, high-precision inspection jigs must be prepared, resulting in high cost.
Under these circumstances, several prior-art techniques based on non-contact probing, i.e., the board inspection free from the problem posed by contact between probes and electrodes are known.
For example, British Patent No. GB2143954A has proposed a technique for positioning a probe electrode at the end of a conductive path to form capacitive coupling between the electrode and the end of the conductive path. An AC signal is applied between the electrode and the one end of the conductive path, and a signal is detected at the other end of the conductive path through the above capacitive coupling. By this technique, a board can be inspected without bringing the probe into contact with the conductive pattern.
Japanese Patent Laid-Open No. 6-34714 (U.S. Pat. No. 5,254,953) is deemed an improved proposal of the non-contact inspection method disclosed in GB2143954A described above.
Japanese Patent Laid-Open No. 5-264672 (U.S. Pat. No. 5,274,336) discloses a capacitive coupling probe (probe chip) used in an in-circuit test for a high-density circuit board.
In the above prior arts, the “non-contact” means coupling free from ohmic contact and is equivalently used as the “capacitive”. That is, a means for capacitive coupling is a capacitor.
The present inventor found that when the above prior-art inspection method and apparatus, however, were applied to a circuit board such as a bare board prior to mounting circuit parts thereon, it was difficult to highly accurately detect the presence/absence of a defect (e.g., a disconnection). That is, even if the prior-art technique is used to inspect a board in which the presence of a disconnection has been confirmed, an inspection result representing the absence of a disconnection is obtained. The present inventor found the cause for this as follows.
FIG. 2
is a block diagram of an inspection apparatus in U.S. Pat. No. 5,254,953. This prior-art technique is an apparatus serving as an in-circuit tester. This tester inspects to find whether a lead wire
111
of an IC package
110
is normally connected to a lead wire
140
on a circuit board by soldering
200
. That is, the tester inspects soldered portions, but does not inspect the pattern itself for any defects.
Referring to
FIG. 2
, an AC signal is supplied from an oscillator
100
to the lead wire
140
between a probe electrode
120
and the lead wire
111
through a capacitor layer formed by air layer and the IC package
110
. A shield
130
is arranged to prevent the probe electrode
120
from picking up EMI (Electro-Magnetic Interference) from various devices (not shown) located above the probe electrode
120
.
If soldering
200
is proper, the AC signal is detected by an electrode
310
and measured by an inspection apparatus
300
. Whether soldering is defective or nondefective is determined by the magnitude of the signal detected by the electrode
310
. Note that the capacitance of the capacitor layer formed by the air layer and the IC package
110
between the probe electrode
120
and the lead wire
111
is as small as several femtofarad (fF), and the amplitude of the signal detected by the electrode
310
is very small.
The present inventor found that when this probe electrode
120
was applied to a bare board
500
, as shown in
FIG. 3
, the measurement of a signal by the electrode
310
upon intentionally forming a disconnection
510
in a lead wire
520
on the board
500
had almost no difference in the amplitude of the detection signal from the measurement of a signal by the electrode
310
through a lead wire
520
free from disconnections.
According to the findings of the present inventor, no difference was found in detection signal between the cases in which the disconnection
510
was present and it was absent because the signal applied to the probe electrode
120
propagated in the electro-magnetic field formed in the air layer and was received by a lead wire portion
520
a
, and the signal on the lead wire portion
520
a
was detected by the electrode
310
.
Although the inspection apparatus in
FIG. 3
has the shield
130
which is effective to protect the probe electrode
120
from the EMI signal coming from above, the inspection apparatus is defenseless against radiant waves from various radiant sources located below the electrode
120
.
In inspecting a bare board, as shown in
FIG. 3
, the probe electrode must particularly come closer to the bare board. In the inspection apparatus disclosed in U.S. Pat. No. 5,254,953 to inspect an in-circuit board which need not bring a probe electrode closer to the board due to the presence of parts, the problem posed by the EMI signal from the board does not arise because the probe electrode is used far away from the board.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a board detection probe and a board inspection method and apparatus, wherein a shield for preventing an EMI signal from acting on a pattern on a board or from being emitted from the pattern in the board inspection apparatus for inspecting the
Armstrong Westerman & Hattori, LLP
Karlsen Ernest
Kobert Russell M.
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