JPH0333665A - Inspecting apparatus for defect of conductor of printed wiring board - Google Patents

Abstract

PURPOSE:To specify the presence or absence of a defect and the position thereof on a conductor to be inspected, by sending a pulse to the conductor and by measuring a waveform of a reflection pulse from the end point of conduction. CONSTITUTION:A high-frequency pulse is sent from a pulse generator 13 into a probe 4-2 being in contact with a start point 3-5 of a conductor 2-3 to be inspected, through a sampler 12. The pulse sent in passes through the conductor 2-3 and reaches a place 11 of a defect, whereat reflection occurs. This reflection pulse passes through the conductor 2-3 again and is displayed, via the sampler 12, on an oscilloscope 14 as a time-to-voltage waveform. By measuring a time delay of the reflection pulse on the oscilloscope 14, a distance from the start point 3-5 of the place 11 of the defect can be specified. In addition, a change in the reflection waveform can be observed also from thickening 9 of a conductor 2-1 or narrowing 10 of a conductor 2-2, and therefore the position thereof can also be specified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for inspecting conductor defects in printed wiring boards.

[Conventional technology]

FIG. 4 shows a conceptual diagram of the configuration of an example of a conventional continuity testing device for printed wiring boards. In the figure, 1 is the printed wiring board to be inspected, 2 (2-1, 2-22-3) are each conductor provided on the printed wire board 1, and 3 (3-1
, 3-2, 3-3° 3-4; 3-5, 3-6) are through holes having lands forming the starting and ending points of each of these conductors 2. Also, 4 (4-1,4
2 and 4-3) are respective probes that are in contact with each through hole 3, and the other ends are all connected to the connector 5. Reference numeral 6 indicates a power source for passing a current used in the test, 7 indicates an ohmmeter for measuring the direct current resistance of the continuity path, and arrow 8 indicates a wire connected from the start or end point of the conductor via each probe 4. A probe (4-1 in the drawing) is shown for sequentially checking continuity in the connector part 5. This figure shows the basic concept of this type of continuity tester.In the actual device, the connector 5 and probe 8 are
C, is configured with a scanning system replaced with relays, etc.

Each inspection probe 4 that has come into contact with each through hole 3 at the start and end points of each conductor 2 to be inspected on the printed wiring board 1 to be inspected connects the power supply 6 and Nu resistor 2 17 inside the inspection device through the connector 5. 1 form a circuit.

FIG. 4 shows an example of a state in which a circuit is formed through the probes 4-1 and 4-2 and the terminals 2#n and the bottom from the top of the connector 5.

At this time, if there is a break in the conductor to be inspected, continuity is lost and the resistance measured by the resistance meter 7 becomes infinite, indicating that there is a break in the conductor. In addition, even if there is no breakage, if a part of the conductor becomes extremely thin, a change in the resistance value of the conductor can be seen, and it can be determined that there is a defect in the conductor. . Also, if you move to the third terminal from the top of test probe 4 or connector 5,
The patterns on the printed wiring board 1 are not connected, and the measured resistance value is infinite. In actual equipment, this switching of the probe 4 is performed by a relay or an IC as described above.
The speed has been increased by using πφ, and currently the system is designed to be able to measure the switching resistance of several dozen measurement conductors in an instant.

The measured connectivity of the conductors is compared with other boards to be measured of the same type, design data, etc. to determine the presence or absence of defects in the conductors.

[Problem to be solved by the invention]

However, since the conventional printed wiring board conductor defect inspection apparatus is configured as follows, for example, the conductor 2-1 shown between the through holes 3-1 and 3-2
A very small chipped (thin) part 10, which may be a change in resistance of the conductor 2-2 between the through-holes 3-3 and 3-4, is overlooked. Further, a break in the conductor 2-3 near the through hole 3-6 shown in 11 is only determined to be a break between the probes 4-2 and 4-3, and the exact position cannot be specified. Furthermore, since the position of the probe 4-1 is neither the start point nor the end point of the conductor, it becomes even more difficult to identify the disconnection point if the test probe is not brought into contact. Moreover, in a multilayer printed wiring board, when a defect occurs in an inner layer pattern, it is extremely difficult to identify the location of the defect such as a wire break.

This invention was made in order to solve the problems with the conventional inspection equipment as described above, and provides a printed wiring board that can determine the presence or absence of defects in the conductor L and can identify the location of the defects. The purpose is to provide conductor defect inspection equipment.

[Means to solve the problem]

Therefore, in the printed wiring board conductor defect inspection apparatus according to the present invention, the continuity of the conductor to be inspected is checked, and a specific frequency pulse is sent from the start point of the conductor and reflected from the end point of the conductor. The purpose is to achieve the above object by configuring the device to observe and measure the incoming pulses.

[Effect]

The printed wiring board conductor defect inspection apparatus according to the present invention having the above configuration uses a time domain reflection (TDR) method that measures a specific pulse sent from the starting point of the conductor to be inspected and a pulse reflected from the ending point of the conductor. ) technique,
By measuring the reflected pulse, it is possible to specify the distance from the starting point of the conductor defect position, and it is also possible to infer the type of defect.

(Examples) The present invention will be described below based on Examples. FIG. 1 shows a conceptual diagram of the configuration of an embodiment of a conductor defect inspection apparatus according to the present invention, and the same (equivalent) components as in FIG. 4 of the conventional example are denoted by the same reference numerals, and redundant explanation will be omitted.

In FIG. 1, 12 is a sampler connected to a probe 4-2 connected to the starting point of the conductor to be tested 2-3, 13 is a pulse generator, 14 is for observing the pulse waveform passing through the conductor to be tested; Shows an oscilloscope for measurements. The oscilloscope 14 measures reflected pulses from the end point of the conductor to be inspected or from a defective location 11 such as a disconnection.

Next, this measurement method will be explained.

In FIG. 1, as in the conventional conductor defect apparatus in FIG. A high-frequency pulse of, for example, IMI+2 or higher is sent from the pulse generator 13 to the conductor to be tested via the sampler 12 through the connecting cable to the probe 4-2 in contact with (. Through the conductor defect point 11
, where a reflection occurs. This reflected pulse passes through the conductor line again and is passed through the sampler 12 to the oscilloscope 1.
4, for example in the second I (a), (b) - an example time versus voltage waveform is displayed. In this case, the pulse would normally reach the end point, through hole 3-6, so
(a) The waveform observed on the oscilloscope 14 must be shown as shown in the figure (b), for example, because if there is a defect on the way, a reflection will occur in front of it.
It will show a specific waveform as shown in . Since the pulse speed propagating within the conductor is constant, the distance of the defective location 11 from the starting point 3-5 can be specified by measuring the time delay of this reflected pulse.

In addition, changes in this reflected waveform can be observed when the conductor becomes thicker (9) or thinner (10), so it is possible to discover and locate conductor defects that could not be identified with conventional continuity tests. can.

FIG. 2(b) shows an example of the relationship between the observed waveform and the type of defect in the conductor. 15 is the reflected waveform of the thick part of the conductor as shown in 9, for example, and T is the reflected waveform from the same part. reflection time,
Reference numeral 16 indicates a reflected waveform of a thick section of the conductor as shown by 1o, T2 indicates a reflection time from the same section, and T3 indicates a reflection time from a conductor disconnection section as indicated by 11.

(Other Examples) In the above example, the defect position of the conductor was determined from the reflected pulse of the pulse sent from the starting point of the conductor, but the voltage ratio of the response pulse could also be measured using the same device. This allows determination by measuring the characteristic impedance of the conductor.

FIG. 3 is a waveform diagram showing the concept of a method for measuring the characteristic impedance of a conductor using the TDR method, and the characteristic impedance 2° of the conductor is expressed by the following equation.

E・+E"xz Z・"E, -E2 Here, 2 indicates the characteristic impedance of the conduction path on the measuring instrument side from the probe 4 to the connector 5 section, and should be measured in advance. .

(Effects of the Invention) As explained below, according to the present invention, the measuring section using the TDR method is arranged in parallel so as to send a pulse to the conductor to be inspected of the printed wiring board and measure the reflected pulse. As a result, the position of the defect in the conductor to be inspected can be specified, and the shape and type of the defect can also be inferred.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a conceptual diagram of the configuration of a conductor defect inspection device according to an embodiment of the present invention, Fig. 2 is an example of a pulse waveform observed by the same embodiment, and Fig. 3 4 is a waveform diagram illustrating a method for measuring characteristic impedance of a conductor, and FIG. 4 is a schematic diagram of an example of a conventional conductor defect inspection apparatus. 1... Printed wiring board 2... Conductor to be tested 4... Inspection probe 12... Sampler 13... Pulse generator 14... ...Oscilloscope In each figure, the same reference numerals indicate the same elements. or equivalent configuration

Claims (1)

[Claims] A conductor for a printed wiring board, comprising a pulse generating means for sending a pulse to a conductor to be inspected on a printed wiring board, and a measuring means for observing and measuring a reflected pulse waveform from an end point of the conductor. Defect inspection equipment.