JPH0574024B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for testing a circuit board, and more specifically, to a novel testing method for an in-circuit tester.

[Conventional example]

When testing circuit boards using an in-circuit tester, a board fixing device called a fixture is used. This fixture is equipped with a large number of probes (test pins) that correspond to measurement points on the circuit board to be inspected, and not only gives a measurement signal through the probes, but also detects the response signal. By comparing the absorbed good product data and its detection signal,
It is designed to determine whether the circuit board is good or bad. That is, basically, a specific probe is connected to a measurement signal source and a detection signal is obtained from the corresponding predetermined probe. There are several ways to do this.

Brute force method: This tests everything between each probe. For example, when testing a network consisting of capacitors C ₁ and C ₂ and resistors R ₁ and R ₂ as shown in Figure 3, , probes 1 to 4 at each measurement point A to D, respectively.
After making contact with A-B, A-B, A-B and
-C, AD, BC, BD, and CD, and the measuring section 7 performs the measurement.

Short group, open group test: When absorbing good data from a good board, a group of probes below a certain level for a specific probe (short group)
A product is determined to be non-defective when the probes in that group are below a certain level and are open to other groups during inspection.

Pin-to-pin test: If there are single products such as L, C, and R, measure between the probe pins. Regarding the example in Figure 3, A-B, B-
Test between C, CD and DA.

[Problem that the invention seeks to solve]

Although the program of the brute force method described above is relatively simple, as the number of measurement points increases, the number of measurement steps increases significantly, resulting in a lack of high speed. On the other hand, although shortening and opening is relatively fast, if it is determined to be defective, it is difficult to locate the defective part and it is inconvenient to repair it. According to the pin-to-pin test, the location of the defective part can be determined with high accuracy and is convenient for repair, but the program is complex and requires considerable effort to design. In this case, the first problem is that it is assumed that the program creator knows not only the measurement method but also the properties and characteristics of the parts to be measured. This means that it cannot be created.

Furthermore, in any case, for example, if a large amount of charge happens to accumulate in the capacitor, the switch contacts of the scanner may be damaged by the discharge current during measurement.
Therefore, generally, for example, a discharge circuit 8 equipped with a switchable resistor is provided, and after the electric charge is discharged, the measurement section 7 performs the actual measurement. For this reason, there are problems in that the device becomes complicated, leading to an increase in cost, and in addition, high speed performance is impaired.

This invention was made in view of the above-mentioned conventional circumstances, and its purpose is to eliminate the need for complicated program design and to enable high-speed inspection of a large number of measurement points without specifically providing a discharge circuit. An object of the present invention is to provide a method for inspecting a circuit board.

[Means for Solving the Problems] Referring to the embodiment shown in FIG. The probes 1, 2, ... of the book), the measurement signal source 5 that supplies measurement signals to the circuit board under test via the probes, and the response signals output from the circuit board under test are also detected via the probes. and a switching means 10 for connecting the probe to either the measurement signal source 5 or the signal detection section 12, the signal detection section 1
In the circuit board testing method for determining the quality of the circuit board to be tested by comparing the detection signal outputted from 2 with a predetermined reference signal, first,
After performing the pin-to-pin measurement intended to discharge the capacitor within the board in (a) below, the main measurement on the circuit network in (b) is performed to determine the quality of the board.

(b) First, switch 1 of one of the probes 1 that contacts measurement point A set at one end of capacitor C ₁ , for example.
a to connect the probe 1 to the measurement signal source 5, and close the switch 2b of one probe 2 that contacts the measurement point B set at the other end to connect the probe 2 to the signal detection section 12. The impedance measurement which also serves as the discharge of the capacitor 1 is performed via these two probes 1 and 2, and this measurement is performed sequentially for the probes that come into contact with the measurement points of each capacitor.

(b) Next, for example, for a circuit network consisting of capacitors C ₁ and C ₂ and resistors R ₁ and R ₂ shown in the figure, N-1 of the probes are connected to the measurement signal source 5.
By connecting the remaining one to the signal detection section 12 and performing this for each probe, the impedance of each measurement point is measured, and the impedance values of (a) and (b) above are obtained. It is characterized by determining the quality of each product.

[Effect]

Prior to inspection, non-defective data (reference data), which serves as a determination criterion, is captured from a non-defective board.
In this data acquisition process, for example, for capacitors, each impedance is measured by a pin-to-pin test conducted through two probes as described in (a) above, and for circuit networks, the impedance is measured as described above.
By switching the probes as in (b), the impedance of each measurement point is measured individually, and the value is stored in the memory. In this way, data is preferably absorbed from a plurality of non-defective boards, and the data is averaged to determine non-defective data that serves as a criterion.

After that, the actual board inspection begins. That is, place a probe at each measurement point on the circuit board under test, and apply the above measurements to each capacitor and network.
The probes are switched in the same order and under the same conditions as when absorbing the good product data shown in (a) and (b), and the impedance at each measurement point is measured. Then, this measured impedance value is compared with non-defective product data, and it is determined whether it is within the allowable range.

〔Example〕

The invention will now be described in detail with reference to the embodiment shown in FIG.

This figure shows an example in which four probes 1 to 4 are brought into contact with each measurement point A to D of a circuit network similar to that in FIG. 3. Each probe 1 to 4 has two changeover switches 1a, 1b, 2a, 2
b, 3a, 3b, 4a, and 4b are connected in parallel. Each of the probes 1 to 4 is connected to a measurement signal source, for example, an AC power source 5, via one of the switches 1a, 2a, 3a, 4a. In addition, each probe 1 to 4 is connected to the other switch 1b, 2b, 3.
It is connected to the signal detection section 12 via b and 4b. In this embodiment, the signal source 5 is composed of, for example, a constant voltage source equipped with two Zener diodes (not shown) for preventing overcurrent output;
2 comprises, for example, a current-limiter type current-voltage converter having a load resistor R ₃ and a protection circuit such as a resistor R ₄ and diodes D ₁ and D ₂ . This signal detection section 12
An A/D converter 14 is connected to the output end of the amplifier 13, and the conversion data is sent to the CPU.
(Central processing means) 15, and the switches 1a to 4b are also controlled by this CPU 15.

According to this invention, board inspection is performed in the following manner. First, non-defective data used as a criterion is obtained from a non-defective board. That is, a non-defective substrate is set in a fixture (not shown), and a press device (also not shown) is operated to press each probe 1 to 4.
is brought into contact with the measurement points A to D on the non-defective board.

Then, as described in (a) of the above explanation of the operation, impedance measurement is first performed, which also serves as discharge, for the capacitor _C1 on the substrate, for example. That is, among the switches 1a to 4a on the AC power supply 5 side, switch 1a is "closed" and the other switches 2a to 4a are "open", and among the switches 1b to 4b on the signal detection section 12 side, switch 2b is set to "close". ``close'',
The other switches 1b, 3b, and 4b are set to ``open''.

As a result, the current flowing from the alternating current 5 is divided into two paths: from the measurement point A to the capacitor 1 and from the resistor R ₂ -capacitor C ₂ -resistor R ₁ , and after merging at the measurement point B, flows into the signal detection section 12. do. This current is converted into, for example, a voltage in the signal detection section 12, applied to an A/D converter 14 via an amplifier 13, and then converted into digital data. This data is the impedance value when the capacitor C ₁ is the main measurement target at the measurement point A of the non-defective board, and the CPU 15 stores this non-defective data in the memory 16 as reference data for the measurement point A.

Next, measurements are taken on capacitor _C2 , for example. That is, switches 1a to 4 on the AC power supply 5 side
Among a, for example, switch 4a is "closed" and other switches 1a to 3a are "open",
Among the switches 1b to 4b on the signal detection unit 12 side,
Switch 3b is "closed", other switches 1b,
Let 2b and 4b be "open".

As a result, the current flowing from the alternating current 5 is divided into two paths: from the measurement point D to the capacitor C ₂ and from the resistor R ₂ to the capacitor C ₁ to the resistor R ₁ , and after joining at the measurement point C, it is sent to the signal detection section 12. Inflow. This current is converted into, for example, a voltage in the signal detection section 12, and further converted into digital data in the same manner as described above, and then stored in the memory 16 as reference data for the measurement point D. Hereinafter, similarly for other capacitors (not shown), the probes that touch the two measurement points sandwiching the capacitors are connected to the AC power supply 5 and the signal detection section 12 using a switch,
Perform impedance measurements and absorb the reference data.

In this impedance measurement, if there is almost no charge in the capacitor, the measurement is completed instantaneously. Further, if an electric charge is generated, it is semi-forcibly neutralized by the measurement signal from the AC power supply 5, and thereafter becomes the original response signal to the measurement signal. Therefore, as described above, impedance measurement that also serves as a discharge measurement is possible.

When the impedance measurement for the capacitor ends and the reference data is taken in, the impedance measurement is performed for the circuit network and the reference data is absorbed.For example, the switch 1a of the AC power supply 5
-4a, switch 1a is "open" and other switches 2a-4a are "closed", and among switches 1b-4b on the signal detection unit 12 side, switch 1b is "closed" and other switches 2b -4b is set as "open". As a result, measurement points B, C,
Since D are at the same potential and only measurement point A is at a lower potential than them, current flows from measurement points B and D toward measurement point A in this example. After this current is converted into, for example, a voltage in the signal detection unit 12, it is converted into an A/D in the same way as above.
The data is converted into digital data by a converter 14. This data is the impedance of the circuit network at measurement point A of the good board, and is
stores this non-defective data in the memory 16 as reference data for measurement point A. Next, AC power supply 5
Among the switches 1a to 4a on the side, switch 2a is set to "open" and the other switches 1a, 3a, and 4a are set to "closed." At the same time, among the switches 1b to 4b on the signal detection section 12 side, switch 2b is set to "closed." ”, and the other switches 1b, 3b, 4b are set to “open”. As a result, the impedance at the measurement point B is detected, and the data is stored in the memory 16 as reference data at the measurement point B. Thereafter, impedances at measurement points C and D are determined in the same manner, and the data is stored in the memory 16 as reference data at the same points C and D. In this way, good product (standard) data is absorbed from the good board as a judgment standard.
Preferably, data is obtained from a plurality of non-defective substrates and the average value thereof is used.

Thereafter, the circuit board to be tested is set in a fixture and the board is tested. That is, the switches 1a to 4a on the AC power supply 5 side and the signal The switches 1b to 4b on the detection unit 12 side are switched to measure the impedance of each measurement point A to D on the circuit board to be inspected, and the CPU 15 compares the measured data with the reference data stored in the memory 16. be compared. In this case, the reference data has a predetermined tolerance range, and if the measured data is within the range, "GO" indicating inspection pass is displayed on the display device 17 such as a CRT, and if it is outside the range, it is rejected. A non-defective product is displayed, for example, "NG" is displayed.

In the above embodiment, the comparison reference value is obtained from a non-defective board, but in some cases, for example, data at the time of design or data written in specifications may be used.

Incidentally, FIG. 2 is a flow diagram showing an example of the case where the impedance measurement of the capacitor is controlled by the CPU 15. In this example,
If the capacitor of the circuit board to be inspected has no charge accumulated and is a good product, the measurement is completed in one cycle of the measurement signal, and the quality can be determined. However, if there is an electric charge, some measurement data will initially fluctuate, so for example, a measurement signal is applied for 100 cycles and the measurement data of 100 times is compared with reference data to make a decision. Even in this repeated measurement, if the impedance of the capacitor does not fall within a predetermined range that includes the reference data, the measurement for the circuit board is discontinued at that point.

〔Effect of the invention〕

As explained above, according to the present invention, for example, for a capacitor, one of the probes that contacts the two measurement points sandwiching the capacitor is connected to the measurement power supply side, and the other is connected to the signal detection section side. is performed for each capacitor in turn to detect the impedance at each measurement point.

Also, regarding the circuit network, among the N probes,
(N-1) Connect the book to the measurement power supply side, and the remaining 1
Switch the main probe to the signal detection section side.
The impedance at each measurement point is detected repeatedly, and pass/fail is determined based on that value.

Therefore, when inspecting a circuit board, it is possible to perform discharge and measurement simultaneously while ensuring the safety of the scanner's contacts by using an AC power supply that does not output current exceeding a predetermined limit and a current limiter type signal detection section. , there is no particular need for a discharge circuit in the conventional device. Therefore, it can greatly contribute to the simplification and cost reduction of the device. Furthermore, it is no longer necessary to perform the original measurement again after discharging the capacitors, making it possible to speed up board inspection.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a flowchart showing an example of impedance measurement under CPU control, and FIG. 3 is a block diagram of a conventional device. In the figure, 1 to 4 are probes, 5 is a measurement power supply, and 12
is a signal detection section, 14 is an A/D converter, and 15 is a signal detection section.
CPU, 16 is memory.

Claims (1)

[Claims] 1. A plurality of (N) probes that contact measurement points on a circuit board under test, a measurement signal source that supplies a measurement signal to the circuit board under test via the probes, and the circuit board under test. a signal detection unit that detects a response signal output from the side via the probe; and switching means that connects the probe to either the measurement signal source or the signal detection unit, and includes a signal detection unit that detects the response signal output from the signal detection unit In the circuit board testing method, the quality of the circuit board to be tested is determined by comparing the detected signal detected by the circuit board with a predetermined reference signal. Connecting one and the other of the pair of probes to the measurement signal source and the signal detection section, respectively, discharges the capacitor and measures its impedance, and performs this for each capacitor probe, and then, Connecting N-1 of the probes to the measurement signal source for the circuit network under test, and connecting the remaining one to the signal detection section,
A circuit board inspection method characterized in that the impedance of each measurement point is measured by performing this for each probe, and the quality of each is determined based on the impedance value.