JPH01172770A - Inspection of printed circuit board - Google Patents

Abstract

PURPOSE:To inspect a large number of measuring points at a high speed, by comparing the detection signal outputted from a signal detection part with a scheduled reference signal. CONSTITUTION:At first, for example, the switch 1a of the probe 1 brought into contact with the measuring point A set to one terminal of a condenser C1 among probes is closed to be connected to a measuring signal source 5. Further, the switch 2b of the probe 2 brought into contact with the measuring point B set to the other terminal of said condenser C1 is closed to be connected to a signal detection part 12. Impedance measurement also performing the discharge of the condenser C1 is performed through said two probes 1, 2. This measurement is successively performed with respect to the probe brought into contact with the measuring point of each condenser. Next, (N-1) probes are connected to the signal source 5 with respect to a circuit network to be measured and the remaining one probe is connected to the detection part 12 and this operation is performed with respect to each probe to measure the impedance of each measuring point. The quality of each printed circuit board is judged on the basis of each impedance value.

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 a circuit board using an in-circuit tester, a board fixing device called a fixture is used. This fixture is equipped with a number of probes (eggplant 1 to bottle) corresponding to the measurement points of the circuit board to be inspected, and it gives a measurement signal through the probes and detects the response signal. The quality of the circuit board is determined by comparing the detection signal with non-defective data previously absorbed from the board. 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 is a method that tests everything between each probe. For example, when testing a circuit network consisting of capacitors C1 and C2 and resistors R0 and R2 as shown in Figure 3, each measurement After contacting the probes 1 to 4 to points A to D, respectively, the signal is transmitted from the signal source 5 via the scanner 6? ll'l regular AC credit AC signal, A-
B, A-C, A-D.

After performing the test steps B-C, B-D, and C-D, a
The dl setting will be performed by the +su section 7.

■Death 1- by short group and open group
(When absorbing good data from a board, a group (short group) of probes below a certain level is created for a specific probe.

At the time of inspection, a product is judged to be non-defective if the probes in that group are below a certain level and are open to other groups.

■ Pin-to-pin test: If there are single products such as R, C, and R, measure between the probe bins. Regarding the example of FIG. 3, tests are performed between AB, B-C, C-ri, and D-A.

[Problem that the invention seeks to solve]

The brute force method described in Section 2 (2) has a relatively simple program, but 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, the short circuit and open circuit shown in (2) is relatively fast, but if it is determined to be defective, it is inconvenient to carry out repairs because the location of the defective part has to be determined. According to point (3), the pin-to-pin test has good accuracy and can accurately locate the defective part, which is convenient for repair, but the program is complex and requires a lot of 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 being measured, and without such comprehensive knowledge, it is impossible to write the program. This means that it cannot be created.

Furthermore, in any of ■, ■, and ■, for example, if a large amount of charge happens to accumulate in the capacitor,
During all-setting, the discharge current may damage the switch contacts of the scanner.

Therefore, in general, a discharge circuit 8 equipped with, for example, a switchable resistor is provided, and after the electric charge is discharged, the actual measurement is performed at the Ube 7. For this reason, there is a problem that the device becomes complicated, leading to an increase in cost, and at the same time, high speed is impaired.

This invention was made in view of the above-mentioned conventional circumstances,
The purpose is to provide a circuit board testing method that does not require complicated program design and can test a large number of measurement points at high speed without particularly providing a discharge circuit. .

[Means for solving problems]

Referring to the embodiment shown in FIG. 1, in order to achieve the above-mentioned object, the present invention includes a plurality of (N) probes 1 that contact measurement points on a circuit board to be measured.
,2. . . . 81 constant signal source 5 which supplies all constant signals to the circuit board under test via the probe, and signal detection which detects the response signal output from the circuit board under test via the same probe. section 12 and switching means 10 for connecting the probe to either the measurement signal source 5 or the signal detection section 12, the signal detection section 12
In the circuit board inspection method for determining the quality of the circuit board to be inspected by comparing the detection signal output from the circuit board with a predetermined reference signal, first, Between the pins? After determining ltq, the main measurement for the circuit network in (b) is performed,
The quality of the board is determined.

(B) First, the switch 1a of one of the probes 1 that contacts the measurement point A set at one end of the capacitor C1 is closed, and the probe 1 is connected to the measurement signal source 5. , the switch 2b of one probe 2 that contacts the lI + q constant point B set at the other end is closed, the probe 2 is connected to the signal detecting section 12, and the capacitor is connected via these two probes 1 and 2. The impedance measurement which also serves as the discharge of step 1 is carried out, and this measurement is carried out sequentially for the probe that contacts the measurement point of each capacitor.

(b) Next, for example, for a circuit network consisting of capacitors C1, C2° and resistors R□, R2 shown in the figure, connect N-1 of the probes to the measurement signal source 5, and connect the remaining probes to the measurement signal source 5. Connect one probe to the signal detection section 12 and measure the impedance of each measurement point by doing this for each probe, and judge the quality of each probe based on the impedance values in (a) and (b) above. It is characterized by

[For production]

Prior to the inspection, non-defective data (reference data) serving as a judgment standard is captured from a non-defective board. This data acquisition work is carried out by 1. 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, as described in (b) above. By switching the probes in this way, the impedance of each measurement point is measured individually and the value is stored in 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, a probe is applied to each measurement point on the circuit board under test, and the probes are switched for each capacitor and circuit network in the same order and under the same conditions as when acquiring non-defective data shown in (a) and (b) above. The impedance of 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 present invention will now be described in detail with reference to the entire embodiment shown in FIG.

The figure shows each measurement point A- of the same circuit network as in Figure 3.
An example is shown in which four probes 1 to 4 are brought into contact with D. Each probe 1 to 4 has two changeover switches la, lb; 2a, 2b; 3a, 3b: 4a
, 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 la, 2a, 3a, 4a. In addition, each probe 1 to 4 is connected to the other switch lb, 2b, 3.
It is connected to the signal detection section 12 via b and 4b.

In this embodiment, the signal source 5 includes, for example, a constant voltage source equipped with two Zener diodes (not shown) for preventing overcurrent output, and the signal detecting section 12 includes, for example, a load resistor R3.
and a current-limiter type current-voltage converter having a protection circuit such as a resistor R4 and diodes D1 and D2. The output side of this signal detection section 12 is connected to an A/
A D converter 14 is connected, and the converted data is sent to the CP
It is processed by U (central processing means) 15, and the switches 18 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 bring each of the probes 1 to 4 into contact with measurement points A to D of the non-defective substrate.

Then, as described in (a) of the above explanation of the operation, for example, impedance measurement that also serves as discharge for the capacitor C1 on the board is first performed. is "closed" and the other switches 28 to 4a are "open", and among the switches 1b to 4b on the signal detection unit 12 side, switch 2b is
``Close J'', other switches lb, 3b, 4b ``Open''
shall be.

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 R2 to the capacitor C2 to the resistor R1, and after merging at the measurement point B, flows into the signal detection section 12.

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 C1 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 performed on capacitor C2, for example. That is, one of the switches 1a to 4a on the AC power supply 5 side, for example, switch 4a, is set to "closed J," and the other switches 18 to 3a are
is set to "open A," and among the switches 1b to 4b on the signal detection section 12 side, switch 3b is set to "closed," and the other switches 1b, 2b, and 4b are set to "open."

As a result, the current flowing from the AC power supply 5 is transferred from the measurement point D to the capacitor C2 and from the resistor R2 to the capacitor C1.
The signal is divided into two paths of the resistor R, merges at a fixed point C at 8'111, and then flows into the signal detection section 12.

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 fixed points sandwiching the capacitors are connected to the AC power supply 5 and the signal detecting section 12 with a switch, the impedance is measured, and the reference data is obtained. absorb.

In this impedance measurement, if there is almost no charge in the capacitor, the measurement is completed instantaneously. Also,
If there is an electric charge, it is semi-forcibly neutralized by a measurement signal from the AC power source 5, for example.

After that, it becomes the original response signal to the measurement signal. Therefore, as described above, impedance measurement that also serves as a discharge measurement is possible.

Once the reference data has been captured in the impedance measurement for the capacitor, the impedance is measured for one circuit network and the reference data is absorbed, for example,
Among the switches 18 to 4a on the AC power supply 5 side, switch 1a
is set to "open" and the other switches 2a to 4a are set to "closed", and among the switches 1b to 4b on the signal detection unit 12 side, switch 1b is set to "closed" and the other switches 2b to 4b are set to "closed".
is "open". As a result, measurement points B and 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. This current is converted into, for example, a voltage by the signal detection section 12, and then converted into digital data by the A/D converter 14 in the same manner as described above. 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, among the switches 1a to 4a on the AC power supply 5 side, the switch 2a is set to "open", the other switches la, 3a, and 4a are set to "closed", and the switches 1b to 4b on the signal detection section 12 side are set to "open". , switch 2b is "closed," and the other switches 1b, 3b, and 4b are "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, non-defective (reference) data as a determination standard is absorbed from non-defective boards, but it is preferable to obtain data from a plurality of non-defective boards and use the average value.

Thereafter, the circuit board to be tested is set in a fixture and the board is tested. Namely.

The switches 18 to 4a on the AC power supply 5 side and the switches 18 to 4a on the signal detection unit 12 side are switched in the same order as the switch switching order in the case of impedance measurement that also serves as discharge for the above-mentioned capacitor and in the case of original impedance measurement for the circuit network. The switches 1b to 4b are switched to measure the impedance of each measurement point A to D of the circuit board to be inspected, and the CPU 15 compares the measured data with reference data stored in the memory 16. In this case, the reference data has a predetermined tolerance range, and if the measurement data is within that range, "0'GO" indicating inspection passing is displayed on the display device 17 such as a CRT, and if it is outside the range, Indication of defective products, e.g. IrNG”
is displayed.

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

Incidentally, FIG. 2 shows a flow diagram of an example in which the impedance measurement of the capacitor is controlled by the CPU 15. In this embodiment, if no charge is accumulated in the capacitor of the circuit board to be inspected and the capacitor 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 a charge, the first few measurement data will vary, so for example, the 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 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, This is performed sequentially for each capacitor to detect the impedance at each measurement point.

Also, for the circuit network, among the N probes, (N-1)
The operation of connecting the book to the measurement power supply side and switching the remaining probe to the signal detection side is repeated N times to detect the impedance at each measurement point, and determine pass/fail based on that value. .

Therefore, when inspecting a circuit board, discharge and measurement can be performed simultaneously while ensuring the safety of the scanner contacts by using an AC power supply that does not output an ill 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 one embodiment of the present invention, and FIG.
The figure 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 source, 12 is a signal detection section, 14 is an A/D converter, is is a CPU, and 16 is a memory.

Claims (1)

[Claims] A plurality of (N) contacting measurement points on the circuit board to be measured.
a measurement signal source that supplies a measurement signal to the circuit board to be tested via the probe, a signal detection section that detects a response signal output from the circuit board to be tested via the probe, and the probe. and a switching means for connecting the circuit board to either the measurement signal source or the signal detection section, and by comparing the detection signal output from the signal detection section with a predetermined reference signal, the quality of the circuit board to be inspected can be determined. In the circuit board inspection method for determining the circuit board, one and the other of a pair of probes that contact measurement points set at both ends of a capacitor on the circuit board to be measured are respectively connected to the measurement signal source and the signal detection section. Discharge the above capacitor and measure its impedance. Then, perform this on the probe of each capacitor. Then, apply one of the above probes to the circuit under test.
Connect N-1 to the measurement signal source mentioned above, and connect the remaining one to the signal detection section mentioned above, measure the impedance of each measurement point by doing this for each probe, and use the value of each impedance mentioned above. A circuit board inspection method characterized by determining whether each is good or bad.