JPH0758317B2 - How to set pass / fail judgment tolerance of circuit board inspection equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a quality determination tolerance setting method when inspecting the quality of a circuit board on which electronic components and the like are mounted. The present invention relates to a quality determination tolerance setting method suitable for inspecting a circuit board on which elements having different impedances for a positive half wave and a negative half wave are mounted.

[Conventional example]

Circuit board inspection devices called in-circuit testers have come to be used for inspection of circuit boards on which electronic components and the like are mounted.

An example of this is shown in FIG. 6. For example, when a measuring AC voltage is emitted from the signal source 1 and applied to the circuit board to be inspected (hereinafter, referred to as “test board”) 3 via the amplifier 2,
A current that is inversely proportional to the magnitude of the impedance Z _X flows through the substrate 3. This current is, for example, taken in by the current detector 4 and detected, converted into a voltage here, then digitally converted by an A / D converter (not shown) and added to the measuring section 5. The measuring unit 5 uses the converted data to calculate the impedance Z _X of the test board 3 and compares it with the reference value Z _S stored in the memory in advance. In this case, as shown in the following formula, if it is within the predetermined tolerance ± α, it is judged as good, and if it is outside the tolerance, it is judged as bad, and the judgment result is displayed on the display 6 or the like. There is.

In determining Z _S -αZ _X Z _S + α determined Z _X <Z _S -α or Z _X> Z _S + α [Problems to be Solved by the Invention] The conventional circuit board inspection method for "bad" in the "good" is An AC voltage for measurement is applied from the signal source 1 to the test board 3, the voltage output from the current detector 4 is measured, and the impedance Z _X is obtained from the data.

However, when the object to be measured is, for example, a diode, the impedance is significantly different between the positive half-wave and the negative half-wave of the measuring AC voltage, and when the ambient temperature changes, each of them changes significantly. It is known that. Therefore, for such a semiconductor element, it has been difficult to set an appropriate tolerance for the quality judgment in the past.

The present invention has been made in view of the above circumstances, and an object thereof is to allow a difference in impedance between positive and negative half-wave periods in a circuit including a diode in consideration of a change due to the influence of ambient temperature. It is an object of the present invention to provide a quality determination tolerance setting method in a circuit board inspecting device, which is configured so that accurate quality determination can be performed.

[Means for Solving the Problems]

Referring to FIG. 1, which illustrates an embodiment of the present invention,
In order to solve the above problems, the following means (a) to (e) are provided.

I. For example, for a plurality of circuit boards that have been confirmed as non-defective in advance, a one-cycle measurement AC signal is added from the signal source 11 for each measurement point, and the response signals for the positive half-wave and the negative half-wave are respectively integrated. Integrator 16,17.

B. For example, the digital conversion data of the integrated voltage obtained from the integrators 16 and 17 is used to measure the impedance when a positive half-wave is applied and the impedance when a negative half-wave is applied to the measuring AC signal by the measuring unit 20 and average each. Value Z
μ determined _A and Zμ _B, the reference data memory 20d that holds this value as a reference impedance at the measurement point.

C. Polarity calculating means 20c for obtaining the ratio (polarity) p = Zμ _A / Zμ _B of the average value Zμ _A of the impedance when the positive half-wave is applied and the average value Zμ _B of the impedance when the negative half-wave is applied.

D. The root mean square values σ _A and σ _B are obtained from the respective impedance data at the time of applying the positive half wave and the negative half wave and their average values Zμ _A and Z μ _B (reference impedance). value sigma _a, tolerance for variations in the impedance Z _X test substrate based on sigma _B alpha _a,
Tolerance setting means 20a that calculates α _B and selects a predetermined tolerance for quality judgment from this tolerance and the tolerance calculated using the above-mentioned polarity.

C. Comparing means 20b for measuring the impedances Z _XA and Z _XB of the test substrate 3 when a positive half wave and a negative half wave are applied, comparing the impedances Z _XA and Z _XB with each other to determine whether the impedances are within the above-mentioned tolerances, and determining the quality.

[Action]

By including the above means, the quality of the impedance of the test board can be correctly determined even if the measured impedance value includes a quantity that changes with temperature.

〔Example〕

In this embodiment, first, a plurality of substrates that have been confirmed to be non-defective are measured in advance and the data are collected, and then a test substrate is measured by the same method, and then the data of both are compared to determine pass / fail. I am supposed to do it.

Referring to FIG. 2 together with FIG. 1 above, for example, a signal source
A one-cycle AC voltage for measurement as shown in FIG. 2A is emitted from 11 and applied to the non-defective substrate 3 via the amplifier 12. As a result, a current that is inversely proportional to the magnitude of the impedance Z _S flows through the substrate 3. in this case,
If a diode or the like is mounted on the substrate 3 in the forward direction with respect to the AC voltage for measurement, the impedance is low for the positive half-wave and high for the negative half-wave, so the current flowing is It becomes as shown in FIG. This current is detected by, for example, the current / voltage converter 13 and then the second
As shown in FIG. 3C, the voltage is converted into a voltage with a predetermined gain and applied to the switch 14.

In this embodiment, the operation of the signal source 11 and the current / voltage converter 13 is controlled by, for example, the measuring unit 20, and
Sends an AC voltage of a predetermined frequency for one cycle as described above. Further, the current / voltage converter 13 detects a current in the positive direction and a current in the negative direction which flow through the substrate, and converts them into positive or negative voltages of the same polarity with a constant gain. The switching controller 15, for example, shapes the positive half wave and the negative half wave of the measuring AC voltage emitted from the signal source 11 into square wave voltages, and outputs the waveform to switch the switch 14 to the second wave.
As shown in FIG. 4D, the positive half-wave period is driven to the contact A side, and the negative half-wave period is driven to the contact B side.

As a result, the converted voltage of the current flowing through the substrate 3 in one half-wave period 0 to π is integrated by the integrator 16 as shown in FIG.
The converted voltage at 2π is integrated by the integrator 17 as shown in FIG. The integrated voltage of these good boards
Assuming V _A and V _B , these two integrated voltages are respectively A / D converters 18 and 1 as shown in (g) and (h) of FIG.
Digitally converted at 9 and sent to the measuring unit 20.

In this case, the integrators 16 and 17 may be rewritten by, for example, a peak hold circuit to hold the peak value of the input signal, and the peak value of the input signal may be digitally converted by the A / D converter in the next stage.

The measuring unit 20 calculates the central impedances Zμ _A and Zμ _B of the non-defective substrate for each of the positive and negative half waves of the measuring AC voltage based on these integrated voltage data, and also the tolerance α _A for the variation in the impedance of the test substrate, If α _B is obtained by, for example, the tolerance setting means 20a, and at the same time, the tolerance of the impedance change due to the temperature change is set, the test board 3 is subjected to the same method as described above in the positive half wave and the negative half wave. After the impedances Z _XA and Z _XB are measured and the data are compared, the judgment result of good or bad and the measurement data are sent to the recording / display unit 21 and displayed and recorded.

Here, the tolerance for the impedance variation will be described with reference to FIGS. 3 (A) and 3 (B).
Now, when measuring the impedance of the positive half-wave period and the impedance of the negative half-wave period at the same measurement point of each good board, if the number of boards is appropriate, the distribution state of the measurement data approximates a normal distribution, It is known that more than 99% of the number of test substrates falls within ± 3σ with respect to the average values Zμ _A and Zμ _B.

Therefore, in this embodiment, the tolerances α _A and α _B with respect to the impedance variation in the positive half-wave period and the negative half-wave period are, for example, α _A = Zμ _A × (± 3σ _A ) [Ω] α _B = Z μ _B × (± 3σ _B ) [Ω] is set and expressed in% based on the average value, and α _A = ± 3 σ _A × 100 [%] α _B = ± 3 σ _B × 100 [%].

Next, with reference to FIG. 4, a description will be given of changes in impedance due to changes in ambient temperature. This figure shows an example of data obtained by measuring single diodes. For example, the forward impedance at room temperature (20 ° C) is used as a reference.
If Z _A is the impedance at other temperatures and Z _A ′ is the ratio, and the ratio Z _A ′ / Z _A is plotted, the general tendency is that the rate of impedance change when the temperature decreases from the reference temperature is higher than the reference temperature. It is bigger than that.

The impedance ratio Z _B ′ / Z _{B in the} reverse direction is also shown in the figure, but the rate of change has the same tendency as in the case of the forward direction. However, comparing the two, it can be seen that the rate of change in the reverse impedance is smaller than the rate of change in the forward impedance.

For a mounting board consisting of a large number of parts, the measured data for a single product is not always applicable, and it is difficult to theoretically analyze changes in temperature and board impedance.
If the ratio p = Z _A / Z _B of the forward impedance Z _A and the backward impedance Z _B at the reference temperature is called, for example, the polarity, the amount of change in the impedance of the substrate due to the above temperature can be calculated from the measured data such as species. It has been found that there is a relationship with the value of this polarity ratio p.

Therefore, in this embodiment, data is collected from a non-defective substrate at room temperature of about 20 ° C., and the upper limit value and the lower limit value for impedance change are calculated using the polarity ratio p, and
The calculated value is compared with the tolerance of the variation with respect to the central impedance to select the acceptable / non-defective tolerance in practical use with respect to the impedance measurement value of the test board.

Next, a method of selecting the quality determination tolerance will be described. In the following description, the average values Zμ _A and Zμ _B are
It is set as 100 [%]. The reason is that, in general, in this type of circuit board inspection apparatus, a predetermined value is set to 100% rather than the measured impedance value, and the range of non-defective products is expressed as ±% for inspection. n is a digit error and is displayed in% with respect to the full-scale value at the time of A / D conversion. For example, if this digit error is 1 bit and the full scale is 8 bits, n = (1 /
256) x 100%. In addition, “10000 / p”, “p / p−n”, and “p / p + n” appearing below as comparison values are obtained by experiments, and “100 ± 3σ _A ” and “100 ± 3σ _B ” are Average value (10
This is the calculated deviation value from (0).

I. When the polarity p is 100% or less (Zμ _A <Zμ _B ) Upper limit of positive half-wave impedance Z _A : (a) If 100 + 3σ _A > 10000 / p, set to 100 + 3σ _A (impedance change amount is (Ignore) ... (a) in FIG. 3 (A).

(B) If 100 + 3σ _A <10000 / p, set it to 1000 / p ... Same figure (b).

Lower limit of positive half-wave impedance Z _A : (C) If 100-3σ _A <p, set to 100-3 σ _A (ignoring the amount of impedance change).

(D) If 100-3σ _A > p, set to p ... (d) in the figure.

Upper limit of negative half-wave impedance Z _B : (e) If 100 + 3σ _B > p / p−n, set to 100 + 3 σ _B (impedance change amount is ignored) ... (e) in FIG. 3 (B).

(F) If 100 + 3σ _B <p / p-n, set to p / p-n ... (f) in the figure.

Lower limit of negative half-wave impedance Z _B : (g) If 100−3σ _B <p / p + n, set to 100−3 σ _A (impedance change amount is ignored) ... (g) in FIG. 3 (B).

(H) If 100-3σ _B > p / p + n, set to p / p + n ... (h) in the figure.

. II polarity index p is greater than 100% (Zμ _A> Zμ _B) when the positive upper limit value of the half-wave direction impedance Z _A: (Re) set to _{100 + 3σ A> p / p} -n if 100 + 3 [sigma] _A (impedance change (Ignore the amount) ... (i) in Fig. 3 (A).

(Nu) If 100 + 3σ _A <p / p-n, set to p / p-n ... (nu) in the figure.

Lower limit value of positive half-wave impedance Z _A : (L) If 100-3σ _A <p / p + n, set to 100-3 σ _A (impedance change amount is ignored) ... (L) in FIG. 3 (A).

(E) If 100-3σ _A > p / p + n, set to p / p + n ... (e) in the figure.

Upper limit of negative half-wave impedance Z _B : (W) If 100 + 3σ _B > 10000 / p, set to 100 + 3 σ _B (impedance change amount is ignored) ... (W) in FIG. 3 (B).

(F) If 100 + 3σ _B <10000 / p, set to 10,000 / p ... (F) in the figure.

Lower limit of negative half-wave impedance Z _B : (Yo) If 100−3σ _B <p, set to 100−3 σ _B (impedance change amount is ignored).

(Ta) If 100-3σ _B > p, set to p ... (ta) in the figure.

Incidentally, FIG. 5 is a flow chart showing an example of automatically setting the above-mentioned respective tolerances by software.

In the above embodiment, each of the above values (a) to
Although (a) is set automatically, it may be set manually after each value is calculated. Further, since the polarity p (= Zμ _A / Zμ _B ) varies depending on the magnitude of the measuring voltage, it is not always a constant value.
It is also possible to prepare a table of polarities according to the measurement conditions and obtain the value.

〔effect〕

As described above in detail, in the present invention, the positive half-wave direction impedance Z _A and the negative half-wave direction impedance Z _B of the non-defective substrate are measured and the center impedance Z of each is measured.
In addition to obtaining μ _A and Z μ _B , the tolerances α _A and α _B of the original substrate variation with respect to the center values are obtained, and then the polarities p = Z μ _A / Z μ _B that represent the ratio of the center impedances are used. After changing the impedance due to, the lower limit value is calculated and compared with the above-mentioned variation tolerance, and the larger value is taken as the allowable upper limit value of the quality judgment, and the smaller value is taken as the allowable judgment lower limit value. It is like this.

Therefore, when the board is inspected by this tolerance setting method, even if the impedance measurement data of the test board includes the variation inherent to the board and the change due to temperature, the quality can be determined with sufficient accuracy in practical use. For example, in the case of a diode, the impedance is low in the forward direction, but the rising part of the forward current is measured during inspection, so it is greatly affected by disturbances in impedance and temperature and other disturbances. In the opposite direction, the impedance is large and almost no current flows, so
The meaning of 1 bit in A / D conversion becomes large, but according to the present invention, it is possible to set the lower limit value taking these into consideration. If the room temperature is normal, it is not necessary to measure the ambient temperature when inspecting the board, which is extremely convenient.

[Brief description of drawings]

1 to 5 relate to an embodiment of the present invention, FIG. 1 is a block diagram showing the configuration of a circuit board inspection apparatus to which the present invention is applied, FIG. 2 is a waveform diagram for explaining the operation, and FIG. FIG. 4 is an explanatory diagram of a tolerance setting method, FIG. 4 is an explanatory diagram of polarity, FIG. 5 is a flowchart showing an example of automatic setting of upper and lower limit values by software, and FIG. 6 is a block diagram showing a configuration of a conventional device. It is a diagram. In the figure, 3 is a circuit board to be inspected, 11 is a signal source, 20 is a measurement unit,
20a is a tolerance setting means, 20b is a comparison means, and 20c is a polarity rate calculation means.

Claims (1)

[Claims] 1. An impedance of the circuit board to be inspected is measured by a response signal obtained by applying a measuring AC signal from the signal source to the circuit board to be inspected, and the measured value is preliminarily obtained from a non-defective board by the same method. In comparison with the imported reference value, in the quality determination tolerance setting method of the circuit board inspection device to determine the quality of the circuit board to be inspected by whether it is within the predetermined tolerance, the positive of the measuring AC signal, Each 3σ is obtained from the distribution characteristic of the impedance variation of each non-defective substrate with respect to each negative half-wave, and the upper and lower limits of each impedance distribution related to the ratio (polarity ratio) of the central values of the two distribution characteristics. A value is calculated, and the calculated value is compared with the above 3σ, and the impedance when the positive half wave is applied and the impedance when the negative half wave is applied are allowed. Furthermore, to set the lower limit value, respectively, quality determination tolerance setting of the circuit board inspection apparatus characterized by a quality determination tolerances for the measured impedance of the circuit board to be inspected.