JPH021570A - Inspecting method for circuit board - Google Patents

Abstract

PURPOSE:To execute a decision by including a temperature difference by setting a tolerance which has added a prescribed value to three times of a square average value of an impedance distribution characteristic of a non-defective substrate, and also, adding a tolerance corresponding to an ambient temperature difference to said tolerance and deciding the quality. CONSTITUTION:The impedance in each measuring point of a circuit board which has been confirmed as a non-defective is measured by a current detector 14, its average value Zmu is set as a reference impedance Zs of a measured value, and also, three times of a square average value sigma of the average value Zmu and impedance measured data, that is, 3sigma is calculated, and a value + or -alpha1=3sigma+ZmuX2% which has added, for instance, 2% of the average value Zmu to said 3sigma is set to a reference data memory 21c as a tolerance to a variance of a test board. Also, an ambient temperature difference DELTAT is detected by a temperature detector 23, and based on this variable DELTAT, the product -alpha2(or +alpha3)=ZmuXk3DELTAT to the average Zmu is added to alpha1 as an impedance variation portion of a diode caused by a variation of ambient temperature.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a circuit board inspection method for inspecting the quality of a circuit board on which electronic components, etc. are mounted. The present invention relates to an inspection method suitable for circuit boards on which such elements and the like are mounted.

[Conventional example]

BACKGROUND ART Circuit board testing devices called in-circuit testers have come to be used to test circuit boards on which electronic components and the like are mounted.

An example of this is shown in FIG. 6. For example, a signal source 1 emits a measuring AC voltage of a predetermined frequency, and a circuit board to be tested (hereinafter referred to as "test board") 3 is transmitted via an amplifier 2.
In addition, a current flows through the substrate 3 that is inversely proportional to the magnitude of its impedance ZX. This current is taken into and detected by a current detector 4, for example, and is converted into a voltage there and then applied to a measuring section 5. The measuring section 5 digitally converts this input voltage, uses the converted data to calculate the impedance of the test board 3, and calculates the impedance Z of the test board 3, which is stored in the memory in advance.
Compare with 3. In this case, as shown by the formula below, if it is within a predetermined tolerance ±α, it is determined to be good, and if it is outside the tolerance, it is determined to be defective, and the determination result is displayed on the display 6 etc. There is.

Judgment of "good" Z9 (!≦ZX≦Zs+α Judgment of "defective"Zx<Zs-α or Zx>z,+α [Problems to be Solved by the Invention] In this conventional circuit board inspection method, generally, the signal An AC voltage for measurement is applied from the source 1 to the test board 3, the average value of the voltage output from the current detector 4 is measured, and the impedance ZX is determined from the data.

However, when the object to be measured is, for example, a diode, it has temperature characteristics such that its impedance changes relatively significantly due to changes in ambient temperature. Therefore, in conventional inspection methods, it is difficult to set an appropriate tolerance for pass/fail determination for semiconductor devices that are significantly affected by temperature.

This invention was made in view of the above circumstances, and its purpose is to automatically adjust the tolerance for low impedance, especially in the forward direction, such as a diode, by taking into account the variation due to the influence of ambient temperature in addition to the tolerance for the original variation. It is an object of the present invention to provide a highly accurate circuit board inspection method that allows accurate judgment of pass/fail by adding the above.

[Means to solve the problem]

Referring to FIG. 1, an embodiment of the invention is shown.
In order to solve the above problems, the following means A to II are provided.

For example, one cycle of AC signal for measurement is applied from the signal source 10 to each measurement point on n circuit boards that have been confirmed to be good in advance, and the response signals for the positive half wave and negative half wave are calculated. Integrators 17.18 to integrate respectively
For example, impedance zsi(i==x
, 2. . . . n), obtains the average value Zμ, and holds this value as the reference impedance Z at the measurement point.

C. n impedance data Z at the above measurement points
5i and its average value Zμ (reference impedance Zs), and for example, based on this root mean square value σ, set the tolerance α1 for the variation in the impedance to be measured Z, and also Tolerance setting means 21a0 for setting the tolerance α2 or α with respect to the change in impedance ZX.2.When measuring the impedance of the test board 13, if the ambient temperature rises or falls from the ambient temperature when measuring the good board, the temperature difference Accordingly, the comparison means 21b automatically adds, for example, the tolerance α2 or α3 to the tolerance α1, and performs impedance comparison according to the following equation to determine the quality of the test board 13.

(Judgment formula) When the ambient temperature rises (z p - a,) -ax≦Z,≦(Z μ+ a,
) -a.

...(1a) If the ambient temperature drops (Zμ−α1)+α, ≦ZX≦(Zμ+α, )+α.

...(1b) (If there is no change in ambient temperature, α2 = α, = 0)
By providing the above means, even if the impedance measurement value of the test board includes an amount that changes depending on temperature, the quality of the test board can be correctly determined.

〔Example〕

According to FIG. 1 above, the signal source 10 is provided with an oscillator that outputs a sine waveform AC voltage for one cycle with a frequency of 1 kHz for each measurement item, and the measurement AC voltage emitted from the signal source 10 is A voltage is applied to the test board 13 via a current amplifier 12.

As a result, a current flows through the substrate 13 in inverse proportion to the magnitude of the impedance ZX, and for example, the current detector 14
After being captured and detected, it is converted into voltage. In this embodiment, the current detector 14 is equipped with a range setting circuit 14a that switches its current/voltage conversion magnification, and the switching operation of this range setting circuit 14a is, for example, C
This is performed using a control signal from the PU 21. That is, the CPU 21 monitors the magnitude of the digital conversion data of the A/D converters 19 and 20, thereby ensuring that the analog voltages to be converted, which are applied to the A/D converters from the integrators 17 and 18, respectively, fall within a predetermined level range. The range setting circuit 14a is switched as follows. As a result, in the current detector 14, the detected current is converted into a voltage at a magnification specified by the range setting circuit 14a.
After being made into a pulsating voltage of either positive or negative polarity by
It is designed to be applied to a switch 16 driven by a switching controller 11.

In this embodiment, the signal source 10 includes, for example, a D/A converter and a voltage amplifier (not shown), and the signal source 10 is composed of, for example, a D/A converter and a voltage amplifier (not shown).
One cycle up to 60°, 1 kl (z sin waveform data is converted to analog voltage and output as AC constant voltage for measurement.

The switching controller 11 includes, for example, a zero-cross comparator and a flip-flop (not shown), and switches the switch 16 to the contact A side and the contact B side in synchronization with the positive half cycle and negative half cycle of the AC voltage generated from the signal source 10. It is designed to drive each.

Therefore, for example, if the switch 16 is driven to the contact A side during a half cycle period from 0 to π of the measurement AC voltage, and is driven to the contact B side during a half cycle period from π to 2π, the absolute value circuit Of the pulsating current voltages outputted from the oscilloscope 15, the voltage during the previous half cycle period is applied to the integrator 17, for example, and the voltage during the subsequent half cycle period is applied to the integrator 18 and integrated. These integrated voltages are digitally converted by, for example, A/D converters 19 and 20 and sent to the CPU 21. The CPU 21 calculates the impedance Z of the test board 13 in the positive half-wave and negative half-wave of the AC voltage for measurement based on these integrated voltage data.

are calculated and compared with the corresponding reference value Zs using the above-mentioned judgment formula (1) to determine the quality, and the results and measurement data are sent to, for example, the recording/display section 22.

Next, a supplementary explanation of the above operation will be given with reference to FIG. In addition, (A) or (C) in Figure 2 is shown in Figure 1.
The same reference numerals are given to the parts where the operations are performed. In this circuit board inspection method, as described above, first measure a circuit board that has been confirmed to be good, store that data in memory, then measure the test board under the same conditions as the good board, and save the data. It is designed to compare.

That is, as shown in FIG. 2(a), for example, when one cycle of measurement AC voltage is emitted from the signal source 10,
A current as shown in the same figure (b) flows through a non-defective board, which is inversely proportional to the magnitude of its impedance ZS. This current is detected by a current detector 14 and then converted into a voltage, and as shown in FIG.

The switch 16 is activated by the output of the switching controller 11 (d) in the same figure.
As shown in, for example, during the positive half-wave period from O to π, the contact point A
During the negative half-wave period from π to 2π, the contact B is driven toward the contact B side. Therefore, the voltage between 0 and π applied from the absolute value circuit 15 is integrated by the integrator 17 as shown in (E) of the same figure, and the voltage between π and 2π is (E).
The signal is integrated by an integrator 18 as shown in FIG. Assuming that the integrated voltages of these non-defective boards are vs^+VS9, these two integrated voltages are digitally converted by A/D converters 19 and 20, respectively, as shown in (g) and (h), and sent to the CPU 21. Using these integrated voltage data, the CPU 21 calculates the reference impedances Zμ and Zμ8 of the good board for the positive half-wave and negative half-wave of the AC voltage for measurement.
At the same time, the tolerances α1^ and α11I for the impedance variation of the test board are determined by, for example, the tolerance setting means 21a.

In this way, when the reference impedance Zμ^ (zsA), Zμ5 (ZsB) and the tolerance αA, α□8 at each measurement point of the non-defective board are taken, for example, by the tolerance setting means 21a, the test board 13 is The impedance ZXAt zxa is measured by the same method as above, and the data are compared using Equation 1 (1).

In this case, the tolerance α1 for impedance variations in equation (1) and the tolerance α2 or α3 added for impedance changes due to changes in ambient temperature. is determined, for example, using the following formula (2). In addition, in the above equation, 0°k2
．． k is a constant and ΔT is a variable related to the difference in ambient temperature.

First, to explain the tolerance α1 with reference to FIG. 3, Zμ on the horizontal axis is the average value of the impedance Z, i measured at the same measurement point of n non-defective substrates, that is, the standard of that measurement point. represents the impedance Z, and both sides represent the deviation from the average value. The vertical axis shows the number of test boards, that is, the number of measurement data.

In the figure, the average value Zμ is (i = 1.2...n), and if n is set to an appropriate value, the distribution state of the number of substrates for each deviation value will be the average as shown by the solid line. Approximate a normal distribution that is symmetrical with respect to the value Zμ. Therefore,
The root mean square value σ is calculated as σ=((1/n) Σ (Z
s i Z p )2)""When calculated from i=1, over 99% of the number of test boards falls within the range of ±3σ, and as is well known, the number outside this range is less than 1%. Become.

In this case, since all the test boards used are non-defective products, it is necessary to determine that the number of deviating from 3σ of 1% or less is also a non-defective product. Therefore, in this embodiment, measurement errors are taken into account, and for example, in equation (2), 1 is set to 3 and k2 is set to 2%, α, = 3 cr + 0.02 Zu (Ω)... (2
a) Or α1=(3σ/Zμ+0.02) X 100(%)
......(2b) is set.

Here, 1. For example, the impedance distribution of the test board is
Assuming that it is as shown by the dotted line in the figure, by applying this tolerance α1, it is possible to perform a pass/fail test for the variation with sufficient accuracy.

Next, the tolerance α for the temperature characteristics of impedance! (
α, ) will be explained with reference to FIG. 4. As shown in FIG. 4 (A), a non-defective board and a test board are measured at, for example, the same circumferential rotation T.

The distribution state of the number of data corresponding to the central value 2μ of impedance and each deviation value is the same as that shown in FIG. 3 above.

For example, if this test board is placed at an ambient temperature T+ΔT different from the above,
, when measured at T-ΔT, the center value is ZX'tz
, 1, in this embodiment, the deviation from the center value Zμ is -α2 or +α3 to the tolerance α1 for the inherent variation of the substrate shown in FIG. 3 above.
is automatically added to prevent a non-defective product from being mistakenly judged as defective even if the ambient temperature changes and the impedance changes.

This tolerance is determined as follows. Figure 4 (B)
shows the voltage-current characteristics of a diode, and if the current that flows when a forward voltage VF is applied to the diode is I, this current I is generally expressed by the following equation.

Ip=Is(exP((IVr/kT) 1)--(
4) Here, Is: Saturation current (A) when reverse voltage is applied q: Electricity of electron 1.6X10-" (C) k: Boltzmann constant 1.38 X 10-" (J/K) T: ambient temperature (K).

As is clear from equation (4), if the applied voltage V is constant, the current IF changes exponentially with the ambient temperature T as a variable, and an example near normal temperature is shown in Figure 4 (C). has been done. In the figure, the ambient temperature T is T1. T2
．． This is an example of the voltage-current characteristic when T3 (T□>T ->Ts) has a negative temperature coefficient of about 2.0 to 2.5 mV per change in ambient temperature IK, and the temperature difference It is known that the axis moves approximately in parallel along the horizontal axis at intervals proportional to . It is noted that the saturation current Is in equation (4) also changes depending on the temperature T, and it is known that when the temperature increases by 10° C., the current almost doubles. Therefore, by replacing changes in current with changes in impedance, the relationship between ambient temperature and impedance can be determined.

Therefore, if the operating temperature range of this device is, for example, 5 to 40°C, the saturation current I3 will be 10°C at the ambient temperature, as described above.
In practice, for example, Isn" l5(n-1+X 2'τjl-7n-1)
/1G , , , , , , (5) (n=1.
2, 3. ) can be approximated as

Here, if the standard ambient temperature at the time of measuring a good board is, for example, 23°C (300K) for simplicity, then the operating upper limit temperature is 40°C (300K) for the saturation current I 5 (xi) at this time.
The saturation current Is'(4a) at 13K) is
4゜) = engineering, (2,,X 2 (40-23)/i(1
Given I 5 (23) X 3.3 ・・・・・・
...(6) Saturation current at a lower operating temperature of 5°C (278K>).

(G) is I! 1(S)=I! 1(231X 2(s"""Press 1
s<xx)73.5 ・・・・・・・・・(
7).

Therefore, if the forward current ratio at the upper limit temperature of 40°C to the standard temperature of 23°C is ΔIF1, then ΔI P1= I P(4◎>/Iv(zs>), so the measurement voltage V is set to 0.35V, for example. and equation (6)
By substituting ΔIFl=IP(
4111(exp(qVr/313k) 1) /
I 8Tai > (exp(qVr/ 300k
) -1) Valve 1.8...
(8) Also, if the current ratio at the lower limit temperature of 5°C to the standard temperature of 23°C is ΔIFt, then ΔIF2 = IF(S)/IP(23), so equation (7) can be transformed into equation Substituting into (4), ΔIrz=
Ir(s>(exp(qVp/278k) 1)/I
8(2a)(19XP('IVF/300k
) 1) Phrase 0.78 ・Old...
...(9) is obtained.

The impedance at the standard temperature, upper limit temperature, and lower limit temperature are respectively z (23) and z (4゜l + Z (s
) Then, the impedance ratio of the upper and lower temperature limits to the standard temperature becomes the reciprocal of the value obtained by equations (8) and (9), so Z(4°+/Z(2,)=1/1. 8″: 0.5
6/ 1 ・・・・・・・・・(10)Z
(51/ Z (23) = 110.78 press 1.3/
1 ・・・・・・・・・(11) Incidentally, the impedance ratio between the lower limit temperature and the upper limit temperature is Z (s)/Z (4a) of course 2.3/1
・1 old...(12).

As described above, the increase and decrease in impedance due to changes in ambient temperature changes in a curved manner almost along an exponential function, but in practice, there is no particular problem in approximating this to a straight line.

Therefore, in this embodiment, in the direction in which the ambient temperature increases from the standard temperature, for example, the additional value per 1°C is: = (0,56-1) / (40-23) valve-2
,6 [%] = -2μX0.026 [Ω], and if there is a difference of ΔT in the ambient temperature, α, =
ΔT=-Z μX0.026XΔT [Q...
......(13a) Or αt=-2.6xΔT[%] ・1 old...(1
3b) is added.

For example, 1 for the direction in which the ambient temperature falls below the standard temperature.
Add 3 to the additional value per °C, = (1, 3-1) / (23-5) valve 1.7 [%
] =ZμX0.017 [Ωko...
...(14), and similarly if there is a temperature difference of ΔT, then α, =, XΔT=ZμX O, 017XΔT
[Ω]・・・・・・・・・(15a) Or α,=1.7XΔT[%] ・・・・・・・・・
...(15b) is added.

Note that if the value of 3σ, which represents impedance variation, is relatively large and there is no need to set the additional value due to temperature change very precisely, use the value of equation (12) to uniformly calculate J per 1°C. = (2,3-1)/(40-
5) To4 [%co=ZμX0.04 [Ω] ・・・・・・・・・
...(16), and the tolerance α8 or α3 is a, = Z μX0.04XΔT [Ω]; -4×ΔT
[%] ・・・・・・・・・(17a)a a
;-Z u X O, 04XΔT[Ω]=4XΔT[
%] ・・・・・・・・・(17b) In this case, the ifA quasi-temperature at which a good board is measured may be any temperature as long as it is within the operating temperature range; It is convenient.

J above, k2. k,,α0. α2. The values of α, etc. are shown as an example, and it goes without saying that the user of the apparatus may appropriately determine the values according to the actual situation of board inspection. For example, the above is α when the impedance distribution characteristics (width of variation) do not change even if the ambient temperature changes.
8. This is an example of setting α, but it may change in reality, so depending on the degree, α2. It is also necessary to adjust the value of α3.

In addition, as an example of application, by appropriately setting the allowable lower limit value and allowable upper limit value (P, Q in Figure 4 (A)), it is possible to detect short circuits, opens, etc. of installed parts caused by temperature changes. It is.

Note that, as described above, ΔT is the difference in ambient temperature between the inspection of a non-defective board and the time of inspection of a test board, and in this embodiment, for example, the temperature detector 23 detects it and inputs the data to the measurement section 21. However, it is also possible to manually enter the value read from an indoor thermometer.

Incidentally, FIG. 5 shows a flow diagram of an example in which automatic setting of tolerances is controlled by the CPU 21.

〔effect〕

As described above in detail, in the present invention, the impedance at each measurement point of a circuit board that has been confirmed to be good is measured, and the average value Zμ is set as the reference impedance Z8 of the measured value, and the average value Zμ Calculate three times the root mean square value σ of the impedance measurement data and the above impedance measurement data, that is, 3σ, and add 2% of the average value Zμ to this 3σ, for example, α, = 3σ + Zμ × 2% as the tolerance for variations in the test board. It is now set as .

In addition, the difference ΔT in ambient temperature between the inspection of the non-defective board and the test board is detected, and this variable ΔT and the operating ambient temperature T
1 to the known constants associated with . and the product of the above impedance average value Zμ at the relevant measurement point - α2 (or +α3
)=ZμXk, ΔT is automatically added to the above α as a change in impedance of the diode due to a change in ambient temperature.

Therefore, according to this circuit board testing method, it is possible to automatically perform accurate pass/fail judgments, taking into account not only variations in the original impedance of the test board but also changes in impedance caused by differences in ambient temperature.

[Brief explanation of the drawing]

1 to 5 relate to embodiments of the present invention; FIG. 1 is a block diagram showing an example of the configuration of a circuit board inspection device to which the present invention is applied; FIG. 2 is an explanatory diagram of the operation of each part; Third
The figure is an explanatory diagram of the principle of setting the pass/fail judgment tolerance α1, and Fig. 4 (A
) to Figure 4 (C) are the addition tolerance α for temperature changes.
2 (α3), and Fig. 5 is an explanatory diagram of the setting principle for the tolerance α1.2 (α3). α
2(α3) is automatically set by the CPU, and FIG. 6 is a block diagram showing the configuration of a conventional device. In the figure, 10 is a signal source, 13 is a circuit board to be inspected, 14 is a current detector, 14a is a range setting circuit, 17 and 18 are integrators, 19° and 20 are A/D converters, and 21 is a CPU. Patent applicant Hioki Electric Co., Ltd.

Claims (1)

[Claims] (1) A response signal obtained by applying an AC signal for measurement from a signal source to a circuit board under test is converted into a voltage using a predetermined range and integrated, and the digital conversion data is used by a CPU to generate a signal at a predetermined measurement point on the board. In a circuit board inspection method that measures impedance and compares the measured value with a reference value taken in advance from a non-defective board, and determines the quality of the board based on whether the impedance is within a predetermined tolerance, the impedance of the board is measured. For variations, a tolerance is set by adding a predetermined value to 3σ of the impedance distribution characteristic of the above-mentioned good board, and for changes in the above-mentioned board impedance due to temperature, a tolerance is set for the impedance measurement time and the impedance measurement time of the above-mentioned good board. A circuit board inspection method characterized by automatically adding a tolerance according to an ambient temperature difference to the tolerance to determine pass/fail.