JPH06103335B2 - Circuit board inspection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a circuit board inspection method for inspecting the quality of a circuit board on which electronic components and the like 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. This kind of device is constructed so that various measurements can be performed depending on the circuit contents of each circuit board to be inspected, and a general example thereof is shown in FIG.

That is, the signal source 1 is, for example, a DC constant voltage source (DC.V) 2,
It consists of a DC constant current source (DC.A) 3 and an AC constant voltage source (AC.V) 4, and sends a measurement signal to a circuit board under test (hereinafter referred to as “test board”) 6 via a scanner 5. In addition, the response signal is taken into the measuring unit 8 by the scanner 7. The measuring unit 8 is, for example, a DC voltage measuring device (DC, V meter)
9, DC current measuring device (DC.A meter) 10, LC measuring device (LC
It is equipped with a meter) 11, and a measuring unit suitable for it is determined by software according to the type of parts on the board to perform measurement. A controller 12 for switching the measurement system is provided.

Some examples of the conventional measuring method using this device will be described. In FIG.
Although an IC element and its power supply circuit are shown, a relatively large-capacity polar capacitor C is generally connected as shown for voltage stabilization. In this case, if an attempt is made to measure the capacitance of the capacitor with an AC signal, the impedance is low and high-speed measurement is not possible, so for example, the DC constant current source 3 is used as a signal source, and the terminal voltage is measured after charging with a constant current for a fixed time . Further, the battery is charged for a predetermined time, the terminal voltage is measured again, the capacity is obtained from the two voltages and the charging time between them, and the quality is judged. Note that the output terminal voltage of the constant current source 3 is measured immediately after the start of the first charge, and if it is equal to the open circuit voltage of this constant current source, the capacitor C is not mounted, and if the voltage measurement does not raise the voltage for the second time. Judge as a circuit bridge.

When measuring the capacitance of the capacitor C in the circuit network as shown in FIG. 7, for example, a voltage having a peak value of about 0.2 V or less is applied from the AC constant voltage source 4 so that the diodes D ₁ and D ₂ do not operate. , The capacity is measured by the LC meter 11. Similarly, apply a voltage with a peak value of 0.2 V or less to the resistor R
The current flowing through the CA meter 10 is measured and the resistance value is obtained. For the diodes D ₁ and D ₂ , for example, a DC constant current source 3
A current in the + direction and a current in the − direction is flown from and the output terminal voltage of the identification current source 3 is measured by the DC.V meter 9.

[Problems to be Solved by the Invention]

According to the above-mentioned conventional inspection method, there is an advantage that a measurement method corresponding to each component on the board can be used. However, on the other hand, various types of signal sources and measuring instruments are required, and the size of the device becomes large. In addition, these devices are operated by an inspection program, but for that purpose, it is necessary for the user to create an inspection program by fully understanding the characteristics of each individual part.
Depending on the skill of the programmer, the defect detection power may differ. It should be noted that, for example, a method of reducing the influence from other parts is also used by the guard processing (G), but in this case, the scanner etc. becomes larger and the guard processing has many so-called cut-and-try elements. It has the drawback of taking a long time to create.

The present invention has been made in view of the above circumstances, and an object thereof is to add a plurality of measurement signals having different frequencies or levels from, for example, a signal source to a measurement target component, a circuit network, etc. By comparing the impedance data measured on the basis of each signal with the reference data obtained by measuring the non-defective board under the same conditions in advance,
An object of the present invention is to provide a circuit board inspection method that does not have variations in judgment and is simple, and does not particularly require a high degree of programming skill.

[Means for Solving the Problems]

An apparatus for carrying out the present invention is shown in FIG. 1. In order to solve the above-mentioned problems, for example, a clock generator 14c capable of transmitting three types of clock pulses having different repetitive synchronizations, and the transmission pulse Counter 1 for counting a predetermined number
A measurement signal source 14 including a 4b and a D / A converter 14a that converts the count data into an analog AC voltage of a desired level and outputs the analog AC voltage is provided.

[Action]

According to the signal source 14, for example, an AC voltage having a desired level and three kinds of frequencies is obtained as a measurement signal. Therefore, when these signals are applied to the measurement target circuit network or the like, the impedance of the circuit network as a whole corresponding to the type of signal is obtained in the measuring unit 18, and the components of the circuit network are not required to be individually measured for the board. The quality can be inspected.

〔Example〕

Referring again to FIG. 1, for example, the desired measuring AC voltage emitted from signal source 14 is applied via scanner 15 to a component or network having impedance Z _x on test board 16 and the response signal is The measurement unit 18 is taken in through the scanner 17 and measured. In this case, the measurement circuit between the signal source 14, the test board 16, and the measurement unit 18 is the board 16
Depending on the measurement points (not shown)
The predetermined measurement signals are selected by the signal source 14, and their operations are controlled by the controller 19 based on the inspection program in the measuring unit 18, for example.

In this embodiment, the signal source 14 emits three measurement signals f ₁ , f ₂ and f ₃ having different frequencies. The frequency and level of each signal are set in two ways as shown in FIGS. 2 (a) and 2 (b). That is, in the figure (a), the frequencies are, for example, 10 kHz and 1 k, respectively.
The same level of about ± 0.2V at Hz and 100Hz, respectively. In (b), f ₁ (10kHz) and f ₃ (100Hz) are, for example, about ± 0.2V at f ₂ (1k
Hz) is about ± 0.5V.

To generate these measurement signals, the clock generator 14
From c, for example, three types of clock pulses P ₁ , P ₂ and P ₃ having different repetition periods are emitted and the counter 14b is caused to count. Count data of counter 146 is D / A
The signal f ₁ is converted into an analog voltage by the converter 14a and is passed through, for example, a low-pass filter and an amplifier (not shown).
To f ₃ are formed.

As a supplementary explanation with reference to FIG. 3, for example, the clock generator 14c divides the parent clock of the measuring unit 18 to generate a pulse P ₁ of repetitive synchronization of 1 μs, and divides it by 1/10 or a repetition period of 10 μs. The pulse P ₂ and the pulse P ₃ which is further divided by 1/10 or has a repetition period of 100 μs are formed, and the controller 19
Control from 100 to 100 in the order of P ₁ , P ₂ and P ₃ , respectively.
Output one by one.

The counter 14b is, for example, a binary 8-bit up / down counter, the start position is 100 count,
Assuming that the lower limit values are 125 and 75, the time required to count 100 of each of the above three types of pulses P ₁ to P ₃ is 100 μs,
It becomes 1ms and 10ms. Therefore, if the count data is converted into an analog voltage by the D / A converter 14a, the frequency of 10kHz, 1
A triangular wave signal of kHz and 100Hz can be obtained. The waveforms of these signals are shaped by, for example, a low-pass filter and passed through a variable gain amplifier to obtain the measurement signals f ₁ to f ₃ shown in FIG.

In the conventional inspection method, generally, for example, when the absolute values of L, C, and R of the components mounted on the board are measured and compared with the standard value, when an alternating current is used for the measurement signal, It is necessary to minimize the waveform distortion that causes measurement error. However, in this embodiment, since the impedances of the non-defective board and the test board are measured and compared under the same conditions as described above, there is no direct relationship between the waveform distortion and the measurement error, so simple waveform shaping is possible. There is no problem in practical use. The counter 14b and the clock generator 14c may be replaced with, for example, a memory to store the waveform data corresponding to the signals shown in FIG. 2, and the address signals from the controller 19 may be used to provide those data to the D / A converter 14a. You may

Next, an example of an inspection method for a circuit network composed of parallel components as shown in FIG. 7 will be described. The relationship between the measured frequency and the impedance is, for example, as shown in FIG. The impedance of the capacitor decreases and the impedance of the coil increases as the frequency increases, regardless of the constant. However, the horizontal axis of the figure,
The vertical axis is on a logarithmic scale.

Here, when the signal shown in FIG. 2 (a) is applied, the cutoff voltage of the diode is about 0.2 to 0.4 V, so that it does not operate and the combined impedance of the resistor and the capacitor can be measured. This measurement value has a predetermined tolerance with respect to the measurement data of the good board,
For example, if it is within ± 3σ, it is determined to be good. The combined impedance of the resistance and the coil can be measured in the same manner. Note that the check of a circuit including a diode or the like as shown in FIG. 2 (b), by changing the frequency of f _1, f _2, f ₃ measured L, C, the part characteristics of R, etc., also, of which It is also possible to determine the characteristics of the diode by setting one wave of, for example, f ₂ to be a signal of 0.5V.

〔The invention's effect〕

As described above in detail, in the circuit board inspection method according to the present invention, for example, a plurality of measurement signals whose frequency and level are variable are emitted from one signal source and added to the same measurement point on the test board, and its response signal is added. The plurality of impedance data measured by the above are respectively compared with the data of the non-defective substrate measured under the same condition, and the quality is judged.

Therefore, when the inspection target is a circuit network that consists of parallel components, it is not necessary to measure the individual component values and compare them with the standard values, making it easy for the user to create an inspection program and performing highly accurate board inspection. be able to. Further, it is not necessary to provide various signal sources and measuring instruments, which can greatly contribute to simplification of the device and cost reduction.

[Brief description of drawings]

1 to 4 relate to an embodiment of a circuit board inspection method according to the present invention, FIG. 1 is a block diagram showing an example of the apparatus configuration, FIG. 2 is a waveform diagram of a measurement signal, and FIG. Is an explanatory diagram of the internal operation of the signal source, FIG. 4 is an explanatory diagram of an example of impedance measurement, FIG. 5 is a block diagram showing the configuration of a conventional device, and FIGS. 6 and 7 are circuit diagrams showing an example of a measurement target. Is. In the figure, 14 is a signal source, 16 is a circuit board to be inspected, 18 is a measuring section,
Z _x is the impedance of the circuit under measurement.

Claims (1)

[Claims] 1. An impedance of the board is measured by a measuring section by a response signal obtained by adding a measurement signal to a circuit board to be inspected from a signal source, and the measurement data is obtained by measuring a good board in advance. In a circuit board inspecting method for judging the quality of the board by comparing with reference data, a plurality of measurement signals having different frequencies or levels are sequentially added from the signal source to the same measurement point of the circuit board to be inspected, and a response signal thereof A method for inspecting a circuit board, characterized in that a plurality of impedance data measured by the method are compared with respective reference data.