JP3856013B2 - Electronic circuit inspection equipment - Google Patents

Description

  The present invention generally relates to an electronic circuit inspection apparatus, and more particularly to an inspection apparatus applied to inspecting connection defects of low-impedance elements connected in parallel.

  In the manufacturing process of electrical products equipped with electronic circuits, when production inspections are performed at the actual product level, inspections are performed at the single-unit level in order to destroy the electronic circuit or to detect early defects. ing. Conventionally, there is an in-circuit tester as an automatic inspection apparatus at a single substrate level.

  The inspection method supplies a weak signal of direct current or alternating current to an element or circuit to be inspected, measures an impedance value in a steady state, and compares it with preset good product data, thereby producing a printed circuit board. This is a method for inspecting an electronic component connection failure.

  In the circuit shown in FIG. 1, when trying to inspect the open connection failure of the diode 2 to be inspected, a DC or AC weak signal conventionally used by an in-circuit tester is supplied, and the impedance value in a steady state is measured. This method overlaps with the characteristics between the base and emitter of the NPN transistor 1 connected in parallel with the diode 2 to be inspected (characteristic that current can be easily passed from the base to the emitter, but current is not passed in the reverse direction). Even if the impedance value is measured, the change cannot be captured.

  In the case of a PNP transistor instead of an NPN transistor, the same applies when a diode is connected in parallel in the forward direction between the base and the collector.

  An object of the present invention is to solve the above-described problems and provide an automatic inspection device for diodes connected in parallel in the forward direction.

  An electronic circuit inspection apparatus according to the present invention includes a pulse signal source that applies a pulse signal to a circuit to be inspected, an analog-to-digital converter that analog-to-digital converts a transient response signal to the pulse signal of the circuit to be inspected, and the digital conversion The processed transient response signal is processed, the frequency of the vibration waveform is extracted based on the peak time or zero-cross time of the transient response signal waveform, and compared with the vibration frequency of the normal circuit, thereby determining the abnormality of the circuit under test. And a display device for displaying the inspection result of the circuit to be inspected.

Since the present invention applies a pulse signal to the circuit to be inspected and inspects based on the waveform of the transient response signal, the low impedance circuit connected in parallel that is difficult to determine by the inspection by applying a DC or AC minute signal Inspection is possible.
In addition, since the abnormality is determined by using a change generally caused by the abnormality of the circuit to be inspected as an index, a versatile electronic circuit inspection apparatus can be provided.

Embodiment 1 FIG.
1 is a measurement circuit diagram of an automatic electronic circuit inspection apparatus according to Embodiment 1 of the present invention, FIG. 2 is a diagram showing a step signal waveform output from a pulse signal source 15, and FIG. FIGS. 4 and 5 are diagrams showing output transient response waveforms measured on the secondary side 3b of the transformer 3. FIG. Specifically, the circuit to be inspected shown in FIG. 1 is an extract of electronic circuit elements related to the inspection method of the present invention from the choke coil current control type single stone self-excited inverter circuit. The pulse signal source 15 is for supplying a pulse signal to the circuit to be inspected for inspection, and the transient response of the circuit to be inspected is measured as a voltage waveform change from both ends of the transformer secondary side 3b. .

  In the circuit operation, when the step pulse waveform shown in FIG. 2 is first supplied from the pulse signal source 15, a transient phenomenon change occurs in the current flowing through the primary side 3a of the transformer 3 in response to the voltage step change. Here, a positive signal is applied to the anode of the diode 2. This change in current causes a change in current on the secondary side 3b of the transformer due to a transformer-induced phenomenon, and is measured as a voltage waveform from both ends of the secondary side 3b of the transformer.

  In the transient response waveform measured from both ends of the secondary side 3b of the transformer, when the diode 2 to be inspected is connected, the vibration of the waveform is attenuated within a short time as shown in FIG. On the other hand, when the diode 2 to be inspected is not connected, the oscillation of the decoy waveform shown in FIG. 5 clearly continues for a long time compared to FIG. Therefore, the state change of the circuit to be inspected can be discriminated by the transient phenomenon waveform measured from both ends of the secondary side 3b of the transformer.

  As shown in the measurement circuit diagram of the inspection apparatus in FIG. 1, the determination method is such that a transient response waveform measured from both ends of the secondary side 3b of the transformer is input through the analog-to-digital converter 11 and the microprocessor 12 performs arithmetic processing. By comparing with a determination value set in advance on the memory 13, the electrical connection failure of the diode 2 to be inspected is determined. The determination result is displayed on the display device 14.

  The determination value is set by measuring a waveform of a normal circuit and setting the waveform based on the waveform displayed on the display device 14. Also, a plurality of set values can be registered according to the inspection object and can be easily selected, so that versatility can be provided.

  Although the present embodiment has been described with reference to determining whether a diode is connected or not, the inspection target is not limited to this, and can be widely applied to an electronic circuit in which a transient response waveform varies depending on an abnormality. In particular, the present invention can be applied to an inspection object that is difficult to discriminate by applying a DC or AC minute signal, such as a low impedance element connected in parallel. In addition, since it is not necessary to apply an actual current voltage to the circuit to be inspected, there is no possibility of destroying the circuit board during inspection.

Embodiment 2. FIG.
In this embodiment, a specific method for calculating and determining a transient response waveform by the microprocessor 12 will be described. In the example of the poor connection of the diode described in the first embodiment, the difference between the normal waveform and the abnormal waveform appears mainly as the difference in the duration of the vibration waveform. In such a case, a method of integrating the effective value or rectified value of the transient response waveform and determining the difference in duration of the vibration waveform based on the magnitude of the integrated value is suitable. If an analog operation processing circuit such as an effective value circuit, a rectifier circuit, or an integration circuit is provided in front of the analog-to-digital converter 11 to perform analog signal processing instead of the calculation by the microprocessor 12, the microprocessor 12 This calculation processing can be reduced, and the determination processing time can be shortened. In addition, it is possible to perform response waveform calculation processing at a higher speed than calculation processing by a microprocessor.

  As another method of calculating and determining the transient response waveform, a method of determining whether the envelope of the response waveform is within a preset range based on the response waveform of the normal circuit can be applied. According to this method, a more general feature of the waveform to be inspected can be inspected, so that a highly versatile inspection apparatus can be realized.

  Furthermore, as another method, a method of extracting the time interval of the peak of the response waveform and the interval of the zero crossing time and inspecting the frequency of the vibration waveform can be applied. Since an abnormality in circuit connection is often accompanied by a change in resonance frequency, a highly versatile abnormality inspection can be performed by comparing and determining the vibration frequency of a normal circuit.

It is a measurement circuit diagram of the automatic electronic circuit inspection apparatus in Embodiment 1 of this invention. It is a figure which shows the step signal waveform output from the pulse signal source. It is a figure which shows the rectangular wave signal waveform output from the pulse signal source. FIG. 4 is a diagram showing an output transient response waveform measured on the secondary side 3b of the transformer 3. FIG. 4 is a diagram showing an output transient response waveform measured on the secondary side 3b of the transformer 3.

Explanation of symbols

  1 NPN transistor, 2 diode to be inspected, 3a transformer primary side, 3b transformer secondary side, 4 capacitor, 5 low resistance, 10 testing device, 11 analog-digital converter (ADC), 12 microprocessor, 13 memory, 14 display 15 Signal source.

Claims (1)

A pulse signal source for applying a pulse signal to the circuit to be inspected, an analog-to-digital converter for analog-to-digital conversion of the transient response signal to the pulse signal of the circuit to be inspected, and processing the digitally converted transient response signal, Extracting the frequency of the vibration waveform based on the peak time or zero-crossing time of the transient response signal waveform and comparing it with the vibration frequency of the normal circuit, and a microprocessor for determining an abnormality of the circuit under test; An electronic circuit inspection apparatus comprising: a display device that displays an inspection result.

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