JPH0829460A - Insulation testing device for substrate - Google Patents

Abstract

PURPOSE:To ensure that any abnormality in insulation resistance resulting from the occurrence of migration can be detected by holding, when an insulated state is judged to be abnormal, abnormality detection even after a normal state has been restored. CONSTITUTION:When a power supply 2 applies a DC voltage to a subject 1 to be tested, an electric field is produced between electrodes 11, 12, and a current I that matches the resistance between the electrodes and the applied voltage flows through a detecting resistance 31, producing a potential difference between both ends of the resistance 31. When this detected voltage is higher (lower) than a reference voltage, a comparator 34 outputs H(L), which is input to an FF 41. When the subject 1 to be tested is in a normal state, therefore, the output 34 is L and the output of the FF41 is also L, and a LED 51 is not turned on. If a resistance value decreases as a result of migration occurring in the subject 1 to be tested, the voltage which was detected 31 exceeds the reference voltage, turning on the LED 51. In this case, even if the voltage is decreased below the reference voltage again by a temporary decrease in resistance and the output 34 varies from L to H to L, the FF41 does not return to L and the LED 51 is kept turned on. Therefore, any abnormality in insulation resistance can be detected even after a normal state has been restored.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for testing whether or not the insulation performance of a printed circuit board, on which electronic parts and the like are mounted and soldered, is normal in an environmental test (high temperature and high humidity condition). .

[0002]

2. Description of the Related Art When the insulation performance of a substrate provided in an electric device is deteriorated (insulation resistance value is reduced), a short circuit occurs between patterns (electrodes) on the substrate, which causes a fire, which is extremely dangerous. Therefore, it is important to test the insulation performance of the board in advance. A typical one of the causes of the decrease in the resistance value is migration. This migration refers to a phenomenon in which, when a voltage is applied for a long time between electrodes that are close to each other on a printed circuit board, the electrode material copper or the like is ionized and moves toward the counter electrode along the surface of the printed circuit board due to an electric field. When such migration occurs, the resistance value between the electrodes sharply decreases, an abnormal current flows between the electrodes to which a voltage is applied, and the electronic circuit is damaged. The occurrence of migration is affected by the characteristics of the printed circuit board itself, residual flux during soldering of electronic components, and the operating environment (particularly high temperature and high humidity). Therefore, in order to improve the reliability of the printed circuit board, the printed circuit board on which the electronic components are actually mounted, or the test printed circuit board provided with electrodes in the vicinity when the printed circuit board is expensive, is subjected to an accelerated test. For this purpose, a method of confirming the occurrence of migration by measuring the change with time of the interelectrode resistance by applying electricity in a hot and humid environment is adopted.

A conventional method for testing the insulation performance of a substrate, particularly a method for investigating migration, is to use a magnifying glass or the like after stopping energization every time a certain time has passed since the start of the environmental test, removing from the environment. It was then necessary to check each sample visually.

[0004]

When migration or the like occurs in the sample, the resistance value at both ends of the measurement sample decreases as shown in FIG. 2. Therefore, by continuously measuring the change with time of the resistance value, the migration It is possible to detect a decrease in resistance value due to occurrence. However, in the conventional method of interrupting the energization test during the environmental test and measuring the resistance value of the measurement sample with the insulation resistance tester, the resistance value of the sample does not change continuously, but the insulation resistance is abnormal. When it occurs, the resistance value between the electrodes sharply decreases (state of point A in FIG. 2), discharge occurs between the electrodes of the DUT, and the resistance value between the electrodes rises to a normal value again. Therefore, in the method of measuring the resistance by interrupting the power supply to the sample,
Since the temporal change of the resistance value is not continuously measured, there is a problem that a temporary decrease in the resistance value, that is, a temporary abnormality in the insulation resistance cannot be reliably grasped. Also,
In order to reliably detect this abnormality, the observer must take out the sample from the test tank at a high frequency and perform a visual check, which increases the number of steps. In order to detect the decrease in the resistance value due to the occurrence of migration or the like, it is necessary to accurately and continuously measure the resistance value of the sample using an expensive insulation resistance measuring instrument, which is costly. In particular, when testing a plurality of samples, it is necessary to prepare a plurality of insulation resistance measuring instruments corresponding to this number, resulting in a significant increase in cost.

An object of the present invention is to provide an inexpensive device which can reliably detect an abnormality in insulation resistance due to occurrence of migration or the like without increasing man-hours and which does not increase the cost.

[0006]

In order to solve the above problems, the present invention provides a board insulation test apparatus for testing the insulation performance of the board based on the insulation resistance between patterns provided on the board. Monitoring means for monitoring the insulation state of the substrate; and holding means for always holding the abnormality detection when the monitoring means determines that the insulation state of the substrate is abnormal, regardless of the subsequent restoration of the insulation state to normal. It is characterized by having.

Further, in a board insulation tester for testing the insulation performance of the board based on the insulation resistance between the patterns provided on the board, a detecting means for detecting the value of the current flowing through the board between the patterns. And comparing the current value detected by the detection means with a predetermined reference value,
When the current value is larger than the reference value, it is determined that the insulation state of the substrate is abnormal.

The monitoring means is composed of the detecting means and the judging means.

[0009]

When the insulation state between the patterns provided on the substrate changes significantly from the reference, the monitoring means judges that an abnormality has occurred and outputs an abnormality signal to the holding means. Since the holding unit continues to hold the received abnormal signal, the abnormal signal indicating the once-determined abnormal condition of the insulating state is held even if the insulating state returns to normal.

When the insulation resistance between the patterns provided on the substrate decreases, the current flowing between the patterns increases. The detection means detects the current. The current value detected by the determination means is compared with the reference value (normal current range), and if the detected current value is larger, it is determined that the insulation state is abnormal. Further, the monitoring means for monitoring the insulation state between the patterns provided on the substrate is a detection means for detecting an increase in current due to a decrease in insulation resistance value, and the detected current value and reference value (normal current range). When the detected current value is larger than that, the judgment means judges that the insulation state is abnormal. In this way, even if the insulation state is restored to normal by the detection means for detecting the current value, the judgment means for comparing the current value with the reference value to judge whether there is an abnormality, and the holding means for holding the result. However, the abnormality of the insulation state once generated is retained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the structure of a substrate insulation test apparatus according to an embodiment of the present invention, in which (a) is a block diagram and (b) is a circuit diagram. Reference numeral 1 is a device under test, and electrodes (patterns) such as comb-like copper foils alternately connected to the printed circuit board
Is formed, and the insulation state of the substrate between the electrodes 11 and 12 is monitored. The distance between these electrodes is 0.15 to 0.5
mm. Reference numeral 2 is a DC power source applied to the DUT.

3 is migration (insulation resistance value is reduced)
In the detection unit, a detection resistor 31 that is connected in series to the DUT and causes a potential difference across the detection resistor 31 due to a current flowing according to the resistance value of the DUT, a voltage generated across the detection resistor 31, and a preset reference voltage. Comparator 34 that outputs H if the detected voltage is higher than the reference voltage, and dividing resistors 32 and 33 for obtaining the reference voltage of comparator 34 by dividing it from the power supply voltage. The detection unit 3 corresponds to an example of the detection unit and the determination unit.

Reference numeral 4 denotes a holding portion, which is a D terminal connected to a power source,
The CK terminal connected to the output of the comparator 34, the power supply voltage connected to the D terminal when H is input to the CK terminal,
The reset switch 42 includes a D-type flip-flop circuit 41 having a Q terminal that outputs continuously until it is reset, and an R terminal connected to the reset switch 42. During normal measurement, the reset switch 42 is set to B
Connected to the side.

Reference numeral 5 is a display unit for notifying an observer of the detection result of the resistance value decrease due to migration, and is composed of a light emitting diode 51 connected to the Q terminal of the D-type flip-flop circuit 41. An alarm device such as a buzzer may be used instead of the light emitting diode of the display unit. The holding unit 4 and the display unit 5 described above correspond to an example of a holding unit. Next, the operation of the board insulation test apparatus will be described.

For the accelerated test of the insulation resistance abnormality, the DUT 1 is in a high temperature and high humidity environment (for example, temperature 85 ° C., humidity 85).
%), And a DC voltage of 16 V is applied from the power supply 2. As a result, the comb electrodes 11 and 12 of the device under test 1 are
An electric field is generated between them, and metal ions (copper ions or the like) generated on the electrode 11 side (+ side) move to the electrode 12 side (− side) along the surface of the printed board (not shown), and the electrode 12 Is deposited in the vicinity of. As a result, the resistance between the electrodes 11 and 12 decreases with time.

The resistance (R) between the electrodes 11 and 12 of the DUT 1 and the current (I) corresponding to the applied voltage (V) are also applied to the detection resistor 31 (R) connected in series to the DUT 1. Flowing. This current (I) causes a potential difference of I × R across the detection resistor 31 (R). This detection voltage (I × R) is input to the comparator 34. On the other hand, the comparator 3
A reference voltage (about 1 V in this case) determined by the power supply voltage and the dividing resistors 33 and 34 is applied to one of the four, and the detection voltage (I × R) and the reference voltage (about 1 V) are compared. If the detected voltage is higher than the reference voltage, the comparator 34 outputs H, and if it is low, L is output. The output of the comparator 34 is input to the CK terminal of the flip-flop 41.

When the DUT 1 is normal, the detection resistor 3
The current flowing to 1 is small and the input voltage of the comparator 34 is lower than the reference voltage, so the comparator 34 outputs L. When this is input to the CK terminal of the flip-flop 41, L is output to the Q terminal, so that the light emitting diode 51 does not light. If migration occurs in the device under test 1 and the resistance value of the device under test decreases, the current of the detection resistor 31 increases, and as a result, the comparator 34
Input voltage exceeds the reference voltage, comparator 34
Outputs H. When this is input to the CK terminal of the flip-flop 41, H is output to the Q terminal, so that the light emitting diode 51 lights up.

In this case, a pulse-like current flows through the detection resistor 31 due to the temporary decrease in resistance, the detection current (I), that is, the detection voltage (I × R) becomes lower than the reference voltage again, and the output of the comparator 34 becomes Even if the insulation state of the device under test (insulation resistance) immediately returns to the normal state by changing from L → H → L, the flip-flop 41 does not return from H to L, and H is continuously output. Therefore, the light emitting diode 51 of the display unit 5
Remains lit, and even if the observer does not continuously monitor the resistance of the DUT 1, the resistance value of the DUT (insulation resistance) drops (abnormal) due to the occurrence of migration.
It turns out that there was. By switching the reset switch 42 to the A side, a reset signal is input to the R terminal, L is output to the Q terminal, and the light emitting diode 51 is turned off. Therefore, the same test object may be continuously tested. Alternatively, a new test can be started by exchanging another test product.

According to this embodiment, it is possible to continuously check the decrease in the resistance value due to migration while the test object is energized. In addition, even if the resistance value is temporarily reduced to cause discharge and the resistance value is restored, the phenomenon that has occurred is held by the holding unit, and the observer does not need to continuously monitor it. The man-hours do not increase. Furthermore, instead of measuring the value of the insulation resistance, in this example, the abnormality is simply detected based on the current (voltage) generated here, so that the components constituting the circuit are inexpensive and the cost can be reduced.

Although the present embodiment is limited to the abnormal detection of the insulation resistance due to the migration, it can be effectively applied to the abnormal detection of the insulation resistance in other phenomena (in particular, the temporary decrease of the resistance value). Further, it may be detected by software by a microcomputer. Further, in the present example, the current is converted into the voltage to detect the decrease in the resistance value, but the present invention is not limited to this, and the decrease in the resistance value may be detected directly from the value of the current.

[0021]

As described in detail above, according to the present invention, it is possible to continuously check the decrease of the insulation resistance value due to migration or the like while the test object is energized. Further, even if the resistance value is temporarily reduced to cause discharge and the resistance value is restored, the phenomenon that has occurred is held by the holding unit, and the observer does not need to continuously monitor it. Furthermore,
The present invention enables an inexpensive device without requiring an expensive insulation resistance measuring instrument, which is very useful for a device for testing the insulation performance of a substrate.

[Brief description of drawings]

FIG. 1 is a diagram showing a substrate insulation test apparatus according to an embodiment of the present invention, in which (a) is a block diagram and (b) is a circuit diagram.

FIG. 2 is a diagram showing the relationship between the passage of voltage application time and the change in resistance value.

[Explanation of symbols]

1 ... DUT 4 ... Holding part 3 ... Detection part 41 ... D-type flip-flop 31 ... Detection resistance 5 ... Display part 34 ... Comparator 51 ... LED

Claims (3)

[Claims] 1. A substrate insulation testing apparatus for testing the insulation performance of the substrate based on the insulation resistance between patterns provided on the substrate, a monitoring unit for monitoring the insulation state of the substrate, and the monitoring unit. A substrate insulation test apparatus, comprising: a holding unit that constantly holds the abnormality detection regardless of whether the insulation state of the substrate is abnormal or not thereafter. 2. A detection means for detecting the value of a current flowing through the board between the patterns in a board insulation test device for testing the insulation performance of the board based on the insulation resistance between the patterns provided on the board. And a judgment means for comparing the current value detected by the detection means with a predetermined reference value, and for judging that the insulation state of the substrate is abnormal when the current value is larger than the reference value. An insulation tester for substrates, which is characterized by being provided. 3. The board insulation test apparatus according to claim 1, wherein the monitoring means comprises the detecting means and the judging means.