JPH065241B2 - Continuity / Insulation tester - Google Patents

Description

The present invention relates to a continuity / insulation tester for conducting a continuity test or an insulation test of a printed circuit board or the like.

[Prior Art] Generally, such a continuity / insulation tester is provided with a large number of probe pins, and a printed circuit board as a device under test is pressed against the probe pin group. Then, a power source is selectively connected to the pair of probe pins, and a continuity test or an insulation test of the printed circuit board is performed between the pair of probe pins. The selective connection of the probe pins is made by a switching element such as a transistor.

A second schematic circuit diagram of such a conventional continuity / insulation tester is shown.
Shown in the figure. A conventional continuity / insulation tester will be described with reference to this figure.

In this figure, _{11 to} 1n are probe pins, and thousands to tens of thousands are implanted in a board called a prober board. At the time of the continuity test, the substrate under test 2 is pressed against the probe pins _{11 to} 1n as shown in the drawing, and the respective test points are brought into contact with specific probe pins.

2A is a constant current source and 2B is a constant voltage source. 3 is a changeover switch, which allows the constant current source 2 to be used in the continuity test.
A is selected, and the constant voltage source 2B is selected during the insulation test. The selected constant current source 2A or constant voltage source 2B is connected between the selected pair of test points to be tested, and the bipolar transistor 4 is connected due to the selective connection.
_{1 to} 4n (upstream side switching element) and bipolar transistors 5 _{1 to} 5n (downstream side switching element) are provided. Further, bipolar transistor switches 6 _{1 to} 6 n are provided in order to input the voltage between the selected test points to the voltage determiner 7 (during a continuity test). Reference numeral 8 is a current determiner.

Circuits for controlling the driving of the bipolar transistors (switching elements) are omitted in the figure.

Next, the operation will be described. Assuming a case of a continuity test, the changeover switch 3 selects the constant current source 2A.
For example, when conducting the continuity test of the substrate under test between the test points in contact with the probe pins 1 ₁ and 1 ₂ , the bipolar transistor 4 ₁ which is an upstream side switching element.
And bipolar transistor 5 ₂ as a downstream side switching element by being allowed to turn on, the constant current source 2A is connected between the probe pins 1 _1, 1 _2. Further, the bipolar transistor 6 ₁ is turned on, and the voltage between the probe pins 1 ₁ and 1 ₂ is applied to the voltage determiner 7.

Here, if between the test points in contact with the probe pins 1 _1, 1 ₂ is conducting normally, the input voltage of the voltage determining unit 7 sufficiently low. On the other hand, if there is a disconnection between the test points, the input voltage of the voltage determiner 7 will be a large value. Therefore, the voltage determiner 7 compares the input voltage with a predetermined determination threshold to determine the continuity between the test points of interest.

In the case of the insulation test, the changeover switch 3 selects the constant voltage source 2B. And the probe pins 1 ₁ , 1 ₂
Between test points that are in contact with
When performing the insulation test, the bipolar transistor 4 _1, 5 ₂ is caused to turn on.

If the test points are properly insulated,
The current flowing through the constant voltage source 2B is sufficiently small, but if the insulation is imperfect, the current increases. Therefore, the current is compared with the determination threshold by the current determiner 8 to determine the insulation between the test points.

[Problems to be Solved] In such a conventional conduction / insulation tester, there is a problem that the breakdown of the bipolar transistor 5 on the downstream side occurs relatively frequently. It is also known that the frequency of such breakdown increases as the voltage of the constant voltage source 2B increases.

[Object of the Invention] It is an object of the present invention to prevent destruction of a switching element such as a bipolar transistor for selectively connecting such a constant voltage source or a constant current source to a probe pin, thereby achieving high reliability. To provide a continuity / insulation tester.

[Means for Solving Problems] According to the research by the inventor, in the conventional continuity / insulation tester shown in FIG. 2, a pair of probe pins 1 in which the constant current source 2A or the constant voltage source 2B is selected. When the upstream-side bipolar transistor 4 and the downstream-side bipolar transistor 5 are turned on to connect to the bipolar transistor 5, a transiently large current flows into the bipolar transistor 5, and this transient current causes the bipolar transistor 5 to be destroyed. I understood.

The transient current flowing at this time is the discharge current of the electrostatic charge accumulated in the substrate under test 2, the prober board in which the probe pins 1 are implanted, the wiring of the probe pins 1 and the like, and is the collector current of the bipolar transistor 5. It turned out to flow to the emitter.

Focusing on such a point, the present invention relates to a switching element for selectively connecting a constant voltage source or a constant current source to a probe pin, and an overcurrent protection circuit for limiting a current flowing through the switching element to an allowable limit or less. Are to be connected.

Therefore, in order to achieve the above-mentioned object
The characteristics of the insulation tester are that the first line is connected to the power source and receives the current from the power source, the second line that returns the current flowing out from the power source to the power source, the first line and the second line. A plurality of series circuits each including a first switching element and a second switching element connected in series between the first switching element and the second switching element, and between the first switching element and the second switching element of each series circuit. A plurality of connected probe pins, a current limiting element that is provided in the second line and through which a current to be returned to the power source flows, and a current flows out to a connection point of the second switching element of the current limiting element, and a steady state is obtained. And a constant voltage circuit for maintaining the connection point at a constant potential when a test current flows, the first switching element of one series circuit having a plurality of series circuits and the other one of the series circuits. And 2 of a switching element to a conducting state, and selects a pair of probe pins to be contacted to the test object.

[Operation] As described above, the current limiting element is provided in the second line for returning the current to the power source, and further, the current is caused to flow to the connection point on the second switching element side of the current limiting element to make the potential here a constant potential. With the protection circuit provided with the constant voltage circuit, the test can be performed in the same manner as the conventional one. Furthermore, since the constant voltage circuit is the current outflow type, even if a large current transiently flows in the second line. Since the potential at the connection point rises due to the current limiting element, the voltage between the first line and the second line is reduced and the current flowing through the switching element is limited, or the switching element turns off. The element is protected.

In this way, the overcurrent protection circuit is connected to the switching element for controlling the connection between the probe pin and the power supply, and thereby the current of the switching element is limited to the allowable limit or less.
Therefore, when the switching element is turned on, the discharge current of the electrostatic charge that exceeds the allowable limit does not flow, so it is possible to prevent the switching element from being damaged by the electrostatic discharge current as in the past, and improve the reliability of the continuity / insulation tester. it can.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic circuit diagram showing a simplified example of a continuity / interruption tester according to the present invention. In this figure,
The same parts as those in FIG. 2 are designated by the same reference numerals,
Description of that part is omitted.

An overcurrent protection circuit 10 is commonly connected to the emitters of the bipolar transistors 5 (bipolar transistors 5 _{1 to} 5n are represented by the bipolar transistors 5) that are downstream switching elements.

The configuration of the overcurrent protection circuit 10 will be described below.
Reference numeral 1 is a resistor, and the emitter of the bipolar transistor 5 is a constant voltage power source 12 of negative polarity via the resistor 11.
It is connected to the. The emitter of the bipolar transistor 13 is connected to the connection point with the resistor 11 and the emitter of the bipolar transistor 5. The collector of the bipolar transistor 13 is connected to a power source 14 of positive polarity, and a series connection body of a resistor 15 and a constant voltage diode 16 (or a zener diode) is connected between the power source 14 and ground. The connection point between the resistor 15 and the constant voltage diode 16 is held at a constant potential, which is connected to the base of the bipolar transistor 13.

In the overcurrent protection circuit 10 having such a configuration, since the base of the bipolar transistor 13 is held at a constant potential, the bipolar transistor 13 acts to make the potential of its emitter constant. That is, when the current flowing from the bipolar transistor 5 into the resistor 11 decreases (increases), the emitter current of the bipolar transistor 13 increases (decreases) and the resistor 11 increases.
Current is made constant, and as a result, the potential of the emitter of the bipolar transistor 13 (the emitter of the bipolar transistor 5) is made constant.

However, such a voltage stabilizing action by the bipolar transistor 13 works effectively because the current flowing from the bipolar transistor 5 to the resistor 11 (at the same time, only one bipolar transistor 5 is turned on, so that it is equal to its emitter current). (Which can be considered) is equal to or less than a predetermined value and the bipolar transistor 13 is in an active state.

In this case, the potential at the connection point between the resistor 11 and the transistor 13 is always a constant potential, so that the test can be performed in a state similar to the state in which the emitter of the bipolar transistor 5 is connected to the ground level. In particular, since the negative polarity constant voltage power supply circuit 12 is provided downstream, it is easy to set the potential of the connection point to the ground potential by selecting the relationship between the resistance value of the resistor 11 and the outflow current of the transistor 13. You can

When the inflow current exceeds a predetermined value, the emitter potential of the bipolar transistor 13 rises, and the base-emitter junction of the bipolar transistor 13 becomes reverse biased. Therefore, the voltage stabilization by the bipolar transistor 13 is not performed, and the bipolar transistor 5
The emitter potential of is increased in proportion to the emitter current. As a result, the base-emitter junction bipolar transistor of the bipolar transistor 5 becomes shallow, and the increase in the emitter current is suppressed.

As described above, by appropriately determining the value of the resistor 11 and the base potential of the bipolar transistor 13, the current flowing through the bipolar transistor 5 can be suppressed below the allowable limit.

Here, as described above, when the bipolar transistor 5 is turned on, the electrostatic charge accumulated in the wiring on the collector side of the bipolar transistor 5 tries to be discharged through the bipolar transistor 5. In the past, no special means was provided for limiting the current of the bipolar transistor 5,
A discharge current that exceeds the allowable limit flows, and the overcurrent causes the breakdown of the bipolar transistor 5.

On the other hand, in the continuity / insulation tester according to the present invention, since the current of the bipolar transistor 5 is limited to the allowable limit or less by the overcurrent protection circuit 10, the bipolar transistor 5 is affected by the electrostatic charge discharge current when turned on. Protected from destruction.

Further, in this embodiment, if the current of the bipolar transistor 5 is below the allowable limit, the emitter potential thereof is made constant by the overcurrent protection circuit 10. Therefore, the base of the bipolar transistor 5 can be stably driven by a relatively simple base drive circuit (not shown) similar to the conventional one.

Incidentally, when overcurrent protection is performed by simply connecting a current limiting resistor in series to the emitter of the bipolar transistor 5, even if the emitter current is within the allowable limit, the emitter potential increases in proportion to the increase or decrease. Will fluctuate. As a result, the base drive of the bipolar transistor 5 is likely to be unstable, and the base drive circuit is complicated to enable stable base drive.

Although the above description has been made in relation to the overcurrent protection circuit 10, the overall operation of the continuity test and the insulation test is the same as that of the conventional one, and therefore its explanation is omitted.

In this embodiment, one overcurrent protection circuit 10 is commonly connected to the emitters of all the bipolar transistors 5, but each one of the bipolar transistors 5 is
Alternatively, similar overcurrent control circuits may be connected for each predetermined number.

Further, the bipolar transistors 4, 5 and 6 can all be replaced with field effect transistors. When the bipolar transistor 5 is replaced with a field effect transistor,
Similar overcurrent protection can be achieved by connecting a similar overcurrent protection circuit to the source.

It is also possible to omit the constant voltage power supply 12 and directly connect one end of the resistor 11 to the ground.

Further, other than the above, the present invention can be implemented by appropriately modifying it.

[Effects of the Invention] As described above, according to the present invention, a switching element for selectively connecting a constant voltage source or a constant current source to a probe pin is provided with a switching element for limiting a current flowing therein to an allowable limit or less. Since the current protection circuit is connected, the static discharge current that exceeds the allowable limit does not flow when the switching element is turned on, so it is possible to prevent the switching element from being destroyed by the static charge discharge current as in the past. A continuity / insulation tester with improved properties can be realized.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram showing an embodiment of the continuity tester of the present invention, and FIG. 2 is a schematic circuit diagram of a conventional continuity / insulation tester. ₁ 1 ~1n (1) ... probe pins, 2 ... to be tested substrate, 2
A ... constant current source, 2B ... constant voltage source, 3 ... changeover switch, 4 ₁ ~4n (4) ... upstream bipolar transistors, 5 ₁ ~5n (5) ... downstream bipolar transistors, 6 ₁ ~6n ... voltage application Control bipolar transistor, 7 ... voltage determiner, 8 ... current determiner, 10 ... overcurrent protection circuit, 11 ... resistor, 12 ... constant voltage power supply, 13 ... bipolar transistor, 14 ... power supply, 16 ... constant voltage diode.

Claims (3)

[Claims] 1. A power source is selectively connected to a pair of probe pins among a large number of probe pins in contact with an object to be tested such as a printed circuit board, and the object to be tested is electrically connected between the pair of probe pins. In a continuity / insulation tester that performs a test or an insulation test, a first line that is connected to the power supply and receives a current supply from the power supply, and a second line that returns the current drained from the power supply to the power supply. A plurality of series circuits each including a first switching element and a second switching element connected in series between the first line and the second line, and a first switching element of each of the series circuits. And a second switching element, a plurality of probe pins respectively connected between the switching element and the second switching element, a current limiting element provided in the second line, through which a current returning to the power source flows, A constant voltage circuit that causes a current to flow to a connection point of the second switching element of the limiting element and maintains the connection point at a constant potential when a test current in a steady state flows; There is one serial circuit first
A continuity / insulation tester, characterized in that the switching element and the second switching element of the other one series circuit are brought into conduction to select the pair of probe pins. 2. The continuity / insulation tester according to claim 1, wherein the current limiting element is a resistor and the switching element is a bipolar transistor. 3. The constant voltage circuit includes a bipolar transistor having an emitter connected to the connection point, a base held at a constant potential, and a collector connected to an operating power supply. Continuity / insulation tester according to the item.