JPH0354489A - Back drive equipment - Google Patents

Abstract

PURPOSE:To realize a more complete safety countermeasure by directly measuring the temperature of a back-driven IC. CONSTITUTION:Test probes 4 and 5 are brought into contact with the cathode and the anode, respectively, of the protective diode 12 of an IC and an ammeter 2 makes a current flow in the diode 12 in a forward direction via the test probes 4 and 5. A voltmeter 3 measures a voltage drop in the diode 12 due to the current. At this time, a control unit 10 outputs a voltage corresponding to a safe operation temperature different depending on the back-driven IC as a reference signal 6. When the voltage drop of the diode 12 is larger than the voltage of the signal 6, a comparator 7 outputs an output signal 8. The control unit 10 stops or outputs a test pattern 9 depending upon whether or not the signal is outputted 6, respectively. A driver 1 lets the diode 12 take a back drive condition by the test pattern 9. That is, the control unit 10 monitors the signal 8, judges that an output detection is near a dangerous condition and prevents the IC from being damaged by a back drive.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a backdrive device, and particularly to a backdrive device used in an in-circuit board tester for digital ICs.

[Technological environment]

Recent board testers use digital I mounted on the board.
When performing C functional tests, a method called backdrive was developed and put into practical use, in which the target IC is electrically isolated from the surrounding circuit elements and a test pattern is applied to it. has been done. But in this case,
Since the peripheral circuit elements of the target IC will be backdriven, the damage caused to them becomes a problem, especially when a digital IC is backdriven.

However, there are still many questions regarding the safety of such pack drives, and no conclusions have been reached at present. However, the effects of backdrive on the failure detection rate of board testers and the reduction in trouble repair efforts are far greater than with other types of board testers, and there is a strong tendency to use them even if it is somewhat dangerous.

In the future, board mounting density will continue to increase.
It is clear that failure detection will become more difficult.Therefore, it is thought that backdrive-based in-circuit board testers will continue to become popular, with the above-mentioned problems remaining. Gender issues are issues that must be resolved as soon as possible.

[Conventional technology]

The safety measures taken in conventional board testers using backdrives are to suppress the temperature rise as much as possible, since damage to the IC due to the backdrive can be avoided by detecting the rise in temperature of the IC. A method is being taken. One method is to provide a hardware timer so that the back drive does not take longer than a certain period of time.

This method is reliable because it is controlled by hardware, but it only manages a certain amount of time regardless of the type of IC, and it cannot handle cases where the temperature rise varies due to variations in the type of IC. . Another method is to perform more detailed control by setting different back drive durations depending on the type of IC using a program. However, even in this case, the temperature rise time varies depending on the operating state of the IC, so it may not be possible to cope with it.

[Problem to be solved by the invention]

As explained above, the safety management of conventional in-circuit board testers using backdrives attempts to indirectly suppress temperature rises by managing the duration of the backdrive. A problem has arisen in that changes due to variations cannot be accommodated, and therefore it cannot be said to be sufficiently safe.

[Means to solve the problem]

The back drive device of the present invention includes two test needles that contact both ends of a protection diode of an IC, a current source that flows a current in the forward direction to the protection diode through the two test needles, and a a voltmeter that measures the amount of voltage drop across the protection diode; a comparator that outputs an output signal when the amount of voltage drop is greater than a reference signal; a driver that puts the protection diode into a backdrive state using a test pattern; and a control section that outputs the test pattern when the output signal is not output, and stops outputting the test pattern when the output signal is output.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

The backdrive device shown in Figure 1 has a driver 1 having a very small output impedance, an ammeter 2, a voltmeter 3, a test needle 4, and a test needle 5, and the output of the driver 1 is 4 and one terminal of each of ammeter 2 and voltmeter 3, and a test needle 5 is connected to the mutually connected point of the other terminal of ammeter 2 and voltmeter 3, and this back drive device Further, the output 1l of the voltmeter 3 is used as one input, and the reference signal 6 is used as the other input, and the magnitudes of the two are compared, and the voltmeter output 1l becomes
A comparator 7 that outputs an output signal 8 when it is larger than the reference signal 6, and a control section 10 that receives the output 8 of the comparator 7 and outputs the reference signal 6 and the test pattern 9.
and has.

This embodiment uses a method of detecting a dangerous state by directly measuring the temperature inside the back-driven IC. This method of measuring temperature takes advantage of the fact that the forward voltage drop of a protection diode attached to the input section or output section of each gate of an IC depends on temperature. The method is to detect the temperature by measuring the temperature.

Next, the operation of the pack drive device shown in FIG. 1 will be explained. The test needles 4 and 5 are brought into contact with the cathode and anode, respectively, of the protection diode 12 of the IC receiving backdrive. First, when performing a test, the ammeter 2 causes current to flow in the direction of the ammeter 2 → test needle 5 → protection diode 12 → test needle 4 → ammeter 2. At this time, the voltmeter 3 continues to output the forward voltage of the protection diode l2 at this time as the voltmeter output 11. On the other hand, the control unit 10 outputs a voltage corresponding to a safe operating temperature as the reference signal 6, which varies depending on the IC to be backdriven. Since the temperature indicated by the protection diode 12 before being backdriven is lower than the reference temperature, the comparator 7 does not output the output signal 8. In this state, when the control section 10 outputs the test pattern 9 to execute a test, this passes through the driver 1 and becomes a back drive signal. When the temperature of the protection diode 12 increases due to this backdrive, the voltage drop in the forward direction of the protection diode 12 increases, and this phenomenon appears in the voltmeter output 1. When the temperature inside the IC subjected to backdrive increases, and as a result, the voltmeter output l1 increases and becomes larger than the reference signal 6, the comparator 7 outputs an output signal 8. The control unit 10 monitors this output signal 8, and when the output is detected, it determines that the situation is close to dangerous and stops the output of the test pattern 9 to stop the back drive. By doing so, it is possible to prevent damage to the IC due to the back drive.

〔Effect of the invention〕

The backdrive device of the present invention can prevent danger by directly measuring the temperature of the IC being backdriven, and since the temperature is directly measured, consideration is given to variations in temperature rise. is unnecessary, the problems with conventional safety technology are solved, and a more complete safety measure is realized, which is a great effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention. l...driver, 2...ammeter, 3...voltmeter,
4... Test needle, 5... Test needle, 6... Reference signal,
7... Comparator, 8... Output signal, 9... Test pattern, 10... Control section, 1... Voltmeter output, l2... Protection diode.

Claims (1)

[Claims] Two test needles that touch both ends of the protection diode of the IC, a current source that flows a current in the forward direction to the protection diode through these two test needles, and the amount of voltage drop across the protection diode due to the current is measured. a comparator that outputs an output signal when the amount of voltage drop is larger than a reference signal; a driver that backdrives the protection diode according to a test pattern; and a driver that outputs the reference signal and outputs the output signal. A back drive device comprising: a control unit that outputs the test pattern when the output signal is not output, and stops output of the test pattern when the output signal is output.