JPH04505962A - Touch sensing for testing integrated circuits - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Touch sensing for testing integrated circuits Background of the invention TECHNICAL FIELD This invention relates generally to the testing of integrated circuits, and more specifically to the testing of devices under test. This technology involves determining whether a probe is in electrical contact with a connection point. be.

The wafer is diced and its chips are processed into integrated circuit devices before being packaged. It is well known to test

In a typical test environment, integrated circuit testing is performed by waving before dicing. Wafers are sorted, in which case the wafers are placed on a vacuum chuck and each die is separated. tested. A probe that uses multiple probe tips to test one die. Align the probe card with the die and touch the corresponding probe tip to each bond pad. let Then, various voltage levels, signals, and combinations of signals are set up under test. Integrated circuit device response under test in addition to the input of the integrated circuit device and at its output Analyze. At this level of testing, the bond pads of the device under test (this is It's just a matter of getting closer to the larger one. However, the number of probes (e.g. 100), so it is a troublesome problem to contact them at the same time.

Furthermore, such tests do not always produce a complete picture. Even one thing It is often necessary to determine the signal response at several or more internal circuit connection points. It may become. Sometimes with a test pad that is much smaller than the bond pad. approach the internal connection point. It is necessary to test the conductive paths in the active area of the chip. Sometimes it even happens.

A typical approach uses a probe with a thin wire tip. current In circuit technology, the conductive paths are very narrow, and direct probes require damage to the tip. Requires going through steps to avoid injury. i.e. excessive mechanical force avoidance of electrical contact, yet be able to accurately determine when proper electrical contact is made. is important.

One approach is to visually confirm contact.

When the probe makes contact and further downward force is applied, the probe slides on the surface of the tip. , it can be detected visually. This method is impractical for automated testing.

One possible approach for automatic touch sensing is to use two closely spaced chips. Use probes with Connect the current detection circuit. When both tips of the probe make contact with the device, the loop the loop is closed and current is detected.

Although this approach may be viable for some applications, it has several limitations. do. For example, if two chips do not touch at the same time, the first chip's contact will cause the second Excessive force is applied before the tip contacts the tip. Furthermore, the contact area is large (this (This may be acceptable when probing bond pads). Change In addition, this dual-tip probe has a reset function when the probe is used in measurement mode. Even if the relay isolates the touch-sensing circuit, it will place an extra capacitive load on it. Become. Additionally, dual-tip probes (close to the actual probe tip) not suitable for use as an active probe (with transistor amplifier) .

This is because the device under test side of the transistor cannot be brought into contact with the probe.

Despite the sophistication of the actual test equipment, the probe does not actually touch the device under test. It will be appreciated that the technique for determining when contact is made is relatively clumsy. . It is a kind of Achilles key.

Summary of the invention The present invention enables establishment of a desired degree of electrical contact between the probe tip and the device under test. To provide a simple and effective technique for detecting whether or not With this technology, the device under test The contact condition can be tested both in the energized state and in the de-energized state, and the Contact status can be tested even when the testing device is activated, and can be used with passive probes as well. It can also be applied to probes.

In a broader sense, the present invention provides a means for grounding or grounding a touch-sensitive device under test. A voltage reference (typically It is intended for touch-sensing circuits that have a ground (mainly earth or ground). current The sensing circuit applies a characteristic signal to one of the terminals of the device under test, such as the ground terminal. It has elements that operate in the same way. This makes the graphs for all devices under test Track the applied signal (relative to a touch-sensing reference). Furthermore, the current sensing circuit is connected to the probe. includes an element connected to the probe and operative to detect the presence of a characteristic signal on the probe. Ru. For example, if the characteristic signal is a sine wave of a certain frequency, such a detection element is a bandpass filter centered near that frequency, and the filter circuit is centered near that frequency. a decision circuit that provides a signal indicating whether a predetermined component of frequency is passed; I'm reading.

The output from the sensing element of this decision circuit is sent to an LED indicator to probe visually indicates that the device under test is in contact with the device under test, and the output above is signal to the optical coupler driver to provide contact status to the rest of the test equipment. tell. Once electrical contact is established, the characteristic signal output is disconnected from the device under test. the ground of the test equipment is connected to the ground of the touch-sensing circuit, and The probe output is coupled to the rest of the test equipment circuit.

The present invention is applicable to single probe mechanisms and multi-probe mechanisms. multiple In the case of lobes, each probe has its own detection circuit and the wafer If you are using a wafer chuck, the characteristic signal is applied to that wafer chuck. Ru. The output of the detector is also connected to an optical fiber.

The idea and advantages of the invention will be better understood from the following description and drawings.

Brief description of the drawing Figure IA-B is a block diagram schematically illustrating the touch sensing circuit of the present invention in touch sensing and measurement mode. This is a diagram.

FIG. 2 is a simplified diagram of a typical active probe.

3A-B are circuit diagrams corresponding to FIGS. IA-H.

FIG. 4 is a block diagram showing an embodiment of a multi-probe.

Description of the preferred embodiment Figures IA-B are block diagrams illustrating a touch sensing circuit 10 of the present invention. touch sensing circuit 10 operates together with a probe 12 having a tip 13 to connect the device under test 15. Detects when chip 13 makes sufficient electrical contact. In a preferred embodiment The device under test is an integrated circuit device (wafer or chip). contact Once created, the probe 12 signal is applied to the appropriate input terminal 17 of the test equipment. (Other than the input terminals of the test equipment are not shown). Figure IA is touch sensing mode The circuit configuration is shown below. The power supply that supplies power to the device under test 12 and the test equipment is Referred to as the test device ground, and shown in the drawing as an ordinary three-line notation to ground. They have a common ground indicated by the number. The elements of the touch sensing circuit 10 are unique. The ground of this power supply is referred to as the touch-sensing ground. Unlike normal symbols, it is represented by a single line and a small circle. Details below As discussed, the degree of isolation depends on various characteristics of the circuit elements.

The basic elements of the touch sensing circuit include a signal generator 20 and a detection circuit 22. signal generator A signal with predetermined characteristics is supplied from the output terminal 25 of 20. In the preferred embodiment, The signal is a sine wave of a predetermined frequency. The detector 22 has an input terminal 27 and an output terminal 28. and this output terminal accepts an input signal exhibiting a sufficient degree of predetermined characteristics as an input terminal. When detected at 27, it generates a signal that is asserted.

The signal at the output terminal 28 of the detector is communicated to a visual indicator 30 and a signal indicator 32. You can also do this. Visual indicator 30 indicates that a signal is asserted at output terminal 28. Preferably, it is an LED that visually indicates. The signal indicator 32 while maintaining isolation between the vice ground and the touch-sensing circuit ground. Sends a signal to the test equipment.

The output signal from the touch sensing signal generator 20 is connected to the connection point 35 on the device under test 15. sent to. Connection point 35 is the ground of the device under test, but typically Can be a pin on the test device.

The signal appearing at probe 12 is sent to input terminal 27 of detector 27. Touch sensing The round and the ground of the device under test are at least partially isolated from each other. Since the signal applied to connection point 35 is It overlaps the level of all connection points of the device under test 15. Probe 12 and under test Once sufficient electrical contact is established with the device 15, the characteristic signal A signal appearing at power terminal 27 and appearing at output terminal 28 of the detector is asserted. .

The measurement mode circuit shown in Figure IB is used after contact is established. a suitable relay Make three connection changes. First, the probe is not connected to the input terminal 27 of the detector. , is connected to the input terminal 17 of the test device. Second, the ground of the device under test. and a touch-sensitive ground are coupled together. Third, the output signal of the signal generator is disconnected from the device under test and is not sent anywhere.

FIG. 2 is a schematic diagram of probe 12. FIG. As a suitable active probe, Nab, FL PICOPROBE (registered trademark) sold by GGB Industries There is a mark). Probes do not form part of this invention, but are typical active probes. Let me briefly explain the probe. The probe tip 13 is a tungsten wire (diameter 10-50 microns, tip radius 0.5-3.0 microns), and this This is connected to the MOS device 350 input (gate). MOS devices are rigid is coupled to amplifier 37 by a coaxial feed 38 of . The output of this amplifier is via coaxial cable 39 to the contact sensing circuit.

FIG. 3A is a schematic diagram of the touch sensing circuit 10 connected in a touch sensing mode. child The circuit has an isolated power supply 40, which supplies a DC voltage with respect to an isolated ground. Ru. The signal generator 20 includes an oscillator 42 and an output driver 43. Oscillator output The force signal is sent to the output driver 43 and from there to the connection on the device under test. point, preferably to ground of the device under test. Typical operating frequency is ]0 KHz, but is not limited to this. The detection circuit 22 is a secondary function. It includes a dynamic filter 45, a peak detector 47 and a decision circuit 48. filter 45 passes the oscillator frequency signal and sends its output to the peak detector 47. In addition, the peak detector 47 utilizes a converter that converts the actual value into direct current.

The output from the peak detector 47 is sent to a decision circuit 48, which Optical coupler 32 is actuated when the force signal exceeds a certain critical value. Op The signal at the optical coupler 32 is referenced as the ground for the device under test. , a signal that tells the test equipment that a contact has been made.

Although various signal levels and threshold values can be used in this preferred embodiment, the oscillator/ The driver is tested with a signal of approximately 10 volts (peak to peak magnitude) The critical value of the decision circuit is that a characteristic signal of approximately 100 millivolts is applied to the device and the critical value of the decision circuit is It is set to give clear contact instructions when it appears in the robe.

Figure 3B schematically shows the connections made once electrical contact is established. Measurement mode , the device under test ground and the touch-sensing ground are shorted together. , the signal from signal generator 20 is connected to (or away from) the ground of the device under test. is disconnected (from the connection point on the device under test to which it is connected), and the probe The signal from is sent to the test equipment rather than to the touch sensing circuit.

FIG. 4 is a block diagram showing an embodiment of the multiple probe of the present invention. Figure IA- The same reference numerals are used as in Figures 3A-B and Figures 3A-B. vacuum chuck 62 Two probe tips 13 are in contact with the surface of the wafer 60 held by the wafer 60 . Up The detector associated with each probe includes a filter 45, peak detector and It is provided with a techer 47 and a decision circuit 48. The output of the decision circuit is a multiplexer 65, the output of which is sent to the signal indicator (optical coupler) 32 and the visible The signal is sent to an indicator (LED) 30.

As explained above with reference to FIG. 3A, the critical value of the decision circuit can be adjusted. critical value The input is a digital to analog converter (DAC) 7 (connected to the output of l). The input of this converter is programmable. Depending on each case, the critical value is (-variant) remains constant and changes depending on the selected probe be able to.

It is theoretically possible to multiplex probes and use a single detection circuit. Ru. However, the detection circuits have delay characteristics due to their RC time constants. . This allows the circuit to stabilize as each probe samples. becomes. This is acceptable if there are only two or three probes, but if there are many Then the delay of the entire system would be prohibitive.

As explained above, during touch sensing a characteristic signal is applied to the device under test and the other contact The tactile ground is isolated from the device under test ground. wafer For testing, it is convenient to apply the signal to the vacuum chuck.

The above description is based on the contact between the probe and the device under test, and the The two terminals are assumed to be insulated from each other. However, "contact" and "abstinence" ``edge'' or ``isolation'' does not have an absolute meaning, but rather a relative or comparative meaning. It should be considered as meaning.

First, when the circuit is in touch-sensing mode, the Consider the required degree of insulation. Signal generation (driving the ground of the device under test) insulation to the extent that the signal from the device 20 is not shorted to the touch sensing ground. Requires.

In the preferred embodiment, the two grounds are connected by a resistor (approximately 10K) and a capacitor in parallel. (approximately 1-10 μf) to reduce noise. But this is a sufficiently large impedance for the characteristic signal from the signal generator. reasonable This level of insulation is sufficient for a characteristic signal of a large magnitude to appear on the device under test. be.

The degree of probe-to-device-under-test contact that provides a clear indication from the detection circuitry Next, consider connection by detecting a characteristic signal of a certain magnitude from the probe. Since touch is sensed, the detection circuitry determines the degree of touch required to give a clear indication. It can be adjusted by adjusting the critical value of .

In conclusion, the present invention is effective when a desired portion of a device under test and a probe come into contact with each other. It will be appreciated that this provides a simple and effective method for determining the This is after that automatically without affecting the test phase.

Although the foregoing is a complete description of the preferred embodiments of the invention, various modifications, alternative configurations and equivalents are available.

For example, the characteristic signal need not be a sine wave. Generation of square waves and other periodic signals (the same type of filter would be most suitable). Characteristics are frequency You don't even have to. Frequency shift keying techniques can be used and characteristic shifts can be used. It is also possible to detect

Additionally, the preferred embodiment determines whether the desired degree of contact has been achieved by decision circuit 48. However, the signal from peak detector 47 is This allows for more nuanced decisions (degree of contact) if desired.

The present invention is limited by the scope of the claims, and the above description and illustrations are It does not limit the invention.

l / touch sensing circuit In this mode +4+ touch sensing circuit ÷　m+ international search report

Claims (12)

[Claims] 1. It has a generator reference terminal and a generator output terminal. generator means for generating a first signal of predetermined characteristics at the output terminal; and A detector input terminal, a detector output terminal and a detector reference terminal coupled to the probe. and generates a second signal at the detector output terminal with respect to the detector reference terminal. Equipped with outlet means, Said second signal is relative to said detector reference terminal appearing at said detector input terminal. represents the magnitude of a signal having defined characteristics device reference terminals are connected to each other and at least partially away from the device under test. The generator reference terminal and the detector reference terminal may be isolated, and the generator reference terminal and the detector reference terminal may be isolated. When at least partially isolated from the device under test, said first signal a terminal of the device, and a probe coupled to said input terminal, said probe being coupled to said input terminal; The second signal indicates the degree of electrical contact between the probe tip and the device under test. A circuit that senses the state of electrical contact between the probe and the device under test. . 2. 2. The circuit of claim 1, wherein the generator means is a sinusoidal oscillator having a characteristic frequency. 3. 4. The detector means comprises a bandpass filter for passing signals at a characteristic frequency. 2 circuit. 4. The detector means further comprises a peak detector connected to the bandpass filter. 4. The circuit of claim 3. 5. 2. The circuit of claim 1, wherein the detector means includes means for defining an adjustable threshold value. 6. visual indicating means for visually indicating a desired degree of contact in response to the second signal; 2. The circuit of claim 1, further comprising: 7. 7. The circuit of claim 6, wherein the visual indicator means comprises an LED. 8. to a reference not isolated from the device under test in response to a second signal. further comprising optical coupling means for generating a signal representative of the second signal. 2. The circuit of claim 1 comprising: 9. It has a generator reference terminal and a generator output terminal, and has a generator reference terminal and a generator output terminal. generator means for generating a first signal of predetermined characteristics at the output terminal; and A detector input terminal, a detector output terminal, and a detection coupled to one of a plurality of probes. a detector reference terminal, and a second signal is input to the detector output terminal with respect to the detector reference terminal. comprising a plurality of detector means connected to each of the plurality of probes for generating a Said second signal is relative to said detector reference terminal appearing at said detector input terminal. represents the magnitude of a signal having defined characteristics device reference terminals are connected to each other and at least partially away from the device under test. The generator reference terminal and the detector reference terminal may be isolated, and the generator reference terminal and the detector reference terminal may be isolated. When at least partially isolated from the device under test, said generator output terminals a test device, and a probe coupled to the detector input terminal; Said second signal indicates the degree of electrical contact between the probe tip and the device under test. Sensing the electrical contact between multiple probes and the device under test A circuit that knows. 10. a multiplexer input coupled to the detector output terminal and a selection of the second signal; further comprising a multiplexer having a multiplexer output outputting one of the 10. The circuit of claim 9. 11. A specified characteristic of the level of at least partial isolation from the device under test. applying a sexual signal to a connection point on the device under test; Plug the signal to a level that is at least partially isolated from the device under test. detecting on the lobe and determining the degree to which the signal on the probe has the specified characteristics. sensing the condition of electrical contact between the probe and the device under test with the step of determining How to know. 12. The device under test is a die on a wafer held in a chuck, and 12. The method of claim 11, wherein the signal applying step applies a signal to the chuck.