WO2019118730A1

WO2019118730A1 - A defect detection system

Info

Publication number: WO2019118730A1
Application number: PCT/US2018/065456
Authority: WO
Inventors: Raul Albert Martin
Original assignee: Photon Dynamics Inc.
Priority date: 2017-12-14
Filing date: 2018-12-13
Publication date: 2019-06-20
Also published as: CN111465830B; IL275202A; JP7303196B2; KR20200099171A; JP2021507222A; CN111465830A; JP2023123640A

Abstract

A defect detection system including a pattern generator for selectably energizing portions of an electrical circuit under 5 test at predetermined times determined at least in part by the electrical circuit under test, a plurality of sensors including at least one thermal sensor and a synchronization generator operative to receive an output of the pattern generator and based on said output to synchronize operation of the at least one thermal sensor with operation of the pattern generator.

Description

A DEFECT DETECTION SYSTEM

REFERENCE TO RELATED APPLICATIONS

Reference is hereby made to U.S. Provisional Patent Application Serial No. 62/598,471, entitled System and Memod for Detecting Defects in Electronic Circuits using Differential Thermal Imaging, filed December 14, 2017, and to U.S. Provisional Patent Application Serial No. 62/615,977, entrtied A Defect Detection System, filed January 11, 2018, the disclosures of which are hereby incorporated by reference and priority of which is claimed.

FIELD OF THE INVENTION

The present invention relates to defect detection in electrical circuits.

BACKGROUND OF THE INVENTION

Various types of defect detection systems and methodologies are known for use with electrical circuits.

One example is the Array Checker AC68xx family of systems, commercially available from Photon Dynamics, Inc., an Orboteeh Company, of San Jose, CA, USA. The defect detection system preferably is employed for testing flat panel displays in accordance with the teachings of U.S. Patent Nos. 4,983,911 and 5,124,635 and preferably employs multiple defect detection heads.

In the semiconductor industry, single camera thermal imaging is employed for differential thermographic defect detection, as described in U.S. Patent No. 9,546,907. Thermal imaging cameras are known to have issues of stability over time. As such, it is customary, as in US. Patent No. 9,546,907, to provide static calibration for one particular frame rate and to have the camera operate with a free- running camera generated trigger without external synchronization. It is not currently known how to employ multiple thermal sensors in an integrated differential thermography system for providing high thermal sensing defect detection throughput due to the requirement that the operation of the multiple thermal sensors be synchronized. SUMMARY OF THE INVENTION

The present invention seeks to provide an improved system and method for defect detection in electrical circuits.

There is thus provided in accordance with a preferred embodiment of the present invention, a defect detection system including a pattern generator for selectably energizing portions of an electrical circuit under test at predetermined times determined at least in part by the electrical circuit under test a plurality of sensors including at least one thermal sensor and a synchronization generator operative to receive an output of the pattern generator and based on the output to Synchronize operation of the at least one thermal sensor with operation of the pattern generator.

Preferably, the at least one thermal sensor includes at least one register operative to record information received from the synchronization generator and to provide an output of the information.

In accordance with a preferred embodiment of the present invention the defect detection system also includes an image processing computer operative to receive thermal image data from the at least one thermal sensor, to receive the output of the information from the at least one register and to output a thermal image. Additionally, the image processing computer is operative, based on the information from the at least one register, to output a thermal image by ascertaining which of the thermal image data are relevant to defect detection, discarding non-relevant thermal image data and utilizing the thermal image data mat is ascertained to be relevant to defect detection to generate the thermal image.

There is also provided in accordance with another preferred embodiment of the present invention a defect detection system including a pattern generator for selectably energizing portions of an electrical circuit under test at predetermined times determined at least in part by the electrical circuit under test, a plurality of sensors including at least two thermal sensors and a synchronization generator operative to receive an output of the pattern generator and based on the output to synchronize operation of the at least two thermal sensors with operation of the pattern generator. In accordance with a preferred embodiment of the present invention each of the at least two thermal sensors includes at least one register operative to record information received from the synchronization generator and to provide an output of the information.

Preferably, the defect detection system also includes an image processing computer operative to receive thermal image data from the at least two thermal sensors, to receive the output of the information from the at least one register and to output a thermal image. Additionally, the image processing computer is operative, based on the information from the at least one register, to output a thermal image by ascertaining which of the thermal image data are relevant to defect detection, discarding non-relevant thermal image data and utilizing the thermal image data that is ascertained to be relevant to defect detection to generate the thermal image.

There is further provided in accordance with yet another preferred embodiment of the present invention a defect detection system including a pattern generator for selectably energizing portions of an electrical circuit under test (ECUT) at predetermined times and providing ECUT-specific external synchronization pulses and a differential thermography subsystem including a plurality of sensors including at least One thermal sensor requiring periodic external readout trigger pulses at at least a first pulse frequency and a s>Tichronization generator operative to receive the ECUT-specific external synchronization pulses from the pattern generator for operating the at least one thermal sensor, the ECUT-specific external synchronization pulses being coordinated with the predetermined times and having a second pulse frequency determined at least in part by the ECUT, the second pulse frequency being greater man the first frequency, to provide the periodic external readout trigger pulses to the at least one thermal sensor in the absence of the ECUT-specific external sjTichronization pulses and to provide ECUT-specific external readout trigger pulses and ECUT-specific relevant readout indicating pulses to the at least one thermal sensor, thereby to synchronize operation of the at least one thermal sensor with operation of the pattern generator, whereby the periodic external readout trigger pulses are not received by die at least one thermal sensor when the ECUT-specific external readout pulses are being supplied to the at least one thermal sensor. In accordance with a preferred embodiment of the present invention the ECUT-specific external sjitchromzation pulses include an initial external synchronization (IBS) pulse which, when received by the synchronization generator causes the synchronization generator to provide a corresponding ECUT-specific relevant readout indicating (RRJP) pulse to the at least one thermal sensor but not to provide a corresponding ECUT-specific external readout trigger pulse.

Preferably, the at least one thermal sensor includes a sensor array and at least one register and is operative when reading out sensor array data from the sensor array to append thereto metadata based on an ECUT-specific relevant readout indicating pulse received at a time adjacent to a time of a received ECUT-specific external readout trigger pulse. Additionally, the at least one thermal sensor is operative when reading out sensor array data from the sensor array to append thereto metadata based on an ECUT- specific relevant readout indicating pulse received at a time just preceding a time of a received ECUT-specific external readout trigger pulse. Additionally or alternatively, the at least one register includes a first register recording timing of receipt of the ECUT- specific external readout trigger pulse and a second register recording timing of receipt the ECUT-specific relevant readout pulses.

In accordance with a preferred embodiment of the present invention the ECUT-specific external synchronization pulses are also supplied to non-thermal sensors forming part of the plurality of sensors.

Preferably, the relevant readout pulses provide metadata which identifies sensor readout information which is relevant to differential thermography defect detection as distinguished from readout information which is not relevant to differential thermography defect detection.

preferably, the plurality of sensors simultaneously view a given portion of the electrical circuit under test

In accordance wim a preferred embodiment of the present invention the plurality of sensors include at least one non-thermal sensor. Additionally, the at least one non-thermal sensor includes at least one optical sensor. Additionally or alternatively, said at least one non-thermal sensor includes at least one electric field sensor. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:

Fig. I is a simplified block diagram illustration of a defect detection system constructed and operative in accordance with a preferred embodiment of the invention;

Fig. 2 is a simplified flow chart of some aspects of the operation of the defect detection system of Fig, 1;

Fig. 3 is a simplified waveform diagram useful in understanding the functionality of a preferred embodiment of the present invention;

Fig. 4 is a simplified block diagram illustration of a defect detection system constructed and operative in accordance with another preferred embodiment of me mention;

Fig. 5 is a simplified block diagram illustration of a defect detection system constructed and operative in accordance with another preferred embodiment of the invention; and

Fig. 6 is a simplified block diagram illustration of a defect detection system constructed and operative in accordance with another preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to Fig, 1_? which is simplified block diagram illustratioft of a defect detection system 100 constructed and operative in accordance with a preferred embodiment of the invention. The defect detection system of Fig. 1 is preferably implemented on a system platform which is one of the Array Checker AC68xx family of systems, commercially available from Photon Dynamics, Inc., an Orhotech Company, of San Jose_» CA, USA. The defect detection system preferably is employed for testing fiat panel displays in accordance with the teachings of U.S. Patent Nos. 4„983;9U and 5,124,635, the disclosures of which are hereby incorporated by reference, and preferably employs multiple defect detection heads (not shown).

In accordance with a preferred embodiment of the present invention, defect detection system 100 employs a plurality of sensors, including thermal sensors and optionally also optical sensors (not shown) and electric field sensors (not shown). One or more sensors are mounted on one or more defect detection heads (not shown). Typically, but not necessarily, a thermal sensor may be mounted alongside an optical sensor and/or an electric field sensor on one or more defect detection heads. The plurality of sensors preferably simultaneously view different regions of an electric circuit under test (ECUT) 110. Typically, the ECUT 110 is a flat panel display, but; alternatively, it may be any suitable electric circuit to be tested. The ECUT 110 is typically stationary during testing and the sensors, mounted on one or preferably more than one defect detection heads, are displaced relative to the ECUT 110 in order to test various regions of the ECUT 110, Preferably, but not necessarily, testing of multiple regions of the ECUT 110 occurs simultaneously or nearly simultaneously in order to enhance testing throughput

As seen in Fig. 1, a supervisory computer 112 provides an acquisition plan, including an Image Definition portion, which is supplied to an image processing computer (IPC) 114, and a Pattern Definition portion, which is supplied to a pattern generator 120.

In accordance with a preferred embodiment of the invention, pattern generator 120 is operative for seleetably energizing predetermined portions of the ECUT 110 at predetermined times determined at least in part by the design of the electrical circuit under test, The pattern generator 120 provides ECUT-specific energizing pulses (ECUT-SEP) to the ECUT 110 via one or more conventional probe arrays ISO, which electrically engage various portions of the ECUT 110 at various times. The pattern generator 120 also provides ECUT-specific external synchronization pulses (ECUT-SESP) for synchronizing the operation of at least one ECUT testing sensor with the energization of portions of the ECUT 110.

A synchronization generator 140 receives the ECUT-SESP pulses from the pattern generator 120 and generates external readout trigger pulses (ERTP) and relevant readout indicating pulses (RRIP) as will be described hereinbelow with reference to Fig. 2 and fig. 3.

In accordance with a preferred embodiment of the present invention, at least one, and preferably multiple, externally synchronized thermal sensors ISO are employed as ECUT testing sensors. Additional sensors, such as optical sensors and electric field sensors (not shown), may additionally he employed. A preferred embodiment of an externally synchronized thermal sensor 150 is an IR-TCM camera, commercially available from Jenoptics GMBH of Jena, Germany, which accepts external readout trigger pulses (ERTP) and relevant readout indicating pulses (RRIP). Thermal sensors 150 typically require non-ECUT specific periodic readout trigger (NECUTS) pulses at at least a first pulse frequency, typically 5 - 7 Hz, determined by the thermal sensor 150, in order to maintain their stability.

Each thermal sensor 150 preferably includes at least one register which records and outputs information regarding the time relationship between receipt of the ERTP pulses and RRIP pulses. More specifically, each thermal sensor 150 preferably includes first and second registers 160 and 170, which respectively record and output information indicating the timing of receipt of the ERTP pulses and Of the RRIP pulses. Metadata downloaded from these registers enables thermal image data which is relevant to differential thermography defect detection to be distinguished from thermal image data which is irrelevant to differential thermography defect detection.

Preferably, the thermal sensors 150 and the image processing computer

114 together provide differential thermography functionality. It is appreciated that in principle the plurality of thermal sensors 150 could include a single thermal sensor 150. The differential thermography system preferably includes synchronization generator 140, which, as noted above* receives ECUT-SESP pulses from pattern generator 120 and, based on the ECUT-SESP pulses, is operative to synchronize operation of at least one thermal sensor ISO with operation of pattern generator 120.

It is appreciated that in order to enable differential thermography, the pattern generator must provide ECUT-SEP energizing pulses and corresponding synchronized ECUT-SESP pulses, which correspond to hot and cold states of a given portion of the ECUT 110, corresponding to energized and non-energized states thereof.

Reference is now made to Fig, 2, which is a simplified flow chart of some aspects of the operation of the defect detection system of Fig. 1.

Initially, an operator programs an ECUT^specific Acquisition Plan (ESAP) On the supervisory computer 112. The supervisor computer 112 distributes an Image Definition portion of the ESAP to the image processing computer 114 and a Pattern Definition portion of the ESAP to the pattern generator 120.

It is appreciated that the term acquisition plan as used herein refers to a list of definitions and instructions, which is typically composed of a list of images to be acquired, the conditions under which they are to be acquired (cold image, hot image, images to be discarded, etc.) and the mathematical operations to be used to create a composite image from the individual images.

The pattern generator 120 provides ECUT-SESP pulses to the synchronization generator 140 and also provides, in synchronization with the ECUT- SESP pulses, via probe arrays 130, ECUT-SEP energizing voltages to the ECUT which either energize or de-energize the relevant portions of the ECUT.

The synchronization generator 140 continuously provides ERTP pulses, which are read by the at least one thermal sensor 150 as FSYNC pulses. The synchronization generator 140 normally provides the ERTP pulses^ as NECUTS pulses at a first pulse frequency, to at least one thermal sensor 150 in order to maintain stability of the at least one thermal sensor 150. However, immediately upon receipt of an initial ECUT-SESP pulse and as long as ECUT-SESP pulses are received with a predetermined frequency, typically 9 Hz, the synchronization generator 140 does not provide NECUTS pulses, but rather provides the ECUT-SESP pulses as ERTP/FSYNC pulses to the at least one thermal sensor 150. The synchronization generator 140 also supplies RRIP pulses slightly following, and synchronized with, the ECUT-SESP pulses. Following receipt of a burst of ECUT-SESP pulses, the synchronization generator 140 returns to providing NECUTS pulses until a further burst of ECUT-SESP pulses is received.

The at least one triermal sensor 150, responsive to me ERTP/FSYNC pulses, irrespective of whether they are NECUTS pulses or ECUT-SESP pulses, that it receives from the synchronization generator 140, integrates and reads out thermal image data. This thermal image data is supplied to the image processing computer 114 together with outputs of registers 160 and 170, which indicate the time relationship between receipt by each thermal sensor 150 of the ERTP and RRIP pulses and enables the image processing computer 114 to ascertain which output thermal images are relevant to the defect detection in accordance with the Acquisition Plan. The image processing computer 114 discards the remaining, non-relevant thermal image data The image processing computer 114 performs computations in accordance with the Acquisition Plan and outputs relevant thermal images of the ECUT 110.

More specifically, it is appreciated mat synchronization generator 140 is preferably operative tor

receive (ECUT-SESP) pulses from pattern generator 120 for operating onft, or preferably more than one* thermal sensor 150, wherein the ECUT-SESP pulses are synchronized with the predetermined times at which the ECUT 110 is energized or de-energized and having a second pulse frequency determined at least in part by the design of the specific ECUT, the second pulse frequency being higher man the first pulse frequency of the NECUTS pulses: and

to provide the NECUTS pulses to at least one thermal sensor 150 when ECUT-SESP pulses are not being received by the syndifonization generator 140; and to provide ECUT-specific external readout trigger (ECUT-S-ERTP) pulses and relevant readout indicating (RRIP) pulses to the at least one thermal sensor 150, thereby to synchronize operation of the at least one thermal sensor 150 with operation of the pattern generator 120, whereby the NECUTS pulses ate not received by the at least one thermal sensor 150 when the ECUT-S-ERTP pulses are being supplied to the at least one thermal sensor 150, thereby preventing incomplete readouts from the at least one thermal sensor 150. Reference is now made to Fig. 3, which is a simplified waveform diagram useful in understanding the above-described functionality of the pattern generator 120, the synchronization generator 140 and at least one thermal sensor 150 in accordance with a preferred embodiment of the present inventi on.

As seen in Fig. 3, the pattern generator 120 generates bursts of ECUT-S-

ERTP pulses, typically at a burst frequency of 3Hz. Each burst, typically incudes an initial external synchronization (IES) pulse and at least two ECUT-S-ERTP pulses thereafter at a typical ECUT-S-ERTP pulse frequency of 9Hz. At a minimum for performing differential thermography defect detection, one pulse is a Hot pulse, corresponding to energizing a portion of the ECUT 110 currently being tested and another pulse is a Cold pulse, corresponding to deenergizing a portion ©f the ECUT 110 currently being tested.

As noted above, this output of pattern generator 120 is received at the synchronization generator 140, which, in the absence of receipt of ECUT-specific pulses preferably continuously provides periodic external readout trigger (P-ERTP) pulses. Immediately upon receipt of the IES pulse and for a predetermined period, typically 200 milliseconds (corresponding to 5 Hz), following me last of the recei ved ECUT-specific pulses in each burst, the synchronization generator does not provide P-ERTP pulses.

In response to receipt of the IES pulse, the synchronization generator 140 preferably produces an initial Relevant Readout Indicating (RRIP) pulse at a fixed time, typically about 90 - 100 milliseconds, following receipt of the IES pulse, but does not produce an ECUT5-ERTP pulse. This is to avoid ambiguity as to which readout from a thermal sensor 1 SO is relevant to the test.

In response to the second ECUT-S-ERTP pulse in a burst, which typically corresponds in time to energization of the ECUT 110, the synchronization generator 140 sends an ECUT-S-ERTP pulse to the thermal sensor 150. The thermal sensor 150, in response to receipt of the ECUT-S-ERTP pulse, reads out its image data to the image processing computer 114, which also receives the outputs of registers 160 and 170. The image processing computer 114 is thus aware that receipt of the ECUT-S- ERTP pulse by the thermal sensor 150 closely follows receipt of the initial RRIP pulse and thus retains the corresponding image data as relevant data. The synchronization generator 140 also produces a second Relevant Readout Indicating (RRIP) pulse at a fixed time, typically about 90 - 100 milliseconds, following receipt of the second ECUT-S-ERTP pulse.

Similarly, in response to the third ECUT^S-ERTP pulse in a burst, which typically corresponds in time to de-energization of the ECUT 110, me synchronization generator 140 sends an ECUT-S-ERTP pulse to the thermal sensor 150. The thermal sensor ISO, in response to receipt of the ECUT-S-ERTP pulse, reads out its image data to the image processing computer 114, which also receives the outputs of registers 160 and 170. The image processing computer 114 is thus aware that receipt of the ECUT-S- ERTP pulse by the thermal sensor ISO closely follows receipt of an RRIP pulse and thus retains the corresponding image data as relevant data.

The synchronization generator 140 may also produce a third Relevant Readout Indicating (RRIP) pulse at a fixed time, typically about 90 - 100 milliseconds, following receipt of the second ECUT-ERTP pulse. In a situation where there are only three ECUT-ERTP pulses in a burst, information related to receipt of mis third RRIP pulse is preferably discarded by the image processing computer 114.

Reference is now made to Fig. 4, which is simplified block diagram illustration of a defect detection system 300 constructed and operative in accordance with another preferred embodiment of the invention. The defect detection system of Fig. 4 is preferably implemented on a system platform which is one of the Array Checker AC68xx family of systems, commercially available from Photon Dynamics, Inc., an Orbotech Company, of San Jose, CA, USA, The defect detection system preferably is employed for testing fiat panel displays in accordance with the teachings of U.S. Patent Nos. 4,983,911 and 5,124,635, ihe disclosures of which are hereby incorporated by reference, and preferably employs multiple defect detection heads (not shown).

In accordance with a preferred embodiment of the present invention, defect detection system 300 employs a plurality of sensors, including thermal sensors and optionally also optical sensors and electric field sensors (not shown). One or more sensors are mounted on one or more defect detection heads (not shown). Typically, but not necessarily, thermal sensors may be mounted alongside optical sensors and/or electric field sensors on multiple defect detection heads. The plurality of sensors preferably simultaneously view different regions Of an electric circuit under test (ECUT) 310. Typically, the ECUT 310 is aflat panel display, but, alternatively, it may he any suitable electric circuit to be tested. The ECUT 310 is typically stationary during testing and the sensors, preferably mounted on multiple defect detection heads, are displaced relative to the ECUT 310 in order to test various regions of 1he ECUT 310. Preferably, but not necessarily, testing of multiple regions Of the ECUT 310 occurs simultaneously or nearly simultaneously in order to enhance testing throughput.

As seen in Fig. 4, a supervisory computer 312 provides an acquisition plan, including an Image Definition portion, which is supplied to multiple image processing computers (IPC) 314, and a Pattern Definition portion, which is supplied to a pattern generator 320.

In accordance with a preferred embodiment of the invention, pattern generator 320 is operative for selectably energizing predetermined portions Of the ECUT 310 at predetermined times determined at least in part by the design of the electrical circuit under test. The pattern generator 320 provides ECUT-speeiftc energizing pulses (ECUT-SEP) to the ECUT 31 Q via one or more conventional probe arrays 330, which electrically engage various portions of the ECUT 310 at various times. The pattern generator 320 also provides ECUT-spedfic external synchronization pulses (ECUT-SESP) for synchronizing the operation ©f at least one ECUT testing sensor with the energization of portions of the ECUT 310.

A plurality of synchronization generators 340 receive the ECUT-SESP pulses from the pattern generator 320 and generate external readout trigger pulses (ERTP) and relevant readout indicating pulses (RRIP) as described hereinabove with reference to Fig. 2 and Fig. 3.

In accordance with this preferred embodiment of the present invention, multiple externally syndironized thermal sensors 350 are employed as ECUT testing sensors. Additional sensors, such as optical sensors and electric field sensors (not shown), may additionally be employed. A preferred embodiment of an externally synchronized thermal sensor 3S0 is an IR-TCM camera, commercially available from Jenoptics GMBH of Jena, Germany, which accepts external readout trigger pulses (ERTP) and relevant readout indicating pulses (RRIP). Thermal sensors 350 typically require non-ECUT specific periodic readout trigger (NECUTS) pulses at at least a first pulse frequency, typically 5 - 7 Hz, determined by the thermal sensor 350, in order to maintain their stability.

Each thermal sensor 350 preferably includes at least one register which records and outputs information regarding the time relationship between receipt of the ERTP pulses and RRIP pulses. More specifically, each thermal sensor 350 preferably includes first and second registers 360 and 370, which respectively record and output information indicating the timing of receipt of the ERTP pulses and of the RRIP pulses. Metadata downloaded from these registers enables thermal image data which is relevant to differential thermography defect detection to be distinguished from thermal image data which is irrelevant to differential thermography defect detection.

Preferably, the thermal sensors 350 and the image processing computers 314 together provide differential thennography functionality. The differential thermography system preferably includes multiple synchronization generators 340, each of which, as noted above, receives ECUT-SESP pulses from pattern generator 320 and, based on the ECUT-SESP pulses, is operative to synchronize operation of a thermal sensor 350 with operation of pattern generator 320.

It is appreciated that in order to enable differential thermography, the pattern generator must provide ECUT-SEP energizing pulses and corresponding synchronized ECUT-SESP pulses, which correspond to hot and cold states of a given portion of the ECUT 310, corresponding to energized and non-energized states thereof

Reference is now made to Fig. 5, which is simplified block diagram illustration of a defect detection system 500 constructed and operative in accordance with yet another preferred embodiment of the invention. The defect detection system of Fig. 5 is preferably implemented on a system platform which is one of the Array Checker AC68¾t family of systems, commercially available from Photon Dynamics, Inc., an Orbotech Company, of San Jose;, CA> USA. The defect detection system preferably is employed for testing flat panel displays in accordance with the teachings of U.S. Patent Nos. 4,983,941 and 5,124,635, the disclosures of which are hereby incorporated by reference, and preferably employs multiple defect detection heads (not shown):

In accordance with this preferred embodiment of the present invention, defect detection system 500 employs a plurality of different sensors, including thermal sensors and other sensors, such as a voltage imaging optical system (VIOS). A preferred VIOS sensor system is described in U.S. Patent No. 4,983,911. One or more of the above sensors are mounted on one or more defect detection heads (not shown). Typically, but not necessarily, thermal sensors may be mounted alongside optical sensors and/or electric field sensors on multiple defect detection heads. VIOS sensors may be mounted alone or alongside optical sensors and/or electric field sensors.

The plurality of sensors preferably simultaneously view different regions of an electric circuit under test (ECUT) 510. Typically, the ECUT 510 is a flat panel display, but, alternatively, it may be any suitable electric circuit to be tested. The ECUT 510 is typically stationary during testing and the sensors, preferably mounted on multiple defect detection heads, are displaced relative to the ECUT 510 in order to test various regions of the ECUT 510. Preferably, but not necessarily, testing of multiple regions of the ECUT 510 occurs simultaneously or nearly simultaneously in order to enhance testing throughput.

As seen in Fig. 5, a supervisory computer 512 provides an acquisition plan, including an Image Definition portion, which is supplied to multiple image processing computers (IPC) 514, and a Pattern Definition portion, which is supplied to a pattern generator 520.

In accordance with a preferred embodiment of the invention, pattern generator 520 is operative for selectably energizing predetermined portions of the ECUT 510 at predetermined times determined at least in part by the design of the electrical circuit under test. The pattern generator 520 provides ECUT-specific energizing pulses (ECUT-SEP) to the ECUT 510 via one or moreconventional probe arrays 530, which electrically engage various portions of the ECUT 510 at various times. The pattern generator 520 also provides ECUT-spedfic external sjoichromzation pulses (ECUT-SESP) for synchronizing the operation of at least one ECUT testing sensor with the energization of portions of the ECUT 510.

A synchronization generator 540 receives the ECUT-SESP pulses from the pattern generator 520 and generates external readout trigger pulses (ERTP) and relevant readout indicating pulses (RRIP) as described hereinabove with reference to Fig. 2 and Fig. 3. In accordance with this preferred embodiment of the present invention, at least one externally synchronized thermal sensor 550 is employed as an ECUT testing sensor. Additional sensors, such as optical sensors and electric field sensors (not shown), may additionally be employed. A preferred embodiment of an externally synchronized thermal sensor 550 is an IR-TCM camera, commercially available from Jenoptics GMBH of Jena, Germany, which accepts external readout trigger pulses (ERTP) and relevant readout indicating pulses (RRIP). Thermal sensors 550 typically require non-ECUT specific periodic readout trigger (NECUTS) pulses at at least a first pulse frequency, typically 5 - 7 Hz, determined by the thermal sensor 550, in order to maintain their stability.

Each thermal sensor 550 preferably includes at least one register which records and outputs information regarding the time relationship between receipt of the ERTP pulses and RRIP pulses. More specifically, each thermal sensor 550 preferably includes first and second registers 560 and 570, which respectively record and output information indicating the timing of receipt of the ERTP pulses and of the RRIP pulses. Metadata downloaded from these registers enables thermal image data which is relevant to differential thermography defect detection to be distinguished from thermal image data which is irrelevant to differential thermography defect detection.

Preferably, the thermal sensors 550 and the image processing computers 514 together provide differential thermography functionality. The differential thermography system preferably includes at least one synchronization generator 540, each of which, as noted above, receives ECUT-SESP pulses from pattern generator 52Q and, based on the ECUT-SESP pulses* is operative to synchronize operation of a thermal sensor 550 with operation of pattern generator 520.

It is appreciated mat in order to enable differential thermography, the pattern generator must provide ECUT-SEP energizing pulses and corresponding synchronized ECUT-SESP pulses, which correspond to hot and cold states of a given portion of the ECUT 510, corresponding to energized and non-energized states thereof. In this embodiment a second synchronization generator 580 is provided for receiving inputs from pattern generator 520 and providing illumination and camera trigger outputs to a voltage imaging optical system (VIOS) 590, which operates 8S described in U.S. Patent No. 4,983,911. Reference is now made to Fig. 6, which is simplified block diagram illustration of a defect detection system 600 constructed and operative in accordance with still another preferred embodiment of the invention. Hie defect detection system of Fig. 6 is preferably implemented on a system platform which is one of the Array Checker AG6&xx family of systems, commercially available from Photon Dynamics, Inc., an Orbotech Company, of San Jose, CA, USA The defect detection system preferably is employ ed for testing flat panel displays in accordance with the teachings of U.S. Patent Nos. 4,983,911 and 5,124,635, the disclosures of which are hereby incorporated by reference, and preferably employs multiple defect detection heads (not shown):

In accordance with this preferred embodiment of the present invention, defect detection system 600 employs a plurality of different sensors, including thermal sensors and other sensors such as a voltage imaging optical system (VIOS). A preferred VIOS sensor system is described in U.S. Patent Noi 4,983,911. One or more of the above sensors are mounted on one or more defect detection heads (not shown). Typically, but not necessarily, thermal sensors may be mounted alongside optical sensors and/or electric field sensors on multiple defect detection heads. VIOS sensors may be mounted alone or alongside optical sensors and/or electric field Sensors.

The plurality of sensors preferably simultaneously view different regions of an electric circuit under test (ECUT) 610. Typically, the BCUT 610 is a flat panel display, but, alternatively, it may be any suitable electric circuit to be tested. The ECUT 610 is typically stationary during testing and the sensors, preferably mounted on multiple defect detection heads, are displaced relative to the ECUT 610 in order to test various regions of the ECUT 610. Preferably, but not necessarily, testing of multiple regions of the ECUT 610 occurs simultaneously or nearly simultaneously in order to enhance testing throughput

As seen in Fig. 6, a supervisory computer 612 provides an acquisition plan, including an Image Definition portion, which is supplied to an image processing computer (IPC) 614, and a Pattern Definition portion, which is supplied to a pattern generator 620.

In accordance with a preferred embodiment of the invention, pattern generator 620 is operative for seleetably energizing predetermined portions of the ECUT 610 at predetermined times determined at least in part by the design of the electrical circuit under test, The pattern generator 620 provides ECUT-specific energizing pulses (ECUT-SEP) to the ECUT 610 via one or more conventional probe arrays 630, which electrically engage various portions of the ECUT 610 at various times. The pattern generator 620 also provides ECUT-speeific external synchronization pulses (ECUT-SESP) for synchronizing the operation of at least one ECUT testing sensor with the energization of portions of the ECUT 610.

A synchronization generator 640 receives the ECUT-SESP pulses from the pattern generator 620 and generates external readout trigger pulses (ERTP) and relevant readout indicating pulses (RRIP) as described hereinabove with reference to Fig. 2 and Fig. 3.

In accordance with this preferred embodiment of the present invention, at least one externally synchronized thermal sensor 650 is employed as an ECUT testing sensor Additional sensors, such as optical sensors and electric field sensors (not shown), may additionally be employed. A preferred embodiment of an externally synchronized thermal sensor 650 is an IR-TCM camera, commereially available from Jenoptics GMBH of Jena, Germany, which accepts external readout trigger pulses (ERTP) and relevant readout indicating pulses (RRIP). Thermal sensors 650 typically require non-ECUT specific periodic readout trigger ONECUTS) pulses at at least a first pulse frequency, typically 5 - 7 Hz, determined by the thermal sensor 650, in order to maintain their stability.

Each thermal sensor 650 preferably includes at least one register which records and outputs information regarding the time relationship between receipt of the ERTP pulses and RRIP pulses. More specifically, each thermal sensor 650 preferably includes first and second registers 660 and 670, which respectively record and output information indicating the timing of receipt of the ERTP pulses and of the RRIP pulses. Metadata downloaded from these registers enables thermal image data which is relevant to differential thermography defect detection to be distinguished from thermal image data which is irrelevant to differential thermography defect detection.

Preferably, the thermal sensors 650 and the image processing computer

614 together provide differential thermography functionality. The differential thermography system preferably includes at least one synchronization generator 640, each of which, as noted above, receives ECUT-SESP pulses from pattern generator 62Q and, based on the ECUT-SESP pulses, is operative to synchronize operation of a thermal sensor 650 with operation of pattern generator 620.

It is appreciated that in order to enable differential thermography, the pattern generator must provide ECUT-SEP energizing pulses and corresponding synchronized ECUT-SESP pulses, which correspond to hot and cold states of a given portion of the ECUT 610, corresponding to energized and non-energized states thereof In this embodiment, synchronization generator 640 additionally provides illumination and camera trigger outputs to a voltage imaging optical system (VIOS) 690, which operates as described in U.S. Patent No. 4,983,911.

It will be appreciated by persons skilled in pie art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention includes combinations and subcombinations of the various features described hereinabove as well as modifications and variations thereof which are not in the prior art.

Claims

1. A defect detection system comprising:

a pattern generator for selectably energizing portions of an electrical circuit under test at predetermined times determined at least in part by said electrical circuit under test;

a plurality of sensors including at least one thermal sensor, and a synchronization generator operative to receive an output of said pattern generator and based on said output to synchronize operation of said at least one thermal sensor with operation of said pattern generator.

2. A defect detection system according to claim 1 and wherein said at least one thermal sensor comprises at least one register operative:

to record information received from said synchronization generator; and to provide an output of said inf ormation.

3, A defect detection system according to claim % and also comprising an image processing computer operative:

to receive thermal image data from said at least one thermal sensor;

to receive said output of said information from said at least one register; and

to output a thermal image,

4, A defect detection System according to claim 3 and wherein said image processing computer is operative, based on said information from said at least one register, to output a thermal image by :

ascertaining which of said thermal image data are relevant to defect detection;

discarding non-relevant thermal image data; and

utilizing said thermal image data that is ascertained to be relevant to defect detection to generate said thermal image.

5. A defect detection system comprising:

a plurality of sensors including at least two thermal sensors; and a synchronization generator operative to receive an output of said pattern generator and based on said output to synchronize operation of said at least two thermal sensors with operation of said pattern generator.

6. A defect detection system according to claim 5 and wherein each of said at least two thermal sensors comprises at least one register operative:

to record information received from said synchronization generator; and to provide an output of said information.

7. A defect detection system according to claim 6 and also comprising an image processing computer operative:

to receive thermal image data from said at least two thermal sensors; to receive said output of said information from said at least one register; and

to output a thermal image.

8. A defect detection system according to claim 7 and wherein said image processing computer is operative, based on said information from said at least one register, to output a thermal image hy :

ascertaining which of said thermal image data are relevant to defect detection;

discarding non-relevant thermal image data; and

9. A defect detection system comprising: a pattern generator for selectably energizing portions of an electrical circuit under test (ECUT) at predetermined times and providing ECUT-specifie external synchronization pulses; and

a differential Ihermography subsystem including;

a plurality of sensors including at least one thermal sensor requiring periodic external readout trigger pulses at at least a first pulse frequency; and

a synchronization generator operative:

to receive said ECUT-specific external synchronization pulses from said pattern generator for operating said at least one thermal sensor, said ECUT-specific external synchronization pulses being coordinated with said predetermined times and having a second pulse frequency determined at least in part by said ECUT, said second pulse frequency being greater than said first frequency;

to provide said periodic external readout nigger pulses to said at least one thermal sensor in the absence of said ECUT-specific external synchronization pulses; and

to provide ECUT-specific external readout trigger pulses and ECUT- specific relevant readout indicating pulses to said at least one thermal sensor, thereby to svncnronize operation of said at least one thermal sensor with operation Of said pattern generator, whereby said periodic external readout trigger pulses are not received by said at least one thermal sensor when said ECUT-specific external readout pulses are being supplied to said at least one thermal sensor.

10. A defect detection system according to claim 9 and wherein said ECUT- specific external synchronisation pulses include an initial external synchronization (IES) pulse which, when received by said syoichronization generator causes said synchronization generator to provide a corresponding ECUT-specific relevant readout indicating (RRIP) pulse to said at least one thermal sensor but not to provide a corresponding ECUT-specific external readout trigger pulse.

11. A defect detection system according to claim 9 or claim 10 and wherein said at least one thermal sensor includes a sensor array and at least one register and is Operative when reading out sensor array data from said sensor array to append thereto metadata based on an ECUT-specific relevant readout indicating pulse received at a time adjacent to a time of a received ECUT-specific external readout trigger pulse,

12. A defect detection system according to claim 11 and wherein said at least one thermal sensor is operative when reading out sensor array data from said sensor array to append thereto metadata based on an ECUT-specific relevant readout indicating pulse received at a time just preceding a time of a received ECUT-specific external readout trigger pulse.

13. A defect detection system according to claim 11 or claim 12 and wherein said at least one register includes a first register recording timing of receipt of said ECUT-specific external readout trigger pulse and a second register recording timing of receipt said ECUT-specific relevant readout pulses.

14. A defect detection system according to claim 9 and wherein said ECUT- specific external synchronization pulses are also supplied to non-thermal sensors forming part of said plurality of sensors.

15. A defect detection system according to claim 9 and wherein said relevant readout pulses provide metadata which identifies sensor readout information which is relevant to differential thermography defect detection as distinguished from readout information which is not relevant to differential thermography defect detection.

16. A defect detection system according to any of claims 1 - 15 and wherein said plurality of sensors simultaneously view a given portion of said electrical circuit under test.

17. A defect detection system according to any of claims 1 - 16 and wherein said plurality of sensors include at least one non-thermal sensor,

18. A defect detection system according to claim 17 and wherein said at least one non-thermal sensor includes at least one optical sensor.

19. A defect detection system according to claim 17 or claim 18 and wherein said at least one non-thermal sensor includes at least one electric field sensor.