Abstract:
A method for testing at least one light source on a printed circuit assembly, includes: detecting a light signal from a plurality of light sources on a printed circuit assembly; generating a plurality of electrical analog signals from an image array, in response to each of the detected light signals; multiplexing the plurality of electrical analog signals; digitizing the multiplexed electrical analog signals; and light signals from the image array; and verifying each of the electrical signals in a sequential manner.

Description:
TECHNICAL FIELD 
     Embodiments of the present invention relate generally to test tools for printed circuit assemblies. 
     BACKGROUND 
     An In-Circuit Test (ICT) process electrically verifies the individual component placement on a printed circuit assembly (PCA). During the ICT process, the verification of light sources is a critical operation that is commonly overlooked due to difficulty and expense. Light source components (typically Light Emitting Diodes or LEDs) provide critical information to the end-user to indicate a warning, fault status, or safe operation. 
     Currently, there are two major designs for validating optical devices. The LIGHTPROBE™ product from OPTOMISTIC PRODUCTS, Concord, Mass. and the FINN™ product from TEST COACH CORPORATION, Hoffman Estates, Ill., are devices that are tuned to validate a specific color source. However, both of the above devices have high maintenance costs due to their fragile nature. Also, both devices utilize custom sensors that are not readily available as “off-the-shelf” components, and this typically results in a long lead time for each unit that is ordered. Both devices are not able to provide consistent results when observing amber and green light sources. Both devices detect only one color (i.e., the devices are single wavelength dependent) and detect only one light source. It is very expensive to verify a light source by a single sensor. Typically, the cost to verify each light source is about $200 to $400. Additionally, the LIGHTPROBE™ product requires calibration prior to installation and may drift with age. 
     Additionally, both of the above devices require critical alignment with the light source. The LIGHTPROBE product must typically be placed less than about 0.05 inches from the light source, while the FINN product must be typically placed less than 0.15 inches from the light source. 
     Thus, the current approaches and/or technologies are limited to particular applications and/or suffer from various constraints. 
     SUMMARY OF EMBODIMENTS OF THE INVENTION 
     At least some of the various embodiments are now described. In one embodiment of the invention, a light image sensor for testing opto-electronics for in-circuit test, includes: 
     an image array configured to detect a light signal from a light source on a printed circuit assembly and generate an electrical analog signal in response to a detected light signal; 
     a sampling stage configured to sample the electrical analog signal from the image array; 
     an analog-to-digital converter configured to digitize the electrical analog signal from the image array into a digital signal for testing by an in-circuit test unit. 
     In another embodiment of the invention, an apparatus for testing at least one light source on a printed circuit assembly, includes: 
     a lens configured to detect a light signal from at least one light source; 
     an image array configured to detect the light signal that passes through the lens and generates an electrical analog signal in response to a detected light signal; 
     a sampling stage configured to sample the electrical analog signal from the image array, the sampling stage including a multiplexer configured to multiplex a plurality of light signals from the image array; 
     an analog-to-digital converter configured to digitize the electrical analog signal into a digital signal for testing by an in-circuit test unit, where the in-circuit test unit can test light signals in a sequential manner. 
     In yet another embodiment of the invention, a method for testing opto-electronics for in-circuit test, includes: 
     detecting a light signal from a light source on a printed circuit board by use of an image array and generating an electrical analog signal in response to a detected light signal; 
     sampling the electrical analog signal from the image array; and 
     digitizing the electrical analog signal into a digital signal for testing by an in-circuit test unit. 
     In yet another embodiment, a method for testing at least one light source on a printed circuit board, includes: 
     detecting a light signal from a plurality of light sources on a printed circuit board; 
     generating a plurality of electrical analog signals from an image array, in response to each of the detected light signals; 
     multiplexing the plurality of electrical analog signals; 
     digitizing the multiplexed electrical analog signals; and light signals from the image array; and 
     verifying each of the electrical signals in a sequential manner. 
     Other embodiments of the invention include, but are not limited to, the various embodiments described below. 
     These and other features of an embodiment of the present invention will be readily apparent to persons of ordinary skill in the art upon reading the entirety of this disclosure, which includes the accompanying drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a light image sensor for opto-electronics, in accordance with an embodiment of the invention. 
         FIG. 2  is a block diagram illustrating an operation of sequentially sampling light signals from a plurality of light sources, in accordance with an embodiment of the invention. 
         FIG. 3  is a block diagram illustrating the interface between an ICT unit and a sensor, in accordance with an embodiment of the invention. 
         FIG. 4  is a block diagram illustrating light images sensors as attached to a fixture, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the description herein, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus, systems, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of embodiments of the invention. 
     An embodiment of the invention advantageously detects the presence of any color in the visible spectrum, where the color is from an optical source (such as an LED) that is placed on a PCA. An embodiment of the invention can validate if the correct color and intensity has been displayed by each optical source on the PCA 
     Other possible advantages provided by embodiments of the invention include the following.
         1. In an embodiment, the same sensor can be used to detect colors from a cluster (e.g., array) of light sources or multiple light sources.   2. Embodiments of the sensor typically cost less than half of the cost of other designs. For example, the sensor can be used to cover multiple light sources, and this leads to a very significant cost savings. As another example, embodiments of the sensor advantageously do not need customized components and can be formed by off-the-shelf components.   3. Embodiments of the sensor do not require internal calibration and have a rugged mechanical design.   4. Embodiments of the sensor permit a low maintenance cost.   5. Embodiments of the sensor are compact and small in size (e.g., 11 millimeters by 11 millimeters).   6. Embodiments of the sensor permit the alignment to a light source (and the distance to a light source) to be less critical as compared to current sensors.   7. Embodiments of the sensor have a very small footprint (e.g., about 10 millimeters by 10 millimeters).   8. Embodiments of the sensor can provide a fast response time (e.g., about 15 frames per second with VGA quality/resolution).   9. Embodiments of the sensor can provide extended detection resolution 640×480 pixels.   10. Embodiments of the invention provide programmability for window size, panning, and gain, and these programmable features are not easily provided by current test tools.       

     The use of a CMOS (complementary metal oxide semiconductor) active pixel image sensor, in one embodiment of the invention, will allow testing of light sources that are placed on a printed circuit assembly (PCA), and will validate the correct color and intensity of each light source. The single CMOS image sensor can detect all visible light output from opto-electronic devices, regardless of the color output of an opto-electronic device. The CMOS image sensor can advantageously detect and verify multiple light sources on the same PCB. The CMOS image sensor is more efficient, less expensive, easier to use and maintain, and has a smaller footprint than previous tools for testing PCBs. 
       FIG. 1  is a block diagram illustrating a light image sensor  100  for opto-electronics, in accordance with an embodiment of the invention. The elements in sensor  100 , as shown in  FIG. 1  may be implemented as discrete components or may be components integrated in a semiconductor package. The sensor  100  includes an image array ( 105 ) for capturing light signals. A representative CMOS image array is integrated into the ADCS-2021 manufactured by Agilent Technologies. The image array  105  can include a plurality of conventional charge coupled device (“CCD”) sensors  110 . Alternatively, the sensors  110  can be complementary metal oxide semiconductor (CMOS) sensors, which are generally much less expensive than CCD sensors, but may be more susceptible to noise. Other types of sensors may be used in the image array  105 . The size of the image array  110  is typically 640×480 to permit VGA resolution. In response to a detected light signal  135  from a light source, the image array  105  will generate an analog electrical signal  137  that has a coded value indicating the color and intensity of the detected light signal  135 . 
     One or more programmable amplifiers  115  are coupled to the image array  110 . The amplifiers  115  provide a suitable gain to improve signal to noise ratio to the electrical signals  137  generated by the image array  105 . 
     An analog-to-digital converter (A/D converter)  120  converts the analog signals  137  from the image array  105  into digital signals  125 . The A/D converter function is integrated into the Agilent ADCS-2021 CMOS image sensor device from Agilent Technologies, Palo Alto, Calif., for example. 
     The sensor  100  further includes a timing controller  130  for providing proper synchronization between the output of the image array  105  and the output of the A/D converter  120 . Typically, the A/D converter  120  has, for example, a 10-bit parallel output. The timing controller function is integrated into the Agilent ADCS-2021 CMOS image sensor device, for example. 
     A conventional clock source (not shown in  FIG. 1 ) provides clock signals  135  to the timing controller  130 . 
     The Agilent ADCS-2021 CMOS image censor provides an I2C serial bus interface  140  to facilitate external read and write of the ADCS-2021 internal registers. The bus interface  140  is a summation of an output bus (DRDY, nFRAME — nSYNC, nROW, nIRQ — nCC). 
     A conventional ICT unit  150  receives the digital signals  125  for analysis to determine if the light signals  135  from a light source match a proven value for a color. The ICT unit  150  can also detect the values of the digital signals  125  in order to determine the intensity of a light signal  135  from a light source. One suitable ICT unit  150  is the 3070 ICT from Agilent Technologies. 
     In an embodiment, the sensor  100  includes a sampling stage  160  that reads the analog output  137  of the image array  105 . In one embodiment, the sampling stage  160  utilizes a Bayer filter pattern and an alternating pixel pattern of red, green, and blue. The Bayer filter pattern is typically used in the majority of today&#39;s consumer digital cameras. The Bayer filter pattern alternates a row of red and green filters with a row of blue and green filters to create an image that the human eye will perceive as a true color. As the image array  105  in the sensor  100  records the light image  135 , each pixel is translated into an electronic signal that can be ported via the analog-to-digital converter (ADC)  120  to the ICT unit  150 . This electronic signal (converted by ADC  120  to a digital signal  125 ) is analyzed by the In-Circuit Tester unit  150  to determine whether the results agree with the proven value for each color. Conventional software tools are typically used by the ICT unit  150  to analyze the signal  125  so that the color and intensity of the light source is determined or validated. 
     The sampling stage  160  advantageously permits programmability for window size, panning, and gain, and these programmable features are not easily provided by current test tools. Thus, to select the window size, or to change panning and/or gain, the sampling stage  160  will sample particular subsets of the sensing elements  110  in the image array  105 . 
     It is further noted that the sampling stage  160  can be implemented in or integrated in the image array  110 . 
       FIG. 2  is a block diagram illustrating an operation of sequentially sampling light signals from a plurality of light sources, in accordance with an embodiment of the invention. A PCA  200  may support, for example, a plurality of light sources  205   a ,  205   b , and  205   c . The number of light sources and types of light sources (e.g., LEDs) may vary. The light sources emit light signals  210   a ,  210   b ,  210   c , respectively. A lens  215  is disposed from any suitable distance to receive the light signals  210   a – 210   c . The lens  215  may be, for example, any general purpose lens. A link  220  (which is typically a fiber optic link) transmits the light signals  210   a – 210   c  to the image array  105 . In response to detection of light signals  210   a ,  210   b , and  210   c , the image array will output electrical analog signals  225   a ,  225   b ,  225   c , respectively. The electrical analog signals  225   a – 225   c  are amplified by amplifiers  115 . 
     In an embodiment of the invention, a multiplexer  230  will multiplex the signals  225   a – 225   c  so that the signals  225   a – 225   c  are output in a sequential manner by the sampling stage  160  to the A/D converter  120 . For example, a timing signal  235  (from the timing controller  130  in  FIG. 1 ) will cause the multiplexer  230  to select signal  225   a  for output at time T1, to select signal  225   b  for output at time T2, and to select signal  225   c  for output at time T3. The output signals  225   a ,  225   b , and  225   c  are then digitized by the A/D converter  120  into digital signals  240   a ,  240   b , and  240   c , respectively. This multiplexing feature is integrated within the ADCS-2021 CMOS image sensor from Agilent Technologies, for example. 
     As a result, the multiplexer  230  permits the ICT unit  150  ( FIG. 1 ) to receive the output signals  225   a ,  225   b ,  225   c  (as digital signals  240   a ,  240   b , and  240   c , respectively) in a sequential manner. Therefore, the ICT unit  150  can sequentially analyze the color and/or intensity of the light signals  210   a ,  210   b , and  210   c  from the multiple light sources  205   a ,  205   b ,  205   c , respectively, and this capability leads to the cost reductions that were mentioned above. 
     In contrast, in one previous approach, U.S. Pat. No. 4,808,815 issued to Frank J. Langley, discloses a probe for testing the optical functions of a wide variety of light-emitting devices and displays. However, U.S. Pat. No. 4,808,815 does not disclose the use of fiber optics for coupling to a lens and also teaches away from using a CCD sensor. 
     IN  FIG. 3 , the following signals embody the hardware interface between the CMOS image sensor and the ICT tester. Signals D 0 –D 9  are the digital data bits output from the CMOS image sensor. DRDY is a handshaking bit that alerts the ICT tester that data is ready. NRst — nSTBY is a signal input from the ICT tester to the CMOS image censor to initiate a reset or to place the device in standby mode. nROW (END of Row) and nFRAME — nSYNC (END of FRAME) signal end of row and end of frame respectively to the ICT tester. The clock signal, pin  17 , is an I2C, 100 khz, SCLK that acts as a transfer sequencer of the data, SDATA — TxD which is pin  18  in  FIG. 3   
       FIG. 4  is a block diagram illustrating light images sensors as attached to a fixture, in accordance with an embodiment of the invention. The sensors  100   a ,  100   b ,  100   c , and  100   d  are similar in functions to the sensor  100  described in  FIG. 1  and  FIG. 2 . A conventional fixture top  405  (of a fixture the an ICT interface) supports the sensors  100   a  and  100   b , while a conventional fixture base  410  supports the sensor  100   c . Typically, the sensor  100   a  will detect the LEDs in LED group  415 , the sensor  100   b  will detect the LEDs in LED group  420 , the sensor  100   c  will detect the LEDs in LED group  425 , and the sensor  100   d  will detect the LEDs in LED group  430 . The sensors  100   a ,  100   b ,  100   c , and  100   d  are routed by wires  440   a ,  440   b ,  440   c , and  440   d , respectively, to personality pins which are fixture resource connections to an ICT interface to permit ICT testing of the LEDs. 
     Reference throughout this specification to “one embodiment”, “an embodiment”, or “a specific embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment”, “in an embodiment”, or “in a specific embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     Other variations and modifications of the above-described embodiments and methods are possible in light of the foregoing disclosure. Further, at least some of the components of an embodiment of the invention may be implemented by using a programmed general purpose digital computer, by using application specific integrated circuits, programmable logic devices, or field programmable gate arrays, or by using a network of interconnected components and circuits. Connections may be wired, wireless, by modem, and the like. 
     It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application. 
     Additionally, the signal arrows in the drawings/Figures are considered as exemplary and are not limiting, unless otherwise specifically noted. Furthermore, the term “or” as used in this disclosure is generally intended to mean “and/or” unless otherwise indicated. Combinations of components or steps will also be considered as being noted, where terminology is foreseen as rendering the ability to separate or combine is unclear. 
     As used in the description herein and throughout the claims that follow, “a”, “an”, and “the” includes plural references unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
     It is also noted that the various functions, variables, or other parameters shown in the drawings and discussed in the text have been given particular names for purposes of identification. However, the function names, variable names, or other parameter names are only provided as some possible examples to identify the functions, variables, or other parameters. Other function names, variable names, or parameter names may be used to identify the functions, variables, or parameters shown in the drawings and discussed in the text. 
     While the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. Therefore, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the present invention. It is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments and equivalents falling within the scope of the appended claims.