Abstract:
A simplified boundary scan test method capable of performing boundary test scanning of semiconductor chips. The test method comprises providing valid test data to a first terminal of the semiconductor device and purposely providing invalid test data to a second terminal of the semiconductor device in a predetermined pattern algorithm. Preload data is also preloaded onto the semiconductor device. The valid and invalid test data is then captured in the semiconductor device. If the captured data is as expected, it signifies that there is no problem with the boundary scan circuitry on the device. On the other hand if the captured data differs from what is expected, it signifies that there may be a problem with the boundary scan circuitry.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to the testing of semiconductor circuits, and more particularly, to the testing of integrated circuits by using a known pattern algorithm of defined voltage level values for both valid and invalid test data to robustly test screen and screen out manufacturing defects of the IEEE 1149.6 boundary scan circuitry on semiconductor chips.  
         [0003]     2. Description of the Related Art  
         [0004]     After an integrated circuit is fabricated, it will undergo electrical testing to determine if the chip operates properly or is defective. Typically the chip is placed onto a test board and electrically coupled to a testing machine. A known sequence of input data signals are then applied to input pins of the chip. In reply, the chip will process the input data signals and generate data output signals. The data output signals are then analyzed. If the state of the output signals are as expected, it indicates that the chip is operating properly. On the other hand, if the data output signals differ from the expected result, it likely means the chip is defective or there is a problem of some kind. The problem could be either with the integrity of the signal received by the chip and/or the path between the input pin where the test signal is received and the test circuitry on the chip.  
         [0005]     Boundary Scan testing is a widely used standard in the semiconductor industry for testing the input-output circuitry on semiconductor chips. IEEE standard 1149.1 provides the specification for the boundary scan testing of digital signals, whereas IEEE 1149.6 defines the standard for analog signals. With either digital or analog devices, the IEEE standard operates essentially the same. A known sequence of input signals defined by the standard is provided to the input pins of the chip. Test receiver circuitry on the chip processes the input signals and provides data output signals to boundary scan circuitry on the chip. Again, if the output data signals are the same as the expected data signals, it is assumed the chip is operational. If output data signals are different, it is assumed that there was a problem with the integrity of the input signals and/or the path from the chip input pin to the test receiving circuitry. For more details on the digital and analog boundary scan IEEE standards, see  IEEE Standard Test Access Port and Boundary - Scan Architecture  (IEEE Std. 1149.1-2001) and  IEEE Standard for Boundary - Scan Testing of Advanced Digital Networks  (IEEE Std. 1149.6-2003), both incorporated by reference herein for all purposes.  
         [0006]     The problem with the aforementioned boundary scan testing standard is that a separate boundary scan piece of test equipment is required to test the chips. These test machines tend to be very expensive. In some cases, the test head used to receive the chip has to be customized for each type of chip. This customization further adds to the cost of using a boundary scan test device.  
         [0007]     Accordingly, there is a need for a simplified boundary scan test method and test apparatus capable of performing boundary test scanning of semiconductor chips in a production test environment without the need of expensive dedicated automated test equipment.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention relates to a simplified boundary scan test method capable of performing boundary test scanning of semiconductor chips without the need of an expensive, dedicated automated piece of test equipment. The test method comprises providing defined valid test data to a first terminal of the semiconductor device and purposely providing defined invalid test data to a second terminal of the semiconductor device in a predetermined pattern algorithm. Preload data is also preloaded onto the semiconductor device. The valid and invalid test data is then captured in the semiconductor device. If the captured data is as expected, it signifies that there is no problem with the boundary scan circuitry on the device. On the other hand if the captured data differs from what is expected, it signifies that there may be a problem with the boundary scan circuitry.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:  
         [0010]      FIG. 1  is a block diagram of a differential input used for boundary scan testing;  
         [0011]      FIG. 2  is a circuit diagram of an exemplary test receiver used in the block diagram of a differential input used for boundary scan testing.  
         [0012]      FIG. 3  is a signal diagram illustrating valid and invalid data input signals; and  
         [0013]      FIG. 4  is a table illustrating a pattern algorithm used to implement boundary scan testing according to the present invention. 
     
    
       [0014]     In the figures, like reference numbers refer to like components and elements.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     Referring to  FIG. 1 , a block diagram of a differential input used for boundary scan testing is shown. The differential input circuit  10  includes a pair of differential input pins  12  and  14 , a differential receiver  16 , and a pair of test receiver circuits  18  and  20 . The input pins  12  and  14  are coupled to the positive and negative inputs of the differential receiver  16  and the test receiver circuits  18  and  20  respectively. A pair of boundary scan circuits (BSCs)  22  and  24  are also coupled to the pair of test receiver circuits  18  and  20  respectively. According to various embodiments, the differential input can be configured to receive either digital or analog signals. For the sake of simplicity, the operation of the differential input circuit  10  is initially described with respect to digital signals.  
         [0016]     During operation, a pair of differential digital signals are applied to the pins  12  and  14  respectively. In response, the differential receiver “differentiates” between the input signals and provides the original signal to the core circuitry on the chip. For example, if the signal at pin  12  is high and low on pin  14 , then a high logic signal is provided to the core circuitry on the chip by the differential receiver  16 . Alternatively, a low logic signal is provided to the core circuitry when the signal applied to pin  12  is low and high to pin  14 .  
         [0017]     The test receiver circuits  18  and  20  are provided to implement the boundary scan testing on the input signals received at pins  12  and  14  respectively. The BSCs provide a known pattern of test signals to the test receiver circuits  18  and  20  respectively. The test receiver circuits  18  and  20  compare the captured differential signals received on pins  12  and  14  with known pattern of test data respectively. If the captured data provided back to the BSCs  22  and  24  are as expected, meaning it matches the known test pattern of data, it indicates the input circuitry is operating properly. On the other hand if the captured signals are different, it indicates that there is a problem of some kind, either with the integrity of the input signals and/or the path from the chip input pin to the test.  
         [0018]     Referring to  FIG. 2A , a circuit diagram of an exemplary test receiver  18  is shown. The test receiver  18  includes an S-R type flip-flop  32 , a pair of comparators  34  and  36 , a pair of offset circuits  38  and  40 , a resistor R and a capacitor C. A signal from the pin  12  is provided to the positive input (+) of comparator  34  and the negative input (−) of comparator  36  through offset circuits  38  and  40  respectively. Vref is applied to the negative input (−) of comparator  34  and the positive input (+) of comparator  36 . The output of comparator  34  is coupled to the S input of the flip-flop  32 . The output of comparator  36  is coupled to the R input of flip-flop  32 . The D input is coupled to the BSC  22 . Vref is set to zero volts (Vref=0.0).  
         [0019]     Referring to  FIG. 2B , a circuit diagram of an exemplary test receiver  20  is shown. The test receiver  20  includes an S-R type flip-flop  52 , a pair of comparators  54  and  56 , a pair of offset circuits  58  and  60 , a resistor R and a capacitor C. A signal from the pin  14  is provided to the positive input (+) of comparator  54  and the negative input (−) of comparator  56  through offset circuits  58  and  60  respectively. Vref is applied to the negative input (−) of comparator  54  and the positive input (+) of comparator  56 . The output of comparator  54  is coupled to the S input of the flip-flop  52 . The output of comparator  56  is coupled to the R input of flip-flop  52 . The D input is coupled to the BSC  24 . Vref is set to zero volts (Vref=0.0).  
         [0020]     Referring to  FIG. 3A , a differential signal diagram illustrating both valid 1 and invalid 0 data input signal values is shown when testing for a valid 1. As illustrated in the waveform, any signal having a voltage equal to or greater than V high  (200 mV) is considered a valid high (H) signal. Any signal having a voltage equal to 0 V and less than V high  is considered a invalid low (L) signal.  
         [0021]     Referring to  FIG. 3B , a differential signal diagram illustrating both valid 0 and invalid 1 data input signal values is shown when testing for a valid 0. As illustrated in the waveform, any signal having a voltage equal to or less than V low  (−200 mV) is considered a valid low (L) signal. Any signal having a voltage equal to 0 V and greater than V low  is considered a invalid high (H) signal.  
         [0022]     When testing for a valid logic one, a logic high (H) signal with its voltage value equal to or greater than that defined as a valid high signal in  FIG. 3A  is provided to pin  12  and a logic low (L) signal is preloaded to the D input of flip flop  32  from BSC  22 . Under these conditions, comparator  34  is active, resulting in triggering the S input of flip-flop  32 . As a result, the flip-flop  32  is toggled, resulting in a logic (H) signal at the Q output. The logic (H) is then captured back into BSC  22 , thus verifying a valid one signal at pin  12 .  
         [0023]     Simultaneously, a logic (L) signal with its voltage value equal to or less than that defined as an invalid low is provide to pin  14  while the BSC  24  preloads a logic (H) signal to the D input of flip-flop  52 . The low voltage of the logic (L) signal at pin  14  will not activate neither the upper comparator  54  nor the lower comparator  56 . As a result, the preloaded signal in the D input of the flip-flop would be captured back in the BSC  24  upon the next clock transition, thus verifying an invalid 0 on pin  14 .  
         [0024]     If captured input signal data in the BSC circuits  22  and  24  matches the expected data compared at TDO (test data output of the BSC chain), then it is assumed that the device is operating properly. On the other hand, if the captured data differs from the expected data, then it is assumed that a problem exists  
         [0025]     Testing for a valid logic zero is essentially the complement of what is described above with a logic low (L) signal with its voltage value equal to or less than that defined as a valid 0 in  FIG. 3B . A detailed description is therefore not provided herein.  
         [0026]     Table I is a truth table that summarizes the logic states for the Pins  12 ,  14 , inputs from the BSC circuits  22 ,  24  and the expected outputs.  
                                       TABLE I                                               Preload               Test   Input Pin   Data Input   from BSC   Capture                           Logic L/   12   H   L   H           Logic H   14   L   H   L               12   L   H   L               14   H   L   H                      
 
         [0027]     It should be noted that test receivers  18  and  20  can also operate in an analog mode. Each receiver includes an AC mode switch. When set to the analog mode, Vref is coupled between the resistor R and capacitor C. Vref is therefore set at a voltage between that of the input pin (either  12  or  14 ) and ground. The operation of test receivers  18  and  20  are essentially the same as in the digital mode. If the analog signal received at the input pin is greater than Vref, than the S input to the flip flop will be high and the R input will be low. If the input signal voltage is less than Vref, then the S input is low and the R input is high.  
         [0028]     The present invention relates to a method of performing boundary scan testing by purposely providing a known patterned algorithm of both valid and invalid test data to the chip and determining if there is a problem by comparing the captured data with the data expected to be captured. In other words, the method involves using the defined voltage level values of Valid and Invalid data as well as the sequence of pattern algorithm to robustly test and screen out manufacturing defects of the 1149 circuitry paths with the use of an Automated Test Equipment (ATE) logic analyzer.  
         [0029]     Table 2 defines a pattern algorithm used to implement boundary scan testing according to the present invention.  
                                         TABLE 2                           Pattern Algorithm                        Preload               Pattern   Input Pin   Data Input   from BSC   Capture   Limits               Valid 1   12   Valid 1   0   H   Vih = 200 mV           14   Invalid 0   1   H   Vil = 0 mV           12   Invalid 0   1   H           14   Valid 1   0   H       Valid 0   12   Valid 0   1   L   Vih = 0 mV           14   Invalid 1   0   L   Vil = −200 mV           12   Invalid 1   0   L           14   Valid 0   1   L                  
 
         [0030]     Table 2 as interpreted as follows. For testing a valid logic 1, a valid 1 is provided to input pin  12  and an invalid 0 is provided to input pin  14 . The BSC  22  and  24  preload a (0) and (1) to the D inputs of flip-flops  32  and  52  of receivers  18  and  20  respectively. The valid 1 at the input pin  12  triggers comparator  34  and provides a logic (1) signal to the Set input of flip-flop  32 . The flip-flop  32  is thus toggled, resulting in a logic (H) at the Q output. The invalid (0), however, fails to trigger comparator  56  or Reset the flip-flop  52 . As a consequence, the Q output of flip-flop  52  is a logic (H). For the next data sequence, an invalid (0) and a valid (1) are provided to the pins  12  and  14 . Logic (1) and logic (0) are preloaded from the BSCs  22  and  24  into flip-flops  32  and  52 , respectively. The circuit is presumed to be operating properly if a logic (H) and (H) are captured into BSC  22  and  24  from the Q outputs of flip-flops  32  and  52 , respectively. The next data sequence is to verify the opposite polarity signals at the pins  12  and  14 . Valid logic low (0) is applied to pin  12  and invalid logic high (1) is applied to pin  14 . If logic low (L) is captured at both Q outputs, then the circuit is operating properly. Finally, an invalid (1) and a valid (0) are applied to pins  12  and  14  respectively. If a logic (L) is captured at both Q outputs, then the circuit is operating properly. If, however, the captured data differs from the expected captured data in Table 2, then it signifies a problem with the signal paths of the boundary scan circuitry.  
         [0031]     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. For example, the substrate  14  and described herein can be made of a number of different materials, such as ceramic or plastic. The substrate  14  can also be a lead frame made of a metal such as copper. In embodiments where the substrate  16  is a lead frame, the die  12  is attached to the die attach pad and the contact pads  22  are leads of the lead frame. Therefore, the described embodiments should be taken as illustrative and not restrictive, and the invention should not be limited to the details given herein but should be defined by the following claims and their full scope of equivalents.