one another adds another dimension to the use of test Whereas functional testing usually involves voltage patterns in LSI testing;an alternative to the use of many swings of 30 volts or less,dc parametric test systems long patterns may be the application of a few worst-case typically can force 100 volts or more.In systems having patterns under varying phase relationships. both functional and parametric test sections,break- Great demands are placed on the drivers of an MOS before-make switching from one to the other is required test system.They must be able to swing 30 volts,at a so that the power available for parametric testing cannot slope of 1 ns/V or better,with minimum overshoot, inadvertently damage the functional-test drivers and ringing,or crosstalk,through cables to automatic hand- comparators. lers or wafer probers.Satisfactory performance results One of the most interesting and significant recent once one recognizes the practical necessity of such cables developments in IC testing has been the growing em- between drivers and the device under test and designs phasis placed on pulse parametric,or dynamic,testing the test system accordingly,using impedance-matching Several factors lie behind this trend.First,speed margins techniques to minimize the effects of cable capacitance. represent the essential differences(and therefore the price Parametric testing.Functional testing,even when premiums)between one device type and another.Second, exhaustively complete,cannot be relied on to determine these differences in operating speed cannot be verified whether an IC will operate in its end use.The test system by dc and functional testing.Third,equipment that can cannot simulate all of the possible circuits in which a reliably measure dynamic performance on a production- device may be used,and it is therefore necessary to line basis has become available only fairly recently measure certain parameters and to compare them against Pulse parametric testing refers to a limited number of specified limits.These measurements will define the time-interval measurements-principally those of propa- fanout capabilities of the device,as well as leakage gation delay,rise time,and fall time.For the fastest current,power dissipation,etc.Usually a few parameters digital devices,these intervals are so short as to challenge are measured for each of a number of input conditions. the state of the measurement art.A test system handling The technique for making dc parametric tests is that ECL and fast TTL logic must be able to measure a of forcing a voltage or current at an input and comparing propagation delay of a nanosecond repeatedly and with the resulting output current or voltage against a limit. a precision of 10 picoseconds. The test result can be taken as a simple go/no-go indica- Some of the key issues in pulse parametric testing have tion,or A/D conversion techniques can be applied to to do with the way parameters are defined and speci- record the actual value of the parameter in question. fied.Rise time,for example,is often defined as the time One such technique is a software-directed sequential it takes a voltage to rise from 10 to 90 percent of its approximation in which a series of go/no-go comparisons maximum value,but,given a pulse with any overshoot is made,the reference converging on the unknown. or ringing,the maximum value and therefore the rise- Since the emphasis in parametric testing is on accuracy, time boundaries are uncertain.A much more rigorous precautions are taken in equipment design to eliminate definition would prescribe actual voltage levels as the stray capacitance and spurious ground currents.Kelvin boundaries for rise and fall times and propagation delay. connections are generally used,in conjunction with The parameters involved in a typical pulse parametric driven guard shields,to minimize cable charging currents test are defined in Fig.4,which illustrates the dynamic that could introduce time-constant delays in circuit characteristics of a typical TTL gate.The rise and fall stabilization. times of the input pulse,t and t,are defined in terms Because a parametric test generally takes much longer of actual voltage levels,not percentages;t and t than a functional test,the interplay between the two are the propagation times from high to low and from low types of test directly affects productivity.The programmer to high levels,respectively,and both are usually specified of a computer-operated system has several options and tested. available to him:He can run all functional tests first, Note that the accuracy with which one can define fpz in order to screen out catastrophic rejects before para and fPLa depends on the accuracy with which the 1.5-volt metric testing;or he may make certain critical parametric thresholds are known,and this in turn is a function of tests first;or he may functionally test,branching into the slope of the voltage transitions (a slow transition a parametric sequence upon failure. rate amplifies any threshold error).Input transition rate should therefore be specified,along with pulse amplitudes and durations Once the characteristics of the input pulse have been FIGURE 4.Dynamic properties of a 5400-series TTL gate specified,the problem becomes one of ensuring that these Pulse parametric system measures rise and fall times characteristics are achieved,not at the output of the and propagation delays tpaL and tpLB. pulse generator but at the test socket.In a self-calibrating system each test pulse is first measured at the test socket tr长 and the pulse generator is automatically adjusted to produce the desired characteristics at the socket. 2.7v 2.7V Early dynamic measurements on ICs were made by 1.5V 1.5V 0.7V 0.7V sampling techniques similar to these well established in high-frequency laboratory measurements.More recently, thet“real-time”ort“single-shot”technique,in which a single time interval is measured in terms of the amount of charge absorbed by a reference capacitor during that time,has achieved widespread acceptance and appears now to predominate. IEEE spectrum DECEMBER 1971one another adds another dimension to the use of test Whereas functional testing usually involves voltage patterns in LSI testing; an alternative to the use of many swings of 30 volts or less, dc parametric test systems long patterns may be the application of a few worst-case typically can force 100 volts or more. In systems having patterns under varying phase relationships. both functional and parametric test sections, break￾Great demands are placed on the drivers of an MOS before-make switching from one to the other is required test system. They must be able to swing 30 volts, at a so that the power available for parametric testing cannot slope of 1 ns/V or better, with minimum overshoot, inadvertently damage the functional-test drivers and ringing, or crosstalk, through cables to automatic hand- comparators. lers or wafer probers. Satisfactory performance results One of the most interesting and significant recent once one recognizes the practical necessity of such cables developments in IC testing has been the growing em￾between drivers and the device under test and designs phasis placed on pulse parametric, or dynamic, testing. the test system accordingly, using impedance-matching Several factors lie behind this trend. First, speed margins techniques to minimize the effects of cable capacitance. represent the essential differences (and therefore the price Parametric testing. Functional testing, even when premiums) between one device type and another. Second, exhaustively complete, cannot be relied on to determine these differences in operating speed cannot be verified whether an IC will operate in its end use. The test system by dc and functional testing. Third, equipment that can cannot simulate all of the possible circuits in which a reliably measure dynamic performance on a production￾device may be used, and it is therefore necessary to line basis has become available only fairly recently. measure certain parameters and to compare them against Pulse parametric testing refers to a limited number of specified limits. These measurements will define the time-interval measurements-principally those of propa￾fanout capabilities of the device, as well as leakage gation delay, rise time, and fall time. For the fastest current, power dissipation, etc. Usually a few parameters digital devices, these intervals are so short as to challenge are measured for each of a number of input conditions. the state of the measurement art. A test system handling The technique for making dc parametric tests is that ECL and fast TTL logic must be able to measure a of forcing a voltage or current at an input and comparing propagation delay of a nanosecond repeatedly and with the resulting output current or voltage against a limit. a precision of 10 picoseconds. The test result can be taken as a simple go/no-go indica- Some of the key issues in pulse parametric testing have tion, or A/D conversion techniques can be applied to to do with the way parameters are defined and speci￾record the actual value of the parameter in question. fied. Rise time, for example, is often defined as the time One such technique is a software-directed sequential it takes a voltage to rise from 10 to 90 percent of its approximation in which a series of go/no-go comparisons maximum value, but, given a pulse with any overshoot is made, the reference converging on the unknown. or ringing, the maximum value and therefore the rise￾Since the emphasis in parametric testing is on accuracy, time boundaries are uncertain. A much more rigorous precautions are taken in equipment design to eliminate definition would prescribe actual voltage levels as the stray capacitance and spurious ground currents. Kelvin boundaries for rise and fall times and propagation delay. connections are generally used, in conjunction with The parameters involved in a typical pulse parametric driven guard shields, to minimize cable charging currents test are defined in Fig. 4, which illustrates the dynamic that could introduce time-constant delays in circuit characteristics of a typical TTL gate. The rise and fall stabilization. times of the input pulse, tr and tf, are defined in terms Because a parametric test generally takes much longer of actual voltage levels, not percentages; tPHL and tpLH than a functional test, the interplay between the two are the propagation times from high to low and from low types of test directly affects productivity. The programmer to high levels, respectively, and both are usually specified of a computer-operated system has several options and tested. available to him: He can run all functional tests first, Note that the accuracy with which one can define tPHL in order to screen out catastrophic rejects before para- and tPLH depends on the accuracy with which the 1.5-volt metric testing; or he may make certain critical parametric thresholds are known, and this in turn is a function of tests first; or he may functionally test, branching into the slope of the voltage transitions (a slow transition a parametric sequence upon failure. rate amplifies any threshold error). Input transition rate should therefore be specified, along with pulse amplitudes and durations. Once the characteristics of the input pulse have been FIGURE 4. Dynamic properties of a 5400-series TTL gate. specified, the problem becomes one of ensuring that these Pulse parametric system measures rise and fall times characteristics are achieved, not at the outptut of the and propagation delays tpHL and tPLH. pulse generator but at the test socket. In a self-calibrating system each test pulse is first measured at the test socket ~ tr ~ ~ tf ~ and the pulse generator is automatically adjusted to | ~~~~~~~~~~produce ' r ' ' the desired characteristics at the socket. 2.7v 2.7VYv, ~~~~~Early dynamic measurements on ICs were made by <1.5V 1.5 V J~0.7 sampling techniques similar to these well established in itPHL~~~~~~~~high-frequency '< laboratory measurements. More recently, VOH ->I tPLH :E the "real-time' or "singie-shot" technique, in which a Jr - ~~~~~~~~~~~~~single ' | time interval is measured in terms of the amount ,, ,/ ~~~~~~~~of charge absorbed by a reference capacitor during that \ / ~~~~~~~~time, has achieved widespread acceptance and appears ~~~~~~~~now vOL S to predominate. 32 ~~~~~~~~~~~~~~~~~~~~~~~~~~IEEE spectrum DECEMBER 1971