ASTM_F_769M_-_95.pdf

Designation:F 769M 95METRICStandard Test Method forMeasuring Transistor and Diode Leakage Currents Metric1This standard is issued under the fixed designation F 769M;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the measurement of leakage currents of transistors and diodes.These procedures are intended forthe measurement of currents in the range from 1011to 103A.1.2 This test method may be used with either a virtual-ground current meter or a resistance-shunt current meter.1.3 This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2.Terminology2.1 Definitions:2.1.1 resistance-shunt metera meter that determines current by measuring the voltage generated across shunt resistors by thecurrent.2.1.2 virtual-ground metera meter employing feedback to the amplifier in such a way as to make the meter input appear tobe at ground potential.3.Summary of Test Method3.1 Ajunction whose leakage is to be determined is reverse-biased with a power supply.Acurrent meter is placed in series withthe junction and the appropriate range is selected on the meter.The current is read directly from the meter readout.4.Significance and Use4.1 Knowledge of diode and transistor leakage currents is very important to the circuit designer.Proper transistor biasingdepends on accurate leakage current data.In addition,these currents are of special interest to the radiation effects communitybecause leakage current is affected by total dose.5.Interferences5.1 Noise generated by thermal agitation in the various resistances in the test circuit sets an ultimate limit of instrumentresolution.The noise current generated in a current meter shunt resistor is proportional to the inverse square root of the resistance,so a high shunt resistance value is desirable.5.2 Other sources of noise are ac signals propagating through the power supply or imposed on the test leads.A meter with ahigh ac rejection ratio and with high common mode rejection ratio will be less sensitive to such forms of noise.A shielded testfixture may be required for proper measurement of low currents.5.3 All components associated with very high resistance circuitry should be mechanically rigid.Movement of a coaxial cablecan produce piezoelectric and triboelectric effects in the cable which result in voltages across the current meter inputs.5.4 When working with a high resistance source,all leakage paths must be high in comparison to the circuit resistance.Phenolicor rubber insulation,for example,may have a resistance of only 109V,causing large errors in measurements with circuitresistances of greater than 108V.5.5 Circuits employing a feedback picoammeter can have measurement errors which result from offset current,offset voltage,drift,and time constants in the amplifier.Amplifier time constants are of particular importance whenever the annealing rate of anirradiated device approaches the sampling rate of the current meter.5.6 The voltage drop across a resistance-shunt type ammeter for a given current varies with the range selected.Therefore,arange which gives maximum meter resolution will also introduce maximum voltage drop error.An excellent way of determiningthe input resistance of an ammeter is by direct measurement using a transistor curve tracer.A range should be selected which has1This test method is under the jurisdiction of ASTM Committee F-1 on Electronics and is the direct responsibility of Subcommittee F01.11 on Quality and HardnessAssurance.Current edition approved Nov.10,1995.Published January 1996.Originally published as F 769 82.Last previous edition F 769 91.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.an associated resistance less than 1%of the equivalent resistance(bias voltage/leakage current)of the test device.5.7 Care must be taken to keep the test device and test fixture free from contamination such as dust,dirt,solder flux,oil films,fingerprints,and water vapor.It is therefore important to perform this measurement in a clean,dry environment.If open-socketmeasurements yield a current value greater than 1%of the test device leakage current,the socket should be cleaned.Methylalcohol will dissolve most common dirt without chemically attacking the insulation.Test devices should be cleaned prior tomeasurement and cotton gloves or some other form of protective covering should be used to prevent subsequent contamination.5.8 Transparent or translucent package types admit light which may generate significant photocur