ASTM_F_1896_-_10.pdf

Designation:F189610Test Method forDetermining the Electrical Resistivity of a PrintedConductive Material1This standard is issued under the fixed designation F1896;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()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the determination of the elec-trical resistivity of a conductive material as used in themanufacture of a membrane switch.1.2 This test method is not suitable for measuring forcesensitive conductive materials.1.3 The values stated in inch-pound units are to be regardedas standard.The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Terminology2.1 Definitions:2.1.1 membrane switcha momentary switching device inwhich at least one contact is on,or made of,a flexiblesubstrate.2.1.2 circuit/test pattern resistanceelectrical resistance asmeasured between two terminations of a circuit trace.2.1.3 squareA geometric unit of a printed conductivecircuit trace/pattern obtained by dividing the length(L)of theprinted conductive circuit trace/pattern by its width(W).2.1.4 resistivityohms per square per mil of a conductivematerial.3.Significance and Use3.1 Resistivity is useful to suppliers and manufacturers asfollows:3.1.1 when designing membrane switch interface circuitry,3.1.2 when selecting the appropriate conductive material,3.1.3 for conductive material quality verification,and3.1.4 for conductive material cure optimization and qualitycontrol.4.Interferences4.1 The precision and bias of this test method are underinvestigation.The accuracy of the resistivity determination willbe improved as the number of squares of the resistance teststrip is increased.The accuracy of the resistivity determinationwill be improved as the width(W)of the circuitry test patternis increased.Some conductive materials resistivity are sensi-tive to temperature and the temperature of the test specimenshould be noted and recorded.5.Apparatus5.1 Resistance Measuring Device,(that is,ohm meter)equipped with test leads and probes.The device should becapable of measuring resistances up to 100 M with anaccuracy of greater than 1.5%of full scale reading.Test probesshould have tips that are 25 to 250%of the width(W)of theprinted conductor test pattern.5.2 Test Surface,to be flat,smooth,unyielding and largerthan switch under test.5.3 Thickness Measuring Device,capable of measuring tothe nearest 0.00005 in.(1.25 m).5.4 Dimensional Measuring Device,capable of measuringto the nearest 0.001 in.(25 m).6.Test Specimen6.1 A resistance test strip of printed and cured conductivematerial with a minimum length(L)to width(W)ratio of 50:1(equal to or greater than 50 squares).A pattern of membraneswitch circuitry is sufficient if a straight measurable strip,witha minimum length(L)to width(W)ratio of 50:1(equal to orgreater than 50 squares),is available.The accuracy of theresistivity determination will be improved as the number ofsquares of the resistance test strip is increased.7.Procedure7.1 Pre-Test Setup:7.1.1 Secure switch/test pattern(that is,printed and curedconductive material)on the test surface.1This test method is under the jurisdiction of Committee F01 on Electronics,andis the direct responsibility of Subcommittee F01.18 on Membrane Switches.Current edition approved May 1,2010.Published June 2010.Originallyapproved in 1998.Last previous edition approved in 2004 as F1896-98(2004).DOI:10.1520/F1896-10.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 7.1.2 Measure the geometry of the test pattern as follows:7.1.2.1 Measure the length(L)of the printed test pattern.7.1.2.2 Measure the width(W)of the printed test pattern.7.1.2.3 Divide the length(L)by the width(W)to calculatethe number of squares of the printed test pattern.Should be 50squares.NOTE1Measuring the length(L)and width(W)of the actual printedpattern checks the accuracy of the actual number of squares printed versusthe artwork.7.2 In-Process Test:7.2.1 Using the resistance measuring device(that is,ohmmeter),measure the resistance of the printed test pattern.Placeprobes at ends of measured length of the test pattern as shownin Fig.1.7.2.2 Record resistance in ohms.7.2.3 Using the thickness measuring device,measure thethickness(t)of the printed test pattern in mils,measure in aminimum of three locations across the test pattern.7.2.4 Record average thickness(t)in mils(1 mil=25 m).7.3 Calculations:7