ASTM_F_1996_-_14.pdf

Designation:F199614Standard Test Method forSilver Migration for Membrane Switch Circuitry1This standard is issued under the fixed designation F1996;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 is used to determine the susceptibilityof a membrane switch to the migration of the silver betweencircuit traces under dc voltage potential.1.2 Silver migration will occur when special conditions ofmoisture and electrical energy are present.2.Referenced Documents2.1 ASTM Standards:2F1596 Test Method for Exposure of Membrane Switches toTemperature and Relative HumidityF1689 Test Method for Determining the Insulation Resis-tance of a Membrane Switch3.Terminology3.1 Definitions:3.1.1 silver migrationA process by which silver,when incontact with insulating materials under electrical potential,isremoved ionically from its original location,and is redeposit asa metal(silver dendrite)at some other location.4.Significance and Use4.1 The effects of silver migration are short circuiting orreduction in insulation resistance.It is evidenced by staining ordicoloration between the cathode and anode conductive traces.4.2 Accelerated testing may be accomplished by increasingthe voltage over the specified voltages.(Atypical starting pointwould be 5Vdc 50mA).5.Interferences5.1 The following parameters may affect the results of thistest:5.1.1 Temperature.5.1.2 Relative Humidity.5.1.3 Electrical Load(that is,current and voltage).5.1.4 Test surface.5.1.5 Flex tail connector area may be susceptible to silvermigration which may or may not be a part of the scope of thistest.If the flex tail is to be excluded from the test it should besealed with an inert compound that has no influence on the testor switch materials.5.1.6 Post test handling may damage or destroy silverdendrites.5.1.7 Dendrites normally grow from the cathode conductorto the anode.To test both electrodes of a switch design connectreplicate specimens so that current flows through them inopposite directions.5.1.8 Without limited current,the migration could occur,causing a short and a dramatic current surge,which thendestroys the short and returns the circuit to a nonstandard,butfunctional condition.If an observer was not present(or thedetails were not continuously recorded)this most dramaticfailure might go unnoticed.5.1.9 Surfactants and other contaminants from the environ-ment can be transferred to membrane switch componentsduring handling.These contaminants can adversely affect theresults of this test.6.Apparatus6.1 Closed Environmental System,with temperature andhumidity control(see Practice F1596).6.2 Current-Limiting DC Power Source.(Series currentlimiting resistor may be used with dc power supply).6.3 Milliamp Meter(see Test Method F1689).6.4 Megohm Meter.6.5 Test Surface,flat,smooth,unyielding,nonporous,andlarger than switch under test.7.Procedure7.1 Pretest Setup:7.1.1 Test specimen(s)shall be permitted to stabilize at 20 to25C and 40 to 60%relative humidity(RH)for a minimum of24 h.7.2 Test Setup(Fig.1):1This test method is under the jurisdiction of ASTM Committee F01 onElectronics,and is the direct responsibility of Subcommittee F01.18 on MembraneSwitches.Current edition approved Oct.1,2014.Published November 2014.Originallyapproved in 1999.Last previous edition approved in 2006 as F199606.DOI:10.1520/F1996-14.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 7.2.1 Secure switch on test surface and measure initialinsulation resistance between test points and record results.Protect connector as necessary(see 5.1.5).7.2.2 Orient switch and flex tail in positions that simulatethe end use application positions unless otherwise specified.The flex tail orientation(bent down,up or back)may differfrom the orientation of the switch(horizontal,vertical orangled).7.2.3 Connect power supply leads to test points.7.3 In Process Test:7.3.1 Apply voltage to the test points.Limit the current toprevent high current from disintegrating the dendrites causedby silver migration.Use a current limiting resistor to limit thecurrent to 2 milliamps or less.(See Fig.1)7.3.2 Expose test specimen(s)to specified temperature andhumidity while under electrical load for a specified duration,(for example,10 days at 55C/85%RH).The ramp rate to thespecified test set points(temperature and humidity)should bechosen to maintain a non-condensing environment.7.3.3 After specified duration disconnect power supply andremove from chamber.Allow to stabiliz