1、Designation: F3147 15Standard Test Method forEvaluating the Reliability of Surface Mounted Device (SMD)Joints on a Flexible Circuit by a Rolling Mandrel Bend1This standard is issued under the fixed designation F3147; the number immediately following the designation indicates the year oforiginal adop
2、tion 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 a means to test a completedSurface Mounted Devic
3、e (SMD) joint for bond strength andinter-layer stress compatibility1.2 A completed SMD joint includes; SMD (LED, resistor,etc), PTF ink land (typically silver), conductive adhesive(typically silver), staking compound (non-conductive), andencapsulant (non-conductive).2. Referenced Documents2.1 ASTM S
4、tandards:F1996 Test Method for Silver Migration for MembraneSwitch CircuitryF2750 Test Method for Determining the Effects of Bendinga Membrane Switch or Assembly3. Terminology3.1 bend, vto force from a straight form into a differentand especially a curved one.3.1.1 DiscussionIn this case, no “hard”
5、or angled creaseor fold is to occur. The substrate will only be formed into aradius.3.2 bend cycle, na bend of a sample around a specifiedmandrel which is “rolled” in one direction, followed by rollingin the opposite direction, returning the sample to its originalposition (see Fig. 1).3.3 conductive
6、 adhesive, na material used for electrical ormechanical bonding, or both, of the SMD to the substrate andland-pad.3.4 encapsulant, na non-conductive adhesive that is ap-plied over or around, or both, the SMD for added bond strengthand prevention of silver migration (F1996).3.5 land-pad, nthe printed
7、 circuit pattern at the locationthat interfaces with conductive adhesive, in this case conduc-tive link circuitry (commonly silver) that will make electricalcontact to the SMD via conductive adhesive.3.6 mandrel, na cylindrically shaped metal rod, such as abrazing or drill rod.3.7 SMD, nabbreviation
8、 for surface mount device (that is,light emitting diode (LED), resistor, capacitor, etc.).3.8 SMD joint, nthe combined interface of silver land-pad, conductive adhesive, staking compound (if included), andencapsulant that holds the SMD in place.3.9 SMD-populated flexible printed circuit, nflexible s
9、ub-strate with conductive circuitry and electronic componentsonlynot to include other laminates.3.10 staking compound, na non-conductive adhesive thatis applied at a location directly under the SMD and betweenconductive adhesive deposits (commonly two or more dis-pensed dots of conductive adhesive)
10、to provide added bondstrength and prevent shorting or silver migration.4. Significance and Use4.1 The existing Test Method F1995, while very useful, isdifficult to conduct if an encapsulating dome is applied, anddoes not reveal the possible failures caused by mechanicalstress incompatibility in the
11、overall SMT joint. This mandrelbend test will reveal possible mechanical stress incompatibilitybetween the various adhesives which can result in latent fieldfailures during production handling or with thermal cycling innormal use.4.2 The existing Test Method F2750 does not includespecifics for SMD a
12、ttachments and only addresses the conduc-tivity change of the conductive trace.4.3 The different combinations of SMD types, attachmentmedias, circuit substrates and process variation can account forsignificant variation in test outcome.4.4 Bending of printed flexible circuit or their componentscan a
13、ffect their visual appearance, mechanical integrity orelectrical functionality. This test method simulates conditionsthat may be seen during manufacture, installation, or use.4.5 Bend testing may be destructive, therefore any samplestested should be considered unfit for future use.1This test method
14、is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.18 on PrintedElectronics.Current edition approved June 1, 2015. Published July 2015. DOI: 10.1520/F3147-15Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshoho
15、cken, PA 19428-2959. United States15. Interferences5.1 The following parameters may affect the results of thistest:5.1.1 Temperature and humidity,5.1.2 Mandrel diameter,5.1.3 SMD type, size, orientation to mandrel,5.1.4 Weight applied,5.1.5 Land-pad design and proper application of adhesives,and5.1.
16、6 Lack of 48-h conditioning at room temperature (UV-cure encapsulant continues to cross-link after cure cycle).6. Apparatus6.1 Mandrel, allowed to rotate smoothly around its longitu-dinal axis, rigid, low friction smooth surface. Diameter to bespecified.6.2 Electronic test fixture, to monitor functi
17、on of SMDsbefore and after bending (and during bend if applicable).6.3 Weights (mass), to hold switch onto mandrel in con-trolled force.6.4 Fixture, to hold test sample securely in place in avertical manner (see Fig. 1).FIG. 1 Bend CycleF3147 1526.5 Mechanism, capable of providing a consistent force
18、 ofpull to the sample.7. Test Samples7.1 If the sample length is too short for the test fixture, asample coupon of the same construction should be provided(minimum, 250 mm length by 25 mm width).7.2 The width of the test sample must not exceed the lengthof the mandrel.8. Pretest Setup8.1 Electricall
19、y test SMD components in the flat conditionfor expected functionality.8.2 Visual InspectionNote any components for improperSMD alignment, composition.9. Procedure9.1 Clamp one end of the test sample to the test fixture thisis the static end of the test sample.9.1.1 SMD side of the test sample faces
20、away from themandrel.9.2 Loop the unsecured end of the test sample around themandrel this later becomes the dynamic end of the testsample.9.3 Clamp the unsecured end of the test sample to the liftingmechanism (no tension).9.3.1 Ensure that both ends of the test sample remainparallel during motion of
21、 the test.9.4 If test fixture allows testing during bending cycle,connect test sample to allow dynamic monitoring.NOTE 1Experience has shown that some conductors recover theirconductive properties if allowed to stabilize after the dynamic portion ofthe test. Therefore, continuous monitoring is recom
22、mended.9.5 Apply the minimum tension load of sufficient magnitudesuch that the test sample contacts approximately 50 % of thecircumference surface of the mandrel. (Typically, this is a kgmass providing the tension load).9.6 Adjust the test fixture to achieve maximum travel of themandrel by pulling t
23、he unsecured end (dynamic end) of the testsample while maintaining 50 % contact with the mandrel.9.7 If monitoring, dynamically verify test sample is func-tional.9.8 Start test.9.8.1 Run mandrel test a specified number of cycles.9.8.1.1 A cycle is defined as travel from maximum exten-sion to minimum
24、 extension and back to maximum extension.9.8.1.2 Time between cycles shall not exceed 3 s.9.8.1.3 The linear speed of the dynamic end of the testsample should not exceed 50 mm/s.9.9 During the flex cycle, monitor and record any changes inresistance for SMD such as resistors, and any flickering of li
25、ghtfor powered LEDs.9.10 Remove test sample from test fixture.9.11 Electrically test SMD components in the flat conditionfor functionality.10. Report10.1 Report the following information:10.1.1 Temperature,10.1.2 Humidity,10.1.3 Results of visual inspection before and after cycle.10.1.4 Number of cy
26、cles per specimen,10.1.5 Part number or description of specimen,10.1.6 Date of test,10.1.7 Orientation of SMDs to mandrel,10.1.8 Diameter of mandrel,10.1.9 Load weight.10.1.10 Electrical test change static (before and after bendcycle),10.1.11 Linear test sample speed, and10.1.12 Electrical test vari
27、ations dynamic (during bendcycle).11. Precision and Bias11.1 PrecisionIt is not possible to specify the precision inTest Method F3147 for measuring bend because inter-laboratory studies have proven inconclusive due to insufficientparticipating laboratories with the appropriate equipment.11.2 BiasNo
28、information can be presented on the bias ofthe procedure in Test Method F3147 for measuring bendbecause no standard sample is available for this industry.12. Keywords12.1 bend; conductive adhesive; encapsulant; land-pad;mandrel; printed flexible circuit; SMD; staking compoundASTM International takes
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