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February 2015 • SMT Magazine 71 Figure 4: Samtec SeArAY connector technology. Objective The objective of the investigation was to determine if the connector has a tin whisker shorting risk that would compromise printed circuit assembly integrity. Test Procedures Test Component The connector is a departure from the tra- ditional connector configuration due to the inclusion of a solder preform on a blade lead geometry (Figure 4). The purpose of the solder preform is to increase the overall solder joint volume and final solder joint geometry. This high-density connector allows for maximum routing and grounding flexibility and perfor- mance up to 18 GHz/pair. The connector tail plating was matte tin over 50 μin of nickel on a copper alloy base metal alloy. Testing Parameters A modified JESD201 test parameter matrix was followed for the testing. The specific test parameters were: • A representative plating lot was tested • A total of 27 connectors were tested • The inspection interval was 500 hours (3 connectors/540 total leads at each inspection interval) • No JESD201 process 'preconditioning' was conducted on the connectors • Conditioning parameters: – Temperature/Humidity: 4000 hours, 85°C and 85% RH, non-condensing environment Inspection Criteria Scanning electron microscope (SEM) inspec- tion was conducted on three connectors (540 individual leads) after every 500 hours interval of temperature/humidity conditioning. SEM in- spection was conducted using 100X to 5000X magnifications. A different set of three con- nectors was inspected at each interval. Once a connector was removed from temperature/hu- midity conditioning and inspected, it was not returned to the chamber. Test results It should be noted that the test vehicles were not cleaned during the entire conditioning se- quence duration to prevent the accidental remov- al of tin whiskers. Assessment of the test vehicles at the 0, 500, 1000, 2000, 2500, 3500 and 4000- hour inspection intervals revealed no tin whisker observations on the SMT pads or PTHs. An iso- lated instance of a tin whisker was observed at the 1500 and 3000 hour inspection intervals. The 500, 1500 and 3000 hour inspection intervals are covered in detail in the following sections. TIN WHISKer rISK aSSeSSMeNT OF a TIN SurFaCe FINISHed CONNeCTOr continues Feature