Whisker assessment and process qualification

AN2035 - Application note

8/11

STMicroelectronics along with their E4 partners have continued to study the Matte Tin-

plating process and the various stresses used to evaluate these processes.

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Test Set #1 (started Jan 2004) completed with final readout at 9360 hrs (13

months)

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Package : QFP 176L Cu leadframes

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Plated in Muar plant

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Solder thickness > 7µm

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Maximum whisker length after 2000 TC (thermal cycles) single whiskers on 1 unit

(27 micron length)

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Maximum whisker length after 9360 hrs (13 months) at 60°C/93%RH, 1 single

whiskers on 1 unit (25 micron length) without associated corrosion.

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No whiskers observed at ambient storage after 9360 hrs (13 months).

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Test Set # 2 (started April 2004) completed with final readout at 3600 hrs (5

months)

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Package: QFP10 x10 Cu Leadframe

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Plated in Malta

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Solder thickess > 7µm

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Mounting on board with SAC solder paste at 250°C max solder reflow temperature

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Maximum whisker length after 3096 hrs (5 months) at 60°C/93% RH, 1 single

whisker on 1 unit (10 micron length).

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Test Set # 3 (started April 2004), completed with final readout at 3600 hrs (5

months)

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Package: QFP14 x14 Cu Leadframe

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Plated in Muar

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Solder thickess > 7µm

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Mounting on board simulated at 215°C max solder reflow temperature

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Maximum whisker length after 3689 hrs (6 months) at 60°C/93% RH, no whiskers

in all tests.

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Test Set # 4 (started Nov. 2004), actual read out 6700 hrs ( 9 months)

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Package: Power SO36L (#2 pcs), Power So20L (#1 pc), DPak (#2 pcs)

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Plated in Muar and Shenzhen plant (2 different chemicals)

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Solder thickness > 7µm

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Mounted on Board with SAC solder paste (NO clean flux)

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NO whiskers found after 6700 hrs exposure at 60°C/93%RH.