7/31/2008 - Ceramic Chip Capacitors
Ceramic Chip Capacitors Purpose:
This experiment documents and monitors tin whisker growth on one lot of pure tin-plated multilayer ceramic capacitor (MLCCs) mounted inside a hybrid using conductive (silver) epoxy and then subjected to extensive thermal cycling followed by long term ambient storage. The experiment was initiated in 2001 by a non-NASA entity who then donated one of their test samples to NASA Goddard tin whisker researchers for continued monitoring. Details of this study and interim observations were formally published in June 2002 at the American Electroplaters and Surface Finishers (AESF) SUR/FIN conference in Chicago, IL. The paper also discusses similar but unrelated experiments by others attempting to induce whisker growth on tin-plated MLCCs.
- J. Brusse, “Tin Whisker Observations on Pure Tin Plated Chip ceramic capacitor“, AESF SUR/FIN Conference, June 2002, pp 45-61
- Slide presentation is also available.
The NASA Goddard Whisker WWW Site will be used to provide updates as monitoring of these specimens continues.
Ceramic Chip Capacitors Background:
In 2001 a hybrid microcircuit manufacturer informed NASA Goddard tin whisker researchers of their surprising observation of profuse whisker formation on pure tin-plated chip ceramic capacitor (MLCCs). The hybrid manufacturer made this discovery during an evaluation intended to assess the electrical and mechanical integrity of joints made between pure tin-plated MLCC terminations and gold-plated substrate pads when using conductive (silver) epoxy instead of solder reflow for mounting. Their experiments included the following basic approach:
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Sample Preparation: Conductive epoxy mount pure tin-plated MLCCs to gold plated termination pads inside of hermetically sealed hybrids |
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Subject sealed hybrids to:
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Condition 1: Temperature Cycling -40°C to +90°C for up to 500 cycles |
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Condition 2: High Temperature Storage (+90°C) for 400 hours |
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Initial Results:
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Condition 1: Whiskers up to 100 um long observed after as little as 200 cycles |
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Condition 2: No whiskers found |
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In May 2001 the hybrid manufacturer donated one thermally cycled evaluation hybrid package (200+ cycles per Condition 1 above) to NASA Goddard for continued observation. The package contained 6 pure tin-plated ceramic chip capacitors (size 0805) all reported to be from one manufacturing lot. As received by NASA Goddard, the hybrid package had already been delidded. The manufacturer supplied photos of the capacitor terminations to illustrate the extent of whisker growth they observed after temp cycle. Upon receipt at NASA Goddard the sample was reinspected and the whisker formation was confirmed to be consistent with the extent of growth reported by the hybrid manufacturer with all 6 capacitors showing clear evidence of tin whisker formation. NASA Goddard has since retained this sample in office ambient storage for ongoing observation and analysis.
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