Issue



Snowstorms and Sockets


03/01/2008







Driving around after a recent snowstorm in the Northeast U.S., and seeing how rapidly the roads are kept clear, got me thinking about socket contact cleaning. Quite a stretch? Not really.

Storms leave varying amounts of ‘contaminants’ (snow, ice, freezing rain, etc.) on the roads. Tailoring the method, materials, sequence, and timing to suit each type of storm, the storm crews clean the roads quickly and effectively. That’s what socket contact cleaning is all about: removing contaminants, with the proper technique, to return them to top operational condition.

I attended a session of probe card cleaning tutorials at the 2007 Semiconductor Wafer Test Workshop. Cleaning regimens and infrastructure for this sister technology to sockets are well established. Device manufacturers recognize the imperatives (e.g. higher yield) for probe cleaning and have defined cleaning recipes, cleaning material suppliers have technologies appropriate for wafer probes, and the two are firmly integrated into both the wafer prober and wafer test operations resulting in a mature in-situ process. Socket contact cleaning isn’t quite there yet.

Robust socket cleaning practices comprise three key elements: recognizing and acting on the need (motivation), suitable cleaning technologies (means) and operational infrastructure (methods). The work described in one paper1 demonstrates all three elements at work in a lab project. The motivation was to reduce retest due to contact failure caused by high contact resistance (Cres); the means was to clean socket contacts in-situ with a surrogate cleaning device; and the method integrated the cleaning operation into the test flow on an automatic handler. This project illustrates the process and yield improvements achieved with a robust socket contact cleaning process, yet the reality is that prevalent socket cleaning practices have a ways to go.

The common method of cleaning socket contacts is to brush them with isopropyl alcohol (IPA) to remove loose particles. With embedded material like solder generally unaffected, its effectiveness is mediocre. Yet there are novel cleaning technologies that report more thorough results. They include those for off-line use: chemical, electro-chemical and composite spray, and highly crossed-linked polymers for in-situ use as surrogate packages. These advanced cleaning technologies are gaining traction yet face obstacles to widespread adoption by socket users. Clearly, motivation and methods are impeding a more rapid embrace of advanced cleaning protocols.

Whether it’s mindset, tradition, process change, or other factors, unseating or complementing the incumbent (brush cleaning) hasn’t been easy going. Making the market aware of the technology is one obstacle to adoption, said David Jackson, Cool Clean Technologies, producer of composite spray cleaning tools. Eric Orwoll of NuSignal LLC, an electro-chemical cleaning and metallic restoration outfit, added that there’s a perception that results are “too good to be true” and that “often no one seems to ‘own’ the socket cleaning operation.” Rudy Sedlak of RD Chemical, maker of specialty chemical cleaners, remarked that not being comfortable with using chemicals is one hurdle. Moreover, the question of ‘unintended damage’ often crops up.

Jerry Broz, Ph.D., Integrated Test Solutions, maker of cross-linked polymer surrogate cleaning packages, says the question of whether its better to run a socket to end-of-life or maintain it to extend its usefulness will diminish as socket costs rise, thus reducing the need for spares or replacements. He adds the overall equipment effectiveness (OEE) – tool utilization - is a critical consideration in selecting a cleaning technology.

The lower retest/higher yield result with cleaner sockets, and the increase in socket life produced by the thorough, effective, and efficient cleaning performed by the newer technologies, are compelling arguments for the adoption of one or more suitable advanced cleaning technologies and to make the operational infrastructure (methods) changes necessary within their processes.

In making method improvements, determining whether offline and/or in-situ cleaning is desirable must also be addressed. This is where test handler and burn-in tooling suppliers are encouraged to integrate the cleaning method operation directly into their tooling, and/or contain the means within their tooling to establish, monitor, track and manage when sockets or burn-in boards need cleaning. Snowstorms and sockets; maybe not so much of a stretch after all. AP

References

1. “Auto Contact Cleaning Engineering Study Applied to Package Test”, by Byron Gibbs and Kevin McNamara, presented at the 2007 BiTS Workshop and at the Test TechXpot at SEMICON West 2007.

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Fred Taber, general chairman, may be contacted at BiTS Workshop, LLC, 34 Kuchler Drive, LaGrangeville, NY 12540; 845-226-7560; Email: taber@bitsworkshop.org.