I echo dave's point of view. (I think Victor is got more than he
bargain for regarding all the infor....;-)
jk
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Hillman
>Sent: Tuesday, September 16, 2003 10:22 AM
>To: [log in to unmask]
>Subject: Re: [TN] Zinc Plating Finish
>
>
>Hi Jay! Good discussion! And yes, sometimes the practicality
>of teaming with your component fabricators is limited in
>assessing plating issues but it has been my experience that
>the level/effort of communication expended directly reduces
>the amount/severity of plating issues on printed wiring
>assemblies. With limited resources, being proactive is getting
>tougher. One of the toughest tasks is getting the
>communication/education down to the third tier supply level
>but those efforts also have the greatest payback. The
>information on the zinc whisker "heat treatment" is contained
>in an internal document but I'll check into the possibility of
>releasing the information to the TechNet community. All
>materials have their disadvantages - zinc plating included -
>but to totally eliminate their potential use without
>considering the use environment and application is equally as
>bad as their blind application. The NASA Goddard webpage is a
>great educational tool for the industry - keep up the good work.
>
>Dave
>
>
>
>
> Jay Brusse
> <jay.a.brusse.1@GSF To:
>[log in to unmask]
> C.NASA.GOV> cc:
> Sent by: TechNet Subject: Re:
>[TN] Zinc Plating Finish
> <[log in to unmask]>
>
>
> 09/12/2003 08:55 PM
> Please respond to
> "TechNet E-Mail
> Forum."; Please
> respond to Jay
> Brusse
>
>
>
>
>
>
>2nd attempt to send (message bounced earlier)...
>Did somebody say "whiskers"? Zinc whiskers?
>
>Those who know me from this forum probably realize that the
>only time I cast in my two cents is when the topic of
>"whiskers" rears its ugly head. I help to maintain the NASA
>Tin and Other (aka ZINC) Whisker WWW Site at NASA Goddard.
>
>http://nepp.nasa.gov/whisker/other_whisker (for lots about
>ZINC whiskers)
>
>Regarding zinc and it's potential to grow unwanted whiskers,
>we have seen it very recently in a GROUND (non-flight)
>application. We believe this particular application of zinc
>plating (with possibility to form whiskers) is potentially so
>pervasive that we have issued a formal Problem Advisory via
>the US Govt and Industry Data Exchange Program (GIDEP) in
>August 2003. I suspect that many of you and your organizations
>may also be exposed to this problem without knowing it. I am
>not authorized to distribute GIDEP documents to a forum such
>as TechNET (i.e., no international distribution allowed...
>GIDEP participants only, etc.), but for an overview of the
>specific situation we have observed, you may view a
>presentation I prepared in April 2003:
>
>http://nepp.nasa.gov/whisker/reference/tech_papers/Brusse2003-Z
>inc-Whisker-Awareness.pdf
>
>
>The problem is one of zinc-coated structures used in the
>manufacture of raised "access" floor structures (commonly
>found in computer data centers). These tiles and the support
>structures they rest upon (pedestals and rails) are frequently
>made with steel that is zinc-electroplated for corrosion
>protection. In the case of the tiles, it is the UNDERSURFACE
>(the side you DON'T) walk on that is the potential source of
>problems. Over periods that may take months if not years, the
>zinc-plated surfaces may grow zinc whiskers. On one tile I
>retrieved from a data center, we estimate 10 MILLION whiskers
>growing on a 4 square foot area of a single tile. Many of the
>whiskers in excess of 2 millimeters. While they live below
>floor they pose essentially no problem. But when they get
>dislodged from the tile or rail/pedestal... they become an
>airborne NIGHTMARE. The subfloor space of many raised floor
>structures is commonly pressurized for cooling of the
>electronics in the room. Tiles with holes or floor vents are
>strategically located about the center to distribute the cool
>air. The problem is that when someone lifts a tile (they are
>called "ACCESS" tiles after all) and slides it across the
>floor or drops it back in place or pulls electrical cable
>under floor, the Zn whiskers become dislodged and away they go
>merrily blowing about the room. The fans on the equipment in
>the rooms are quite efficient at pulling in air to keep them
>cool. Along with the air comes a fog of conductive zinc
>whisker debris... Result... intermittent glitches...
>catastrophic shorts... and as Joyce Koo remarked...the bullet
>that killed the beast is so difficult to see due to small size
>or gets melted during the event... or gets blown away from the
>crime scene... that detection of this problem is HARD!!!
>
>This is not a "rare" situation as I have seen it myself in at
>least three different data centers in the last 8 months and in
>researching the matter I have talked to many (at least 7)
>others who have faced this beast as well.
>
>In my review of this problem, I have spoken with more than one
>manufacturer of electronic equipment who have told me that
>they too have dealt with zinc whiskers growing from the Zn
>plated equipment racks or from the Zn-plated chassis housing
>their system. The fact that this type of problem isn't
>PUBLICLY reported is often a matter of each company's choice
>to go public or to quietly address the problem internally. I
>think I am echoing Joyce Koo's comments here.
>
>Dave Hillman's suggestion to work closely with your supplier
>is a good idea, but is frequently impractical. The company I
>buy a bolt from may not be the one doing the plating. The
>company I buy the relay from may be using Zn-plated structures
>INSIDE of the relay that they buy from somewhere else (by the
>way Zn whiskers have grown from inside of such devices leading
>to field failures). Dave also mentioned that Zn plating can
>be rendered immune to Zn whiskers by "annealing". I am very
>interested to learn more about that this practice and to find
>out if such practices are indeed industry standard approaches.
> Also as Joyce remarked, I know of no accepted test
>methodology by which one could evaluate a particular product's
>propensity to whisker in 1 year, 2 years, 10 years, etc. The
>floors in many of our facilities have been in use for 30 years
>or more in some cases.
>
>Just to cloud the whisker issue a bit further, I've recently
>seen pictures of Zn whiskers from Hot Dip Galvanized Steel
>(albeit rarely).
>
>Just this week during an audit of a manufacturer of electronic
>components, they told me they had recently received a survey
>from a major client asking them about whether their products
>may be prone to "tin whiskers" through the vendor's choice of
>pure tin finishes. The vendor, clueless about what a tin
>whisker is, responded... "Not a problem for us" because they
>interpreted the question to mean are they using pure tin
>"solder" to make solder joints. Of course the vendor does NOT
>use pure tin SOLDERs but they do use pure tin-plated terminals
>and other mechanical items in the construction of their
>product. Buyer Beware!
>
>Cheers,
>
>Jay
>--
>Jay Brusse
>QSS Group, Inc at NASA Goddard
>301-286-2019
>
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