Russ,

Thought you might want some more input on your original question. I just
removed a 256 pin Qlogic part and had the exact symptoms you originally
described, where it looked like quite a few pads had no solder on them. I
took a look under a microscope and indeed, there was absolutely no trace of
solder on several of the pads, when those right next to them had solder.
From what I could see, there was indeed a pad still completely attached to
the trace of the component, but the surface was a very dull gray color.
When I scraped it with an x-acto knife, it was shiny underneath, looking
almost like when you scrape the terminals of your car battery. Don't know
what the material is, but it certainly gave the appearance of some sort of
lead alloy.

From what I could see, it definitely looks like it is part of the
fabrication of the part. Maybe one of the chip makers sites would provide
some insight into the fab process for these parts?

Regards,

Rick Thompson
Ventura Electronics Assembly
2665A Park Center Dr.
Simi Valley, CA 93065

+1 (805) 584-9858 voice
+1 (805) 584-1529 fax
[log in to unmask]

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Russ Winslow
> Sent: Sunday, February 07, 1999 1:37 PM
> To: [log in to unmask]
> Subject: [TN] Defective BGAs?
>
>
> Technetters,
> In our BGA reballing services we are finding a high
> percentage of components
> with serious dewetting and/or non-wetting on the component
> pads after board
> removal.  These components have not been deballed with vacuum tools or
> solderwick as evidenced by the large icicles on pads
> surrounding some of the
> defective pads.
>
> We are seeing this problem on BGA's from many different
> sources and are
> beginning to see a trend which concerns us.  Our evidence
> suggests that the
> failure mechanism is between the solder ball and the
> component rather than
> between the ball and the board.
>
> My question's are:
>
> 1.  If you have removed BGA's from the board do you see the
> same phenomenon?
> 2.  Upon removal from the board, do you believe that a
> component should ever
> be left with a "bare pad" (no solder bump and no icicle) ?
> 3.  If a component can exhibit this effect and not be a "defective
> component" then what mechanism would cause such an effect?
> 4.  Do you see "bare pads" on the board after desoldering the
> BGA from the
> board?
>
> Please help!
>
> Russ Winslow
> Six Sigma
> 1940 Concourse Drive
> San Jose, CA  95131
>
> (408) 526-1350
> [log in to unmask]
> http://www.sixsigmaservices.com
>
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