I think Earl Moon hit the nail on the head.  Now that there are printed
circuit boards (officially called substrates)in component assembly the
problems they are facing are the same as the board industry has faced for
years.  Only its new to many of them!

I took a couple of photos of the BGA substrates and it clearly shows the
defects.  I'll scan them in and e-mail them to anyone who wants them.  I'm
off to do an XRF (X-Ray Fluorescence) measurement of the metals on the
exposed surface.  I suspect we will see nickel with a bunch of tin/lead
spots.  One wonderful thing is my sample parts have an array of gold pads in
the center.  This means I can measure the gold and nickel thickness on the
same defective components.  I'll pass on the XRF results offline if you are
interested.  If the nickel is 100 microinches or more then I suspect that it
is just heavily oxidized.  If the gold is too thin (<5 microinches) then I
suspect that this may be why the nickel is bad.  Of course it could also be
caused by the use of ineffective flux in semiconductor assembly.  It's my
understanding that they are quickly converting to no-clean. If so, I bet we
will see a lot of these BGA failures.

Anyone else out there see this problem?  Go out there and check those BGAs
you thought were board assembly failures.  Then share what you find!

Regards, Russ Winslow

Six Sigma
1940 Concourse Drive
San Jose, CA  95131

[log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Rick Thompson
Sent: Monday, February 08, 1999 3:51 PM
To: [log in to unmask]
Subject: Re: [TN] Defective BGAs?


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]

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