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December 2011

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Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
Date:
Tue, 20 Dec 2011 14:46:22 -0500
Content-Type:
text/plain
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text/plain (160 lines)
LOL! Good one Joyce!

Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, December 20, 2011 2:10 PM
To: [log in to unmask]
Subject: Re: [TN] QFP center slug over signal vias

If you ask the designer to (1) tape the kapton tape on a piece of clean
glass (cleaned using IPA and DI, followed by IPA rinse and dry)(2) cut into
small pieces of the size using knife - under microscope if it is necessary,
(3) put the piece on to the PWB at desired location using tweezers with
proper ESD protection/with ionized gas blow on his hands.  I am sure you
will never, ever see the same mistake again from the whole design group (the
words get around very very quickly ;-).  My 1.92 cents. 

Joyce Koo
Materials Researcher - Materials Interconnect Lab
Research In Motion Limited
Office: (519) 888-7465 79945
Mobile: (226) 220-4760


-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]] 
Sent: Tuesday, December 20, 2011 1:39 PM
To: Joyce Koo; TechNet E-Mail Forum
Subject: RE: QFP center slug over signal vias

Yeah, that was my first solution but unfortunately it is too small to
put Kapton on reliably (.006" x .015").   I tried to get it die cut but
could not get a quote.

-----Original Message-----
From: Joyce Koo [mailto:[log in to unmask]] 
Sent: Tuesday, December 20, 2011 10:32 AM
To: 'TechNet E-Mail Forum'; Bavaro, Phillip @ MWG - TW
Subject: RE: QFP center slug over signal vias

Based on my book, solder mask is not consider as valid dielectric for
signal.  (Kapton tape would be). 

Joyce Koo
Materials Researcher - Materials Interconnect Lab Research In Motion
Limited
Office: (519) 888-7465 79945
Mobile: (226) 220-4760

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: Tuesday, December 20, 2011 1:26 PM
To: [log in to unmask]
Subject: [TN] QFP center slug over signal vias

We found an existing design which has a device (QFP with center slug)
that has too small of a center slug pad on the PWB.  Within the
corresponding area where the center slug pad should have been, the
designer put some signal vias.  Therefore the only thing preventing the
signal via from shorting out to the center slug (ground) is the solder
mask. No failures to date have been reported, even after a 20g vibe
test.

Is this a violation of J-STD-001 or perhaps IPC-2221 -6.3.4 regarding
minimum electrical spacing?  








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