Hi Frank!
I am in complete agreement with everything you have said, and I didn't mean
to sound as if I thought all designers didn't care about how their designs
come together on the manufacturing floor.
But I would have loved to have the designer who put this out to the floor
actually have the chance to sit down and do what he asked us to do in this
design:
http://stevezeva.homestead.com/files/Quad_Stack.JPG
Might have had second thoughts about designing something like this. BTW,
these are 0402's...
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Frank Kimmey
Sent: Tuesday, December 20, 2011 3:44 PM
To: [log in to unmask]
Subject: Re: [TN] QFP center slug over signal vias
I think you would be surprised to see how many Designers would agree.
As a Designer, I want to have the best possible understanding of how things
are made and/or repaired.
Surprisingly, or not it seems Management does not see any value add in
allowing Designers to better understand what they are trying to do.
Since we seem not to be allowed on the floor, then the best we can hope for
is good communication between Assembly, Fab and Design.
Unfortunately, most of that communication never reaches the Designer (it
tends to get stopped at the Design Engineer, Quality Engineer or Process
Engineer, etc.)
Try inviting the Designer in for a tour and I bet you will get Engineers
whose jobs are to tell the PCB Designer what to do.
I can't speak for all PCB Designers but I know that those who I work with
would love a chance to learn how to do better designs.
Also, we are seeing more Engineers designing PCB, this is another issue as
they are not specialists who have that extra pride in being a PCB Designer.
And as we all know, they are smarter than us so we need to just do as we are
told whether we agree or not as to the proper way to design a PCB.
Just a PCB Designer's opinion,
FNK
Frank N Kimmey CID+
Manager - PCB Design
Powerwave Technologies Inc.
Mobile - 916-670-0645
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, December 20, 2011 12:03 PM
To: [log in to unmask]
Subject: Re: [TN] QFP center slug over signal vias
I think there should be some sort of requirement for a designer to spend at
least a few weeks on the manufacturing floor before they start laying out
boards...
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: Tuesday, December 20, 2011 2:52 PM
To: [log in to unmask]
Subject: Re: [TN] QFP center slug over signal vias
I agree completely. Sharing the pain always is a good learning experience.
-----Original Message-----
From: Joyce Koo [mailto:[log in to unmask]]
Sent: Tuesday, December 20, 2011 11:10 AM
To: Bavaro, Phillip @ MWG - TW; TechNet E-Mail Forum
Subject: RE: 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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