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Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Guy Ramsey <[log in to unmask]>
Date:
Wed, 21 Dec 2011 08:30:22 -0500
Content-Type:
text/plain
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text/plain (533 lines)
Good observation, yes. Once everyone gets the concept it is remarkable how
many opportunities there are to optimize. Suppliers are certainly part of
the equation. Smart suppliers often have new products that provide huge
opportunities, though reliability can be an unknown.

Guy

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Frederick Miller
Sent: Wednesday, December 21, 2011 8:22 AM
To: [log in to unmask]
Subject: Re: [TN] QFP center slug over signal vias

How about bring the suppliers into the class? I have run classes with
suppliers and designers and you should see the engineers defending their
designs. The idea is to have an open mind and understand the bigger
picture. The supplier may be able to reduce the total assembled cost
even if his part will cost more.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Wednesday, December 21, 2011 8:04 AM
To: [log in to unmask]
Subject: Re: [TN] QFP center slug over signal vias

A related "other salt mine" story.

I once taught a three day a DFM / DFA seminar for a large maker of radar
equipment. Top management selected a team of PCB designers to attend.
Two
hours in to the first lecture portion of the program, before the first
break
I asked for questions. One of the designers raised his hand, "Not really
a
question, just a comment . . . and perhaps a rhetorical one," he said.
"You
are preaching to the choir. Where are the program managers, system
engineers, buyers, manufacturing engineers?"
 
In response, during the subsequent break, I called the guy who had
signed
the PO. We spent the next two hours rearranging the class roster.
Reconvened
after lunch, and had an dynamic and much better two and one have day
seminar. 

Guy

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Wednesday, December 21, 2011 6:13 AM
To: [log in to unmask]
Subject: Re: [TN] QFP center slug over signal vias

HI
One of my aphorisms/sayings is "You can never plumb the depths of other
people's ignorance, but lack of knowledge isn't stupidity". And another
is
"Just because you know something, doesn't mean the other guy does". 

I think what we are looking at is a symptom of our specialized and
dispersed
age, where manufacturing , design, marketing/sales etc may never even
meet
let alone talk. What does one engineering discipline really know about
another? In a former salt mine we tried to address this 
1) by making people into product teams, even if only virtual and meeting
by
conference call. This gave them all a stake in the product.
2) by swapping people interdepartmentally for a month. 
3) by taking designers , quality people etc to customers/shows so they
could
see stuff and ask questions.
I will always remember one of our designers saying: So THAT's what a
printer
looks like, I had imagined something much smaller. Now I finally
understand
what you have been telling me......

It was difficult to keep doing this, as once it started working managers
could only see the short term disruption and not the long term benefit.
So
we stopped untill someone said " I've got this great idea, why don't
we..."

And us older timers would catch each others' eyes and...


MERRY CHRISTMAS

Regards

Mike 


 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, December 20, 2011 10:58 PM
To: [log in to unmask]
Subject: Re: [TN] QFP center slug over signal vias

Frank, I have all the respect for designer.  Part of the problem is the
product cycle is getting shorter: a designer never got chance to see (1)
MFG
data - production yield, can do and can't do stuff (new machine
capability
matrix for example) and (2) reliability data of his-her own design and
(3)
market data - field return and touch and feel feed back: all etc,etc,
you
would expect a design to learn, mature, refine.  The fast product cycle
produce someone hand over a hot potato before jump into another "newer,
better, bigger" thing.  The designer didn't got chance to face his own
music,  that is why many poor design come out.  Not totally designer's
fault.  The current environment "promote" bad designer and many get away
with it. Sad (don't get me start "good old days" rap). 
--------------------------
Sent using BlackBerry


----- Original Message -----
From: Frank Kimmey [mailto:[log in to unmask]]
Sent: Tuesday, December 20, 2011 03:43 PM
To: [log in to unmask] <[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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