Oh heavens. Our legal department shudders collectively with fear every
time Dave and I leave the building and go out in public. When we go to
IPC meetings, the Valium and Lithium intake there increases exponentially.
Doug Pauls
From: Joyce Koo <[log in to unmask]>
To: <[log in to unmask]>
Date: 08/08/2013 07:57 AM
Subject: Re: [TN] QFN solder voiding
Sent by: TechNet <[log in to unmask]>
"I haven't seen any published data on that aspect of QFNs so it may not be
a significant issue." - hmmm, not sure if it is valid assumption. Not
when you have lawyers and legal department review your paper. How long
you have to wait for the corona arcing to be published? Tin/zinc Whiskers
on electronics? 10 to 20 years? Dave, you are very courageous. (even
without lawyers, did you see start up publish defect tracking data? Even
less than the lawyer reviewed one).
Joyce Koo
Researcher
Materials Interconnect Lab
Office: (519) 888-7465 79945
BlackBerry: (226) 220-4760
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, August 08, 2013 8:40 AM
To: [log in to unmask]
Subject: Re: [TN] QFN solder voiding
Hi Bryan - concerning the voiding of the center pad, I'll have to steal
Doug's answer of "it depends". We use a requirement of 50% maximum void
unless there is a functional circuit requirement such as grounding or
thermal. As a number of TechNet folks have detailed, there are various
ways to easily achieve that 50% maximum void. There are always going to be
some voiding but we routinely keep the voiding under 25% of the center pad
area. Out of the couple 100 QFN packages we deal with, there has only been
two cases where the 50% maximum requirement wasn't sufficient. We made
stencil adjustments to insure we hit a 20% maximum value and the QFN
packages were suddenly very happy (both cases involved signal grounding).
As you mentioned, the peripheral pads are a whole other story and I
suspect voids have a bigger impact there - I haven't seen any published
data on that aspect of QFNs so it may not be a significant issue. There
were some very good papers at the 2012 SMTAI conference on QFNS which
would be useful too. Good luck with your process development.
Dave
From: "Kerr, Bryan (UK)" <[log in to unmask]>
To: <[log in to unmask]>
Date: 08/08/2013 02:55 AM
Subject: Re: [TN] QFN solder voiding
Sent by: TechNet <[log in to unmask]>
Hi All
Thanks for all the responses. I'm sure that in most cases we have little
choice but to develop our processes to suit these problematic component
styles however I think the aspirations of the expected soldering standards
vary considerably. I think there is a general acceptance that 50% coverage
of the base is enough although some people, customers and component
suppliers, are beginning to demand more. Peripheral pads are not specified
within any standard I know of and these can show a level of voiding too so
this still needs to be developed.
Bryan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: 08 August 2013 01:12
To: [log in to unmask]
Subject: Re: [TN] QFN solder voiding
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From: [log in to unmask]
Sent: Wednesday, August 7, 2013 7:47 PM
To: [log in to unmask]
Reply To: TechNet E-Mail Forum
Subject: Re: [TN] QFN solder voiding
Steve and all others.
Void free center pads are achievable but you have to really think out of
the box to arrive at a solution. I have worked with parts 1.6mm square to
parts as large as a postage stamp and the same basic techniques work.
Helpful hints;
Solder mask is your enemy and the proper aperture will look very different
than what you usually see.
Little blocks of solder paste will only result in voids.
Think out of the box.
Due to my work I really cannot reveal the secrets but the results can be
achieve.
John
On Wed, 7 Aug 2013 14:12:02 -0600, Steve Gregory <[log in to unmask]>
wrote:
> (background chorus) I want my...I want my...parts void free!
>
> Steve
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey
> (EHCOE)
> Sent: Wednesday, August 7, 2013 1:47 PM
> To: [log in to unmask]
> Subject: Re: [TN] QFN solder voiding
>
> Striking a familiar chord; Excellent!
> Dewey
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