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August 2013

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From:
Douglas Pauls <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 8 Aug 2013 08:02:39 -0500
Content-Type:
text/plain
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text/plain (210 lines)
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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