On 14 Dec 2011 at 10:28, Leif Laerum wrote:

> The below recommendation was posted on Technet. I did not keep the
> email and I can not remember who to give credit for it. 

It was Julie Silk <[log in to unmask]>
Re: [TN] [DC] QFN layout
Thu, 13 Oct 2011 12:06:49 -0500

> Once implemented we dramatically reduced defects. My policy is to
> go with what I know. The component vendors are not right often
> enough with respect to manufactuing recommendations for me to trust
> them everytime. 

The vendor recommendations vary widely concerning quality. Question 
always: did they do just guesswork or at least some calculations or 
did they try their recommendations in real life? I was involved in 
the design of many test boards for QFN and other leadless packages 
(mostly for discrete RF devices) from a bigger semiconductor 
manufacturer - they made really very many soldering tests with 
zillions of different pad and stencil geometries and board surfaces, 
and the results were used in their application notes and assembly 
guidelines.

And perhaps we remember the early Philips guidelines (1990 and 
earlier, good old times when Philips made the full bandwidth of 
passive and active components AND assembly and soldering equipment), 
They were much better than everything else available at that time 
(I'm sorry, even including the old IPC-SM-782..).

Best regards
Matthias Mansfeld

--
Matthias Mansfeld Elektronik
* Printed Circuit Board Design and Assembly
Neithardtstr. 3, D-85540 Haar, GERMANY
Phone: +49-89-4620 0937, Fax: +49-89-4620 0938
E-Mail: [log in to unmask]
Internet: http://www.mansfeld-elektronik.de


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------