You are definitely in search of the Holy Grail.  Sorry, I don't know the 
answers.  Auuuuuuuuuuuuuuuuu

Lamar Young
Specialty Coating Systems, Inc.
7645 Woodland Dr.
Indianapolis, IN 46278
(317) 244-1200 Ext. 276
www.scscoatings.com



From:   Alan Young <[log in to unmask]>
To:     <[log in to unmask]>
Date:   02/22/2013 12:25 PM
Subject:        Re: [TN] 48-pin QFN  via-in-pad solder slug problem.
Sent by:        TechNet <[log in to unmask]>



Hi folks,

Please forgive me if this topic does not belong to this group.

Let me explain my predicament.
I'm a PCB layout guy who has been asked to look at a soldering issue we 
are having with a 48-pin QFN 7mmx7mm [EMBER CORP - EM357-RTR], the solder 
slug under the part is not soldering/bonding to the PCB. The pcb footprint 
is made per the manufactures specification with a 5.3mm x 5.3mm solder 
slug pad with 9 vias finished drill size of 0.254mm. There are no 
soldermask features on the component or solder side over the vias.

When the board has been reflowed, all of the 48 pins solder well but the 
slug has not bonded to the pcb. There are signs of solder in the slug vias 
on the opposite side of the board. If the part is ripped off the board, 
the slug is clean and solder free.

I do not have any information about the paste screen setup or the oven 
profile.

The questions I have are;

1 - Any ideas on why this is happening?

2 - Are the vias in the slug causing this problem?

3 - Would soldermaks capping the vias on the component side help resolve 
this?

4 - Would plugging (no capping) of the vias with epoxy help?

5 - Do north African sparrows fly faster then European sparrows (just 
seeing if anybody is reading this :-)

I do have some photos and x-rays of the device if this will help.

Again any help or comments would be greatly appreciated.

Regards,

Alan Young.



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