If you qualify a product without the appearance of the stuff, you have problem (something changed - process and material change are the major change). If you have not yet qualify the product for intended use, you should study detail of the nature of the stuff and make sure it comply with your specs. Assessing the risk with presence of the stuff on the pwa for the duration of your mission - you don't have chance to rework, repair and overhaul in space, unless you have double redundancy with a dynamic feedback loop for switch.
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 Wayne Thayer
Sent: Thursday, October 03, 2013 11:31 AM
To: [log in to unmask]
Subject: Re: [TN] Grey Matter
Hi Wee Mei-
For space application you should probably make an effort to identify the contaminant as that is the only sure path to evaluating whether it could be a reliability problem.
Somehow this seems a bit unfair, since there are probably a bunch of other contaminants on the board which are not visible, but those are really what the "unidentified" categories are supposed to cover with things like isolation testing. So first you try to eliminate contaminants, then you identify and evaluate those which you couldn't eliminate, then use application oriented qualification tests to cover the stuff you can't see as well as overall board construction.
Sorry for such a non-committal answer!
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lum Wee Mei
Sent: Wednesday, October 02, 2013 8:19 PM
To: [log in to unmask]
Subject: [TN] Grey Matter
Steve has kindly post this picture for me.
Anyone saw such phenomena before on delivered bare boards? Are those grey matter found on recess between solder pads and soldermask acceptable? My PCB supplier said that since the PCBs passed isolation test, those residues should not pose any problem. In addition, as IPC has no such reference in 6012 and 600, my PCB supplier suggest that I use them as UAI. I am concern about long term effect on reliability after assembly, especially such PCBs will be used for space application. Your expertise and opinion will be greatly appreciated.
Thanks and Regards,
~wee mei~
"Successful people aren't born that way. They become successful by establishing the habit of doing things unsuccessful people don't like to do. The successful people don't always like these things themselves; they just get on and do them." - William M Thackeray
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Thursday, 3 October 2013 2:46 AM
To: Lum Wee Mei
Subject: RE: Grey Matter
Hi Wee Mei!
Hmmm, not so sure, depends on what it is? Is this on bare boards that have not been assembled yet? Have you tried cleaning it?
Anyways, I have your picture posted, it's here: http://stevezeva.homestead.com/LumWeeMei.JPG
Maybe you can get some good input from the group from someone who might have seen this before...
Kind regards,
Steve
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