Howard et al, when the bigwigs ask "How did that escape inspection?" I, assuming it is an honest question, tell them "Sit at one of those inspection stations for 4 hours and you will get your answer." 

I haven't seen any technical literature on this point, but The New Yorker had an article by Malcolm Gladwell a few years ago reporting how, as the rate of occurrence of an event decreases, the probability of its detection decreases.

Louis Hart

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Watson, Howard August
Sent: Wednesday, June 03, 2015 3:41 PM
To: [log in to unmask]
Subject: Re: [TN] PCB blob defect

Thanks all for your comments and suggestions. The response from the fabricator is that the blue blob is blue resist film that did not strip off, and it should be an easy repair. It does seem strange that this defect got through their inspection, but our QA also missed it!

Thanks,
Howard



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Louis Hart
Sent: Tuesday, June 02, 2015 5:47 PM
To: [log in to unmask]
Subject: Re: [TN] PCB blob defect

Let me disagree with Ted and say I think it is a fragment of plating resist that did not get developed away. Compunetics has blue plating resists, if I have observed correctly. I've never done that job myself but have seen stuff in process.  The solder resist did not seem to set the area around the blob.  I'm not going to speculate about that behavior.  Louis Hart

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