The reason why I suggested it was a solder resist repair was the dark ring around the defect, close to the SMT pads, that clearly shows missing solder resist and then the solder resist starts again.
Also, there appears to be a flake of solder resist on the top portion of the pad, upper left corner of the pad as if someone was picking at or around the area.
Finally, if you look at the Blob_close.jpg you can clearly see exposed copper so, the repair happened after surface plating process? If it was photo resist I would expect there would be no exposed copper around the area and we would see the surface finish instead of exposed copper.
Ted T.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Wednesday, June 03, 2015 11:46 AM
To: [log in to unmask]
Subject: Re: [TN] PCB blob defect
Easy to tell--if you scratch at it and there's copper underneath the whole blob, not just where the edge should be, then Louis is correct.
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Louis Hart
Sent: Tuesday, June 02, 2015 7:47 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
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Theodore J Tontis
Sent: Tuesday, June 02, 2015 7:09 PM
To: [log in to unmask]
Subject: Re: [TN] PCB blob defect
It looks like a solder resist repair and they used blue instead of green. It would be interesting to find out when the repair happened, at the board house or assembly house. It's difficult to tell because the silkscreen looks to be repaired as well.
Ted T.
Sent from my iPhone
> On Jun 2, 2015, at 5:56 PM, Watson, Howard August <[log in to unmask]>
wrote:
>
> Hi all,
>
> My PCB fab knowledge is limited, and a very unusual defect was
> discovered
(too late) in assembly. I'm wondering if anyone has seen something like this before, or has an idea what this could be. The blue color seems noteworthy to me. This is for IPC class III, space. I will return this to the fabricator, but I wanted to get educated in case there is a debate regarding the cause. Thanks for your help!
>
> Steve put the pictures here:
>
> http://stevezeva.homestead.com/Howards_Blob.jpg
>
> http://stevezeva.homestead.com/Howards_Blob_close.jpg
> Howard A. Watson
>
> ______________________________________________________________________
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