Guenter

Having seen your photos, it is difficult to be categorical. I suspect that what *may* have happened is that the copper surface was contaminated with a large drop of water  in which a chemical was
dissolved. This probably dewetted on the surface, drawing up into small globules which dried up. The mask was applied over this. The actual attack of the copper may have occurred before or after the
masking, the latter because humidity is drawn in through the mask. This hypothesis is consistent with:
- the shape of the overall area
- the shape and distribution of the individual spots
- the appearance between the spots
- the non-adhesion of the mask on the spots
- the apparent thickness of the discolouration,
but it is only a hypothesis.

If this was an isolated incident, it could simply be an accident (someone sneezed on the board or carelessly splashed a solution about). If more consistent through a batch, then I'd guess better
housekeeping is needed in the fab shop.

Best regards

Brian

Guenter Grossmann wrote:

> Hi all
>
> I have a case here where I am not sure what I see.
> - There are dark spots visible below the solder mask on the surface of the traces on a PCB. I attached 2 Pictures in JPEG that show a view onto the surface of the traces with 10x and 40x magnification.
> - In microsections we see clearly a cavity between the traces and the soldermask.
> - EDX is hopeless, since the dark layer is so thin that the background covers all but the copper peak.
>
> Before I start to work with TOF SIMS, Spectroscopy and other expensive analysis methods I'd like to ask whether one of you knows what the dark spots are.
>
> Thanks in advance. Have a great day.
>
> Guenter
>
> Guenter Grossmann
> Swiss Federal Institute for Materials Testing and Research EMPA
> Centre for Reliability
> 8600 Duebendorf
> Switzerland
>
> Phone: xx41 1 823 4279
> Fax :      xx41 1823 4054
> mail:     [log in to unmask]
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
> the body:
> To subscribe:   SUBSCRIBE TECHNET <your full name>
> To unsubscribe:   SIGNOFF TECHNET
> ##############################################################
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
> information.
> If you need assistance - contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> ##############################################################

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################