0402 res?

Lyon Yuan


-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]] On Behalf Of
stephen gregory
Sent: Monday, July 15, 2013 11:03 AM
To: [log in to unmask]
Subject: [TN] Soldermask thickness causing 0402 tombstones?

Hi all,
 
Have any of you ever had thick solder mask cause you tombstones? I'm
thinking that maybe that has happened to me. We built a board last week that
we built before without any problems. It does have quite a few 0402's. We
had a few random tombstones last build, but not anything like we had this
time! Tombstones all over the board! Nothing changed from the last build
except the datecode on the PCB's. They were supplied to us from our
customer.  
 
I'm pretty sure that the board was double masked. The fab drawing calls out
for SMOBC, and then when you look farther down in the notes section it calls
out for a matte black mask. It looked to me that there may have been a green
LPI first put down, then a matte black mask put over top of it. 
 
I don't have pictures now, but I'll get some tomorrow. I've found some links
that talk about mask causing
tombstones:http://blog.screamingcircuits.com/2007/11/soldermask-and.html
http://communities.mentor.com/mgcx/message/2726
 
So I know it can happen. I just want to check with you guys to find out if
it happens often.
 
Thanks!
 
Steve

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