9 Jul
2007
9 Jul
'07
7:39 a.m.
"Mike Hatch" wrote:
I'm not sure that was an accident. Before SMOBC was the thing to do I
remember seeing SM done after HASL more than once - especially in very
low cost... I can't say for sure but I think it done that way on purpose
- i.e. it was specified.
Message: 3
Date: Fri, 6 Jul 2007 11:39:56 -0700 (PDT)
From: David Griffith <dgriffi at cs.csubak.edu>
Subject: trace wrinkles
I haven't heard anyone discuss this yet: what causes traces on some old
PCBs to wrinkle and not others? My guess is a combination of suboptimal
glue and wide temperature swings.
Caused by the hot air solder levelling process when a manufacturer skips a
process or has the process order slightly out. The solder should only be deposited on the component
pads, but some
manufacturers used to put the solder on before the silk screen, then level
the board. The solder melts during levelling and aggregates under the mask
forming the "wrinkles".
exactly; expecially for larger areas...
-brad