Technetters: We currently have a high mix of boards, older products with
.0003 and .0005" thick tin/lead reflow finish, and newer products with
Solder Mask Over Bare Copper (SMOBC). We have mixed technology: Surface
Mount (SM) and through hole (TH). We have been experiencing recent
(7/97-12/97) solderability problems with the tin/lead reflow finish:
unfilled holes at dips, axials and vias. We use a Nordson spray fluxer with
Multicore X33-04 no clean flux on an Electrovert Econopak II wave solder
machine. Our topside temp is 250F going into the wave, the conveyer speed
is 4 feet/min (fpm). Our glass slide shows 2" of contact (resulting in
about 2.5 sec in the wave).

We have NO problems with the SMOBC boards. We use several PCB vendors, and
the problem seems to be worse with one vendor, but also exists with the
others. The vendors say the high temp alkaline environment during develping
of the mask is oxidizing the tin/lead surface. An immersion tin rework
improves solderability for about a 2 week period (supporting their claim?).
The vendors don't want to gaurantee solderability on the tin/lead reflow
process, and want us to switch to SMOBC on all products.

I have begun the process of qualifying our old products with SMOBC finish,
but now the lack of solderability gaurantee on the tin/lead boards puts me
in bad shape. My vendors say that SMOBC is the way to go, that tin/lead
reflow is going away.

What is your experience? All our new products have been SMOBC for several
years. I am happy with SMOBC, but the time and effort to convert old
products is very expensive.

Should I be changing process parameters at the wave for SMOBC vs tin/lead
reflow? I'm not sure why I would need to change now, when they worked fine
before, but it is easier to change conveyor speed (or whatever) than
convert to SMOBC. Any ideas?

Thanks in advance for your ideas...

Joe Wackerman
Sr. Mechanical Engineer
Parker Hannifin
Compumotor Division
http://www.compumotor.com
voice 707-584-2522
FAX 707-584-8015
e-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.
For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311
##############################################################