I had a customer that didn't hear about double-reflow/selective solderwave
and it was sort of funny (not) how we got tons of power-to-ground shorts
(you can't see even with xray) under the decoupling caps when they were
dragged through molten solder. Remember the epoxy you need to hold the part
in place also raises the component off the board so a micro-hair of solder
can bridge underneath the part. I just changed the process so it was
double-reflow/selective solderwave and didn't tell them until they asked
after the % of assemblies that fired up the first time went from 0% to 75%
and higher. One of the reasons the customer wanted the entire bottomside to
go through solderwave was to fill various test/power? vias so the ICT test
pins had a good domed surface to bite into. I would fill the smaller vias
with the first pass stencil and exposed the really large vias to solderwave.
They changed their design rules to include a 200 mil keepout area around
every component pin and large via hole so a good quality selective
solderwave fixture could be made. (A larger keepout area is needed if a SMD
component near the pin/via is over 100 mils tall.)

Dorothy

> ----------
> From:         Kevin Stokes[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.
> Sent:         Thursday, August 16, 2001 1:26 PM
> To:   [log in to unmask]
> Subject:      To wave or not to wave, that is the question...
>
> Old problem: mounting ceramic capacitors to the bottom side of an assembly
> and your customer wants you to wave them on.
>
> We are having problems with 0805 0.22 uF and 0.1 uF caps going through
> wave and cracking during the process.  We are following all of the
> standard protocols (preheat, etc.).  My understanding is that 0805s are
> typically capable of handling this process.
>
> Anyone got any ideas short of moving the cap to the top or doing a double
> sided reflow?
>
> Kevin
>
> Kevin Stokes
> Reliability Manager
> Kimball Electronics Group
> (812) 634-4207
>
>

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------