David
a) I'm not the only brain on TechNet, but it's flattering to be called
so :-). I'm probably not the only Brian, either!
b) I think it is a big mistake to wash straight from the wave. Quite
apart from the problem you evoke, the sudden cooling will not do
components any good, possibly even the metallurgy of the solder joint
(I've never studied the effect of cooling rate on solder, but I could
well imagine that dropping rapidly from, say 150°C to 50°C will produce
a different structure than doing the same more gradually) and, if there
are any problems in the hermeticity of a component, I could well imagine
it sucking in contaminated water prestissimo as the air temperature in
it dropped. I believe the ideal would be to have the board and
components at about the same temperature as the water, on first contact.
Brian
David Fish wrote:
>
> Brain: Continuing with your thoughts, we have been able to create white res on WS fluxed
> boards by washing them blistering hot, straight out of the wave. So, even when we were shrewd
> enough to control our was temps, we were still able to beat ourselves. Tricky eh? Dave Fish
>
> Brian Ellis wrote:
>
> > Jon
> >
> > This is a truth that many people overlook. Many WS flux/paste
> > chemistries use amine- or amino acid-hydrohalide activators and these
> > have a behaviour like egg white - they dissolve well in cold but set at
> > higher temps in the presence of water. I recommend a max of 50°C for the
> > wash cycle with these. Rinse temps can be progressively higher. If a
> > prewash is possible (or use of a chelating neutraliser, which I
> > recommend), then this is best at cold.
> >
> > Brian
> >
> > Jon Moore wrote:
> > >
> > > Janice,
> > > What temperatures are your wash / rinse cycles? I found white residues
> > > routinely with water soluble chemistries and OSP panels following wave
> > > solder, and it turned out that my temperatures were set too high.
> > >
> > > Jon Moore
> > >
> > > ---------------------------------------------------------------------------------
> > > 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
> > > 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
> > > ---------------------------------------------------------------------------------
> >
> > ---------------------------------------------------------------------------------
> > 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
> > 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
> > ---------------------------------------------------------------------------------
>
> ---------------------------------------------------------------------------------
> 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
> 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
> ---------------------------------------------------------------------------------
---------------------------------------------------------------------------------
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
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
---------------------------------------------------------------------------------
|
