Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Dave Mucha" <dave_mucha@y...>
wrote:
> --- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan 
> <stefan_trethan@g...> wrote:
> > On Thu, 06 May 2004 15:42:48 -0000, javaguy11111 
> <javaguy11111@y...> 
> > wrote:
> > 
> > > If you see solder paste under a microscope it a bunch of
> > > solder balls a few thousands of an inch in size.
> > > My guess for needing the refrigeration is to keep flux viscous 
> enough
> > > to keep the solder balls from settling and squeezing out the
flux
> > > in between.
> > >
> > 
> > 
> > seems to make sense...
> > 
> > Do you think it would be possible to see if a paste is good or
bad?
> > 
> > ST
> 
> I'm not entirely sure the paste actually goes bad.  I think the gel 
> part gets thicker and it is just harder to spread.
> 
> the real test is to heat it and see if it solders properly.
> 
> Dave

My guess is the solder itself has not changed and would probably melt
if it can get out of the syringe. I think the problem may be if the
ratio of solder to flux gets changed, then the overall quality of the
 solder joint is affected. Probably not enough flux present to allow
good cleaning and wetting. May not be a big deal for a few hobbyist
boards, but would be a big deal in mass production environment.

What usually happens when I have problems is that I will have paste
coming out, then only flux, then nothing at all. I was getting a lot
of that in my year old paste, but I just squeezed out about an eight
of the tube and the problem went away. Whether that was happening
because of settling of the solder, thickening of the flux  or
something else is hard to say.