Welcome to Board Talk. This is Jim Hall and Phil
Zarrow of ITM Consulting, bringing you Board Talk. Let's see, this looks like a solder paste question.
This question comes from W.O. While running a solder paste comparison through
our SMT and ICT processes (that's in circuit test) we found that one
solder paste is harder than the other.
Pin impact into the solder on test points was less on one type than the
other. The two solder pastes use the
same powder, a 63/37 Eutectic, but different carriers and actives.
One paste is designed to overcome poor
wetting head-in-pillow effects that come with soldering lead-free components in
a tin/lead SMT process. The other is a
longstanding tin/lead solder paste. What
could be causing the difference in solder joint hardness?
I assume that he's
talking about penetrating the flux residue as opposed to making little dents in
the solder joints.
both 63/37, there should be absolutely no difference in penetration just into
the metal. So we're obviously talking about a residue.
What jumps out at me is that one paste is
designed for a specific thing, overcoming head-in-pillow. The reality is that the chemistry
of solder paste is very complex. All of
the manufacturers would love to come up with the ultimate solder paste that
minimizes all defects and gives you good processing parameters, including
ICT test penetration in the residues.
But the reality is they're not there yet, and I don't know
if they ever will be. Nature doesn't
tend to be completely harmonious, so there are tradeoffs.
Manufacturer's optimize paste to get rid of one defect, and you tend to reduce some other parameters. It
sounds like one of these pastes, and I’m guessing it's the one that was formulated
to avoid head-in-pillow, has the chemistry that
produces a harder residue which is more difficult for
the test probes on your ICT, or bed of nails fixtures, to
I want to compliment this questioner for doing a solder paste comparison. You are doing the
right thing. You're trying to find
the best paste for your process, and you're doing the tests that are important to
you. That's excellent work. Now, armed with this information, I would talk to this paste
other paste vendors, and see if they have another formula that gives you
better compromise between head-in-pillow, if that's the defect you're
Most solder manufacturers will be able to
talk to you in a helpful way.
someday somebody will come out with a "TempurPedic "solder flux residue that serves all purposes. In any given
marketplace, whether we're talking about the Americas, Asia or Europe, there are at
least 20 different solder paste manufacturers competing with each other, and
they're all trying to out-do each other.
They are working to give you a better process, to make your
So I guess no matter whether you're going to be
doing in-circuit testing, whatever you do
when you solder those boards ...
Don't solder like my brother.
Please don't solder like my brother.