Soldering chemicals - fluxes - can be susceptible to high humidity levels.
The sensitivity depends on the type and specific individual formulations
within that type. The seriousness of the effect on performance change
induced by the humidity will depend on the sensitivity of your process.
In solder pastes high humidity can cause the flux to become more active
leading it to react wit the solder powder reducing its (the flux)
effectiveness on reflow and causing rheology changes leading to poor print
performance. Generally the viscosity will rise. Water soluble materials are
affected more than resin based materials. Additionally you may have
increased cleaning difficult with water washable products.
Ingress happens at the print stage effectively degrading performance there
and all down the line. And after printing before placing. 
Whether these performance changes are significant depends on your process.
Very fine pitch is clearly going to suffer more and sooner.
Very low humidity can also sometimes be an issue, fortunately the optimum
for solder paste is pretty much the same as for humans and static control.
On wave soldering high humidity used to be a real problem when foam fluxing
as the flux is continuously exposed to the air through the working shift.
The increased water content would mess up the SG/solids ratio, giving
falsely higher solids contents for a given SG. Spray fluxing clearly is not
going to be affected in this way.

Regards 
 
Mike Fenner 
Bonding Services & Products
M: +44 [0] 7810 526 317 
T: +44 [0] 1865 522 663
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg
Sent: Tuesday, July 23, 2013 8:48 PM
To: [log in to unmask]
Subject: [TN] Humidity Issues

Hi Technetters,

Been rummaging through the archives looking for info on humidity issues in
soldering process, found some interesting info on why keeping boards sealed
and if not, baking, is important to preclude delimination problems. Hoever
what I was looking for seems to elude me. 

Assuming that boards are stored properly and are below the levels of
moisture content that can cuase problems, and that MSDs are also stored per
industry standards, what other issues does humidity induce in the sctual
soldering process itself? If the humidity gets too high, even though a
facility has air conditioning it may only control temperature and not
humidity level, will this cause additional problems in the process itself? 

Thanks,

Blair



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