Cleaning Pb free (including water soluble) is harder overall per Bixenmans
and Owens (Kyzen/ Electrovert) Apex 2004 paper "Lead free soldering: DOE
study to study its effects on Electronic Assembly Defluxing".
They concluded for the [then] water soluble Pb-free materials tested a small
amount of something needed to be added to water for total effectiveness.


Regards 

Mike 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: 12 June 2004 08:13
To: [log in to unmask]
Subject: Re: [TN] ASSY: Aqueous Batch Cleaning Equipment


Cleaning residues after lead-free soldering (I have only theoretical
experience of this) will be both easier and more difficult. Easier
because all the main metallic salts will be much more soluble than lead
salts. More difficult because the soldering temp is higher. I would say
it is a mistake to simply increase the pressure. Either the time or the
mechanical energy can be increased (or both). Higher wash temperature is
a big no-no: many water-soluble fluxes contain organics that "set" in
water at high temps, like egg-white does if you drop it in hot water. I
recommend washing at a nominal 55°C, with 60°C as an outside limit.

I would say that my golden rule of ~2 kW of pump/m of wash bar would
still be about right, but you may need to increase the time by 10%. If
you increase the energy, you will have to adjust the nozzles, to keep
the pressure reasonably low: this will cause a higher flow rate for a
given pressure.

There is no reason to think that WS lead-free soldering residues cannot
be washed with water alone, provided the flux residues are soluble and
the machine design is correct. After all, Arrhenius' equations are based
on absolute temperature and the difference between 518 K and 533 K is
only 3%. I'm sure there are higher tolerances than that in the overall
process. Remember, also, that WS flux contains sufficient surfactant to
reduce the surface tension of the wash water to something like 25 - 30
dyn/cm, so penetration under even tight components should be good
enough, provided you have the right flow pattern.

As I'm now retired, after over 25 years of making aqueous cleaners for
electronics, I can no longer be accused of bashing the competition, but
I must say that I've been appalled at some of the machine design and at
the bulls**t that some manufacturers (and others) have come out with to
try and flog their c**p. I have fond memories of a case where a client
bought a $150,000 in-line machine which could not give better than about
2 µg/cm2 eq. NaCl without slowing it down to about 0.2 m/min. The guy
was very dischuffed and, when the manufacturer would not take it back or
get it working properly, he asked me to see what I could do. I spent a
week with two guys from their maintenance department, changed all the
pumps, pipework and nozzles, added a couple of airknives and blowers for
them. First production test gave a constant residual contamination of
about 0.3 µg/cm2 eq. NaCl at 1.5 m/min. That manufacturer changed hands
shortly thereafter and then went out of business a couple of years
later. I recount this as an illustration of the need to switch off your
credulity when it comes to evaluating machines on paper: a good pinch of
sodium chloride is required, combined with physical proof of adequate
performance for your needs under production (not lab or demo room)
conditions at your rate of throughput. Of course, there are some serious
manufacturers, so sift the good from the bad.

Brian

John Parsons wrote:

> We are looking at adding to our current batch washer (Older Aqueous Tech
> unit) and I am interested in hearing some thoughts as well as first hand
> experience on how the following two cleaning systems work with regards
> to low profile (BGA's etc.) devices run as both conventional and
> lead-free processes.  We are currently running water soluble flux and
> are not using saponifiers for the cleaning process.  I have listed the
> two machines we are considering along with my thoughts.  I am interested
> in hearing yours.
>
>


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