Hans
Unlike the others, I am conditionally in favour of oil, especially on older machines
like the Hollis, which have a fairly big drop causing excessive drossing. Rationale:
reduces dross formation by typically 70% and tin oxide is a costly beast to
manufacture. It also produces thinner, more regular solder joints which are easier to
inspect (and consume a tad less solder). My conditions: the machine is in clean and in
perfect working order and (with the Hollis) you see that clean oil is coming up evenly
across the wave in very fine droplets which spread immediately on surfacing. Another
condition is that the oil is provenly compatible with the cleaning process.
No oil has a long working life at 240°C or thereabouts. Mineral oils should be changed
after a couple of 8 hour shifts. Vegetable oils after a couple of hours (I adapted one
of the very first Fry's Flowsolder machines ca. 1959 to inject a very fine curtain of
hot peanut oil for 1/4 second onto the top of the wave just before a circuit arrived.
The oil was not recirculated but accumulated on top of the solder bath and thence into
an overflow. Used about 1 l of oil over a busy 8 hour day.). Glycol based (water
soluble) "oils" have a lifetime of ca. 200 hours but, beware, they slowly polymerise
over this time, making board cleaning increasingly problematic, with a consequent drop
of SIR: it is false economy to allow it to stay too long on the machine, IMHO.
It is certain that using oil requires careful (and costly) maintenance. My policy is to
fill the clean machine with the right quantity of oil. Every day, thereafter, remove
the dross without being too careful about not removing any excess oil (do this before
switching on the pump). If anything, remove some of the oil deliberately, say 5 or 10%,
and then top up the level of solder and oil, as required. Even though you are diluting
the dirty oil with fresh stuff daily, remove all the oil you can at the specified
intervals because some of the oldest oil will still be there and will polymerise.
Remember, your used oil contains lead oxides and is therefore toxic. It is a hazardous
waste. If acceptable to your dross recycler, just bung it in with the dross. If not,
you will have to send it for proper destruction. Do not simply incinerate it unless you
have an approved incineration installation, as both the ashes and the fumes will
contain heavy metals.
All in all, using oil is a compromise and, if done properly, is probably worthwhile.
The cost of the oil and the consequent maintenance is set off partially by the reduced
dross but, above all, by a reduction of inspection time and manual retouching (with a
Hollis machine, 25 years ago, we found that closing the oil down increased the retouch
rate by nearly 200%, although I'm reasonably certain that some of this was for purely
cosmetic reasons because of more irregular solder joint topography).
Finally, I found that using hollow jet (Schleuniger-type) and curtain (some EPM
machines) waves without oil converted the equipment from soldering machines to dross
factories. I have never tried oil on controlled atmosphere machines. I imagine that its
disadvantages would outweigh its advantages with a virtual oxygen-free machine (e.g.
Soltec) but I'm not sure about tunnel machines with the air just purged by the inert
gas (e.g. Seho or Electrovert).
Brian
Hinners Hans Civ WRALC/LYPME wrote:
> Hi Everybody,
>
> I've been asked to troubleshoot a BIG problem with our wave flow soldering
> machine and I could use some advice. I'm in the beginning stages of
> learning about wave flow soldering.
>
> We use Tin Lead 63/37 solder with Kester-5738 Dross Inhibiting Oil and, to
> date, my solder analysis has come back fine.
> And recently, we've been getting alot of bridging on assemblies (multilayer
> FR-4). No surprise really, there is an embarrassing amount of scum
> (dross-?) and our Tinning oil is gunking up. We've only used this oil for a
> few months so it's the only reported process change. The joints look It's
> an old Hollis machine (bought in '83) that has seen better days. The first
> thing management said was, "Should we go and buy a new machine?" Showed
> Kester the pics and they said the oil was at the end of its life and broke
> down.
>
> I threw a couple of pictures on my public drive starting with the word
> 'Solder -'. I kept them fairly large (~500 k each) so people can get a good
> idea of what I'm up against. For the digital buffs, they're scaled down 60%
> from the originals using a Sony DSC-D700 camera.
>
> http://www.driveway.com/share?sid=a8f3cb1d.96df8&name=Pictures
>
> Thoughts, questions, suggestions, . . . . prayers?
>
> Do we just need to scoop the gunk out (that was my weekend) and keep going?
> Start over with a fresh bath of solder?
>
> The more I do, the more I learn . . . the hard way.
>
> Hans
>
> ~~~~~~~~~~~~~~~~~~~
> Hans M. Hinners
> Materials Engineer (Process & Manufacturing)
> Warner Robins Air Logistics Center
> Avionics Production Division
> Manufacturing Branch
> 380 Second Street, Suite 104
> Building: 640, Mail Stop: LYPME
> Robins AFB, GA 31098-1638
> Voice: (478) 926 - 1970 Fax: (478) 926 - 7164
> mailto:[log in to unmask]
> http://www.robins.af.mil
>
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