Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!tektronix!tekig5!brianr
From: brianr@tekig5.PEN.TEK.COM (Brian Rhodefer)
Newsgroups: sci.electronics
Subject: Re: Rosin remover
Summary: Don't just spread it
Keywords: Naptha rosin
Message-ID: <4555@tekig5.PEN.TEK.COM>
Date: 24 Jul 89 23:42:17 GMT
References: <1254.AA1254@americ>
Reply-To: brianr@tekig5.PEN.TEK.COM (Brian Rhodefer)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 75

In article <1254.AA1254@americ> erk@americ.UUCP (Erick Parsons) writes:
>
>Naptha works pretty good barring the health hazards that it poses. 
>The fumes will send you into a low Earth orbit and I've been told
>that it is a Carcinogen. I've never tried to ignite it but judging
>from the fumes I would guess that it is flammable too. Can someone
>tell us, Is it a Carcinogen ? Flammable ?
>


1) All that applying a rosin-dissolving solvent to dirty circuit boards
   does is to distribute the original clumps of rosin into thin coatings
   of rosin, depending on the area that the solvent spreads over.  In order
   to actually CLEAN boards with solvent, you must either remove the "dirty"
   solvent before it evaporates and re-deposits the rosin, or dunk the board
   into such a huge quantity of solvent that the resulting "rosin concentration"
   is low enough that when the board is removed and dried, an insignificant
   amount of rosin remains.

   Naptha has an astonishingly high rate of evaporation, making it difficult
   to remove contaminated naptha before it evaporates and drops the rosin
   somewhere else.

   The best practical way of removing the contaminated solvent is to simply
   let it drain off the board, replacing it with a continual stream of fresh
   solvent until the rosin is gone.  Obviously, if the solvent is noxious or
   expensive, this method has its drawbacks.  There ARE water-soluable rosin
   fluxes available, however, which allow such a "one-pass" cleaning treatment
   with an inexpensive solvent (water).  You just stick your dirty boards
   into a dishwasher, toss in some generic detergent (unless you object
   to drops that spot), and let 'er rip.

   For non-aqueous solvents, the best method is one of those vapor-phase
   degreasers, where the board is held in a refrigerated zone above a boiling
   vat of solvent.  Pure solvent condenses on the board, dissolves rosin,
   and dribbles off into the vat.  Pure solvent also condenses out on the
   refrigeration coils, and this winds up dribbling into a "pure tank", which
   acts as a reservoir to supply a spray gun.  The spray gun can be used
   on the dirty boards to accelerate the cleaning process.  Periodically,
   solvent from the "pure reservoir" is diverted into a holding tank, and
   the distillation process is driven until the goo in the boiling vat is
   a near-saturated rosin solution.  The goo is disposed of, the solvent
   from the holding tank is returned to the vat, and the system is "topped
   off" to compensate for the various losses.

   Unfortunately, these machines are pretty serious emitters of ozone-harming
   substances (since the solvents generally used are blends of ethanol and
   chlorinated flourocarbons).
   
2) Some electronic components don't take well to these "mass-production"
   cleaning techniques.  The lubricants of components with moving parts
   (e.g., switches and potentiometers) are often leached out along with
   the rosin, degrading the performance of the now un-lubricated parts.
   Also, some of the non-aqueous solvents can damage electrolytic capacitors,
   if they are able to leak in (through anti-explosion vents, for example).

   If you're serious about cleaning, you'll have to make sure that whatever
   process you choose won't harm your components.  

   
On the subject of naptha toxicity:

   While I was in college, I worked for a small firm that made instrument
   panels for aircraft.  One of the manufacturing steps involved scrubbing
   the panels, by hand, in open vats of naptha, in a poorly ventilated work
   area.  Rubber gloves were available for the workers, but not always used.

   I don't mean that I approve of such practices, or that there aren't
   many long-term health risks, but in the short term, the naptha fumes
   didn't seem to be as intoxicating as the original poster implies.  At
   least,  the employees in that part of the plant didn't seem outwardly
   affected.


Brian Rhodefer