Ron,
Here's some info from Metcals website (www.metcal.com) that should
answer some of your questions. There are many excellent technical
bulletins on this website. If you need specific questions answered you
can email their technical dept (which has always returned with an
answer). Hope this helps!
Jeff
=======copied from Metcals Website===========
NO CLEAN SOLDERS TEND TO BE LESS ACTIVE THAN TRADITIONAL RMA SOLDERS
At soldering temperatures, the iron plating of the tip is constantly
oxidizing. If the flux is not active enough, it will strip the oxides at
a slower rate than the oxidation buildup. In other words, it is like
trying to shovel snow off a driveway during a snowstorm. As long as the
snowfall is light, you can keep the driveway clear. As the rate of
snowfall gets faster relative to the speed of shoveling, at some point
you canŐt keep the driveway clear.
To solve this, it is necessary to either increase flux activity (shovel
faster) or decrease the oxidation rate (slower snowfall). One way to
decrease oxidation is to solder at lower temperatures. The rate of
oxidation is strongly dependent on temperature. In several cases,
reducing the temperature by 100 ˇF has been enough to allow No Clean
solder flux to keep pace with the oxidation and eliminate dewetting.
Periodic tinning of the tip with a large diameter RMA flux core solder
or solder paste during soldering can be used to strip off excess oxide
<http://www.okinternational.com/glossary.html> buildup during soldering.
At regular intervals during soldering with a No Clean, tin the tip with
an RMA solder, wipe it off on a clean, wet sponge, then continue
soldering with the No Clean solder.
NO CLEAN SOLVENT CARRIERS ARE MORE VOLATILE THAN IN TRADITIONAL RMA
FLUXES
Because of this, at traditional soldering temperatures, the flux solvent
carrier volatilizes too quickly, carrying the flux away from the tip
before it has a chance to strip the oxide.
Again, to solve this, solder at a lower temperature. This slows down the
volatilization rate, giving the flux time to react and strip the oxide
from the tip.
NO CLEAN FLUXES COMMONLY USE SYNTHETIC RESINS INSTEAD OF NATURAL ROSIN
At high temperatures, there is some evidence that these synthetic resins
and activators may be polymerizing, coating the soldering iron tip with
a non-wetting <http://www.okinternational.com/glossary.html>, polymer
film. This film appears as a blackish residue on the tip. This dewetting
failure is different from the more common dewetting caused by thermal
oxidation.
If this is occurring, solder at a lower temperature. This reduces the
chance of the polymer film forming. Also, you can remove the polymer
film (black residue) from the tip with a commercial tip tinner. There
are also fiberglass brushes, tinning "blocks", and glass filled rubber
eraser-type products that can be used to remove black residue from the
tip without harming the iron plating. However, the permissible use of
the brushes or erasers must be evaluated within the context of
site-specific safety and cleanliness standards.
There is a third alternative put forth by some flux manufacturers Ń to
use a No Clean flux that makes use of natural rosin and not a synthetic
resin. However, as the ability to do this varies from manufacturer to
manufacturer, you should check with your flux supplier.
In general, a No Clean hand soldering process is less robust than one
using a more active flux, like RMA. This means the process is more
sensitive to operator technique - or operator error. Hand soldering and
tip care practices that were acceptable with RMA solders may not be with
No Cleans.
> -----Original Message-----
> From: Ron Hollandsworth [SMTP:[log in to unmask]]
> Sent: Friday, August 14, 1998 8:15 AM
> To: [log in to unmask]
> Subject: [TN] MetCal Irons
>
> We are using a no-clean handsoldering flux. I have seen and
> heard
> many stories of how good MetCal irons are for a no-clean
> operation.
> Maybe I could get some listners here to take note of the
> importance of
> iron temperature and no-clean if you TechNet buddies out in the
> World
> would drop a line or two onto the TechNet about the pros and cons
> of
> the MetCal soldering irons. Perhaps I may be able to convince
> others
> in this organization that this is the way to go for tip
> temperature
> control.
>
> I would appreciate the help.
>
> Thanks
> Ron Hollandsworth
> Operations Task Leader
> Advanced Manufacturing Engineering
> [log in to unmask]
>
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