Lou
IMO, the dumb answer is not to confuse temperature with heat. You must
pump enough heat, as rapidly as possible, into the parts to be joined to
raise them to about 230-260°C. This is a matter of calories, joules or
watts, not °C (or °F). To do this, one applies the second law of
thermodynamics which, in context, states that the soldering iron must be
at a higher temperature than the temperature you wish to achieve.
Provided that the iron is capable of transferring the heat available
rapidly (in theory), a few degrees difference is sufficient. In
practice, it is usually necessary to have a differential of 50-100°C.
However, how do we get the heat where we want it? By stocking as many
calories or whatever as possible as close to the work as possible and
ensuring the lowest thermal resistance between the heating element and
the tip of the soldering iron. This means that the best tip is the very
largest one that you can physically use to do the job in hand.
Obviously, a tip weighing 50 g is hardly practical to solder a small
passive SMD (if it were, you could drop the temperature to about 280°C,
quite comfortably).
There are many other factors to consider. For example, if you are using
a "no-clean" wire with only 1% flux, using too high a temperature will
cause the flux to self-destruct before it can finish doing its job of
helping a joint to be made.
There are, again IMO, many factors to consider and probably the most
important is the design of the soldering iron. Probably 99% of those
commercially available are poorly designed in that the thermal
resistance is far too high. The best I have ever seen was produced by GE
about 30 or 40 years ago (with a beautifully comfortable wooden handle,
to boot) where the 6 V heating element was actually integral with the
tip. There is the shape of the tip. Long, thin ones, coming to a point,
are worse than short, stubby, screwdriver-shaped ones, where the store
of heat can get to the work fast.
The best way of determining is to profile the temperature curves as
close to the working part of the tip as possible and in the joint
itself, using the finest chromel-alumel wires you can lay your hands on.
The tip temp must never drop below your desired soldering temp: if it
does, the bit is too small and/or the thermal resistance of the iron is
too high. The joint profile should rise from ambient to your desired
soldering temperature as quickly as you can. If it significantly
overshoots before the joint is finished, your bit temp is too high. If
it "plateaus" below the desired temp, change the bit design to one that
can pump more heat into the joint, without raising the temp. This is
especially important if soldering through-holes of multilayers.
Too high a temperature will cause the residues to be difficult (read,
often impossible) to clean off.
Finally, remember that most iron thermostats are widely inaccurate, no
matter their style and that the resultant temperature, where you want
it, may be tens of degrees out.
IMH(?)O! Hope it helps.
Brian
Lou Hart wrote:
>
> TechNetters, believing that the only dumb question is the one you don't ask, let me inquire - How do you choose temperature for a hand soldering iron? (I'm not referring to the Metcal ones with those special tips.)
>
> I am working with our production people to prepare work instructions. For hand soldering, some people say 700 F, some 750 F. My suspicion is there may not be one temperature to use all the time. Any comments would be much appreciated.
>
> Lou Hart
> Quality Assurance Manager
> Compunetix
> 412-858-6184
>
> ---------------------------------------------------------------------------------
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
> Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
> ---------------------------------------------------------------------------------
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
