I'm pretty sure one could easily model the process with the heat equation:
du/dt= K ∗ grad2 u = 0
However the basic idea is that either it works or it doesn't. If it doesn't
just turn up the temperature until it does. That's why a high wattage
temperature controlled iron is useful. If it senses the tip dropping below
the set temperature then the power kicks in and heats it fast until it does
but the total temperature doesn't exceed the max set.
I think that's a lot better than having a hot iron with no temperature
feedback loop.
I burned a lot of soldermask and lifted a lot of pads with the $10-30 irons
from radioshack. $100 to get the temperature controlled one (with the hot
air) was way better.
On Fri, Oct 16, 2009 at 11:30 AM, Stefan Trethan <stefan_trethan@...>wrote:
>
>
> You are right, the melting point of solder is below 200C. But with
> manual soldering it is not enough to just reach that melting point,
> the whole joint area must be elevated above that temperature and that
> in a short amount of time (overall soldering time should not exceed 5
> seconds). The soldering process is very complex, it's not just a
> matter of putting material down, the surfaces must be wetted and
> cleaned by the flux, the solder must flow correctly and cool uniformly
> without forming a cold joint. I'm no expert on soldering so I can't
> explain what happens physically but I know that the iron must be well
> hotter than the melting point for best results.
>
> 250C is definitely towards the low end, I don't think I could work at
> that temperature. If the temperature is too low, the flux does not
> clean as well and the solder tends to bridge a lot (in fact if I need
> to make a solder bridge somewhere I switch the iron off and let it
> cool a little. 300C is probably where I would feel comfortable working
> with, but 350C also allows me to work reasonably well on leadfree
> soldered production boards. This temperature does not damage PCBs or
> components.
>
> Of course it also depends on tip geometry, and joint size, how well
> any one temperature will work. But if you read for example the guide
> to better soldering by Weller they also write of 700 to 800F as the
> usual range.
>
> ST
>
> On Fri, Oct 16, 2009 at 6:52 PM, Henry Liu <henryjliu@...<henryjliu%40gmail.com>>
> wrote:
> > Isn't 350C a bit high for leaded solder? I thought 60/40 leaded solder
> > melts around 183C: http://en.wikipedia.org/wiki/Solder
> > Lead free seems to be around 220ish.
> >
> > On my temp controlled iron I set it to 250C and it melts almost
> > immediately. I think 350C would burn the board much easier.
> >
> > Also I push the idea again to buy the 825D hot air gun and soldering iron
> > combo. I set the hot air to 300C and the iron to 250C and it works
> great.
> > At $100 you can't lose.
> >
> > If you have a temp controlled iron, it's one of those things where you
> just
> > turn the dial to see what works and when it does you don't need to fiddle
> > with it anymore.
> >
> > Also the hot air gun + paste is so much better than the soldering iron
> for
> > SMD. Paste is around $20 for a syringe and the iron/air gun is $100 so
> > that's pretty affordable. Cheaper than a few overcooked chips and lifted
> > pads for sure. http://www.zeph.com/zephpaste.htm has a video showing
> how
> > effortless it is with the hot air gun but you don't need the hot air
> heater
> > below - hot air alone is enough.
> >
> > For a microscope, I have a stereo Nikon SMZ with a boom arm. I bought it
> > off ebay for around $300 but I think it's a $2000+ microscope new so
> there
> > are good deals to be had. Beautiful optics.
> >
>
>
>
[Non-text portions of this message have been removed]