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@...> 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.
>