Re: OT: Soldering SMDs (was Re: [avr-chat] isp-usb)

[Erik Walthinsen]

Erik Christiansen wrote:
> One day I must try the upturned (clothes) iron method, where the PCB is
> slid onto the hot iron, and off again when the solder has reflowed,
> after a few seconds. It's only going to work for the one side, I guess,
> but so far I've only put a few componenets on the back. They could be
> hand soldered afterwards. (And now, more easily. :-)
The best method I've found, from a site I can't remember off the top of 
my head, is to use a cheapo ($20) electric skillet.  Place the board in 
the skillet, turn the heat on, and wait for it to reflow.  Get one with 
an appropriate cover (which I did), and you can put a fume extraction 
system on it (which I have half done).  The fumes aren't so nice, though 
I don't get the impression there's anything particularly fatal in there. 
 However, make certain any cover you put over the thing is *clear*, so 
you can actually see when it reflows <g>

A specific note about "after a few seconds": if you were able to heat it 
up that fast (which a clothes iron can't anyway, in ambient air), you'd 
literally cook off the chips.  Reflow profiles generally specify 
anywhere from 2 to 5 minutes of warmup at a specific rate, or you risk 
the moisture in the chip literally blowing it to pieces.  I've found the 
cheap skillet I have takes about 2.5min from cold for the tiny boards 
I've done so far, which is just about perfect.

> I like the idea of most of the heat reaching the solder before the
> chips.
This is the main reason that the site I found the idea on came up with 
the idea.  They were soldering surface-mount USB connectors with a 
toaster oven, and the connectors' plastic was melting before the solder 
paste did.  Whoops.