AVR-Chat

Hi Thomas,

On Tue, Dec 23, 2003 at 04:14:06AM -0000, nangkon wrote:

> I wonder if solder paste is easier for soldering
> atmega128 on a board. I tried solder wire and
> the result is not too good and bridges formed
> frequently. It could be that I am using wire
> that is too thick. And my inexperience on soldering
> SMT parts definitely did not help at all. :)
> 
> If solder paste will do wonders, any recommended
> brand. I can use just regular iron with it, right?
> No hot air blower required?

Solder diameter makes a big difference.  Too large a diameter and you
end up applying too much.  I found that even a 0.03 inch diameter
solder is too big to reliably solder the ATmega128 by hand.  I use a
0.015 inch diameter flux core solder: Digikey part # KE1203-ND.  Use a
smallish iron tip, my iron tip is a general purpose chisel tip.  You
can see photos and a tutorial on my site here:

	http://www.bdmicro.com/smt/

Set your iron rather hot - I use 630 F.  Use the iron to heat the pin
near the knee of the pin.  Bring in the solder near the foot of the
pin.  It should melt instantly - you only need a small amount of
solder, perhaps 1 or 2 mm worth.

If you cause a bridge, a bit of desoldering braid and/or some flux
will correct it.  However, with a little practice you should be able
to solder without making any bridges.  I can't remember the last time
I made a bridge doing ATmega128's, and I solder them a lot :-)

Also, while my eyesight is very good, I still use a 5x magnifying
visor which helps a great deal.

I've used solder paste, but only when using a surface mount oven.  I
usually only do that when I need to make up 10 or more boards.  In
that case, a stencil helps a lot to apply the solder.  The stencil is
a stainless steel template that is an exact cut-out of all your solder
pads.  You position that over your board, then squeegy the solder
paste over the stencil and lift it off.  It leaves just the right
amount of solder on each pad.  Place your parts, pop it into the oven,
bake until done :-) Afterward there are usually 2 or 3 bridges to
clean up.  I got my stencil from these guys:

	http://www.stencilsunlimited.com/

I was very happy with their quality and service.

-Brian
-- 
Brian Dean, bsd@bdmicro.com
BDMICRO - Maker of the MAVRIC ATmega128 Dev Board
http://www.bdmicro.com/