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Old 04-04-2011, 11:50 AM   #4588 (permalink)
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Originally Posted by jackbauer View Post
Paul i got the boards today thanks. Question. Do we have software for this new board or does it run the same as the 2c? Now i gotta solder that smt current sensor. I hate smt parts. Bring back valves (tubes) i say
A bunch of interesting parts are available only in surface mount.

Small boards like this are way easier than you expect. The critical element is a solder mask layer on the PCB.
I've been amazed at how well it works.

I use solder paste (not "soldering paste" e.g. flux) and a hot air gun.
Specifically the inexpensive "Mechanics" brand bought from DealExtreme and a $10 hot air gun from Harbor Freight.

Dab a tiny amount of paste on each pad, place the part, wiggle a bit and remove it to make certain that the ink-like paste has spread evenly. Reversing the part helps even out the paste. Smearing outside the pads is no problem, it actually helps see melting progress later.

Once everything is placed, put the board on a level heatproof surface. With low air speed heat the board from far enough away that you don't blow the parts away. Nothing will happen for the first 30 seconds or so, then the solder will suddenly "flash". All of the paste smeared on the solder mask will just instantly disappear, sucked into the joints or left as almost invisible grains that dust away later. Keep heating for another 10 seconds or so. Now the hardest part: don't touch the board for five minutes. I've picked up boards after seemingly minutes (OK, maybe only 20 seconds) only to watch parts shift or slide off, molten solder trailing.

This doesn't work as well on bigger boards will different/bigger size parts. There you have to gently preheat everything to a controlled 100C or 125C, and be careful to use the hot air evenly during the re-flow stage. The preheat keeps the big parts from absorbing so much heat during reflow, and it needs to be gentle to drive off moisture so that you don't get micro steam explosions.

Last edited by DJBecker; 04-04-2011 at 12:02 PM..
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