Re: SMD soldering?

I've done a lot of SMD work without buying a rework station. Scott's
advice is good.

Don't bother with the "soak and wick" method. The wick may suck away too
much solder from some pins and you'll end up with a weak connection. My
approach is to put a small amount of solder on the tip of the iron and
just touch it to the end of the pin/pad. If you've used enough flux on
the pins and pads, it will suck the solder off the tip and onto the pad,
leaving a nice fillet behind the pin. If you use wick, it will remove
that conection, leaving a very thin layer of solder on the pad and lower
edge of the pin. That's not enough to provide much structural strength.

For desoldering, use ChipQuik. Works very well and no chance of damaging
pins. But for practice boards, just use a heat gun to melt off all the
chips.

-Nate

Scott wrote:
> Andre'
> 
> Make sure the glue that held down the old IC is removed, you can do this by
> over curing it with your soldering Iron. Then prep the pads, use flux and
> leave a small amount of solder on the pads. This solder will make the joint
> for you.
> 
> I then tack down opposites corners of the IC using just enough solder on the
> iron to make it conduct. If the IC's pins are not bent most of the other
> legs will fall in place. If they don’t, carefully move them over with a
> sharp pointed object, I usually use an Explorer (dental tool).
> 
> Once you have everything aligned. Soak the pins will a good flux. I still
> prefer rosin flux because no clean evaporates too fast. Now, hold the pin
> down with the Explorer and touch it with your Iron. If you have enough flux
> on the leads you shouldn’t have to worry about bridging the pins. So don’t
> be overly concerned about touching more than the leg you want to solder. 
> 
> Once everything Is tacked down, clean then reapply flux and re-solder using
> the explorer to get that clean finish. Then take the explorer or exactor
> knife and carefully run it between the legs of the Ic to make sure there are
> no bridges. Observe with a magnifying glass. Clean again and your done. 
> 
> Of course make sure you bounce back and forth when soldering, left side of
> the chip to the right side, this way you won't overheat the IC. And most
> important, your Soldering iron tip temperature should turn to a nice golden
> brown after solder is applied. If it turns the flux in the solder black then
> you are way to hot. 
> 
> Anyway, all steps are important. But To answer your question, I normally
> just tack down the corners first. 
> 
> -----Original Message-----
> From: owner-cbm-hackers@musoftware.de
> [mailto:owner-cbm-hackers@musoftware.de] On Behalf Of "André Fachat"
> Sent: Sunday, November 01, 2009 06:31
> To: cbm-hackers@musoftware.de
> Subject: SMD soldering?
> 
> 
> Hi,
> 
> I know some of you do SMD soldering. I did already solder 1.27mm distance
> packages, but now I have to solder some 1.0 or .8mm pins - and I find it
> quite difficult to position the SMD part correctly. I only have normal
> pincers as help. I solder one pin and by resoldering that pin I can actually
> correct the position before soldering the other pins - but that seems
> difficult with those smaller parts.
> 
> What do you use to position those SMDs? Do you have vacuum pincers /
> airpicks (or whatever they are called)? Or do you use other tools? Like glue
> to keep the part in position when positioned? 
> 
> Any help appreciated
> 
> Thanks
> André
> 

-- 
Nate


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