[sdiy] Hand soldering TQFP packages

[Joe Grisso]

Seb Francis wrote:
> Hi,
>
> Does anyone on the list have any experience hand soldering TQFP 
> packages?  I'm wondering what the minimum pitch is that's not too 
> tricky to solder.  Mostly devices seem to be available with a 0.8mm 
> lead pitch which I think will be ok to hand solder.  But some newer 
> devices are only available with a 0.5mm lead pitch.  I'm thinking this 
> is going to be much more tricky to solder.
>
> Anyone tried hand-soldering these 0.5mm pitch SMT packages?
>
> Seb
>
    Three things make hand-soldering TQFPs easy: A fine point yet curved 
tip, solder paste, and (if possible) a microscope. I would hope if 
you're seriously going to endeavor doing SMT rework and assembly that 
you'd have the first two.The method I use is crude, but it gets the job 
done.
    First, I load up the pads on the PCB with solder paste - not 
spreading it like peanut butter, but usually just dabbing on a bit to 
each pad using a toothpick or metal dental pick. If I get too much on I 
don't worry - usually it wicks away through capillary action or I go 
back later cleaning it up with some very fine-pitch solder wick.
    Next up, I solder one corner pin and align the rest of the chip. 
Once the chip is aligned, I tack an opposing corner pin to keep it in 
place, then run the back of the curved edge of the solder tip across the 
row of pins gently but slowly, ensuring each pin melts the solder and 
hopefully adheres the pad properly.
    Finally, I check for pad adhesion solder bridges by pushing on each 
pad carefully and checking under my microscope. If there's a bridge I 
clean it up with solder wick. I usually attack 0.5mm pitch devices with 
a hot air pencil and an x/y table - but it can be done with the method 
above by keeping a steady hand, a low-temp soldering iron, and lots of 
patience.

Best Regards,

Joe Grisso
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