Stuffing boards with pulled QFP chips

[Jon Elson]

On 03/31/2017 12:55 PM, Jim Brain via cctech wrote:
> On 3/31/2017 12:51 PM, allison via cctech wrote:
>> Is this something that an experienced hand can manually do?
>
> I can verify that it is indeed possible.  I lay down 
> xc95144xl-tq100s all the time with my iron and some flux 
> and some wick, and I get nearly 100% rates.  My eyes are 
> not what they used to be either, so a magnifying glass and 
> a light touch makes all the difference.
>
> I am sure others on list are even better than I, but I 
> recommend flux, place the IC, and then carefully set the 
> board aside to dry. The flux will dry, turn into "glue" 
> (as the alcohol evaporates), and that helps with soldering.
For chips of the 0.65 mm lead pitch, you should be able to 
lay a bead of solder paste down with a syringe, and then 
tack down 2 corner leads.  Once that is done, you can draw 
the soldering tip across the leads and solder one whole side 
in about 10 seconds.  A big solder short will just roll down 
from lead to lead until it is at the end.  You need the 
soldering tip to be pretty hot to draw the solder along with 
it.  It does take some skill to know just how much solder 
paste to put down -- you want very LITTLE paste for the draw 
the blob along trick to work.

Jon