Stuffing boards with pulled QFP chips
elson at pico-systems.com
Fri Mar 31 20:15:39 CDT 2017
On 03/31/2017 06:28 PM, allison via cctech wrote:
>>> Is this something that an experienced hand can manually do?
>> Yes, definitely. 100 lead PQFP is perfectly doable if the lead pitch is not insanely small. It takes a good fine tip soldering iron (mine is a Weller with a PTS tip), fine solder (preferably real, i.e., 63/37 non-PC solder). Liquid flux is a big help, as is a magnifier and bright light or modest magnification microscope.
>> If you have to do a couple of dozen boards this gets very tedious, but for 5-ish it isn't a big deal.
I have a project I do from time to time using 128-lead 14mm
TQFPs with 0.4mm lead spacing.
I use a stereo zoom microscope with a home-made LED ring
light. First, I rub the pads with a pencil eraser to remove
oxidation caused by reflow temps on the rest of the board.
I put a tiny dab of solder on two pads at opposite corners.
I then place the chip in place and reflow those pads. If
the alignment is not good enough, I can "walk" the chip a
bit by reflowing one, then the other pad. Then, I apply
liquid flux to the rows of leads with a wire dipped in the flux.
And, then solder down the rows with a fine-tip soldering
iron. If a bridge develops, solder wick fixes it.
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