19 Mar
2015
19 Mar
'15
6:33 p.m.
On 03/19/2015 03:59 PM, John Wilson wrote:
Same experience here. Many fried boards until I tried
touching the (bare -- not sheathed) thermocouple to the
board (doesn't have to be in a PTH, although that might
stop it from occasionally twanging and sweeping components
off). I've only minimally tried BGAs (just liquid flux
w/no solder paste at all seemed to be the answer there)
but I've had fantastic luck with QFPs, SOICs, TSSOPs, and
and all kinds of SMT passive components.
www.oshstencils.com makes it just too easy. John Wilson D Bit
Right, I've
never tried the BGAs either. I have done many
thousands of SOIC and TSSOP parts, and a few thousand QFPs
up to 128 pin 0.5mm pitch parts. I've probably done over
100K passives, generally 0805, but I have one board that is
0603 that now works pretty well. I do have a pick and place
machine.
I make my own stencils with gear I used to use to make PC
boards. I get brass .003" shim stock and laminate it on
both sides with dry film etch photoresist, just as if it was
a PC board. I have a laser photoplotter I made, and make
the artwork for the solder stencil with that. I make a
normal and a mirror image, and glue them together on a light
table, with a little spacer between to compensate for the
shim stock thickness. I just glue one edge and let the glue
dry. Slip the shim stock with resist between the artwork,
expose both sides and develop and etch. It took a while to
get the whole process dialed in just right, but now it works
quite well. Part of the trick is to reduce the apertures to
be smaller than the solder pads on the board.
Jon