1 Apr
2017
1 Apr
'17
7:41 p.m.
On Fri, Mar 31, 2017 at 11:32:08AM +0000, David Griffith via cctalk wrote:
One of the biggest challenges for the last
run was getting the QFP-packaged 100-pin chips[1] in a state such that the
pick-and-place robot wouldn't throw a fit about slight differences in lead
position. The stuffing house insisted that I send them new chips.
What an odd problem! Well I have no idea what it feels like to be a CV
system so I don't know how to make one happy, but if it were my design I'd
lean toward (1) re-design using still-available chips (and hoard the hell
out of them this time), and/or (2) hand-soldering. Everyone's jumped in
with lots of QFP soldering thoughts. Have some more:
- www.oshstencils.com is awesome.
- RoHS solder is *fine*. Maybe it wasn't in its infancy but it is now.
I don't understand all the hate. I've been using it for almost everything
for ~10 years now. Yes I have to use higher temps but that's the iron's
problem (PTA8 tip instead of PTA7 on my WTCPT, and twiddle the knobs on
the other thingies).
- I do QFPs (0.5mm and 0.4mm) using a cheap eBay binocular microscope,
Ameritronics solder paste, and a toaster oven controlled by an Arduino
with a homemade shield on it (with a MAX6675 for a K-type Sparkfun
thermocouple which I position touching the PCB somewhere, START and RESET
buttons, a header for LCD status display, and terminals for an SSR which
turns the toaster oven on/off). It's *fantastic*. Push the START button
and everything's done when you come back (it follows the usual temp profile
automatically). I often have to do some soder-wicking afterward (maybe I
should be using thinner stencils, and I always overdo it when I use a
syringe directly), but the chip stays aligned as the paste melts and the
success rate has been excellent. And solder bridges are self-fixing.
John Wilson
D Bit