Stuffing boards with pulled QFP chips

[John Wilson]

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