20 Nov
2001
20 Nov
'01
7:35 a.m.
On Tue, 20 Nov 2001 dmc!njc(a)opal.tseinc.com wrote:
Richard Erlacher
Actually 25 or 20 mil QFP stuff is easy to do with just a
soldering iron, the secret is to make surface tension do the work. This
requires large amounts of rosin flux... I just solder the whole mess (all
the leads shorted together) and then using adequate flux, and tilting the
board, drain the excess solder off by dragging the iron along the pins.
Done it hundreds of times - works like a charm, but sometimes you have to
use solder wick to unshort the last 2 pins on each side.
Hot air works too but you have to be careful not to burn the PCB
(if using a standard hand held hot air gun).
I've used a standard hot air gun to solder 388 and 516 pin BGA
stuff too. Not that hard but you have to make a jig to hold the BGA part
in place (with a little (.007 maybe) slop). I make the jig from 4 pieces
of scrap circuit board material tack soldered to the proto board. Surface
tension will pull the part into place when all the solder melts. You can
tell when the solder melts because the BGA chip will sink about 10 mils
(which is one of the reasons that the jig cannot be too tight) I wouldn't
solder a very valuble BGA part by hand this way but I have a 70% or so
success rate which is ok for protos. When soldering BGA parts on a proto,
solder the BGA part first, so that you can sight down all the rows of
solder balls to make sure that you dont have a short...
If you want to translate a schematic from the old TTL SSI/MSI devices to a
programmable device in a dense package, it's much more likely to happen easily
in a CPLD than an FPGA, though people keep telling me that FPGA's provide more
logic at lower cost. I agree that it's more difficult to make it happen in
FPGA, but for a circuit the size of a Multibus-1 or (somewhat smaller) S-100
board, a moderately priced CPLD should get the job done pretty well, though they
used enough one-shots to complicate the job considerably.
With device pin-pitch at 20-25 mils, (actually the metric equivalent) it's
unlikely one will hand wire anything with them. Therefore one's limited to
using PCB mounted parts. Since disposal of PCB-related materials is so costly
these days, it's unlikely one will want to do that at home. What this leaves is
a need for an adapter for some fairly standard-packaged-CPLD and/or FPGA, and
then simply work within the confines of what one can have made up by way of an
adapter from that package to something that one can hand-wire or wire-wrap.
Actually I'm about to attempt to learn hwo to do just that, hand
solder qfp chips to a carrier board with DIP header endings. I have an
eZ80 that I want to brain transplant into a spare HCS II (uses a
Z180). I've checked out Don Lancasters page on how to build your own
smt hot air iron and may attempt it this winter. I'll start by working
on low cost parts and work up from there.
--
Linux Home Automation Neil Cherry ncherry(a)home.net
http://members.home.net/ncherry (Text only)
http://linuxha.sourceforge.net/ (SourceForge)
http://hcs.sourceforge.net/ (HCS II)
Peter Wallace