Greetings folks,
I have tried to sidestep most of the controversy associated with Occam and
solderless assembly as much as possible to focus on getting projects done.
However some controversy is, I suppose, good as it keeps interest alive. As
Yogi Berra might have noted: "If it wasn't controversial, everybody would not
stop to avoid talking about it"... ;-)
So I thought it might be worth while to give everyone here a way to make
their own Occam type assemblies using legacy through hole components at their
desk in a matter of minutes. This will allow folks to form their own opinions
as to the fundamental viability of the concept for the future.
This is only for demonstration purposes but I trust it will open some minds
to the possibilities that exist in the fundamental concept. The following
will work for one or more metal layers but designs should be kept simple for
practical reasons.
1) Obtain a piece of corregated cardboard box (Option: draw your circuit
layout on the surface)
2) Tape a piece of clear polyethylene (a half a common sandwich bag will
do) to the cardboard
3) Place a second larger piece of card board underneath to keep the desk
or other surface clean
4) Clip the leads down slightly (one can intuit for themselves how much
to clip off)
5) Push the leads through the polyethylene into the card board at (the
polyethylene should seal the leads reasonably well but there might be some
small leakage to the card board) Pin holes might be required as starters for many
leaded devices. Shorter clipped leads will be easier.
6) Cut a hole in another piece of cardboard that will encompass the
components and provide a resin dam wrap polyethylene around the exposed edges
(this step is optional depending on size of the assemlby)
7) Mix up some 5 minute epoxy and pour over components (try not to get
too many bubbles entrained)
8) Remove the assembly and trim the leads as necessary
9) Using a silver ink pen (available from some circuit equipment
providers) draw your interconnections between contacts
10) If cross overs are required, use some nail polish at the intersection.
It can be used for cover coating if desired.
11) Attach battery and go have some fun. :-)
Notes. 1) If you want to include connectors, have the mated portions in
them in case some wicking occurs.
2) Small batteries (or screw top battery holders) can be embedded if
desired.
3) Dome switches are a low profile choice.
4) A piece of 100 mil center "bread board" without plated through holes can
be used in place of the cardboard for greater placement accuracy if that is
of interest.
5) The process will work for SMT devices as well but the devices need to be
kept flat and a sanding step will likely be required to clean off resin from
contact surfaces.
6) The conductivity of silver ink is about 10% of copper so stay away from
high power designs. (keep it simple)
This is obviously not a production technology but it does provide a simple
demonstration. I sent Steve Gregory a photo of a simple assembly for those
interested to view what such a simple assembly looks like and he has kindly
consented to post it. Here is the link:
http://stevezeva.homestead.com/files/Through_hole_Occam_prototype.jpg .
It could also serve the needs of some hobbyists and could be a fun project
for anyone having children interested in electronics.
While I appreciate the skepticism of those who question the potential of
solderless assembly, including many long time friends whom I respect and hold
dear. I trust that there will be some increase in acceptance of the concept
with the data that we are in the process of generating.
It may well be that the final versions of Occam assemblies will not look
very much like today's assemblies. They could well appear to look more like
metal jacketed bricks with interconnections on the surfaces to which other
assembly elements (keyboards, displays, etc.) can be joined using other solderless
techniques such low profile connectors or conductive and/or anisotropic
conductive adhesives.
The brick like structure should also prove great for product design
security. Remember when Apple announced the I-Phone last year? 3 days later there
was a public tear down of the product design an everyone could see what was
going on. It will be much more difficult with the solderless brick approach.
Fortunately, wholesale change within the industry is not required for the
process as identified. The equipment, materials and chemistry exist for every
process required. More importantly, there are some new materials and
processes on the horizon that appear extremely well suited to the solderless
approach.
Another point that needs to be addressed related to the process environment.
A number of folks have registered alarm or at least concern at the thought
of having plating equipment under the same roof as pick and place equipment
(or vise versa). To allay such concerns, one need only go to just about any PCB
shop in the world to see precision equipment (drills, lasers and imaging
equipment) under one roof with a plating shop. The process areas are physically
and environmentally separated of course. The PCB industry has operated in
such a fashion since the 1960s.
Changing topics, I found the following quote from a Test and Measurement
World article from October of last year.
http://www.tmworld.com/article/CA6482921.html
"In 1999, Stig Oresjo, then of Agilent Technologies, conducted a major study
of solder-joint defects on printed-circuit boards (PCBs). The study, which
at the time provided the most definitive data on the subject, involved 15
companies and more than 1 billion solder joints. Oresjo concluded that although
companies claimed defect levels in the range of 75 to 150 defects per million
opportunities (DPMO), the reality was 5 to 10 times that high."
In Oresjo's original study, he found the following defect distribution:
1) 41% Solder Opens
2 ) 20% Shorts
3 ) 20% Solder Quality
4 ) 8% Placement
5 ) 8% Electrical
6) 3% Other
It appears that almost 80% of the problems are related to soldering (90% if
the 8% for placement is included but I am sure it is much better these days.)
The 8% electrical problems cited are, I assume, parts related problems of
unspecified cause.
While on the subject of electrical failures, does anyone here have any data
on how many components are damaged by the temperatures associated with the
soldering process? Also how many of the electrical failures might have been
caused by poor cleaning? I have heard a lot of anecdotal information but no
hard facts. I guess I am wondering, has there been an identified and measured
effect of the lead-free assembly on first pass product assembly yield compared
to tin-lead solder?
I would prefer an open forum answer to these questions but I realize that
there might be some discomfort so if anyone prefers to respond off line, that
is fine. Thanks in advance for any input on the topic.
Best wishes to all and have some fun with the table top solderless
assembly...
Joe
**************Ideas to please picky eaters. Watch video on AOL Living.
(http://living.aol.com/video/how-to-please-your-picky-eater/rachel-campos-duffy/
2050827?NCID=aolcmp00300000002598)
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