[hpsdr] Bare Boards

Fri Feb 16 04:48:56 PST 2007

Hi Bill, et. al.,

For me it entails all of your reasons, and two more.  I teach EE classes
here at Walla Walla College, and we have a big need for fast prototypes,
and have developed some techniques to deal with them that make stuffing
boards pretty easy.  

Using a controlled toaster oven allows better solder connections than I
ever am able to do by hand.  (They are absolutely beautiful.)  It is at
least 10 times, and (maybe 100 times faster if step 1 below is done
already) than assembling a through hole board of equivalent complexity,
especially when you have a solder stencil, which we can make with a
special computer controlled router.  The procedure is:

1) Get the parts in hand.  (This is the most time consuming and often
difficult part.)  I am frugal as well, and I like to get samples where I
can.  This often means some substitutions and re-engineering.  My parts
cost is nearly always almost free.  Once in a while I purchase a kit,
because I can skip this step.

2)  Use an ordinary transparency and roue it with the router as the
solder stencil.  The input file is one of those generated by the CAD
software.

I have this idea that if a lot of us want to build our own boards, I
could produce a few solder stencils and they could be passed from person
to person via snail mail, as they are re-usable.  The big draw back to
this is if they get stuck with someone who doesn't have the toaster
ready, or doesn't have time to use them.  I haven't tried it yet, but I
suspect I could produce a dozen at a time with the router if they were
all identical.

3)  Stencil the solder paste on.

4)  Place the parts.  It isn't hard to place them with tweezers, but we
have something even better.  I don't know what you call them, but they
are platforms that are made for placing small parts.  Air vacuum holds
the parts and releases them where you  want them.  They are made for
hand placement.

5)  We pop them in the controlled toaster.  They come out beautiful, and
rarely need any touch up.

My students last quarter programmed toaster oven controllers so you
could duplicate this part pretty easily.  The toaster ovens need to be
ones with the elements shielded, because you don't want infrared
radiation to heat the black components on your board.  We found toasters
for around $20 at Walmart.  The other parts were around $50 with our
process used.  Here is a link to one of their write-ups on this:  
http://cherrysandtree.viviotech.net/asm/1151/index.html

6)  Then of course there is the debugging if you made any mistakes.  

I would be happy to test boards in the future.  I don't usually have a
lot of time in the school year, but during school vacations, I do get
some, and if step 1 is already done, the rest can be done in an
afternoon, even for boards that are as large as Janus and Ozy put
together.

We also have developed methods of making single sided boards in house
quickly, by using very thin circuit board material, and printing on it
directly using a Tektronix Phaser wax ink printer.  

I used to think my prototyping days were over because surface mount
techniques were coming down the pipe, but now I hate through hole by
hand methods instead, and love the results of surface mount parts.
(Less parasitics, and fast high quality assembly.)  You can see some of
the details at:  
http://www.wwc.edu/academics/departments/engineering/students/classes/engr357/pcbtut/index.htm

I hate to admit it, but the IS department at our university has
deteriorated to the point where the main web server went down a day ago
and hasn't been restored yet (over 24 hours later).  It is simply
embarrassing.  So you may have to look at Google cache to read the pages
if you are in a hurry to see them.  The first link above is on another
system, and works fine.

73,

Rob, KL7NA

On Thu, 2007-02-15 at 23:37 -0600, Bill Tracey wrote:
> ***** High Performance Software Defined Radio Discussion List *****
> 
> I'll admit to being surprised at the amount of interest in bare boards, 
> turns out to be running a bit higher than I'd expected it would be.
> 
> I'd be interested to hear from the folks looking at the bare board option 
> their reason for going that route.  Is it a cost issue?  Or really want to 
> know the technology and figure building the board helps in getting to know 
> how it works?   The ship building feeling one gets putting something like 
> this together?
> 
> I'll admit I like building these things.  Having built two sets of these 
> and done major repair work (FPGA replacement) on one, I'll happily go the 
> built and tested route on this round of boards.    As others have pointed 
> out, these are not beginner SMT boards.   The first set I did,  I did w/o a 
> microscope using a fine tipped iron.  Doable but right at the margin of my 
> skills w/o a microscope.   The 2nd set I did with a microscope and a mix of 
> fine tipped iron and hot air and paste technique - this one was much easier 
> with the microscope - I'll never consider doing 100+ pin 0.5mm pitch parts 
> w/o a microscope ever again.     The other parts on the board that are 
> somewhat troublesome to hand assemble are some of the resistor packs which 
> are a leadless package (Personally, I do hope there's a special place in 
> hell for the geniuses that came up with leadless packages)
> 
> I don't mean to discourage anyone from going the bare board route if that 
> is what they want to do.  Just interested in folks reasons for building 
> their own and want to make sure folks are aware how small/tight pitched 
> some of the parts are.     Actually I'd hope to recruit some of the folks 
> with the skills and tools to build this kind stuff by hand to get involved 
> in some of the future projects.
> 
> Cheers,
> 
> Bill  (kd5tfd)
> 
> 
> 
> _______________________________________________
> HPSDR Discussion List
> To post msg: hpsdr at hpsdr.org
> Subscription help: http://lists.hpsdr.org/listinfo.cgi/hpsdr-hpsdr.org
> HPSDR web page: http://hpsdr.org
> Archives: http://lists.hpsdr.org/pipermail/hpsdr-hpsdr.org/
-- 
Rob Frohne, Ph.D., P.E.
E.F. Cross School of Engineering
Walla Walla College
100 SW 4th Street
College Place, WA 99324
(509) 529-3585
http://www.wwc.edu/~frohro/

 1171630136.0