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Greetings,<br>
<br>
I thought I would provide you with a short update on my experience
building Hermes. There are some notes and links to photos on the <a
href="http://openhpsdr.org/wiki/index.php?title=Hermes_Board_Build_Notes">Wiki</a>
too. I wanted to test our stencil technology out with Hermes,
because it is a little more challenging than most of what we have
done in the past here. The basic method is seen in <a
href="http://www.youtube.com/watch?v=0FHvikd3BkY&feature=youtu.be">this
video</a>. We make the stencil on an LPKF engraving machine. The
solder stencil is used to lay on the solder paste on the board. The
components are then placed with tweezers or what have you on the
pasted board, and then it is baked in the reflow oven or toaster if
you don't have a regular reflow oven.<br>
<br>
We had to modify the gerbers that Abhi provided because they were
just for solder mask, and the holes need to be smaller than that.
We then engraved one for the back and one for the front. The back
was done first, and was quick, about an hour to place the parts and
bake it. It worked very well. The front was more challenging. It
took about fifteen hours to place the parts. It is like putting
together a puzzle, except you don't try pieces for fit, you find
them and then carefully place them. Terry Long, N8AB, provided some
help with finding the more common parts through his documents, but
the longest part of the process is still like playing <a
href="http://whereswaldo.com/index.html#findwaldo/map1">"Where's
Waldo?"</a> I wish we had the original design files in Kicad or
some open source format, because then you could quickly use the
computer to search for and locate the parts. As it is, the gerbers
are vector graphics files (including the text) so there wasn't an
easy way to find the parts. <a
href="http://people.wallawalla.edu/%7ERob.Frohne/Hermes/1010_HERMES_PROD_BOM_N8AB.xls">Terry's
files</a> were searchable, because he labelled the parts. There
were some errors, which I hope Terry will fix for us. It took me
about a week (where the solder paste was just sitting drying on the
board) to fit in the fifteen hours to place the parts. I was a
little worried that the paste would harden, but that didn't turn out
to be a problem. I probably wouldn't leave it sitting around much
more than a week though. There is always a risk something might
bump it and the parts go everywhere. I had mishaps placing the FPGA
and the LTC2208, and both of them had to be slid over, smearing the
solder paste a bit. There were about 60 solder bridges, mostly on
the FPGA, but none evident on the LTC2208. It took about an hour
and half with very tiny solder wick (about 1/16") and a good Metcal
iron to remove the bridges. Having the right wick and a good iron
is important. You need to use a new piece of wick on each bridge.
<br>
<br>
I am still waiting for some Mouser parts that I neglected to order
until this week, so I haven't powered it on yet. <br>
<br>
The cost of the board and parts was about $450 without the LTC2208
or the Altera FPGA which I had on hand already.<br>
<br>
I am planning on making several more stencils, and passing on the
ones I used, so that others can build their own the same way I did.
If you are ready for one (and will pass it on within a couple of
weeks to someone else on the list), send me a personal email. I'll
send my stencil set on, and over the next couple of days, we will
make a few more sets. I will send John Melton one or two to send
around Europe as well.<br>
<br>
73,<br>
<br>
Rob<br>
KL7NA<br>
<pre class="moz-signature" cols="72">--
Rob Frohne, PhD, PE
Professor
EF Cross School of Engineering
Walla Walla University
100 SW 4th Street
College Place, WA 99324
(509) 527-2075</pre>
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