As I might have mentioned before, none of the holes on our boards are
plated through. That means a wire has to be soldered into every via for it to
connect the top and bottom layers. This can turn out to be a big job if the
board is very complex.
Suppose you have created a board like this:
Here is a way to make the installation of the via wires a little less
unpleasant. It's important to do this part before you have installed any
other components. The method I'm describing works best if there is nothing
on the board sticking up higher than the via wires you are about to add.
Prop the board up a short distance above the table. I like to use two
stacks of Post-It notes, each about 1/4" high. You can also set the whole
thing on some flat object (a plain piece of paper works) so that later you
will be able to rotate the whole thing without disturbing the wires.
Cut a bunch of short solid wires that are more than twice as long as
the height of your board off the table. The picture shows stripped 30 gauge
wire-wrap wire, but you can use anything as large as 24 gauge for the small
vias usually created by Eagle. But if you have larger vias, use larger solid
wire because it is easier to handle.
Insert the short wires into the vias so that the bottom of each wire
touches the table and the top is sticking out of the hole.
Solder the wires into the vias. I recommend always laying the
soldering iron down along the trace that connects to the via. Since solder is
attracted to the iron, it will tend to go along the trace rather than some
other direction where it could short to something else. If you have the whole
assembly sitting on a sheet of paper, then you can rotate it to get the
current via's trace to point toward the soldering iron.
Straighten the wires and trim them off with wire cutters so they are
about the height of the Post-Its.
Now turn the board over and set it back down on the Post-Its. The ends
of the wires that were recently sticking out the top should now be
approximately against the table. This will prevent the wires from falling out
when we apply heat to this side of the board.
Solder all the vias on the bottom side. Some of the wires might drop a
little when they get hot, but none should fall out.
Trim all the excess wire from the tops and bottoms of all the vias
using a pair of wire cutters. Cut as close to the solder joint as you can.
You now have a board with all the vias finished.
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