photos in
http://tech.ph.groups.yahoo.com/group/Homebrew_PCBs/photos/browse/b888My first attempt at a double sided board using smt and PLCC hardward.
Using a max resolution of .010" traces with .010" between them I
managed (using PressNPeel) to successfully create this board. The
technique I used to locate the top transfer to the bottom is outlined
below
1 I placed pads with a 1mm dia hole on the four corners of both the
top and bottom tranfer images.
2 Drill out the corner holes of the PnP tranfers both top and bottom
3 Ironed on the top transfer
4 drill out the four corner holes on the top PCP
5 Using Push Pins through the drilled holes on the pcb I Located the
bottom tranfer to the pcb
6 Tack ironed the bottom transfer to the pcb
7 Remove the Push pins and finished the transfer to the bottom of the PCB
Using the technique I manages to align both bottom and top images by
with .020" not quite close enough but by making sure that anywhere I
was going thru hole I did not have any traces closer that .020" all of
the thru holes lined up close enough to solder.
In the process I discovered that as you tack the PNP it will slightly
stretch in the direction you are ironing and the PNP will appear
wrinkled so if you tack both the bottom and top PNP transfers in the
same directing trying to duplicate the exact method of transfer both
top and bottom you will achive better result than the .5mm error I had
on this example. Just remember to leave the push pins in for location
while tacking then remove the Push pins and finish the tonal transfer
One thing I did on the development board was to use 74ls04's to drive
leds on each channel of the PIC. This only places a .5ma load on each
channel of the pic while giving a visual indicator when any port pin
is turned on. It really lets you see whats going on on all ports at
any time! It also allows all the channels to drive other devices
without the addition load of driveind a led. I also included a LM34
temp probe, vref+, vfer- pots, and a 32.768khz osc that can be
disabled with jumpers. Also Soic pads for a 24C256 not in place yet.
Shown is a LCD displaying time and temperature using timer1 with the
32.768 crystal and the LM34Z probe
Regards
Dennis Waggoner