--- In Homebrew_PCBs@yahoogroups.com, "Steve" <alienrelics@...> wrote:
>
> --- In Homebrew_PCBs@yahoogroups.com, "jc805sb" <jc805sb@> wrote:
> >
> > --- In Homebrew_PCBs@yahoogroups.com, "javaguy11111" <javaguy11111@> wrote:
> > >
> > > Are you trying to mount MEMs devices on a pcb or using a pcb for making MEMs devices?
> > >
> >
> > I am etching copper patterns which operate as the MEMS
> > (the field calls it MEMS although there's nothing mechanical).
> > I have pictures on my blog here,
> > http://88proof.com/synthetic_biology/blog/archives/280
> >
> > The pictures show pretty poor etch results which
> > I am trying to improve using the best SMT techniques first.
> > Pad size/spacing is 1mm x 1mm with 0.125mm gap, or smaller!
>
> I tried to leave this comment on your blog, it said it was too "spammy":
>
> Nice!
>
> What method are you using to make the PCBs?
>
> Are there any issues from the current flow or from copper going into solution?
>
> Steve Greenfield
>
For the board in those pictures, it is made with a Laserjet
3330 to xerox business paper, then toner transfer with iron,
then soak paper in water to remove, then etch in HCl + H2O2
etchant. The result was lacking because the toner is porous,
and the fibers in the paper did not completely remove from
the toner, and some of the toner remained on the paper.
Additional step: To make the narrow junction ("spark gap"),
the toner is cut through to the copper with a razor blade
prior to etching, in the grid pattern. These cuts create
a gap measured at 20-50 micron I believe.
Now I am trying Pulsar's equipment, which does yield very
clean traces. (Print to laserjet on pulsar paper, then
toner transfer with laminator, then soak paper, then
laminate green foil, then etch.) Same step here, make
manual pads with razor blade prior to etching.
The picture does not show this well, though there is a plastic
film on top of the contacts, and the film is made hydrophobic.
These are necessary steps otherwise the droplet will stick
with surface tension. Instructions: get a thin plastic film
(i.e. saran wrap), spray with Rain-X, let dry. Paint surface
of PCB with mineral oil, shake away oil. Lay plastic film
on top, Rain-X side up. Dispense droplet onto top of film
from a tiny coffee straw, that will make a small droplet.
Now zap electrodes with +1000V and see what happens.
By the way at high voltages like +1000V it is not so necessary
to etch a custom board. I have moved droplets on pre-fabbed
SMT protoboards "Surfboard" brand from Digikey, using this
plastic film method, though it is not necessarily predictable.
The drawback is that lack of quality control in fabrication
leads to sparks across the spark gap, which ruins the effect
and possibly damages the board.
The current is <100uA because there is no conduction path,
it is like capacitor charging. So it is possible to build
a simple HVPS to use (which I just posted schematic + layout
to as well).
This is a bit off topic now, I will post subsequent results
to my blog with pics. Though I am still focusing on
getting the etch quality much more predictable.
BTW the new generation of cell phones use "liquid lens"
technology, which is the same effect as this droplet, the
voltage (~50-65v stepped up from cell phone battery) causes
the drop to deform thus focal length changes and a
non-mechanical "lens focus" can be made. The major difference
is the PCB contact pattern, which instead of causing the droplet
to move in the plane, causes the droplet to grow taller or
shorter. Maybe you want to try it, create some interesting
effects with laser pointers or something.