Re: RF Prototyping on a Shoe Box

Larry Brasfield wrote:

> At one startup I worked for, we had a little hand tool in
> the lab to cut small isolated pads in a copper clad sheet.

I have made several such tools.

Take an old screwdriver, use a file to change the blade into two sharp
points.
Like a straight fork.
Make one of the points a little softer and 1 mm shorter than the other.
Cut away material on one side of the rounded point so it becomes a
cutting edge.

This means that we need to think through the function.
Put the halfmade tool vertically on a piece of pcb board.
Turn the tool, see how the longer point digs into the copper and into
the pcb material under it.
So its position stays fixed.
The soft point will just glide around in a circle around the sharp
point.

We need to remove material from the soft point to create a flat
surface perpendicular to the movement, on one side of the soft point,
the side which is leading when the tool is turned clockwise.

When that side presents a flat vertical area it will cut away copper
easily. It can be made slightly spoon-shaped with a rotating minidrill
tool. Keep the edges of this flat or spoonshaped area sharp.

I use two different sizes, one for 3mm pads, one for 6mm.

> Most of the copper was ground plane, of course. It
> worked great when common transistor packages were
> larger. Anymore, I think inexpensive etched prototypes
> are the way to go. It's very difficult to build stuff by hand
> as small as it can be when layed out on a regular PCB.

Why worry about space?

The board will be inside a box if it is in use, so the pcb design or
size are of very little significance.

In fact, it is a great advantage to have a fairly open circuit where
there is space enough for changes and repairs.

Use simple pcb laminate, single or doublesided, which is very cheap
when you find it in a surplus shop.
A lifetime supply can cost 20 dollars or so.

Then just cut suitable pieces, clean it with a kitchen sponge, groove
it with a sharp tool, to get the number of pads you think you need.

Start building, and you can add the methods from manhattan and dead bug
style, and make new pads with the rotating tool we made above.

If you need a groundplane, or if you want to build on both sides, use
doublesided pcb laminate.

Basically you need no holes, which saves a lot of work. Old components
can easily be soldered to a flat surface with some ingenuity, cut
wires, bend wires, and solder. New smd components are placed over a
groove and soldered at both sides.

Integrated smd circuits are a problem, because of the many pins tightly
packed, but that is a problem with most simple building methods, and
can only be fully solved by designing and etching your own circuit
boards.


--
Roger J.
.

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