Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Alexandre Guimaraes"
<listas@l...> wrote:
> Hi, Curt
> 
>     Do you have any pictures of the setup and process ? You make it
sound so 
> simple !! Can you show us some more of it ?
> 
> Best regards,
> Alexandre Guimaraes

Hi Alex,

It is very simple!  It takes only 2 pieces of 1/4 inch guage plate (
or any flat steel you have ) with holes drilled along the X and Y
coordinate axes at, say, 1/2 inch intervals.  The 0,0 hole is filled
with a piece of 1/8 drill rod which is a press fit.  The rest of the
holes on the lower (or base ) plate are a snug fit for two more pieces
of drill rod which are moveable alignment pegs for the outside corners
of the circuit board.

The top plate is drilled at the same time as the base and has its
holes reemed for a sliding fit on the alignment pegs.  My press is 4
inch by 6 inch, but you could make one to any size needed, since you
can place scrap pieces of circuit board under the off side corner to
balance the press.

If you wish to make a 2" by 4" board you put the pegs in the 2 inch
and 4 inch holes in the x and y axes  on the base plate.  You then cut
the individual layers for the board BEFORE you etch or print resist
and use the top plate to drill 3 alignment holes in the stack all at
the same time  ( I use 1/16 inch thick one sided glass epoxy board ).   
With care in alignment of the artwork on the individual layers you can
easily do .010 inch spacing for DIPs. ( Take care to keep traces that
run through the space between pins on the component side of the board) 

When I assemble the boards I use 3M or similar quality epoxy, not the
hardware store 5 minute stuff!  You must use a thin layer of epoxy on
each circuit board layer and I find a window squeegee works well and
is easy to clean.  I preheat the press to 150 degrees ( F ) and lay
the board up after a quick spray of silicone to stop sticking. I then
 place the top plate on the stack and use scraps under sides away from
the pegs to keep everthing in balance.  The weight of the top plate is
usually enough to stick the layers together, although it easy to add
more weights if needed.  After a few hours your board is ready to drill.

I first drill from the top side using the smallest bit that will allow
insertion of the pins.  I use a Harbor Freight mini drill press ( ~$40
) and carbide drill bits (  Drill Bit City ) with good results.   For
through holes you carefully drill a slightly larger hole for each
layer.  It's not as tricky as it seems since you can feel each copper
layer as you get near to it.  For a four layer board for an
instramentation amp where you need guard rings on the inputs you would
start with a #72 top drill then step drill from the bottom using a #68
and then a #60.  

When I solder the board I put a bit of solder paste in the through
holes and then place the chips and solder as normal.

The alignment holes make nice mounting points for the finished board
although you can trim them off with a paper shear if you wish ( and
have used good quality epoxy! ).

This low tech approach requires some thought on trace layout due to
the stepped through holes, but they are not a major problem.

I'm sorry for the length of this post, but it will take a while to get
 pictures from film to scanner to the web, so I hope this ( very! )
detailed description will get you started. Feel free to ask any
questions to clarify the process.

Curt Richards