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Subject: Re: [Homebrew_PCBs] Re: Selecting Method For Prototype Boards

From: Eldon Brown <eldonb46@...>
Date: 2014-07-22

I have made a lot of Home Toner Transfer PCB over the last few years.

Must of my SMD boards are small (less than 6x6) with 6 or 8 mil traces and 40 mil via pads.

Single sided boards take about 10 minutes; time measured after pressing "print" on the computer to "soldering" on the bench. Double sided boards take an additional 15 minutes for alignment of the second side and processing.

Alignment of 40 mil via's is always "ify", due to copper clad expansion and laser print distortion. But it can be done.

if the board has more than about 80 via's I would rather send them out for processing, some examples of my processed boards may be seen on my blog, at:

http://wa0uwh.blogspot.com/
and in particular, my last board, at:
http://wa0uwh.blogspot.com/2014/07/minima-damage-report.html

For via's, I use 11 mil holes and 10 mil stripped wire wrapped wire, the wire will stand straight up in a snug fitting hole. The 10 mil wire can be bent over and cut to fit the pad with an X-Acto knife. With this treatment, they will not fall out. I microscope necessary for working at this small size

I arrange the layout for soldering on the backside for all through hole header and other components that cover the pads, extra via's are generally necessary.

Homebrew Toner Transfer boards are FUN, but I only do it as a hobby, and for one-off boards.


Regards,
Eldon Brown

73 - Eldon - WA0UWH - CN88xc - http://WA0UWH.blogspot.com/




On Mon, Jul 21, 2014 at 2:49 PM, Paul Alciatore palciatore@... [Homebrew_PCBs] <Homebrew_PCBs@yahoogroups.com> wrote:
 

Great responses. Thanks to all.

As I said, I will order greater quantities from a commercial PCB
maker. I have no intention of making hundreds of them at home.

The home made boards, ONE, TWO, or at most THREE, would be ONLY to
verify the PCB layout. With that in mind, I would HAVE to make those
few, home brew boards DIRECTLY from the layout that I create in a PCB
design program. Otherwise, it is still prone to mistakes and
therefore useless.

Vias are a problem, but my circuit is simple so this may not be
overly difficult. First, I can probably solder some wires in vias
that are under the chips. Just use a close cutting pliers to trim
them as flat as possible. The specs for a -DW Plastic Small Outline
package, which I intend to use, show a 0.004" to 0.012" clearance
between the bottom of the package and the board. The copper thickness
will add a bit more to this. I would verify the connection(s) before
installing the chip. A little extra bending on the chip leads will
create a bit more space for them. Tedious, but possible. And this is
ONLY to verify the design.

Sounds like toner transfer may be the way to go. I could always get
laser/Zerox style copies made at a local service. I have the ability
to drill it, no problem there.