Homebrew_PCBs

I just received my first order of epoxy/glass copper clad (thus far I
have been using 30+ year old phenolic) and the weave pattern is from
the glass is *very* pronounced on the surface of the copper. Is this
at all common? Have I purchased a low-grade board? I did some
googling, and all I could find in reference to the weave patterns was
in relation to the performance of high-frequency circuits.

Although I am not concerned about high-frequency performance, there is
enough surface irregularity to substantially effect toner transfer.
It actually takes a fair bit of sanding (i.e. I need to start with 100
grit paper) to clean the board up and get things flat.

I also discovered two tips that I did not come across in my reading on
PCBs. Probably preaching to the choir here, but just in case...

1. 30% HCl works brilliantly for cleaning any tarnish off a board.
Just wipes it right off like magic. I can't imagine why so many
people recommend Tarn-X. That stuff doesn't work for crap and leaves
an evil film. $5 wasted IMO.

2. It is ridiculously easy to tin your entire board using nothing
more than a broad-tipped iron. Just put a tiny bit of solder on the
tip of the iron and drag it across the board. It will bridge up
smaller holes so those are best drilled after tinning the board. I'm
glad I didn't waste $15 (or much more) on Liquid-Tin.

-p.

"Peter Johansson rockets4kids@... [Homebrew_PCBs]"
<Homebrew_PCBs@yahoogroups.com> writes:

> 1. 30% HCl works brilliantly for cleaning any tarnish off a board.
> Just wipes it right off like magic.

That's because the tarnish is copper *oxide*, and as I mentioned
earlier, HCl needs an oxidizer - so it etches the copper oxide but can't
etch the copper. Be careful, though, HCl is a nasty chemical to work
around. Note that copper oxide is also one of the possible starters for
a CuCl etchant - which *will* etch copper.

Me, I use a green scrubbie. Prepping a board for TT or UV is more than
just cleaning the copper - you need to make a mechanically rough surface
for the toner to cling, and the scrubbie does that. Toner won't stick
well (or at all) to a mirror finish (which is why it releases from
transparencies).

> 2. It is ridiculously easy to tin your entire board using nothing
> more than a broad-tipped iron.

Unless you're doing fine-pitch surface mount parts, in which case the
uneven surface of the solder messes you up a lot.

Liquid tin is a lot easier to do, too, and you don't risk lifting the
copper traces off the pcb.

 

I just received my first order of epoxy/glass copper clad (thus far I
have been using 30+ year old phenolic) and the weave pattern is from
the glass is *very* pronounced on the surface of the copper. Is this

The weave is usually visible to some degree.  Remember the copper layer is very thin, so well, that's to be expected when it's bonded.

On Wed, May 14, 2014 at 7:01 PM, DJ Delorie dj@...
[Homebrew_PCBs] <Homebrew_PCBs@yahoogroups.com> wrote:

> That's because the tarnish is copper *oxide*, and as I mentioned
> earlier, HCl needs an oxidizer - so it etches the copper oxide but can't
> etch the copper.

Oh yes, it was exactly looking at the chemical reactions which
prompted me to try HCl as a board cleaner.

> Be careful, though, HCl is a nasty chemical to work
> around.

Indeed, but less nasty than I had worried about. One of the first
things I did was put a single drop on my skin to see just how nasty.
It did not really seem to do anything in the few seconds I left it
there before washing it off. Vapors in the eyes and lungs, those I am
worried about. Running a fan over the work area seems to take care of
that.

> Me, I use a green scrubbie. Prepping a board for TT or UV is more than
> just cleaning the copper - you need to make a mechanically rough surface
> for the toner to cling, and the scrubbie does that. Toner won't stick
> well (or at all) to a mirror finish (which is why it releases from
> transparencies).

Good to know. I was trying it on some boards that I had already
etched, handled carelessly, and then let sit for a week.

> Unless you're doing fine-pitch surface mount parts, in which case the
> uneven surface of the solder messes you up a lot.

I can see where that would be a problem. I am only *just* making the
jump from TH to SMD, and I'm starting with the coarsest pitch
components I can find. It would certainly be possible to drag the
iron away from the pads on fine-pitch parts and leave them bare.

> Liquid tin is a lot easier to do, too, and you don't risk lifting the
> copper traces off the pcb.

I was worried about lifting traces too. I tried to be pretty brutal
on my test boards and was rather surprised that I didn't lift any
traces. I suppose this depends on the thickness of your copper and
how well it is bonded to the substrate.

I've read conflicting reports on the Liquid Tin. Some people love it,
other people claim it provides little to no long-term protection for
your boards and doesn't really help with soldering SMD parts either.
One thing is for sure though -- it does make your boards look
beautiful!

-p.

"Peter Johansson rockets4kids@... [Homebrew_PCBs]"
<Homebrew_PCBs@yahoogroups.com> writes:

> I can see where that would be a problem. I am only *just* making the
> jump from TH to SMD, and I'm starting with the coarsest pitch
> components I can find.

I like 0603 and 0.5mm pitch myself. But I'm "that crazy guy that makes
insanely small pcbs at home".
http://www.delorie.com/pcb/inkjet/insanity_II.html

> It would certainly be possible to drag the iron away from the pads on
> fine-pitch parts and leave them bare.

Design note: if you're hand-soldering fine-pitch SMT ICs (like TSSOP or
TQFP), make the pads on the footprints stick out 1-2mm more than normal.
This gives you some exposed pad to "drag away" any excess solder.

> I've read conflicting reports on the Liquid Tin. Some people love it,
> other people claim it provides little to no long-term protection for
> your boards and doesn't really help with soldering SMD parts either.

It reduces copper oxidation, that's all I use it for. I don't think
it's intended to help with soldering. It "helps" with SMD only because
it's not lumpy solder :-)

> One thing is for sure though -- it does make your boards look
> beautiful!

My favorite "pretty" trick is to use another layer of etch-resist film
as a solder mask, over the tin. It gives a deep blue hue to everything.
http://www.delorie.com/electronics/adapters/r8c-pillar.html

On Wed, May 14, 2014 at 10:50 PM, DJ Delorie dj@... wrote:

> My favorite "pretty" trick is to use another layer of etch-resist film
> as a solder mask, over the tin. It gives a deep blue hue to everything.
> http://www.delorie.com/electronics/adapters/r8c-pillar.html

Is there a reason you use etch-resist film instead of an solder mask
proper? I had been considering getting set up for solder mask as well
as Liquid Tin for long-term protection of my boards. I probably will
go that route (solder mask) eventually but for the short term I think
just coating with solder will do just fine.

-p.

 

Is there a reason you use etch-resist film instead of an solder mask
proper? I had been considering getting set up for solder mask as well

Dynamask film is harder to get and significantly more expensive.

Unfortunately nobody in China, and I mean NOBODY in China, seems to sell Dynamask (or any similar dry film soldermask), while dry film resist is everywhere. 

I suppose it's simply down to the PCB fabs not using dry film for solder mask, so there's no "surplus" like there is with resist.

 

Interesting.  What about the liquid stuff?  I have seen an application technique where you put a dollop in the center of your board, cover it with a piece of cellophane, and then squeegee it out to the edges.  I don't even think you need to wait for it to dry, you expose it right through the cellophane.

That's the theory.  The practice is it's a complete PITA to work with the liquid stuff, very messy, hard to get a good smooth surface without bubbles, exposure time varies radically with colour, thickness of application etc.

There was discussion on this list recently about air-brushing it on and pre-baking to dry it before exposure which would give better results, but you need to quite precisely control the temperature (apparently, I can't reproduce the results yet, don't have a good enough oven) in order to hit a temperature which will dry it, but not kill it's ability to cure.

For very small boards it's not too bad, but anything over 2 or 3cm per side, it's just frustration city for me.

Like James said, it's expensive and difficult to get. Most of the time
I don't bother with the extra step anyway.

Like the surface flatness or lack of it, the adhesion of the copper to the backing will vary with different types and brands of copper clad. I have seen some that was so bad that a 0.1" wide trace with a 0.2" pad on the end of it would almostly instantly peel off with the application of a 700 degree F iron. Almost every repair job on those boards required replacing the foil. Others are more robust and can take higher temps for longer periods with no problems.

Of course, smaller traces will lift off faster. I sometimes etch some lettering into the foil on home brew boards and I always use a fat font and the bold setting. It is best not to touch this lettering with the soldering iron.

 

At the moment I have neither laminator nor UV source

I use a clothes iron to adhere dry film on boards smaller than the iron, on a very cool setting, works well, clean and dry board (and slightly warm if it if it's cold), remove protective layer from film, smooth on with fingers avoiding bubbles, cover with paper, put clothes iron 50 to 75 degrees C on top, too hot and it will blister, wait about 30 seconds, then iron and press like your shirt for another 30s or so, paying special attention to edges.

Unless you live on Antarctica at the moment you have a UV source for a few hours a day at least :-)