Homebrew_PCBs

Hi Stefan,

Answers to your questions...

I am still using the iron method - that fuser I got from my friend
was a dead one.

I suspect that the copper is an applied sheet bonded to the glass
with adhesives and a press of some sort. However, if the copper
sheet isn't flat, consistant thickness to begin with, then the
resulting product would have variations too.

The funny part about this last board is that the only places I had
trouble were in the areas where I remember seeing texture problems.
Furthermore, this happened to be an area of a very wide trace
(.187") and most of it didn't stick. All the surrounding traces
which were .010 ~ .015" wide were fine.

As for cleaning, I used 0000 steel wool and acetone - scrub one
direction, then 90 degrees to the original.

All around pretty strange. I have 10 sheets of this material so I
will have plenty of opportunities to investigate further :-)







--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
<stefan_trethan@...> wrote:

>
> On Thu, 02 Mar 2006 16:24:08 +0100, lcdpublishing
> <lcdpublishing@...> wrote:
>
> > Hi Guys,
> >
> > I etched a board the other day using some new PCB material I

got. I

> > did the usual cleaning and polishing process that has been

working

> > good for me. However, I did have some toner transfer problems -

and

> > even etching problems on these PCBs.
> >
> > The best I could determine is that the suface of the copper is

very

> > slightly rippled - sort of like the threads in fabric - but more
> > course. This seems to be the cause of the toner transfer

problem -

> > toner not sticking in these areas.
>
> You are seeing the glass fabric of the PCB. This is normal, and

varies

> between PCB brands.
> What do you use again to fuse the toner? I don't have problems

with _very_

> patternd boards.
> To me this seems amplified by the light reflection, there doesn't

seem to

> be much depth to it.
>
> >
> > After etching, I also found that some small spots didn't etch all
> > the way through - ie. a dot of copper is left on the board. I am
> > guessing that this was a small void in the glass backing (FR4)

and

> > when the copper was applied, it was thicker in the area of the
> > dimple - thus taking much longer to etch. Something like this, I
> > don't believe there is anything at all that can be done to

correct

> > it so I am not too concerned at this time.
>
> Well, usually they apply a foil of even thickness ;-)
> Did you think they suqeegee molten copper onto it?
>
> There probably was some "dirt" of sorts on the spot that acted as

a bit of

> a resist.
>
> >
> > Howver, the toner transfer process seems to require that you

have a

> > smooth and flat surface for good transfer and adhesion. If I

had a

> > micro scope, or some such device, I would look much more closely

at

> > the surface texture of the copper to validate this. With the

naked

> > eye, or even a loupe, I can't really see much deformation on the
> > surface. I do suspect though, that even a deformation of .0001"
> > would be enough to cause problems.
>
> i can see the pattern well on some boards, but it never seemed to

be a

> problem.
>
> >
> > When pressing the paper onto the PCB, I use a paper based shop

towel

> > between the iron and the PCB to act as a pad and to also help
> > accomodate surface irregularities. However, I am going to look

for

> > something that will work better.
> >
> > I guess what I am saying is this. The next time you get "Missed
> > spots" with toner transfer, take a really close look at that

area on

> > the copper to see if it is in fact flat and smooth.
> >
> > Chris
>
> Certainly requires further investigating, but i don't think the

glass

> pattern is causing your problems.
>
> ST
>