Homebrew_PCBs

How much overexposure (%?) can cope the UV sensitive coated PCB, please?
Cristian

Impossible to say, it depends on the opacity of your mask and how fine
your traces are.
Usually one does a step test, where a strip of mask is withdrawn or
uncovered step by step in timed intervals, to determine the ideal
exposure.

<https://www.youtube.com/watch?v=iIb8l2fccRE>

ST

On Thu, Jul 7, 2016 at 4:59 PM, Cristian crissstian@...
[Homebrew_PCBs] <Homebrew_PCBs@yahoogroups.com> wrote:

> How much overexposure (%?) can cope the UV sensitive coated PCB, please?
> Cristian
>
>
>
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> Posted by: Cristian <crissstian@...>
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At 08:16 PM 07-07-16, you wrote:

>
>
>Impossible to say, it depends on the opacity of your mask and how fine
>your traces are.
>Usually one does a step test, where a strip of mask is withdrawn or
>uncovered step by step in timed intervals, to determine the ideal
>exposure.

My question was about the amount (% or so) of the tolerated
over-exposure (over the normal exposure), if available, not about
how to determine the right exposure.
Sorry,
Cristian

"Cristian crissstian@... [Homebrew_PCBs]"
<Homebrew_PCBs@yahoogroups.com> writes:

> How much overexposure (%?) can cope the UV sensitive coated PCB, please?

Along with "it depends" - some anecdotal information...

When I was calibrating my UV box (get a transmission step wedge, they're
cheap and you'll know you're doing it right) I found that +- about 2-3
steps would still come out usable. That works out to a 50% to 200%
exposure.

So there's a pretty big range of "works" with a smaller sweet spot in
the middle that you should aim for.

>
>When I was calibrating my UV box (get a transmission step wedge, they're
>cheap and you'll know you're doing it right) I found that +- about 2-3
>steps would still come out usable. That works out to a 50% to 200%
>exposure.
>
>So there's a pretty big range of "works" with a smaller sweet spot in
>the middle that you should aim for.

Thanks, dj.
That means 100% overexposure-good news for me.
I work to use a Blu Ray module with my CNC PCB milling machine (CCD2
made in Germany by Bungard).
Cristian

"Cristian crissstian@... [Homebrew_PCBs]"
<Homebrew_PCBs@yahoogroups.com> writes:

> That means 100% overexposure-good news for me.

No, that means if you're off by 100% from the sweet spot, you'll start
having problems in some boards. It's easy to find the sweet spot, and
IMHO stupid to skip that step, since it's so cheap and easy and make
sure your boards *always* expose properly.

If you don't have one, buy one of these (T2115, the 21-step version):
http://www.stouffer.net/TransPage.htm

It's $7 plus shipping and will save you a lot of headaches.

At 11:18 PM 08-07-16, you wrote:

>
>
>
>"Cristian crissstian@... [Homebrew_PCBs]"
><Homebrew_PCBs@yahoogroups.com> writes:
> > That means 100% overexposure-good news for me.
>
>No, that means if you're off by 100% from the sweet spot, you'll start
>having problems in some boards. It's easy to find the sweet spot, and
>IMHO stupid to skip that step, since it's so cheap and easy and make
>sure your boards *always* expose properly.
>
>If you don't have one, buy one of these (T2115, the 21-step version):
>http://www.stouffer.net/TransPage.htm
>
>It's $7 plus shipping and will save you a lot of headaches.

I'll never under-expose. Is not possible.
My problem is that at the beginning of a trace will be a little over-exposure.
First the UV is ON and after a while it moves = overexposure.
My UV source is moving to expose that trace.
Cristian

And what's around it?

ST

On Sat, Jul 9, 2016 at 5:22 PM, Cristian crissstian@... [Homebrew_PCBs]

> My UV source is moving to expose that trace.
> Cristian
>
>

At 07:25 PM 09-07-16, you wrote:

>
>
>And what's around it?
>
>ST
>
>On Sat, Jul 9, 2016 at 5:22 PM, Cristian crissstian@... [Homebrew_PCBs]
>
> > My UV source is moving to expose that trace.
> > Cristian

My concern was: is the overexposure negative or the UV coating will accept it?
And how much.
I've got the answer.
Cristian