Homebrew PCBs

Hello, I'm new to this group, though not new to electronics.  Does anyone out there have experience with exposing a photosensitive board through a negative to sunlight?  A man at Injectorall told me that about six minutes at noon on a bright sunny day but that doesn't seem to work.

No idea but I doubt it will work well even if it does work.

A UV light box is cheaply made or bought, and will give much faster and consistent results. Waiting for a bright midday sun is just going to annoy you.

Otherwise, consider the Toner Transfer method. If you've got a laser printer you've already got half of what you need - then you just need a laminator (preferred) or some skill with a clothes iron.

I prefer that method as there's less chemicals to buy etc.

--- In Homebrew_PCBs@yahoogroups.com, James English <jimenglish123@...> wrote:

>
> Hello, I'm new to this group, though not new to electronics.  Does anyone out there have experience with exposing a photosensitive board through a negative to sunlight?  A man at Injectorall told me that about six minutes at noon on a bright sunny day but that doesn't seem to work.
>

Probably depends on your latitude to some extent, James but 6 minutes 
might be too short an exposure.

I have used the method a couple of times but it is very hit or miss. For 
example, a cloud can drift over and greatly reduce the amount of UV 
light available, even on a bright day. Actually on my last attempt, one 
of the family cats decided that the exposing pcb would be a good place 
to take a nap, totally ruining the exposure.

At my latitude, around 41 degrees South, I was using times more like 15 
minutes, from memory.

Bill

On 8/05/2011 9:01 AM, James English wrote:
> Hello, I'm new to this group, though not new to electronics.  Does anyone out there have experience with exposing a photosensitive board through a negative to sunlight?  A man at Injectorall told me that about six minutes at noon on a bright sunny day but that doesn't seem to work.
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
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[Non-text portions of this message have been removed]

I've done it not with Injectorall but with Kinsten,  I was able to expose for 
2-2.5 minutes of very bright sun.  Works ok but yield is not good.  If you can 
tolerate some scraped attempts it might be ok.  


Good Luck, Tom

For those interested in youtube videos of my Homebrewed Printed Circuit Board
fabrication, PIC chip experiments, High powered LED projects, Arduino
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Back from Silicon Valley _ LeCroy WaveAce 112
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________________________________

From: James English <jimenglish123@...>
To: Homebrew_PCBs@yahoogroups.com
Sent: Sat, May 7, 2011 7:01:17 PM
Subject: [Homebrew_PCBs] Length of sunlight exposure of photosensitive boards

  
Hello, I'm new to this group, though not new to electronics. Does anyone out 
there have experience with exposing a photosensitive board through a negative to 
sunlight? A man at Injectorall told me that about six minutes at noon on a 
bright sunny day but that doesn't seem to work.



[Non-text portions of this message have been removed]

On 08/05/2011 00:01, James English wrote:
> Hello, I'm new to this group, though not new to electronics.  Does anyone out there have experience with exposing a photosensitive board through a negative to sunlight?  A man at Injectorall told me that about six minutes at noon on a bright sunny day but that doesn't seem to work.

It depends where you are, to some extent. I think it takes a lot longer 
than that.

Make yourself a UV exposure unit like this one of mine:

http://www.leonheller.com/Photos/UV%20unit.jpg

It'll work a lot better.

Leon
-- 
Leon Heller
G1HSM

--- In Homebrew_PCBs@yahoogroups.com, Leon Heller <leon355@...> wrote:
>
> On 08/05/2011 00:01, James English wrote:
> > Hello, I'm new to this group, though not new to electronics.  Does anyone out there have experience with exposing a photosensitive board through a negative to sunlight?  A man at Injectorall told me that about six minutes at noon on a bright sunny day but that doesn't seem to work.
> 
> It depends where you are, to some extent. I think it takes a lot longer 
> than that.
> 
> Make yourself a UV exposure unit like this one of mine:
> 
> http://www.leonheller.com/Photos/UV%20unit.jpg
> 
> It'll work a lot better.
> 
> Leon
> -- 
> Leon Heller
> G1HSM
>
                I have got a face tanner,,guess its the name..hmm
Philips make them with 4 small tubes.. get them in a flee market..I payed same amount as 3 pound for such a tanner. and it takes around 3 minutes to exposure in a distance of 13 cm..and there are a timer build in too.. have not used it as I'm not sure its acurate enough.
alex

One very important aspect is how you make the negative?  I am using Vellum 
drafting film trade name is  "Clearprint" or "Dietzen" brand.  I am curious what 
otheres might be using to make there negatives with?


For those interested in youtube videos of my Homebrewed Printed Circuit Board
fabrication, PIC chip experiments, High powered LED projects, Arduino
applications, QRP kit builds, and Electronics Tourism, Please take at look and
subscribe to my new improved youtube channel "Hamradio2008"
link...
http://www.youtube.com/user/HamRadio2008
heres a current video; Back from Silicon Valley:
Back from Silicon Valley _ LeCroy WaveAce 112
http://www.youtube.com/watch?v=MQ2-a1oB57Q

 



________________________________

From: Leon Heller <leon355@...>
To: Homebrew_PCBs@yahoogroups.com
Sent: Sun, May 8, 2011 6:23:56 AM
Subject: Re: [Homebrew_PCBs] Length of sunlight exposure of photosensitive 
boards

  
On 08/05/2011 00:01, James English wrote:
> Hello, I'm new to this group, though not new to electronics. Does anyone out 
>there have experience with exposing a photosensitive board through a negative to 
>sunlight? A man at Injectorall told me that about six minutes at noon on a 
>bright sunny day but that doesn't seem to work.

It depends where you are, to some extent. I think it takes a lot longer 
than that.

Make yourself a UV exposure unit like this one of mine:

http://www.leonheller.com/Photos/UV%20unit.jpg

It'll work a lot better.

Leon
-- 
Leon Heller
G1HSM



[Non-text portions of this message have been removed]

James English <jimenglish123@...> writes:
> Does anyone out there have experience with exposing a photosensitive
> board through a negative to sunlight?

Sunlight is very variable, but in general, anyone doing UV exposure
should have a "transmission step wedge" - this is a plastic film with
various calibrated shades of grey printed on it.  Using this, you can
calibrate *any* UV source and, with a little math, figure out the ideal
exposure time in one trial run.

http://www.stouffer.net/TransPage.htm - you want T2115 as that's the
most common one to see on film specs, and it's only $6.55.

http://www.thinktink.com/stack/volumes/volvi/filmimag.htm#Photo_resist
for instructions on how to calibrate.

For initial exposure testing remove the variable of the negative by instead
placing guaranteed opaque objects on the photosensitive layer.

For example place a coin and maybe black electrical tape.

It is easy to be fooled by a poor negative that is partially transparent.

 

Also do a step exposure.  Double the exposure time for each test.  You could
have multiple little PCBs or just one and selectively cover areas for the
same result.

Expose the whole board for let's say one minute.

Cover one section of the board with a second PCB or something opaque.

Expose the rest of the board for another minute and then cover up an
additional section.

Expose the rest of the board for 2 minutes, cover up...

Expose for 4 minutes, 8 minutes, 16,  .

After development you can see how long time is needed for the exposure.

 

Afterwards you need to evaluate your negative to see how much light you lose
and how transparent the black it is.  Ideally you should not lose anything
and it should block 100% in the black areas.

As DJ suggested, a step wedge is very useful and a big timesaver.  When I
used to do PCBs I always included one on the edge of the PCB to verify that
the process is under control.

 

As many have suggested, there are lots of UV sources that are repeatable and
works 24 hours a day.

Bertho



[Non-text portions of this message have been removed]

On 08/05/2011 12:32, Tom Biery wrote:
>
>
>
> One very important aspect is how you make the negative?  I am using Vellum
> drafting film trade name is  "Clearprint" or "Dietzen" brand.  I am curious what
> otheres might be using to make there negatives with?

I print my positives on Mega Electronics JetStar Premium film using a 
cheap HP inkjet printer. They work very well.

Leon
-- 
Leon Heller
G1HSM

On 08/05/2011 12:55, DJ Delorie wrote:
>
> James English<jimenglish123@...>  writes:
>> Does anyone out there have experience with exposing a photosensitive
>> board through a negative to sunlight?
>
> Sunlight is very variable, but in general, anyone doing UV exposure
> should have a "transmission step wedge" - this is a plastic film with
> various calibrated shades of grey printed on it.  Using this, you can
> calibrate *any* UV source and, with a little math, figure out the ideal
> exposure time in one trial run.

I found the optimum exposure for my process by sliding a piece of 
cardboard across a test piece of laminate with a test piece of artwork, 
moving it at 1 minute intervals.

Leon
-- 
Leon Heller
G1HSM