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UV PCB exposure unit

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2010 - » Archive through 01 June, 2011 » UV PCB exposure unit « Previous Next »

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alec_t
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Username: alec_t

Post Number: 627
Registered: 03-2009

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Posted on Thursday, 28 April, 2011 - 08:26 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I'm thinking of making a small, cheap unit for single-side UV exposure of PCBs up to about 6in x 4in (15cm x 10cm). Any recommendations for the tubes (size, wavelength, price, UK availability)? I'm proposing to drive the tubes with ballasts stripped from CFLs (8-15 W rating).

Alec
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joe
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Post Number: 1086
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Posted on Thursday, 28 April, 2011 - 08:36 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

You can use UV LEDs:
http://hobbyelectronics.weebly.com/uv-exposure-unit.html

Or standard UV tubes; as sold by Rapid in the UK. Part number: 34-0709 - 15 Watt replacement tubes, or 34-0707 for 8 Watt tubes.

I would probably go for the smaller wattage tubes as depending on the transparencies you will be using, the 15 watt may be too bright.

Brighter is not always better.

Joe
Read my ramblings - www.techbites.com/joe-farr
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terrym
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Posted on Friday, 29 April, 2011 - 03:23 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I saw a site just recently where they used a single 5w UV LED. Worked, but exposure time was about 6 minutes.
Boards were max about 100mm square from memory.
Will post link if I can find it.

This is'nt the one I saw, but it also uses a single 5w UV LED:-

http://yveslebrac.blogspot.com/2010/11/single-led-uv-pcb-exposure-box.html

TM
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alec_t
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Posted on Friday, 29 April, 2011 - 12:22 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks for the suggestions, guys.

Alec
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mikeb
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Posted on Friday, 29 April, 2011 - 03:21 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

With s bit of thought, you could make the box a little deeper and leave space for two sheets of glass plus the pcb.

This will give you an easy transiton to double sided, which is only a matter of time.

rgds

mb
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hackinblack
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Username: hackinblack

Post Number: 544
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Posted on Wednesday, 04 May, 2011 - 09:19 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

would the UV led's actually, produce the right wavelength UV? i think they are normally used to make things flouresce under their beam,not expose PCB phototresistthough i could be (and frequently am!)wrong
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terrym
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Posted on Thursday, 05 May, 2011 - 02:29 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

They are pretty close, somewhere around 405nm as opossed to 365? or so needed for PCB's.

They just take a little longer to give the correct exposure.

TM
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joe
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Posted on Thursday, 05 May, 2011 - 06:54 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The UV resist on the board is sensitive to wavelengths around the 340nm to 420nm mark.

Traditional UV tubes emit UV light at a wavelength of around 350nm.

UV LED's (though I suppose it depends on the type of LED of course), emit at 400 to 405 nm.

Exposure time is directly related to the light output strength of the UV source, distance of the board from UV source and the type of media used for the artwork.

Joe
Read my ramblings - www.techbites.com/joe-farr

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