dimanche 28 novembre 2010

Single LED UV PCB exposure box


  • 1 UV LED
  • 1 LM117 (TO3)
  • 1 RESISTOR 1ohm 2W
  • 1 Piece of wood
  • 1 Piece of Aluminium
  • 1 Piece of plastic (transparent)
  • 2 magnets
Having seen several attempts to make a PCB exposure box with LEDs instead of tubes, i decided to make my own.
I wanted a smal one because i make prototypes one of a kind pcbs, and they are always small.
One wich could hold an arduino shield would be large enough.
Other projects i saw are using a large number of low power uv leds wich are in the miliwatt range. 80 Leds seems to be the minimum number to achieve 1W of UV radiated power, wich is what is needed to expose the PCB in a decent time.
This big number of leds needs a big PCB with a big number of holes and solder, and i don't like holes !

So i decided to use a single high power UV led.

The LED is 5W and is the higest power i could find at an affordable price.
It can output up to 1.5W of 400 nm UV radiation at 1500mA.
With high power leds, you should not mess with the current, moreover if you want to push it to the limits. If you go over 1.5A, it will bee VERY hot and its life much shorter than the expected 100.000 h. If you go below, you will have only a fraction of the expected output.
Never use a constant voltage driver, but use a constant curent one.
For this first test, i used a simple classic linear curent injector with a LM117.

This is the schematic of this simple regulation
The Vin supply comes from a wall adapter and can bee between 7V and 12 V DC with at least 1.5A. With 12V the LM117 can become quite hot without a heatsink, but it is ok because it is not used for a long time. A switching regulator would be better, but our main goal was simplicity.

The "mechanical" part is also very simple.

I cut a wooden board 16 X 16 cm for the base, and in the center i made a recess to accommodate the PCB. I did fill this recess with foam slices to press the PCB against the cover when it is closed.
The cover is a 8 X 14 cm acrylic rectangle inserted in an aluminium tube which serves as a hinge.
A magnet is inserted in the base and anoth
er on is glued to the cover.

Support for the LED, which is also its heatsink, is made from a folded piece of aluminum. The LED is screwed at the top. The aluminium plate is the ground return, there is only one wire going to the led.

The LM117 is glued to the board upside down and the 1 ohm resistor is soldered directly on it.
A power switch is also glued on the base and a DC jack for the power supply.

This first "proof of concept" has no timer built in, but this will be added in the next release with the help of a Tiny45.

I was really positively surprised by the result.
I used simple laser printed transparent sheet and an exposure time of 2 min for the few tests i made.

First board is an arduino shield which has big traces and is easy, but the second one with 0.5mm pitch chip and 10 mils traces is a real test and was a 100% succes.

Thank you HackADay for posting this.

From  the comments  i read on HackAday, i must give some more details.
Of course, the UV light does not remove the copper !

I use Pre-Sensitised Copper-Clad Board.

After exposure i develop it (liquid NaOh diluted in water 1/10), about 1 min.

Next, i etch it with a 5/1 mix of HCL (chloridric acid) and H2O2 (oxygen peroxyd), 3 to 5 min.

18 commentaires:

  1. very useful, good idea!

    what is the reference of the led ?

  2. What is the distance betwen LED and PCB? many thank, very usefull!

  3. those boards look really nicely done. fantastically simple and very usable. just like things should be done. well done and thanks for sharing

  4. the distance is 10 cm, it could be increased to cover a wider pcb.For example 15cm should cover a full eurocard. Just put a sheet of paper under the led to see the spot, but it is important to have uniform coverage, my dimension where based on a 40° angle to have less than 15% intensity delta between edges and center.
    Some Fresnel lens could help to reduce the distance, but what for ? you need to be able to open the cover!

  5. Hi, 10 mils trace is really good :) where you buy the led!?

  6. Hi,
    Nice design !
    I'm from Kortrijk (West-Vlaanderen) who's your supplier for the LZ1-10UA05??

  7. Sounds good, thanks for your work, i am sure this information will be helpful for all of us in getting our work done, keep us update with new updates.

  8. WOW, thanks for posting such an informative post, i am really glad to check out this information, i am also looking forward for more updates, keep posting.

  9. Low power leds are much better then high power, its time and money also. However your blog contain a lot of useful information.

  10. Congrats on your success i have also try to work with PCB box but after many tries i was not successful, but now i think i will do this after getting some ideas from your post.

  11. Awesome stuff, thanks a lot. They gave me more ideas for new projects that are coming up…

  12. The Vin accumulation comes from a bank adapter and can bee amid 7V and 12 V DC with at atomic 1.5A. With 12V the LM117 can become absolutely hot after a heatsink, but it is ok because it is not acclimated for a continued time. A switching regulator would be better, but our capital ambition was simplicity.to

  13. I've been thinking about building an exposure box that would utilize high powered uv leds. Just for the simple fact that I wouldn't have to use many of them. I'm tryig to figure out how many of these leds to use as well as how to diffuse the light evenly.

  14. I didf built one as per your advice, worked very good, so thanks for that. Now finding a replacement LED is not that easy, the existing one seems to got out of production, just bouht a similar one from mouser , but onl 700mA. Not that good at electronics, but can figur out that the R needs to change. Any comments to this new LED

  15. Hi, good design, worked ine until I be misstake fried my LED. Trying to find a new but the model seems gone out of business. Find a other Power LED, but only 700mA, any comments?

  16. It's good to see this information in your post, I was looking the same but there was not any proper resource, thanks now I have the link which I was looking for my research.

  17. Excellent post. I want to thank you for this informative read. Keep up your great work.