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In this instructable I will show you how I made a simple and expandable UV LED exposure unit. Exposure unit is a necessity for anyone who wants to make PCBs with the Photographic method. It will allow you to make high quality PCBs in no time. This is project is a great for beginners because of it's simplicity.

WARNING: Never look directly at UV light as it might damage your eyes.

Step 1: Photographic Method of Making PCBs

I did not make this video.

If you are not familiar with this method you can find out about it in the video above.

Although he said you can use a CFL bulb for exposing, you might not get as consistent and fast results as with LEDs. Nevertheless I encourage anyone to find out which method works for them.

Step 2: Parts List

For one small exposure unit you will need:

some perfboard such as this 9x15cm or this 18x30cm. I would recommend the bigger one so that you don't need to connect multiple modules as I did.

1x - step up DC-DC converter such as this XL6009 boost converter

1x - 12V-32V wall adapter

60x or more - UV LEDs - I recommend the flat top ones because they have beam angle of 120°. That means you can space them farther from each other so you don't need as many of them. Don't buy exactly the amount you need because some of them might not work.

6x - 150 Ω resistor

1x - 2.1mm female power jack

4x - M3 screw 6mm long

2x - M3 screw 10mm long

6x - M3 nut

4x - long M3 male standoff/spacer or you could use anything that does the job(long screw etc.)

hookup wire

Step 3: Schematic

The exposure unit is a very simple device that consists of just a power supply and LEDs with current limiting resistors.
The voltage drop of an UV LED is in the range of 3.2 V to 3.8 V and if we put 10 of them in series that means we need a power supply capable of outputting up to 38V. Although it turned out that the voltage drop of my LEDs was a bit lower so 31V was enough for me. But you never know what LEDs you will get. Therefore I recommend to set the voltage of the converter lower and instead measure the total current drawn by the module. The LEDs are rated for 20mA continuous current but I've found out that their brightness at 5mA is enough for me. It should also increase their lifecycle if we run them on lower current.

So start with the lowest voltage set on the boost converter and increase it until your ammeter is showing 5 mA x 6 rows = 30mA.

Once the boost converter's voltage is set you can remove the ammeter.

Step 4: Expand It

If you need to expose bigger PCBs you can build more of these modules and connect them together. Just make sure that their total current draw suits the equation (5mA) x (number of rows) = total current. This bigger one draws 90mA.

Step 5: Conclusion

At first you will need to experiment with the time of exposure until you find the right one. Mine was 1 minute and 30 seconds.

Now you should know what an exposure unit is and how to make one.

If you manage to build one don't forget to post pictures of it in the comments. Good luck.

<p>Seems like a neat idea, just worried about how even the light is, have you tried it, does it work? Can you wash away all the coating you planned to?<br>Maybe board or UV panels need to be moving to get an even exposure?<br>Other questions are, is the light strong enough, how long does it take for an exposure? <br>I have only handled professional equipment and homemade versions with fluorescent tubes before. Haven't explored the option with UV-leds. <br></p>
<p>You'r right, howewer I made my comment because them most people don't have a 36V PS. Allmost ewerbody got some sort of a 12~24V power supply, that's why another kind of grouping.</p>
<p>I don't see a problem in using a 12-24V wall adapter and then boosting it with this <a href="http://www.ebay.com/itm/DC-DC-Boost-Buck-adjustable-step-up-down-Converter-XL6009-Module-Solar-Voltage-/161270864741?hash=item258c7e1b65:g:-soAAOSw9GhYfJW8" rel="nofollow">boost converter</a>. I think that it is worth the 2 dollars.</p>
<p>You are so right. How &quot;stupid of me&quot;? I kind'a missed that with a booster. It's absolutely correct as You discribe it. </p><p>1 question: what kind of UV-led you used? UVA or UVB or could there be some pros. by using a &quot;mix&quot; of both. Gonna absolutely build one and &quot;add&quot; a timer there. For now I have a &quot;555&quot;/relay based timer for my 300W &quot;Solar UVA&quot; lamp, (yes, you read it right, three hundred Watt), :)</p>
<p>I actually used these <a href="http://www.ebay.com/itm/100pcs-F5-5mm-Round-Ultra-Violet-LED-UV-Light-390-395nm-Purple-Lamp-/400985315501?hash=item5d5c9658ad:g:9csAAOSwBP9UWtyX" rel="nofollow">UV LEDs</a> but as I said in the instructable, they don't have as wide beam angle as the ones I recommended, so if I were to build this again I would probably use the flat top ones, although they are twice as expensive.</p>
<p>Although the UV light on the picture is not as uniform, I am able to expose the board evenly without moving the panels. The exposure takes 1 minute and 30 seconds.</p>
<p>I made one similar to this a while ago, it works very well, so UV LED's certainly work. My power supply is different though, I published the schematic here (PDF in step 1): </p><p>https://www.instructables.com/id/Somewhat-Complete-PCB-Fabrication/</p>
<p>Hi. Niiiice job. Just some propose&rsquo;s: I would rather make them pattern&rsquo;s, (column&rsquo;s), with 5 in each, thus gaining to use &frac12; of the Voltage e.g. instead of ~38V you need only 18V or use pattern&rsquo;s of 3 = 3,3V*3= 9,9V and use a 12V power. Of course the layout would be a bit more complicated but not much, (just a couple more resistors and wiring). This allso gives you the benefit of need to drop the voltage just 12V - 9,9 = 2,1V with the resistors, and this way you get the poss. to use higher mA with less power loss. </p>
<p>actually the resistors drop very little voltage, remeber that if there is 10 LEDs in series and suppose that each LED has a voltage drop of 3V then there would be 30V dropped across the LEDs. </p>
<p>Nice job. I&rsquo;ve been making of these photores. PCB&rsquo;s for decades (~ 30+ years), both single- &amp; double sided. Yet, thanks to You, I&rsquo;ll got some good hint&rsquo;s here. <br>I&rsquo;ve be&rsquo;n allways using a &rdquo;solarium UV-light&rdquo; but that&rsquo;s NOT practical thus be&rsquo;ing a 300W one. Gonna build a LED-frame like Your&rsquo;s.<br>Some hint&rsquo;s from my behalf: <br>1. After developing, rince the PCB under such hot water You ewer can, thus making the PCB-copper to be warm. This decreases the etch time. <br>2. I use to clean the PCB from the resist &rdquo;before&rdquo; drilling, and I&rsquo;ll do that with &rdquo;technical pure aceton&rdquo;, because the nail-polish-remover has oil in it, and that&rsquo;s not so good.<br>3. If You use &rdquo;acid&rdquo; etching, put the PCB facing down in the bath, reason: in the reaction it creates gas-bubbles &amp; lift&rsquo;s up the board so the etch-side isn&rsquo;t in the etchant. This method allso results in pro: them bubbles tend to move around the board a bit, thus giving ewently contact with the etchant.<br>4. Making double sided ones. The main problem is to get them both sides aligned? <br>Well, in Your layout-design make some guide-holes of a size ~ 0,8mm in the corners. On them &rdquo;both&rdquo; film&rsquo;s, punch holes in them guide markers with a needle, (of course You can use some of them component-holes if You don&rsquo;t have guide-holes).Tape the first layout on the board, (say the solder side), drill them holes for them guide-holes , (use a small hole e.g. 0,8mm.) . Put drill bit&rsquo;s in them holes, place the top layer film in place by using them drill bits to go through them punched needle-holes, and tape it in place, (remember to remove them bits before continuing  ).<br>5. Now it comes to &rdquo;saw&rdquo; the PCB to it&rsquo;s actual size. I used to saw them PCB&rsquo;s with a hacksaw with a &rdquo;pain&hellip;. pain&hellip;pain&rdquo; never getting quite good reults, (allways had to file them to acchive good result). Until I read a instr. : &rdquo;Use a box-cutter knife &amp; a metallic ruler, then make several cut&rsquo;s on both sides along the same line, (if there&rsquo;s copper where You&rsquo;r cutting, make sure to cut at least through the copper), then just bend the PCB against ex. Your table edge, and &rdquo;crack&rdquo;, (the noice, not the stuff)&rdquo;, and voil&aacute; You got a nice cut-out .<br>6. I&rsquo;ve even made double sided PCB&rsquo;s with another methode, with succes. I bought of them resistive board&rsquo;s with a thicknes of 0,8mm. Made them separately as one sider&rsquo;s. Keep in mind with this methode; the TOP-layer has to be &rdquo;mirrored&rdquo;. My &rdquo;pcb-design&rdquo; program allows this to be done. Then I drilled them both, (separately). Then &rdquo;sandwitched&rdquo; them, no glue no nothing needed, just put some components in place and solder them. NOTE a con. here: this isn&rsquo;t plated through, so, some component&rsquo;s &rdquo;cower&rdquo; them pad&rsquo;s so You can&rsquo;t solder them from the component side pad, thus not create connection with both sides. Allso remember Your &rdquo;via&rsquo;s&rdquo;.<br>Your instr. Was GREAT  </p>

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