This post is the first of a series about building a tool to simplify the production of PCB boards at home. I was inspired by this post about using diode lasers to prepare PCBs for etching - it seemed far quicker than the toner transfer method I'm currently using (in terms of active 'hands on' time at least) and the results seem to have a much higher precision. I already have a 3D printer so I was hoping to make an attachment to the print head that would hold a laser diode and use it to prepare the boards for me.
The trouble with things like this that you find on the internet is that they cannot always be replicated - so the first step was to see if I could access a laser diode and use it to burn paint from a PCB. This post is all about that process.
I must point out that playing with lasers is inherently dangerous and you MUST take all precautions before doing so - even reflected laser light can permanently damage your eyes.
Here are some simple precautions you need to take before trying this for yourself:
- Make sure you have a pair of laser safety glasses suitable for the wavelength of laser you are going to be using. These are relatively cheap and easily available. Wear them every time you use the laser.
- Do not point the laser directly at yourself - reflected laser light (even at the relatively low powers being used here) can permanently damage your eyes, direct light can cause permanent blindness.
- Lasers generate a lot of heat in a very small area - this is a fire hazard and you need to take it into account.
Generally you should treat a laser as if it were a power tool - it's useful but if used without due caution you could easily lose a limb or a major organ.
Getting a Laser Diode
The easiest way to acquire a laser diode with reasonable amount of power is to extract one from an old DVD/RW drive. These drives will generally contain two diodes, a 300mW to 400mW red (650nm) diode and an infrared one - we are only interested in the red diode. The diodes are in a TO-18 package, it looks like a small tin can with the diode lens at the top and three legs out the bottom.
There are plenty of tutorials on the internet showing how to extract the diode but I found that not all DVD drives are the same (the images in this post are from my third diode extraction - each of the drives was different). What is shown here is repeated elsewhere on the internet but I'm trying to be as generic as possible - rather than a specific set of instruction this is more of a guide of what to look for.
NOTE: This is a time consuming process which requires some patience and care. If you are applying excessive force at any step you are probably doing it wrong, step back - take a breath - and think it through. It is very easy to damage the diode so you do need to be careful to get the optimum results.
Tools and Parts Required
Before you begin make sure you have everything you need handy. I wound up using the following tools:
- Jewellers Screwdrivers - the standard set of phillips and flat headed drivers you can buy from most hardware stores will do the trick.
- Needle nose pliers - something with a good grip and small gripping area at the tip.
- Small Wire Cutters - the wire cutter on the pliers will not be good enough, you need something with a cutting edge at the tip.
- Small Files - not your normal woodworking files, you need something small. I have a set I got from a hobby shop for working with plastic models - they work well with soft metal as well.
- Dremel - any rotary tool really. You will need a cutting disk to go with it.
- Helping Hands - something to hold small parts firmly in place while you work on them.
- Soldering Iron.
- 3V Battery Pack - you will use this to do basic testing of the diode. I used a small 2 x AA battery pack for this.
Obviously you will also need a DVD/RW drive. I recommend collecting a few (at least two) before starting. It took me three attempts to extract a completely undamaged laser diode (the first two still worked despite the damage but were not optimal). The older the drive the easier it is to extract the diode, newer drives have more compact write heads and more tightly packed components.
And it goes without saying that you have the necessary safety equipment - most importantly a pair of laser safety goggles. At various times during the process you will need to apply power to the laser diode to test it - at these times please ensure the following:
- You are wearing your laser safety goggles.
- Always point the laser away from you (one of the lasers is an infrared laser and shows no visible beam).
- Make sure there are no metal fragments or shiny material in front of the laser - you do not want any reflections coming back at you.
Step 1: Expose the Read/Write Head
This is the simplest part - the laser diodes are on a small assembly that is moved back and forward over the surface of the DVD. All we want to do is extract that assembly and leave the rest of the drive untouched. We need to expose that assembly so we can get at it and unfortunately I didn't take any photographs of this part so you will have to go by description alone. Thankfully it's pretty straightforward.
First you will need to remove the outer metal shell of the DVD drive. Usually this involves removing 4 screws that hold it into place (there may also be a plastic clip connecting the front panel to the shell that you will have to release).
Once the metal case is removed you need to open the DVD tray to give yourself a bit of room to work in. There is usually a plastic slide you can push to do this. After that you need to remove the logic board - first unplug (or cut through) any cables connected to it and then detach it from the case. In all of the drives I have worked on it is simply attached by a plastic clip, some of the examples I have seen on the internet show it attached with screws - it should be fairly easy to disconnect and remove regardless. At the end of this you should be looking at something like the image to the left.
Step 2: Remove the Read/Write Head
The Read/Write head is suspended between two metal rods (see the image above), we need to remove it from the rods and (preferably) leave everything else intact. Generally you can achieve this by undoing a few screws and sliding the assembly off the rails it is attached to.
The image to the right shows it removed (the head assembly is in the bottom left of the image). In this photo I have re-attached the sliding rod it was attached to - this could be re-used at a later date for a small plotter or CNC machine.
Step 3: Remove the Laser Diode Assemblies
When you look closely at the read/write head assembly you can see the laser diodes attached to it. These consist of the laser diodes themselves wrapped in a heat sink and some wiring attached to it. At this stage we want to remove the laser diodes and heat sinks, the wiring is not of any use to us so we can sacrifice it. It is easiest to simply cut away any connecting wires and get them out of the way first.
In most cases I've found that the heat sinks are held in place by a mix of mechanical force and some waxy substance. You can scratch away the wax, check for any screws that may be present and remove them in necessary and then gently wriggle the heat sinks away from the main assembly - what you will end up with should look like the next image.
As I mentioned earlier there are two lasers in a DVD drive - one is a low power infrared laser (and doesn't generate any visible light), the other is red diode that we really want. At this stage we need to test both diodes to determine which one is the one we want to continue working with. The remaining parts you can either discard or keep for use later - I added everything I didn't use to a junk box on the assumption it might be useful later (one of the reasons the 'Garage Lab' requires a garage and not just a cupboard).
Step 4: Identify the Red Laser
As I mentioned in the previous step you should have removed all connecting wires to the laser diodes. You may need to make use of a solder sucker, desoldering braid or other desoldering tools as well as judicious use of side-cutters to achieve this. The end result should look something like the image to the right.
You can use a simple two AA (or AAA) battery pack to check the laser output, this will provide enough power to activate the laser diode without damaging it. Before you do this step make sure that;
- The lens of the laser is pointing away from you and there are no reflective surfaces in it's path.
- Wear your laser safety glasses.
The markings on the laser aren't very clear so you will need to test each pin combination. Simply attach the ground to one pin and touch the positive wire to each of the other pins in turn; repeat this process for each pin combination until you get a result.
One of the lasers will generate red light, the other generates infrared which you will not be able to see. If you don't get a response from either diode it has probably been damaged either before or during the removal process - you will have to start again with a different DVD drive.
Step 5: Remove the Heatsink
The diode needs to be removed from the heatsink material so we can insert it into a lens assembly. They are packed very firmly into the heatsink so trying to remove it by force (just pushing it out) will only damage the head of the diode. Luckily the heatsink is made of very soft metal so the safest way to remove it is to cut through the heatsink and then peel it away from the diode.
The technique I have used with some success is to carefully cut through the thinnest part of the heat sink with a dremel using a cutting disk. You need to take some care that you don't cut into the diode itself so check how deep the cut is at regular intervals. When the cut is deep enough you can grip each end of the heatsink with a pair of pliers and peel it apart.
This process involves a bit of trial and error - if you find yourself applying a lot of force with the pliers you probably need to cut some more before trying again. The end result should be a nice (and hopefully undamaged) laser diode:
Now we have a laser diode and we have proven it works. The next step is to build a decent power supply for it, add a lens to concentrate it on a specific point and see if it can do what we want it to. I will cover these steps in the next post.