DIY PCB (printed circuit board)

 

This is my DIY PCB tutorial, I am going to do a walk through of creating a printed circuit board for a reprap. Specifically it is the PCB for the Gen 7 electronics version 1.4.1. I’ll also make some some opto-stops and expansion boards. This are just examples though, this technique is used for making all manner of printed circuit boards.

Here is a picture of my very first printed circuit board, it was just a simple little buzzer circuit made with an oscillator circuit driven by the famous 555 integrated circuit. It sounds like a British siren, only the frequencies were off by just the right amount to make it annoying as hell.

buzzer_1buzzer_2

 

The first thing we need to do is create artwork for the PCB ( printed circuit board ). This is done with software like Geda, Eagle, and some others. For a lot of projects though you can simply download the artwork that you need, with the Rep Rap, you can get the artwork from github. Once I’ve got the artwork in an image file the first thing I usually do is print it out on ordinary paper, then I take some of the parts I have and hold them over to make sure they look like they are the correct size. I find it is easiest to not mess around with numbers and converting between units and what not, rather just print some out and then scale the image using the percentage on the print properties page.

 

artwork_for_etching_3

artwork_for_etching_2

 

 

Once I’ve got the print out at the correct size, then I load some of the clear plastic film into the printer. Overhead transparencies are what you need for this, you can get them here.

 

transparencies transparencies_2

 

There are three steps to making your own printed circuit board,

1) making the artwork

2) developing, and etching.

3) drilling and soldering

 

When I first started making my own circuit boards, I bought this photo-fabrication kit, UV light, and etching kit.

First you’re going to need a pre-sensitized copper plated circuit board. You need some kind of ultraviolet light to expose the Photo-resist. The back of the package of the pre-sensitized board tells you how long you need to expose it for. The one I used was eight minutes.

presensitized_boards_3 presensitized_boards_2

 

For the developing step, I use a small plastic bin. you want to mix one part developer to 10 parts water, if you’re just making a couple of boards I find it works great to use one cap full of developer to 10 cap fulls of water. Then we take the exposed board and dunk it into the developing solution. I use a small foam brush to clear off the photo-resist.

developing_1 developing_2 developing_4

developing_14 developing_12 developing_10

 

Here is what the final result looks like.

developing_17

 

The next step in the process is etching, you are going to need Ferric Chloride or Ammonium Perchlorate to do this, I’ve always used ferric chloride and it works really well. You want to make sure you wear some rubber gloves and safety glasses when using this stuff I’ve got a little bit on my skin and it doesn’t seem to bother me but it’s not something you want to do. It’s also very messy and will stain pretty much anything it touches. I keep mine inside a plastic container, which is then kept inside a large plastic bin. This stuff will cause nearly any metal to rust, so you want to keep only plastic parts and contact with it.

In order to etch the circuit board, that is remove copper everyplace the photo-resist is does not remain, it’s simply a matter soaking it in the ferric chloride solution. The amount of time it takes to etch depends on 3 things

1) The temperature of the etching solution,

2) How long you have been using that batch of solution.

3) How much aeration or agitation you have


Eventually the solution will get saturated with copper and stop working, or just become painfully slow. This is quite a large amount I have here. I’ve made dozens of circuit-boards with it, and it has not slowed down a bit, also you want to use aeration, that is blowing bubbles in the solution while it etches.

In my experience the temperature of the solution is the most important factor, if you get your solution pretty warm to nearly hot it will etch fairly quickly. A board of the size is fully etched in about 15 minutes, it can take up to an hour the solution is not warm.

I find the easiest way to warm the solution up is just to take the container containing the ferric chloride, and soaking it hot water, here am using a small waste can that’s a little bit larger my container, that I’m using the hottest water that my tap can provide, then I let it sit for about 10 or 15 minutes, then dump the water out and repeat a couple more times.

 

etching_3etching_2etching_1

 

Here’s what it looks like partly through etching, it’s not quite finished but were getting there.

etching_6

Here’s what the final etched board looks like, next were ready to drill holes.


etching_8etching_34etching_31

 

This is actually a bit harder than it sounds, because these holes are very small and you need to specialty drill bits to do it, even the smallest drill bit that you usually find it Home Depot is much too large. You will need to buy drill bits made specifically for this purpose, take a look here.  You also need to be careful because drill bits this small are very easy to break. You really want a small drill press for this.

drilling_3 drilling_6drilling_1

Once the holes are drilled, we are ready to start soldering parts. I find it works best to use a little piece of Scotch tape when starting out, get one or two terminals soldered in, then you can take the tape off and solder the rest. I’m not going to show every little part getting soldered in, but here a series of pictures that highlight it.

pcb_assembly_3pcb_assembly_7

pcb_assembly_25pcb_assembly_27pcb_assembly_29

 

the soldering is a little bit more difficult with a board you manufacture yourself, soldering on to the bare copper takes a little more finesse than the green boards you’ll likely get with a kit. It helps to use very small solder, keep the tip of your soldering iron clean, and always practice on some scrap boards before diving in to an actual project.

 

 

 Posted by at 12:27 pm

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