Keyword: print the circuit, pcb, printed pcb circuit board, PCB developer
Although i linked to some DIY tutorials on printed pcb circuit board making in the past, i decided to write my own tutorial to cover all the bits and pieces so that any beginner with no knowledge can obtain a PCB using the photo etching method. Lets start with the tools and materials i used:
Canon MP160 Ink-Jet Printer
Transparent paper for Ink-Jet printer
Photo PCB (this type of PCB already has that photo-resist layer applied on it )
UV Exposure unit
Developer (I used this custom PCB developer)
Ferric Chloride
Acetone
A piece of glass (preferably taken from a photo frame)
Electric Driller
I got the materials by ordering online at an electronics hobby shop from my country, but they are available at any electronics hobby shop.
WARNING: The ferric chloride and the developer are dangerous chemicals so do not try this if you dont know what youre doing.
The first step is to design your desired PCB circuit board in one of the many available PCB designing software. I used Eagle, and i recommend you use it too, its pretty simple to work with and in Shareware version you can use it for non profit with the following limitations:
The usable board area is limited to 100 x 80 mm (4 x 3.2 inches).
Only two signal layers can be used (Top and Bottom).
The schematic editor can only create one sheet.
I designed a small test board, just for the purpose of this tutorial. Its a PIC16F877 with every pin linked to a connector. Im not gonna present the designing of the circuit in this tutorial because there are many well documented resources on this subject available on the web.(just use google)
The second step is to print the circuit on the transparent paper. We start by preparing the printer for printing on transparent paper. You need to go to Printing preferences and on Media type if you have the option Transparent Paper select that, if not which is my case too, you can use High resolution paper or even Photo Glossy Paper.
Next on Print Quality if you have both black & color cartridges installed, select High and dismiss the following step. If you only have Black cartridge you should select Standard and follow the next step. On Color intensity select manual and click Set , now move both Intensity and Contrast sliders all the way to the right. Now you can click ok and again ok to close the printing preferences panel.
(as a note: on High print quality setting the printer uses both color and black cartridge to create the black color and the result is good enough so that we dont need to mess with the color intensity and contrast. On Standard print quality, the printer only uses the Black cartridge to create the black color, so we need to enhance it a bit. If you have a more expensive printer its possible that none of these setting need to be made, you just select transparent paper and youre done)
The next step is the actual printing and we will start by printing on a normal sheet of paper just to see if everything is ok. After youve placed the paper in the sheet feeder open Eagle go to File and hit Print.
In this windows select the Black option, this option will print our board black. If you hit ok your printing should start, and the paper should start to appear.
If everything looks ok on normal paper, its time to print it on transparent paper. I got my transparent paper from a local printing center for $1 a piece but these days you can get it from many places, from online shops to electronics hobby stores. The one i bought has this thin strap of paper on the opposite side of the printing face. This means that this kind of paper can only be printed on one side.
The correct side can also be determined by touching the paper with your fingers; you should feel something a bit sticky on the correct side for printing, while the other side feels like plastic. After youve placed the transparent paper into the sheet feeder just as with normal paper go to File > Print and hit Ok. After the printing is done, be careful not to touch the printed section of the paper when you reach for it. Now you should let it to dry on a horizontal surface for 5 to 10 minutes.
Although you cant really see this in the picture, the printing quality was not too good, so in order to get better results with the PCB i decided to print again. To do that you need to place the transparent paper in the sheet feeder in the exact same position. Next in Eagle, go to File > Print and click Page. From this menu we can control the place where the circuit will be printed on the paper. We can control 3 positions on vertical axis and 3 on horizontal axis. The default setting is Vertical:Top , Horizontal:Left. If you want to print next to the first circuit printed earlier, you just have to select Center on the Horizontal axis.
For better results i recommend using 2 pieces of transparent paper with the same circuit, layered one on top of the other. Now, this depends on the power of the UV lamp your using for exposing. Mine is 125W so if i use a single sheet of transparent paper the light could go trough it and damage my circuit. Thats why i need to use 2 pieces of paper. If you need to print an additional circuit on the same paper just wait for the previous one to dry, than load the paper into the printer and change the horizontal setting to Right. This is how it should look after the third printing. (under the transparent paper is the first printing on normal paper).
The next step is cutting the paper and obtaining 2 identical circuits that were gonna place one on top of each other. (were going to discard the one in the left, the one with poor quality). You should be careful when cutting the paper, because you can easily damage the ink.
Now you should have 2 pieces of transparent paper looking like this:
For the next step Im using a 913 cm glass panel that was removed from a photo-frame costing approximately $2. Why from a photo-frame ? because its really thin and light, we dont need any bulky piece of glass to work with. Here is a picture with my glass panel.
Next you have to align the two pieces of paper one on top of each-other, a very precise operation, and secure them on the glass panels surface. You can do this by using some transparent sticky tape. Be careful on which side you place the pieces of paper when you secure them to the glass panel because if you place them on the wrong side you will get your circuit mirrored.
The next step is to prepare the PCB. As i mentioned in the materials list Im using photo PCB, this means the PCB already has the photo-resist substance applied on it, so i dont have to worry about spraying anything on it. To protect the photo-resist layer the PCB is covered with a blue sticker that is UV protective. I had my board cut-ed and prepared earlier.
Now you need to place and secure the PCB with the copper side down on top of the layered transparent paper pieces and align it accordingly. Your glass panel should now look like this looking trough it:
Now Im gonna tell you a few words about my exposure unit. I used an old computer ATX case from which i removed everything. Than inside i placed a mercury light bulb with the outer shield removed so that it emits UV light. The light bulb is the type used in public lights, its made by Philips if i remember correctly and has 125W. In series with this light bulb i used a 150w ballast.
Both the light bulb and the ballast were bought for approximately $15. The UV light emitted by this unit is very powerful and dangerous, if you make something like this at home, use it with caution, never look into the light, thats why i placed it inside the ATX case. Its safer to buy a commercial exposure unit if you can afford it, they are much safer to operate. In my ATX case the light bulb its placed on top of the cd-rom bay area, and the pcb is inserted trough the last bay. The distance between the light bulb and the PCB is approximately 10 cm thus resulting an 8 min exposure time.
There is no given formula that you can use to calculate the exposure time because of the so many variables that count. You have to determine your exposure time by experimenting with little pieces of PCB, each being exposed different lengths of time. Ok, enough about my exposure unit, next we place the PCB with the copper side facing the light bulb, inside the exposure unit.
No i just have to wait 8 minutes for the exposure to occur. In the meantime Im preparing the developer. As i stated in the materials list Im using this commercial developer that i found on a online electronics hobby shop, it comes in these bags with unknown language printed on them :) . There is an alternative to the commercial developer; you can make your own alkaline solution by dissolving caustic soda in watter. But as you may know caustic soda is very dangerous and can cause serious burns. So far i touched my commercial developer and nothing happened, so it must be safer.
I use a teaspoon of this developer mixed with water in a plastic container. I use about 1-2 cm of water, just to cover the pcb. You have to mix it very well together until the developer completely dissolves.
After 8 minutes have passed, i removed my board from the exposure unit and pealed it away from the glass panel. Now you need to move relatively fast and place it inside the developer, because if you keep it too much exposed to light, other areas of the photo-resist could react and this will mess your board. All i have to do now is place it into the developer. How long do you have to keep i there ? again there is no given formula to determine the time needed to develop. It pretty much depends on how strong your developer is. In my case 2 minutes is enough. The first 10 seconds after you place the board into the developer are the best indicator on how strong is your developer: if the copper tracks start to appear immediately your developer is probably too strong, if they dont appear at all or too little in the first minute, than your developer is too light. You will have to find the balance yourself.
As you can see in the picture Im using a wire strap to move the board around. Also you can notice in the picture the developer is working and the photo-resist substance is being removed from the board. After the developing is complete, you have to wash the board thoroughly under running water. This is how your board should look after developing and washing.
The next step is to prepare the Ferric Chloride(actually its better to have it prepared earlier). Im using this bags of Ferric Chloride that i bought from an electronics hobby shop. I mixed one of these bags with 0,5 l of water. The resulted solution etches my boards in 10 to 15 minutes.
For this board i used as an etching container a small 0.25ml bottle with its head cut-ed off. After 15 minutes in the etching solution the board is almost complete, only a small area of copper remaining. If you wish to accelerate the etching process you will have to heat the Ferric Chloride up to 40 degrees Celsius and gently shake the container to move the etching solution around.
After all the unwanted copper was etched, its time to remove the board from the Ferric Chloride solution and wash it under running water. Be careful to have plenty of water running when youre working with Ferric Chloride because this thing will eat or stain every metal it gets in touch with. After being washed, your board should look like this:
The next step is to clean the photo-resist layer from the copper tracks, you can do it with some acetone. In the next picture you can see that the place where the board was cleaned with acetone appears brighter.
After a complete clean with acetone and another washing with water, your board should look like this:
The board is now ready to be drilled. The drilling can be done with different tools according to your budget. Im using a cheap driller that fits into my palm. It runs from 9-18v and can achieve up to 18000 rpm.
A better solution would be a drill press, which features a nice handle that you press to bring the drill bit into the board. You can use any option you have available for drilling, but for better results i definitely recommend the drill press. Also to keep your drill bit sharp and to obtain perfect holes the driller should be running at high RPM. You should keep your drill bit diameter smaller than the pads, so that you have copper left to solder on it. And thats it after drilling your board is ready to be assembled.
I hope that my experience reflected in this tutorial will help many beginners to start with this photo-etching technique. In my opinion this is the technique that provides the best possible results when working at home but keep in mind that this is just one of the many ways to make PCBs.
