Friday, 21 October 2011

PCB etching tutorial

Hi this is my next good one for you

How to make PCBs at home

What you need

 Required materials

  Magazines or advertising brochures

   Laser printer 
Alternately, a photocopier should work

    Household clothes iron

   Copper clad laminate

    Etching solution Ferric chloride solution,
about 1 liter/ 0,26 gallons

     Kitchen scrubs

     Thinner (e.g. acetone)

        Plastic coated wire

How it works

Laser printers and photocopiers use plastic toner, not ink, to draw images. Toner is the black powder that ends up on your clothes and desk when replacing the printer cartridge. Being plastics, toner is resistant to etching solutions used for making PCBs - if only you could get it on copper!
Modifying a printer for working with copper is out of question, but you can work around it with the toner-transfer principle. Like most plastics, toner melts with heat, turning in a sticky, glue-like paste. So why not print on paper as usual, place the sheet face-down on PCB copper, and melt toner on copper applying heat and pressure?
Almost right. Right now you got paper toner-glued to PCB copper. Last step is to find a way to remove paper leaving toner on the copper, and you’re done.
I must credit Thomas Gootee for finding a solution putting glossy, inkjet photo paper in his laser printer. He found that the glossy coating dissolves in water. As most of the toner does not penetrate the glossy surface, you can easily remove the paper support with water: the gloss dissolves and you can remove paper.
Clever, isn’t it?

Unfortunately, the kind of paper used by Thomas is being replaced by new, improved, WATERPROOF (!) photo paper. This is good for your photo prints, but doesn't work anymore for PCBs.

While searching for more information on the subject, I found a newsgroup thread that suggested replacing expensive inkjet photo paper with glossy paper recycled from magazines. Magazines use ink, not toner, for printing, so previous printing shouldn’t affect the process. Another great idea! I tried it and worked so well that I decided to spread the word. Read on for a complete tutorial and my hands-on tips.

Finding the right paper

The perfect paper should be: glossy, thin, and cheap. The kind of stuff that looks lustrous and shiny when new, but so cheap it quickly turns into pulp when wet. If you ever found a mailbox full of squashy mail on a rainy day, you already know the answer: paper used for most mail advertising and magazines fits perfectly the requisites. I tried pages from the free advertising magazine IEN,catalogues , travel agent’s brochures, TV programme magazine, and all worked well. I don’t expect great difference using paper from most magazines. As a rule of thumb, if humidity in your bathroom turns your magazine in bad shape, it should be OK. If the humidity on your fingertips is enough to feel a sticky sensation while touching its gloss coating, it should be OK. Feel free to experiment: almost any glossy magazine paper will work. I like thin paper over thick one, and prefer recycled paper over new paper.

Paper preparation

I discard pages heavily printed, preferring pages with normal-size text on white background. Although ink usually does not transfer on the PCB, heavy print of headlines sometimes accumulate so much ink that some gets on copper.
Cut the paper to a size suitable for your printer. Try to get straight, clean cuts, as jagged borders and paper dust are more prone to clog printer mechanism. An office cutter is ideal, but also a blade-cutter and a steady hand work well.
Be careful to remove all staples, bindings, gadget glue or similar stuff, as they can damage printer’s drum and mechanisms.

Printer setup

Laser printers are not designed for handling thin, cheap paper, so we must help them feeding the sheets manually instead of using the paper tray. Selecting a straight paper path minimizes the chances of clogging. This is usually achieved setting the printer as if it were printing on envelopes.

You want to put as much toner on paper as possible, so disable “toner economy modes” and set printer properties to the maximum contrast and blackness possible. You want to print your PCB to exact size, so disable any form of scaling/resizing (e.g. “fit to page”). If your printer driver allows, set it to “center to page” as it helps to get the right position using a non-standard size sheet. 


Disclaimer: your laser printer is not designed to handle this kind of paper. Feeding your printer with paper other than special laser printer paper could damage it and potentially voids the warranty. So you are warned: do it at your own risk.
Print your PCB layout as usual, except you must setup the printer as described above and you must print a mirrored layout.
This is my PC thermometer circuit printed on IEN magazine paper. Notice that it is a mirror image of the circuit (the word PCTHERM is reversed). Placing some text helps recognizing when the layout is mirrored. Text will read straight again once the image is transferred on copper. If you look it very closely, you can see that toner is not opaque enough to 100% cover the words underneath, but this won’t affect etching.

How to cut raw material

PCB material is fibreglass like, and a trick to cut it effortlessly is to score a groove with a blade cutter or a glass cutter. The groove weakens the board to the point that bending it manually breaks it along the groove line. This method is applicable only when cutting the whole board along a line that goes from side to side, that is you can’t cut a U or L shaped board with it.
For small boards, I lock the PCB material in a vice, aligning vice edge and cut line. I use an all-aluminium vice which is soft and doesn’t scratch copper, if you use a steel vice protect copper surface with soft material.
Using the vice as a guide, I score BOTH board sides with a blade cutter (be careful) or another sharp, hardened tool (e.g. a small screwdriver tip). Ensure to scratch edge-to-edge. Repeat this step 5-6 times on each side.
Bend the board. If groove is deep enough, the board will break before reaching a 30 degrees bend. It will break quite abruptly so be prepared and protect your hands with gloves.
To make paper alignment easier, cut a piece of PCB material that is larger (at least 10mm/0,39 inch for each side) than the final PCB.

Cleaning the board for transfer

It is essential that the copper surface is spotlessly clean and free from grease that could adverse etching. To remove oxide from copper surface, I use the abrasive spongy scrubs sold for kitchen cleaning. It’s cheaper than ultra-fine sandpaper and reusable many times. Metallic wool sold for kitchen cleaning purposes also works. Thoroughly scrub copper surface until really shiny. Rinse and dry with a clean cloth or kitchen paper.
TIP: "...I had a bar of "Solvol" soap in the kitchen cupboard, This stuff is like normal soap but with sand mixed in with it or something. Mechanics and so on often use it as its really good at cleaning the grease and stuff off your hands. It is like soap with built-in sandpaper. Not much effort with some Solvol soap cleaned copper right up..."
Robert Davidson

Preparing for transfer

To make paper alignment easy, cut excess paper around one corner (leave a small margin though). Leave plenty of paper on the other sides to fix the paper to the desk. As the board is larger than the final PCB, there is large margin for easy placement of paper on copper.
Turn the iron to its maximum heat (COTTON position) and turn off steam, if present. While the iron warms up, position the materials on the table. Don’t work on an ironing board as its soft surface makes it difficult to apply pressure and keep the PCB in place. Protect table surface with flat, heat-resistant material (e.g. old magazines) and place the board on top, copper face up. Lock the board in place with double-adhesive tape. Position the PCB printout over the copper surface, toner down, and align paper and board corners. Lock the paper with scotch tape along one side only. This way, you can flip the paper in and out instantly.

Iron it!

Flip out the paper, and preheat copper surface placing the iron on top of it for 30 seconds. Remove the iron, flip back paper into its previous position over the copper. It is essential that paper does not slip from its position. You can also cover with a second sheet of blank paper to distribute pressure more evenly. Keep moving the iron, while pressing down as evenly as you can, for about one minute.
Remove the iron and let the board to cool down.


This is the fun part. When the board is cool enough to touch, trim excess paper and immerge in water. Let it soak for 1 minute, or until paper softens.

Cheap paper softens almost immediately, turning into a pulp that is easy to remove rubbing with your thumb. Keep rubbing until all paper dissolves (usually less than 1 minute). Don’t be afraid to scratch toner, if it has transferred correctly it forms a very strong bond with copper.

The board with all paper removed. It is OK if some microscopic paper fibres remain on the toner (but remove any fibre from copper), giving it a silky feeling. It is normal that these fibres turn a little white when dry.

Magnified view of the tracks, these are 1206 pads and SO8 SMT pads, connected by 20 mils tracks. Some white fibres show up on the black toner surface.

The hanger tool

The optimal way to etch is keeping the PCB horizontal and face-down (and possibly stirring). This way dissolved copper gets rapidly dispersed in the solution by gravity. Stirring keeps its concentration even, so the solution close to the PCB does not saturate and etching proceeds quicker. Unfortunately it is not easy to keep the PCB in place in an highly corrosive acid. This hanger is my best attempt to solve the problem. I made it with plastic-insulated copper wire. The wire must have a rigid core, but must be also easy enough to adapt to the board by hand without tools. Core diameter of 1 to 2mm is fine. Give it the form of an “arm” (the handle) ending with 4 “fingers”.
Each finger has a ring tip that fits a corner of the board. Close fingers around board corners: now you can use the handle to splash the board into the etching solution, stir, and inspect how etching proceeds.


There are many alternatives for etching liquids, and you can use the one that suits your taste. I use ferric chloride (the brown stuff): it’s cheap, can be reused many times, and doesn’t require heating. Actually, moderate heating can speed up etching, but I find it reasonably fast also at room temperature (10…15 minutes).
The down side of this stuff is that it’s incredibly messy. It permanently stains everything it gets in contact with: not only clothes or skin (never wear your best clothes when working with it!), but also furniture, floor tiles, tools, everything. It is concentrated enough to corrode any metal – including your chrome-plated sink accessories. Even vapours are highly corrosive: don’t forget the container open or it will turn any tool or metallic shelf nearby into rust.
For etching, I place the container on the floor (some scrap cardboard or newspaper to protect the floor from drops). I fit the board on the hanger, and submerge the PCB. Stir occasionally by waving the hanger.

First impression may be that nothing happens, but in less than 10 minutes some copper is removed, making first tracks to appear. From now on, stir continuously and check often, as the process completes rather quickly. You don’t want to overdo it, otherwise thinner tracks start being eroded sideways. As a rule of thumb, stop 30 seconds after you don’t see any copper leftovers over large areas.

Rinse the board with plenty, plenty, plenty of water
I store the etching solution in the same plastic box used for etching. When the job is done I just put the hermetic lid on. To further minimize risks of leakage, I put the container inside the bigger one I use for rinsing, put the second lid, and store it in a safe place.

Disclaimer: These are dangerous chemicals. Always read the labels that come with the solution, handle it wearing protective gloves and goggles, keep windows open, don’t inhale the fumes.

Finishing touches


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