PCB is not a new thing for any electronic student. A printed circuit board (PCB) is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. If you open a TV remote, we can find a simple PCB on which certain components like small capacitors and micro processors. We can typically call it a board which can be used to support different electronic devices to design a required component.

This is how it looks like if we open a remote and the green thing which is used as a holder to support all the equipment is the PCB which we are talking about.

PCBs are inexpensive, and can be highly reliable.

DESIGNING OF SUCH PCB

The materials that we need to design PCB are

  1. Hard paper magazines. Hard and flexible enough for printing on it such that it is not easily tore down.
  2. A laser printer.
  3. A house hold iron box.
  4. A small copper foil sheet i.e., a Copper clad laminate.
  5. Etching solution like Ferrite Chloride solution.
  6. House hold kitchen scrubs.
  7. Acetone (Nail polish remover)
  8. Plastic insulated copper wire.
  9. Another little things like a blade cutter, scotch tape, sandpaper, kitchen paper, cotton wool, vice, hacksaw.

DESIGNING PART

  • Finding the right paper:

The paper used should be glossy and thin such that it shouldn’t get wet easily.

  • Paper preparation:

Discard the heavily printed pages. Later cut the paper suitable for the printer. Try to get straight, clean cuts, as jagged borders and paper dust are more prone to clog printer mechanism.

  • Printer set up:

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.

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 fiberglass 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-aluminum 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.

  • 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.

  • 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.

·         Peeling

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.

·         Etching

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.

·         Finishing touches

A few drops of thinner (nail polish remover works well) on a pinch of cotton wool will remove completely the toner, bringing back the copper surface. Rinse carefully and dry with a clean cloth or kitchen paper.
Trim to final size and refine edges with sandpaper.

After printing as per the required parameters it can be used as above. Hope you like it. Cheers…

courtesy:  internet and few technical websites

Posted by

Gopi Chand ( MGIT ECE 4th yr)

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