This guide will explain to the electronics hobbyist
how to produce a professional
easily and efficiently
, without professional etching
You will need to build two pieces of equipment: an ultraviolet
exposer and an etching tank.
exposer is simple to make, build a small wooden box with glass on the top and place a 2 or 4 tube (4 tube is better) fluorescent
light fixture in the bottom. Instead of putting regular white fluorescent tubes in it, place blacklight
bulbs in it.
There are many different variations of etching
tanks. The basic idea is to agitate
solution with your circuit board
inside, and optionally, for faster etching, heat the solution. The two most common ways of agitating the solution is to blow bubbles through it with an air pump (as in a bubble-etch tank) or to hold the circuit board
out of the solution
and use a pump to spray the solution
onto the board. When constructing
tank, NEVER use metal parts and fittings. Circuit boards are usually etched with ferric chloride
, which attacks metal (which is what we want). Your best bet is to use PVC
tubing and fittings.
, heavy rubber gloves, and an apron are also recommended for most steps where chemicals are involved, and safety glasses should be worn whenever drilling circuit boards as fibreglass
particles irritate the eyes.
A drilling stand is recommended for straight holes. Tungsten-carbide bits should be used. You will need 3 or 4 0.8mm bits, 1 or 2 1.0mm bits, and 1 each of 1.2 to 1.5 for larger components.
You should also have a guillotine
for cutting boards to size. A hacksaw
will work, but is tedious, time consuming, and tends to dull the blade quickly.
You should always use good-quality positive
pre-coated photoresist fibreglass
board. Check for scratches on the coating and on the protective covering before using. Boards can be purchased at many electronics supply houses. Boards should be handled in subdued light. Its not necessary to use a safe light, but they should not be exposed in direct sunlight and minimize unnecessary light exposure.
It is recommended that you use a silicate-based developer such as sodium metasilicate pentahydrate. Sodium hydroxide
works, but is highly sensitive to temperature, concentration
, and is very caustic
. If you absolutely have to use sodium hydroxide
, to mix it correctly: add 200cc of "water glass
" (sodium silicate
solution) to 800cc of distilled water
. Then add 400g of sodium hydroxide. When adding the sodium hydroxide
to the solution, take care _never_ to touch it with your hands, and add it a small amount at a time, as it produces a lot of heat when it dissolves.
hexahydrate is recommended as an etchant
. Its cheaper and easier to obtain than most of the alternatives
. It attacks most metals, so it should be stored and handled with only ceramic and plastic apparatus
. The FeCl comes as a powder
, it should be dissolved
in warm water until saturated
Step 1: The Artwork
The first step in the circuit board production process is to design the layout
of the circuit board
. Producing good-quality PCB
artwork is beyond the scope of this article (however, I may write an article on this subject later). Lay tracks
out with careful condsideration to scale
, the size of devices, current
, and soldering
A mirror-image positive
of the artwork (i.e. black=copper) should be printed exactly to scale on acetate
, preferably on a laser printer
or photocopied onto the acetate
. The idea is to get the black as dark as possible, as it will be blocking the ultraviolet
light. The artwork is mirrored because when it is exposed
, it should be face-down on the board, leaving no space between the image and the board to prevent blurriness
Step 2: Exposing the Circuit Board
If producing a double-sided circuit board
, tape both halves of the artwork together to form a "pocket" for the board, making sure they are exactly lined up.
If producing a single-sided circuit board
, the artwork should be taped to the board taking care to leave no gap between the artwork
and the board itself.
The board and artwork should then be placed face down on the exposer
. The time to leave them on depends on the brand of board, and your exposer. You should put test pieces on first and expose
them for 2-8 minutes in 30 second intervals
to determine the best exposure
time. As a general rule, overexposure
is better than underexposure
when exposing PCB
s. After exposure, you should be able to see a faint image of the artwork on the circuit board.
Step 3: Etching the Circuit Board
note: you should ALWAYS wear gloves, safety goggles, and an apron for this step, etchant is caustic and can damage eyes and permanently stain clothing
Time for etching a board depends on how fresh the etchant
is, agitation, and temperature. Fresh, hot etchant
can etch the board in under 5 minutes, and as long as an hour without heat or agitation. Etching boards faster produces a sharper image
, slow etching
may lead to blurriness.
The etched board should be thoroughly rinsed and dried. Methanol
, available at most paint suppliers and hardware stores) or Isopranol
(available at any pharmacy) can be used to remove the remaining photoresist from the board.
Step 4: (Optional) Tinning
a circuit board is optional, but makes soldering
a lot easier by preventing the copper
upon contact with air. If you decide not to tin the board, leave the photoresist
on to protect it from oxidization
Room temperature tin-plating
crystals are the best to tin boards with. They produce a good finish
in a short amount of time. Made-up tinning solution deteriorates
over time, so you should only make up exactly as much as you need. Take care to avoid contamination
, clean and dry the pan before tinning, and keep a pair of tongs
to be used only for tinning.
Ensure the copper is absolutely clean before tinning. Remove all residual photoresist and scrub the surface with steel wool
until it is shiny.
Put the board in the tinning solution
. After about 30 seconds, the copper tracks should turn silver. Leave the board in the solution for another 5 minutes, agitating
it occasionally. Rinse the board and rub it dry with a paper towel
to remove any remaining tinning crystal deposits.
Step 5: Drilling
note: safety glasses should be worn when drilling.
should be drilled with consideration
to the sizes of terminals on components to be installed. Find datasheets
on components before drilling to find out the correct size.
If you followed all these steps correctly, you should have a good professional quality printed circuit board