Etching a PCB

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Creating a PCB from Scratch - Chemical Etching Process

Preparing solution

-creating cupric chloride

Cupric chloride is used to etch the board. It is made by mixing 2 parts  3% hydrogen peroxide 

with 1 part hydrochloric acid (muriatic acid). The hydrogen peroxide acts as an oxidizer, 

allowing the acid to pull the copper from the board. Add the acid to the hydrogen peroxide, 

not the other way around. 

A scrap copper clad board can be used to start the process. The initial reaction is aggresive and 

not suited for etching boards. Once the solution has turned green, it can be used to etch boards.

Etching time will vary, but it should take less than ten minutes with a fresh batch. 

https://mad-science.wonderhowto.com/how-to/create-pcb-etchant-automatically-improves-after-each-use-0135192/

-reactivating cupric chloride

If the cupric chloride is being used again, but has been left sitting in a jar, the solution will need

to be reactivated. This can be done by adding some more hydrogen peroxide to the solution or by 

aerating it. Aerating will take longer, but it works. A wooden air stone will work quicker than a single

air line left dangling in the acid. This process will take at least 2 hours before it will begin etching 

copper again, but 6 hours to a day is typical. 

http://jimlaurwilliams.org/projects/seychellePaper/index.html

Preparing board

*Consider scuffing board with volcanic ash or a brillow pad before applying photoresist and solder mask

https://youtu.be/Su0PIw5OaYQ - Professional PCB production process

-applying negative develop photoresist

The board will need to be wiped down with acetone to ensure a clean surface before application.

Cut a section of photoresist a bit larger than the board it will be applied to. Use 2 pieces of clear tape 

to pull the protective film from one side of the photoresist. The unprotected side of photoresist is the 

side that will be applied to the copper clad board. Set the board down in a shallow dish filled with 

distilled or deionized water and float the photoresist on the water above the board. Carefully push the 

photoresist down into the water so it falls onto the board. Starting from one side of the board, thumb 

the photoresist down, pushing it along the surface of the board, pushing out the water from underneath.

once the photoresist is on the board, carefully pull the board out of the water and set it onto a work surface.

Work the photoresist onto the board further, squeezing out the water and making sure there are no bubbles 

trapped beneath the surface. This is an important step as poor adhesion here will result in poor etches. 

Once the water has been removed from the board, take a razor and cut along the edges of the board to remove 

excess film. Place the board with the freshly applied photoresist into a food dehydrator for 1-2 hours to completely

dry the board and ensure all the water has been pulled away. 

-creating circuit transfer sheet and mask layer

Using A-SUB brand waterproof inkjet film 8.5"x11" sheets (http://www.koalagp.com/) create a transfer sheet and 

mask for the photoresist. Export your fritzing file in the PDF format and find the files required to create the traces 

and mask, such as the etch copper bottom and etch mask bottom. Open the copper bottom file with Gimp and import 

it with the resolution set up to 1000. Invert the color and export or overwrite the file. This will be used to create the 

circuit transfer sheet. Cut a sheet of plain paper and tape it over the top of the transfer sheet, making sure that smooth side of the transfer sheet is touching the plain paper. One piece of tape at the bottom of the plain sheet will suffice, just be sure the top of the plain paper and the top of the transfersheet are lined up square and even. Set the paper into the printer with the plain paper on top and prepare to print. Open the printer dialog and switch the settings

so that paper is set to t-shirt transfer and size is set to A5. The circuit transfer will require only 1 pass through the 

printer, but the mask will require 2 passes for proper exposure in a later step.

-exposing photoresist to UV

Place the board under a UV light source, preferably UV bulbs at a distance of 3 inches from the board surface, then

place the circuit transfer on top of that oriented properly. Place a sheet of glass on top that to hold it in the proper

position and allow curing for 7 minutes. Remove the PCB and develop the photoresist. 

-developing photoresist in sodium metasilcate solution

Mix a developing solution of sodium metasilicate with 3 grams of TSP-90 in 100 mL of warm water. Place the board 

into the solution and lightly brush with a toothbrush until the exposed photoresist begins to scrub off. Once all the

photoresist for the traces has been removed, quickly rinse the board in fresh running water, making sure to remove 

all sodium metasilicate. 

Etching board

depending on strength of solution, this could go quick or be very slow.

a freshly prepared solution of cupric chloride will etch the board in 10 minutes or less,

but a reactivated solution may take significantly longer depending on how saturated it is. 

Saturation can be determined simply by looking at the color. light green is fresh, dark green 

or almost black in color is saturated. 

Make sure that the board stays moving in the cupric chloride to ensure proper etching. An air stone will agitate the 

solution well enough for this. Remove the board from the cupric chloride once it is fully etched and rinse under fresh

running water. 

Applying solder mask

*Look into doing this with a silkscreen and photo emulsion - products on amazon

-removing the photoresist

mix another batch of sodium metasilicate at higher strength for photoresist removal. 10 grams of metasilicate to 

100 mL of warm water. Let sit momentarily (about 30 seconds) then begin scrubbing the photoresist off with a 

toothbrush. Once the photoresist is completely removed, rinse under fresh running water.

-preparing the board

lay the board down on a sheet of plain paper and wipe the board down with acetone to clean the surface and 

prepare for solder mask. 

-applying the UV curable mask

squeeze or spoon a line of UV curable solder paste down the center of the board. Preferable to use the jar of 

mask paste as the shelf life on the tubes seem to be shorter. Will cause separation of hardener and mess up 

curing times.

-spreading the mask 

cut a section of the transfer sheet used for the circuit or mask and gently lay it with the smooth side down onto

the paste. With a heavy piece of glass placed on top of the transfer sheet, gently rock the glass, spreading the paste

evenly across the board until only a thin layer of paste is left on the board and the excess paste squeezed off the

sides of the PCB. 

*Technically the solder mask should be baked in the oven before exposing it to the UV, then it gets done in the oven

again to finish curing post exposure. https://youtu.be/Su0PIw5OaYQ

-curing the mask

Remove the heavy glass and take the board with transfer sheet attached to the UV curing station. Carefully line up the

mask transfer sheet onto the circuit and place a sheet of glass onto it once it has been properly positioned. Allow the

paste to cure for 10 minutes. Remove the board from the UV cure station and remove the mask transfer sheet.

Carefully pull the transfer sheet away from the UV paste at a sharp angle, making sure to keep pressure applied to the

surface of the board with the transfer sheet so it doesn't pick the UV paste up with it. Once the sheet is removed the

uncured paste can be cleaned off the board with a cotton swab or paper towel and some acetone or rubbing alcohol. 

Place the board into the food dehydrator for 15 minutes, then place the board under the UV bulbs for another 15 minutes

to completely cure it. 

Completing the PCB

-drill hits

using a drill press and properly sized drills, drill the holes that are required on the board.

-outline cut

use a dremel with a cutting disk to cut out the board in the proper shape, then use a piece of sand paper to clean it up.

Use a razor blade to cut just inside the edge of the board outline, along the copper to remove the edge of UV mask. 

Addition curing under UV light may be necessary at this point if UV mask is still wet underneath. 

-soldering components

Solder all the components to the board and call it complete.