PCB etching went wrong or what?

Question

I was trying to etch a PCB of 12x23 cm using FeCl3 powder. Below are the pictures of the process:

1. Before dipping into etching solution (some tracks were corrected using permanent marker):

2. After copper was etched:

What are those white spots at some places on the top right of the PCB?

After this the board was washed with water and left to dry. After it dried the board looked like this:

Some tracks were removed by ink where the discoloration happened.

Where did this discoloration come from? What did I do wrong?

Some other information which may be of help:

1. FeCl3 powder was more brownish than when it was bought. It was packed back in the same container after first use.

Answer 1

Seems that you are using toner thermal transfer method.

You definitely haven't completed etching process. At the process end, etched areas will shine to the light. Your FeCl3 solution looks having very low concentration. It should be dark and PCB will be invisible when immersed.

Bad transfer quality (absent lines) can be caused by:

• bad PCB washing. Recommended: finest sandpaper or pencil eraser to remove oxide, then acetone, then immediately isopropanol, than immediately air blow-off (compressed or from rubber pear at least, sold in pharmacy)
• low temperature or short process. Recommended about 150°C, cooling together with hotplate.
• low or uneven pressure during baking (transfer). Over-pressure isn't bad until we don't need high resolution (0,5 mm and less). Hotplate should has good flatness. Applying pressure through a piece of knitted cloth will help to make it uniform.
• low quality glossy paper. Should look really glossy, without roughness, and be dense enough, but not cardboard.

White marks look like contamination from dirty solution. Before inspection it is good to rinse PCB with water and blow it away with air.

Using marker for retouching is very unreliable because lines are very thin and porous and will etch. Women nail varnish is one of the best solutions. Removable with acetone. Remove unneeded marks with toothpick before it dries completely.

In order to decrease etching time and reduce etchant consumption, you can fill large unused areas with polygons, not connected to other lines. Also, you can draw them by hand and paint after transfer.

At my experience, it is nearly always better to cut out exactly required size of board at the beginning.

As other people wrote in comments, FeCl3 is quite unhealthy thing. Healthy etchant that i use:

this amount should be enough for etching 100 cm2 of 35 um thick copper.

• 30 g of citric acid (from food shop)
• 5 g of salt (NaCl)
• 100 ml of 3% hydrogen peroxide solution (from any pharmacy)

Etches faster when heated a little. It can not be stored for long time. It is colourless and will become light-blue during etching. While nearly drinkable before begin, it is poisonous at end. Remember that copper salts are poisonous! Wish you fine PCBs!