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):

enter image description here

  1. After copper was etched:

enter image description here

enter image description here

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:

enter image description here

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.
  • 4
    \$\begingroup\$ Why does it look like there is copper where it should have been etched away and no copper where the traces are? \$\endgroup\$
    – Rodo
    Commented May 11, 2022 at 18:40
  • 4
    \$\begingroup\$ It looks to me like the PCB was not fully etched. There is a lot of copper areas left where an isolation is needed and there should be only the PCB base material without any copper. \$\endgroup\$
    – Uwe
    Commented May 11, 2022 at 18:43
  • \$\begingroup\$ It looks like the mask you used didn't cover the tracks you want properly, and also, the PCB wasn't fully etched; there's still copper left inbetween the tracks. What method did you use to mask the tracks/transfer your design to the blank copper? \$\endgroup\$
    – ocrdu
    Commented May 11, 2022 at 19:03
  • \$\begingroup\$ I know it's fun to play with poisonous chemicals sometimes (Unless making the PCB is part of your required academic work) ---- but it should be mentioned --- You could have a professional PCB house make that board for you stupid-cheap, with all the holes drilled, etc.... There are many places in China, US and other countries that offer this service. Well under USD $100 for sure, depending how fast you need it. \$\endgroup\$
    – Kyle B
    Commented May 11, 2022 at 19:11
  • \$\begingroup\$ That certainly looks straightforward - you had defects in the photoresist which allowed etchant to attack the copper in those areas. I'm going to guess not enough exposure, or perhaps contamination of your resist medium or insufficient cleaning. \$\endgroup\$ Commented May 11, 2022 at 22:10

1 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!

  • \$\begingroup\$ From all the comments and your answer I have understood that the PCB was not etched completely but what I am not able to understand is why the discoloration happened after it was washed with water and left to dry and ruined the PCB completely? Shouldn't it be like just some unetched copper left between tracks? Can it be due to maybe improper cleaning of copper board before toner transfer process? Thank you for a very detailed answer by the way. I will the points you mentioned next time. \$\endgroup\$
    – tinkerer
    Commented May 12, 2022 at 1:11
  • \$\begingroup\$ Also even if it was because of contamination, I should have seen some discoloration while it was being etched I guess. But it only happened when it was left to dry after washing with water and that is the part which is confusing me. \$\endgroup\$
    – tinkerer
    Commented May 12, 2022 at 1:41
  • 2
    \$\begingroup\$ During etching copper film becomes matte and brown-reddish-bluish (hard to describe colour). The matt is caused by non-uniform etching at micro-level because of copper micro-grain structure. Colouring is caused by redeposition of thin layer of CuCl2 and FeCl2 (as i remember, may be wrong) onto PCB surface. It will go away when etching completes. I think that here this effect is enhanced by FeCl3 low concentration. Acid-peroxide etchant does not cause such coloration. \$\endgroup\$
    – Vladimir
    Commented May 12, 2022 at 22:08

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