"Etching is uneven! The board isn't all done at the same time."

Uneven etching has always been the name of the game when etching with a "rocking tray" or a "bubble tank". The expensive "spray etcher" at least has consistent etching results but that's a small consolation for the high price of this type tank.

The rocking tray has to be the worst idea ever since the middle of the board is always the last area to etch because the sloshing etchant back and forth (resembling a "standing wave" in the middle of the tray) so there is much less agitation ever getting over the copper.

The bubble tank is almost as bad as the rocking tray. The rising bubbles is making a "current" straight up the board. Newer etchant is rising to the top of the tank, circles around the outside of the tank and comes back to the center of the tank to rise again. The etchant always makes first contact with the board at the very bottom of the tank. As the etchant rises up by the currents being formed by the rising bubbles, the fluid is more and more saturated all the way up the board in a continuous manner. The bottom always finishes etching first! Now you have to wait until the top of the board is done, meanwhile the bottom of the board is "over cooking"! And if you have very fine traces, they might be in jeopardy of getting eaten up.

Even our "Contact Etch" technique (see "No Etching Tank?") can give you uneven etching if you "overlap" strokes which is one of the first precautions when "wiping" the board. It's always best to have a sponge the full width of the board so you are only wiping in 1 dimension, from one side to the other with no overlapping strokes like you would have if the sponge was too small.




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