Etch factor

Updated November 5, 2009

Click here to go to our main page on printed wiring boards

New for November 2009! Etch factor must be considered in manufacturing planar circuits on hard or soft boards, particularly when a wet etch is used on thick copper. When designing a MMIC, you don't consider etch factor, because a lift-off process defines the metal dimensions. Typically the etch factor is equal to the height of the metal, as the copper is etched its Z-axis profile is close to a 45 degree angle. Yes, we could use a picture here... the trace is undercut, so that it is thinnest at the substrate, and thickest at the top surface.

In order to compensate for etch factor, artwork is often "bloated". This means that the final dimensions of the artwork are larger than the intended dimensions of the circuit. You can get in trouble if you don't understand this, and use measurements from a mask in analyzing a circuit.

More to come!