Etch Factor

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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. 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. The etched dimensions at the surface of the substrate are what you should analyze. Bloating should not be confused with mask scaling, which is necessary in some LTCC manufacturing because of shrinkage when the product is fired.

bloating versus scaling




Author : Unknown Editor