Etchant/Panel Interface and Its Effect on Etching (and What You Can Do About It)
As most of us who depend on some form of etching
for making a living know, the etch ratc on the top
side ofthe panel being etched in a horizontal etcher
is not even across the entire panel. Features towards
the edges ofthe panel tend to etch faster than the
same size features in the center ofthe panel. Isolated
features etch faster than the same size features that
are packed tightly together without a lot of space
between them. As the panel sizes get larger, the
discrepancy in the etch rate at the edges versus the
etch rate at the centcr ofthe panel increases until it
becomes a major problem. In general, the problem is
attributed to etemot puddling or pooling on the top
surface, where the etchant sprayed on the centcr of
the panel tends to be relatively stagnant and slower
moving than the etchant on the edges of the panel.
This is certainly true, but careful measurements on
the bottom side show that the phenomenon of faster
etching on the edges and around isolated features is
also present here, although to a much lesser extent.
A quick perusal of Perry's Chemical Engineers'
Handbook shows there is a mechanism that
describes this behavior and understanding it can be a
help in reducing its effects.
Don Ball, Atotech USA