I would agree with Ed. I have done close to 50 microns deep in the past just
using standard Shipley 1813 (~2 micron) and 7:1 BOE.

Thorough cleaning, dehydration and priming of the glass is important.
Unfortunately I can't remember whether it was soda-lime or borosilicate
glass but generally soda-lime etches faster.


On Wed, Nov 4, 2009 at 01:51, Edward Sebesta  wrote:

> I am somewhat surprised to hear that you can't just etch with Buffered
> Oxide Etch with 13:2 ratio. Make sure your glass is very clean, use
> vapor prime and thick positive resist. Bake it well so HF can't
> penetrate the resist. Don't use HF, but use BOE.
>
> Ed
>