Look at the two papers in
http://microlab.berkeley.edu/labmanual/chap1/JMEMSEtchRates1(1996).pdf
http://microlab.berkeley.edu/labmanual/chap1/JMEMSEtchRates2(2003).pdf
These cover mixing BHF and many other etchants and give etch rates for fused
quartz, Pyrex 7740 glass, several deposited oxides, and many other
materials.
Note that BHF will faster and less controllably immediately after mixing.
It's best to buy it premixed, or mix it and let it sit for a day before
using.
    --Kirt Williams

----- Original Message -----
From: "Barbara Cortese" 
To: "mems-talk" 
Sent: Friday, January 19, 2007 12:56 AM
Subject: [mems-talk] BHF solution

Hi to all

I'm etching glass and quartz by a wet etching solution of BHF, but my recipe
isn't too good. I've tried differrent solutions with no success. Has anyone
a good recipe to suggest me?(not just saying BHF 6:1! but the effective
quantities!).