If you want a safer alternative, (safer meaning chemical stability and
ease of waste handling) then use Nanostrip. It is stabilized so it is
not exothermic and it cleans and strips just as well as Piranha mix. It
has been used at our facility for almost 10 years and no-one has been
able to prove it unacceptable when compared to Piranha. Nanostrip is
available through a couple of vendors, just search on the web.

FYI

Joe Lonjin
Penn State Nanofabrication Facility