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Peroxy-Sulfuric Etching Module
Chemical Analysis/Stabilizer/Catalyst analysis II

Permanent Stabilizers
Stabilizers that require replenishing only as a result of bath drag-out tend to produce somewhat less aggressive etchants. In spite of reduced etch rates, their near total immunity to uncontrolled exothermic reactions, reduced H2O2 consumption and higher allowable operating temperatures (55 degrees C) makes members of this class the preferred stabilizers for peroxy-sulfuric etchants used in high-throughput production environments.

Production operations usually call for the use of more expensive spray etching equipment that, in many cases, allow these less vigorous etchants to meet or exceed the performance of their more aggressive cousins. Even low-cost, low-pressure randomized spray etching with these etchants can achieve etch rates acceptable for most PCB prototyping houses. Unfortunately, corrosive aerosol generation is still a problem and must be dealt with to insure your safety and the health of the environment.

Permanent stabilizers are so effective in stabilizing the peroxide against the effects of heat and dissolved copper, it is very unlikely that solution effervescence will be observed, even in severely depleted baths. A simple, but reliable technique devised by Bill Good of the M.F. Good Co. (Westminster, CA) follows.

Equipment needed:
  • 2 ea. Pyrex brand test tubes
  • metal test tube stand
  • 4 quart sauce pan
Reagents needed:
  • ferrosulfate indicator solution (F)
  • 50% stabilizer solution (S)
  1. fill the sauce pan with water and pre-heat to 82 degrees C (130 degrees F)
  2. pipette a 50 ml sample of the etchant into the two test tubes
  3. identify the samples as 'A' and 'B'
  4. add 1 ml of F to each sample tube (this will increase the instability of the peroxide)
  5. add 1 ml of S to sample tube 'A'
  6. set the test tube rack (with the sample tubes) into the hot water for 30 minutes
  7. the test samples will reach equilibrium with the hot water in 3 - 4 minutes. At this temperature, some out-gassing (mild effervescence) will be evident even when the stabilizer content is optimum.
  8. remove the rack from the hot water (be careful, it is very hot) and quickly cool the sample tubes by dipping them in cold water
  9. carefully analyze both samples for peroxide
Small differences in peroxide concentration, in the tested samples, are normal. However, if the peroxide content of 'A' is higher than that of 'B' by 2% of the volume of the sample (e.g. H2O2 content of 'A' is 8% vs. 6% H2O2 for 'B'), additional stabilizer is needed in the bath. Add 1% by volume of stabilizer and repeat this test in 2 hours.

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