Hi Larry,
Ireland calling after Paddy's day. One thing that is commonly overlooked with an ammoniacal etcher is that the pH goes mad if you add water. Try it with a probe in a beaker. All the ammonia is then lost and the thing collapses 'sludges'.If too much fresh etchant exits with the dry film this reaction happens in the first rinse, all be it for a limited time on the surface of the dry film.  I think this might be worth investigating and improving the pinch rollers both after etching and replenisher rinse.
If you take a sample panel straight out of the etching chamber and lie it in a sink of water it will strip!

This might help if all the 'normal' rules are not being broken.

Slan

Ken McGowan
  ----- Original Message ----- 
  From: Larry J. Fisher 
  To: [log in to unmask] 
  Sent: Sunday, March 18, 2001 11:32 PM
  Subject: [TN] Dry Film Breakdown In Ammoiacal Etching


  I am hoping someone can give me some guidance to help solve a dry film 
  breakdown issue in ammoniacal etching. The dry film(s) seem to be processed 
  perfectly normally (optimum conditions) through the developing step. An 
  overview of the etching consists of: 

  1. Main etching chamber, with vent 

  2. Cascading replenishing section about 50% longer than the main etch 
  chamber, with vent (either closed or only barely open). Fresh etchant fed 
  into the replenishing section, then cascading into the main etch chamber. 

  3. Ammoniacal etchant  in main chamber at 124 deg F and pH of 8.2 to 8.3. 

  4. Copper level at about 22-23 ounces/gallon 

  5. Main etchant controlled by specific gravity at 1.21. 

  6. pH of fresh etchant - 9.9 

  7. pH of cascading etchant feeding into the main chamber (after traveling 
  thorough the cascading replenisihing section) - 9.3-9.5 

  8. Etching spray pressured - Approx 35 psi 

  9. Dwell time in main etch chamber - 45-50 seconds 

  10. Dwell time in replenishing section - 60-75 seconds 

  Through these etching conditions, there can be dry film lifting along the 
  circuit traces and/or broken tents. After consulting the literature and 
  talking to a few experts, my thoughts on how to correct these problems 
  consist of: 

  1. Increase the venting in the replenishing section so that the pH of etchant 
  coming into the main chamber will be lowered to about 9.0 and this will also 
  reduce the amount of ammonia fumes in the replenishing section. 

  2. Lower the copper content a little, increase the temperature a little 
  and/or lower the specific gravity a little so that the etch rate will 
  increase and the panels will go through faster and the dwell time in the main 
  chamber/replenisher will be lower. 

  3. Set up a "Y" connection from the fresh etchant so that some goes into the 
  main chamber and some into the replenishing section. This will maintain pH in 
  the main etch chamber and allow the ammonia/pH in the replenishing section to 
  go down. 

  4. Feed fresh etchant only into the main etch chamber. Install fresh etchant 
  into the replenishing section and change out once per week. Use squeegee 
  rollers in the replenishing section to prevent "drag out" of copper into the 
  fresh rinse section (after replenishing section). 

  Do you think I am on the right track here, or am I "all wet". Also, do you 
  have any other ideas that may help me out here. I would appreciate any input 
  from all you capable "TechNetters". 

  Regards, 

  Larry Fisher 

  Allen Woods & Associates 


  4.