HELP - What's the secret to making wire-bondable gold?
     
     Our ppm failure rate on wire bond sites is a little too high for our 
     customer.  Smallest wire-bond pad is about .014"x .050" and wire 
     mat'l is Al (generally higher failure rates on smaller pads).  The 
     highest percentage culprit has been described as an [arguably] 
     visible "orange stain" - very thin with a Carbon/Oxygen signature.  
     Board is double-sided with the following route: Drill, panel plate 
     Cu, image & plate gold (DuPont 9020), strip resist (RR3), image 
     (cover gold), cupric etch circuitry, pumice w/brushes, LPISM 
     (Probimer-65), solvent develop, bake & UV cure, legend, ET, Entek 56. 
      Gold parameters: 83-85 knoop, Ni content: 30-40ppm, As,Cu,Pb,Co, all 
     less than 3 ppm, Gold conc. is on low side: Au strike: 0.15-0.25 
     tr.oz./gal, Au Plate: 0.4-0.6 tr.oz./gal @ ~2 ASF.
     
     Questions: 
     - What are the most common contributors to wire-bond failures? 
     - Is LPISM residue one of them?
     - Are aqueous developable LPISMs generally more successful?
     - What are the, say, 3 most critical parameters to control at deep 
       gold?
     - How critical is gold surface topography (roughness)? 
     - Are ET pin dents a failure cause?
     - Can pumice operations be detrimental to the gold surface? 
     - Is low Au concentration necessarily a liability?
     
     Any input will be greatly appreciated.
     
     J.Felts
     PC World, Toronto

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