Al,
  
     You could very well be right about not knowing of the problem. We wave 
  A LOT of bottomside parts here (chips, Gullwing and J-leaded IC's), and 
  we do not x-ray. However, we've never had any complaints from our 
  customers with the problem that you're speaking of. 
  
     We also have Electrovert machines and DO USE the omega every now and 
  again...but still no complaints.
  
     I don't doubt that you're seeing something, but may I ask what kind of 
  x-ray equipment you're using? I had the opportunity at another job to 
  fiddle with a Nicholet x-ray machine at one time (It was on a trial for a 
  30-day evaluation). We used it to look at our solder joints and it looked 
  like we were building boards that had voids in the fillets...it was very 
  disturbing to say the least!
  
     To make a long story short, after we messed around with our reflow 
  profiles and weren't able to eliminate the occurrence of them to the 
  point that we felt comfortable, we finally found that what we thought 
  were voids were actually minor plating imperfections on the chip 
  termination's, HASL imperfections, and the like. Our misinterpretations 
  may have been because of our lack of experience in interpreting what we 
  were seeing, or because of limitations in the equipment. 
  
     The machine that we had would x-ray straight down through the leads, 
  fillet, pads, laminate, etc., and basically gives you an image of the 
  different densities in the area that it is pointed at. Yes, you might 
  very well see something, but you wouldn't REALLY know where it's at. 
  Nicholet is unlike a Four Pi system that looks at an area 3-dimensionally 
  in 1/10,000th of an inch slices, then you can pinpoint EXACTLY where 
  something is at...do you think that maybe it could be something going on 
  INSIDE the IC instead of your soldering?
  
     Again, I don't doubt that you see something, and you have really got 
  my curiosity up now! I'm wondering,...do we have the same problem and not 
  know it? Can you see this with your naked eye? If you don't mind, keep in 
  touch with me about this, and in the meantime I'm going to really 
  scrutinize our boards!!
  
                         This is the kinda' stuff 
                         that keeps things interesting...huh?
  
       
                       ////  
                                           
                      |  @@ /      Steve Gregory                         
                      C   )        Process Training Engineer   
         ////  
       \_o         Pragmatech Incorporated               
        |  @@ /                    101 Nicholson Lane          
        C   )                      San Jose, California 95134            
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                   |  @@ /         Phone:(408) 943-1151                  
                   C   )           Fax:(408)943-1461           
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  ....the views expressed above are my own, not my employers...