Address:
     
     Question:  What is the minimum soldermask dam from via-via and         
                via-pth without solder bridging? (equipment=Dual Wave       
                Solder)
                If the via pad is .0275" and the drill size is .012". what  
                is a safe soldermask clearance (that will keep solder       
                bridging from occuring)?
     
     What evaluation tests were preformed to prove your answers?  Please 
     explain.
     
     
     Hitachi HISTORY:
     
     ORIGINAL PROCESS #1
     In the past soldermask covered the component side vias (dotprint) and 
     the solder side vias had soldermask encroach up to the knee of the 
     barrel or 1-2mil annular ring (sometimes tangency).
     
     dotprint
     advantage: -at the time, it assisted vacuum at pcb electrical test.
                -solder balls
     dotprint
     disadvantage:      -soldermask peel/flaking
                        -possible flux entrapment          
                        -soldermask blow hole (from compside)
                        -solder side mis-registration over vias
                        -exposed copper
                        -difficult for vendors
     *over time we found most of the disadvantages were not major 
     non-conformances.
     
     ECR PROCESS #2
     
     Soldermask clearance the component side vias and dot print the solder 
     side vias.
     
     advantages:        -no flux entrapment
                        -no soldermask peel/flaking
                        -no blow holes
                        -no exposed copper
                        -no solder balls
                        -easier process for vendors                   
                        -good vacuum at pcb electrical test
     disadvantages:     -cannot access vias for pcb electrical test
                         due to time, via points for netlist test were not  
                         known prior to pcb manufacturing.
     
     ECR PROCESS #3
     
     Soldermask clearance the component and solder side vias.
     
     advantages:        -no flux entrapment
                        -no soldermask peel/flaking
                        -no blow holes
                        -no exposed copper
                        -no solder balls
                        -standard process for vendor                  
                        -good access at pcb electrical test
     disadvantages:     -minor solder balls under scope
                        -solder bridging on solder via-via
                                                   via-pth               
                                
     PROBLEM:
     
     The solder bridging on Proces #3 is due to high density bareboards 
     with approximetly 3500 .012" (.3mm) vias (3-5kmax holes).  Note: we 
     are limited on controlling design at this facility.  Refer to top for 
     questions.  Please call me at 405-360-5500 x634 if you need additional 
     question.  ask for John Gulley (PCB Project Coordinator).  Thank you
     for your time.