Anyone with a response? John Gulley ______________________________ Forward Header __________________________________ Subject: Soldermask via coverage (URGENT) Author: JOHN GULLEY at HICAM-HDQ-OK Date: 5/3/95 5:41 PM 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.