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Date: | Wed, 03 May 95 15:54:13 PST |
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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.
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