Hi Pradeep,
NO, smear will not form uniformly.
YES, smear will affect the quality and reliability of the PCBs at every stage
of subsequent work and operational use.
THEREFORE, effective desmear is a must.
HOWEVER, that does not mean that you need a lot of positive etchback, because
that too degrades quality and reliability.
You need to be aware that desmearing Pb-free soldering compatible PCB base
materials, typically phenolic cured, do not respond to smear removal like the
traditional FR-4 PCBs.
All of this, and of course much more, is detailed in my White Paper
"Recommendations for PCB FAB Notes and Specifications in Printed Circuit Board Drawings
for SnPb and Lead-Free Soldering Assemblies, the Qualification of PCB Shops
and Activities to Assure Continued Quality."
Werner
Future workshops:
Reliability Issues with Lead-Free Soldering Processes, September 22,
Schaumburg
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture,
ENIG), September 22, Schaumburg
Solder Joint Reliability: Parts 1 & 4, Oct. 9, Moscow, Russia
Solder Joint Reliability: Part 4, Oct. 17, Timisoara, Rumania
Solder Joint Reliability: Parts 1 & 4, Oct. 22, Tallinn, Estonia
**************
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