Evaluation of Laminates for Pb-free HASL Process
Paper covers an evaluation of four FR4 laminates to determine their survivability for the lead-free hot air solder leveling process.
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Authored By:
Khaw Mei Ming, Andrey Lee
Agilent Technologies
Bayan Lepas, Malaysia
Summary
An evaluation of four FR4 laminates in commonly used stack-ups was done to determine their survivability for the Pb-free HASL process followed by a worst case Pb-free manufacturing environment of 6 X reflow @ 260°C and 1 X wave @ 270°C. The work also includes a laminate compatibility study in a Pb-free hot air solder leveling (HASL) profile.
Conclusions
An important consideration for Pb-free materials, before any of the long-term reliability considerations are addressed, is the survivability of the laminates without degradation after the Pb-free assembly process. This survivability is further stressed if Pb-free HASL is used, which adds another thermal cycle to the board during the fabrication process. The HASL profile shows that any laminate that is currently coated with tin lead HASL should be able to withstand the Pb-free HASL processing temperatures under the same dip time conditions.
The voiding of Pb-free HASL boards was the same as in the immersion silver boards after extreme assembly conditions. As a chosen Pb-free compatible material approaches the 6 reflow and 1 wave thermal cycle limit, it is evident that we are very close to discovering more potential problems, with the early onset of voids. This project concluded that material survivability performance of a Pb-free product depends on the type of material that is used and layer count of the board.
Initially Published in the IPC Proceedings
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