Pan Pacific Symposium Conference Proceedings


LEAD-FREE PRODUCT AND PROCESS CONVERSION PHASE III - REFLOW PROCESS OPTIMIZATION*

Author: Hana Hsu et al.
Company: Mitac International Corp.
Date Published: 2/25/2005   Conference: Pan Pacific Symposium


Abstract: As a Phase III project for Lead-Free process conversion, the optimization of reflow process is studied. A test vehicle with major representative package types of FCBGA, PBGA, CBGA, QFP, SOIC, RN, passive, press-fit, PTH etc were laid out with daisy chain structure to achieve the real-time monitoring in reliability test. The test vehivle fab is either 14 or 26 stack-up layers with a raw material of Polyclad dielectric 370HR Novelac and a glass transition temperature (Tg) of 175°C that stack-up layers intertwined with 1 and 2 oz copper foils to total thickness of 93 and 150 mils in TV dimension of 16 x 20.875".

Symmetrical stack-up was designed into the layer structure to reduce PCB warpage. Major Lead-Free reflow control variables such as ramping rate, soaking temperature, soaking time, dwelling time, peak temperature, reflow environment, and cooling rate were factored into design of experiment (DOE) by Taguchi method to optimize the processes. The testing boards with different thickness and various surface finishes of Immersion Ag and Ni /Au were used. Package and solder joint quality responses will be correlated to physical properties, PCB warpage, solder diameter and circularity, standoff, wetting, and microstructure. A rationale and optimized reflow profile by systematic DOE approach is achieved.

Keywords: Lead-Free, Reliability, Taguchi method, Solder joint Reliability.

*This study is a work of YAMI team in Taiwan for knowledge sharing and facilitation of technology evolution. No product endorsement, business implication, and working preference in any forms are associated with this publication.



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