SMTA China Conference Proceedings

The Study of Mini-wave Soldering Process in Lead Free Assembly (CHINESE)

Authors: Harvey Chang, Jay Huang, J.L. Ku, Ander Hsieh, Andrew Lee
Company: Wistron Corporation
Date Published: 4/22/2007   Conference: SMTA China

Abstract: The mini-wave soldering process is used for the rework and assembly of through hole components. Due to the Restriction in use of certain Hazardous Substance in electrical and electronic equipment (RoHS), lead free solder such as SAC305 is replacing the conventional tin lead solder. However, indirect materials and process parameters used in lead free mini-wave soldering process are not well defined. While the melting temperature of SAC305 solder is 37oC higher than that of Sn63/Pb37 solder, concerns include insufficient hole fill in the plated through hole and difficulties in removing and/or replacing components such as DIMM and PCI devices, as well as the dissolution of copper from PCB bonding area into the molten solder.

This research characterizes the preheat of PCB through a batch process to decrease the dwell time required for the PCB to be in contact with molten solder during mini-wave process. This helps to reduce the copper dissolution. Secondly, the effects of fluxing scenario and flux materials are explored to ensure the desired hole-fill ratio can be achieved. Finally, process parameters such as solder contact, dwell time, preheat temperature are investigated through Taguchi based experimental design. Performance of hole-fill is obtained through the 2.5D and 5D X-ray analysis. The influence on copper dissolution is then determined by cross-sectioning followed by SEM measurement. The induced board warp distortion is also characterized. The statistical results help to establish operational procedures that can be used for mini-wave soldering process concurrently satisfying several critical response variables. Key words: mini wave soldering, PTH hole fill, copper dissolution, thermal relief.

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