SMTA International Conference Proceedings

Lead-Free Vapor Phase Assembly Compatible Materials For A High Performance Smt Daughter Card Connector

Authors: Matt Kelly, Ying Yu, John Healey, Wai Ma, Emanuele Lopergolo, Jing Zhang, Jay Diepenbrock, Theron Lewis, Vijay Khanna, Ruediger Kellmann, and Jim Bielick
Company: IBM Corporation
Date Published: 10/16/2011   Conference: SMTA International

Abstract: With the possible future expiration of European Union (EU) Restriction of Hazardous Substances (RoHS) exemptions, allowing the use of leaded solder for the assembly of Server, Storage, and other high performance, high reliability systems, comes the need to establish new lead-free assembly processes. As the conversion to lead-free (LF) printed circuit board assembly (PCBA) processing continues to extend into high performance Server hardware platforms, new challenges have been encountered with high density, high complexity connectors. One such case involves various configurations of an SMT daughter card connector used across mid-range and high-end Server systems. This very dense, large thermal mass connector system creates significant challenges for the SMT assembly process. A basic requirement for transitioning from a leaded to a lead-free SMT solder assembly process is that connector materials be capable of surviving higher temperature exposures. At the same time, these materials must meet electronic signal integrity requirements. Furthermore, connector long-term reliability in the field environment, as simulated by accelerated thermal cycling, must not be compromised. This paper characterizes several material options for an SMT daughter card connector which is exposed to a lead-free vapor phase solder assembly process. The characterization includes base material properties, warpage during reflow, post-assembly inspections and measurements, signal integrity, and thermal fatigue performance. Key words: daughter card / backplane connectors, lead-free compatible materials, high complexity SMT connectors, lead-free vapor phase assembly

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