SMTA International Conference Proceedings

Pb-Free Design and Implementation Guidance in High Performance Engineering Design

Authors: Anthony J. Rafanelli, Ph.D., PE
Company: Raytheon Company
Date Published: 9/17/2017   Conference: SMTA International

Abstract: Since the mid-1990’s, in anticipation of enactment of the July 2006 European Union Restriction of Hazardous Substances regulation [1], the aerospace, defense, and other high performance (ADHP) electronics industries have been working to address the challenges of incorporating Pb-free (elemental lead-free) materials in electronics, i.e. as interconnection media (solder joints) and for surface finishes (e.g. pure tin). While these companies continue to be excluded from the restrictions, the impact is still significant since the commercial supply chain has converted to Pb-free solder for the majority of their products.

ADHP industry dependence on commercial-off-the-shelf (COTS) products has led to concerns as to how these products will perform under the harsh service, environmental, and storage conditions typical of many system life cycles. Prior to Pb-free solder, tin-lead (Sn-Pb) solders were the standard interconnection material for most electronics. A substantial database was generated to help predict performance behavior thus facilitating design and manufacture of ADHP products. Pb-free performance characteristics in ADHP applications are, to date, minimal or unknown thereby warranting generation and comprehension of a new performance database. Given the variety of Pb-free choices in the marketplace, generating this database is an overwhelming task. While some suppliers continue to provide tin-lead products, this “luxury” is viewed as a limited resource since consumer market demands may force reduction/termination of leadbased production lines. New products (as well as updates to traditional parts) are being introduced exclusively in Pb-free form. Figure 1 illustrates ADHP dependence upon the global supply chain. In general, ADHP companies must address two major concerns with the inception of Pb-free technology: 1. performance of the soldered interconnection and 2. potential deleterious effects of tin whisker formation from Pb-free finishes using pure tin. The first concern becomes more complex expanding into a long term issue that centers around the use of Pb-free and mixed Pb-free assemblies and the ability to sustain systems that use them. For example, when using mixed technology in repairing assemblies, remember that the Pb-free solder may require higher reflow temperatures. Thus, in addition to concern about Pb-free performance, one also needs to consider how much of the life time is impacted as a result of exposure to the higher temperature [2]. Thus, the first concern results in a third concern of long term sustainment of Pb-free and mixed assemblies.

Therefore, in order to aid the designer in “tolerating” the impact of a Pb-free supply chain, the IPC PERM Council and its Research Coordination/Technical Guidance team initiated an effort to generate a guide. The sole purpose of alerting users to the properties, impact, effects, and challenges (risks) associated with Pb-free materials as interconnection media and plating finishes.

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