ICSR (Soldering and Reliability) Conference Proceedings


EFFECT OF SILVER IN COMMON LEAD-FREE ALLOYS

Authors: Ranjit Pandher and Tom Lawlor
Company: Cookson Electronics Assembly Materials
Date Published: 5/22/2009   Conference: ICSR (Soldering and Reliability)


Abstract: Silver bearing alloys have been used in electronics soldering for many years. Silver has been used in tin-lead solders (Sn62Pb36Ag2) to combat silver scavenging from silver plated electronic components as well as to improve thermal fatigue resistance. Many of the common lead-free alloys contain some amount of silver. Silver bearing alloys have good electrical and thermal conductivity as well as the ability to wet to the common surface finishes used in printed wiring assemblies, thus giving it all the attributes needed for an electronic solder alloy. Presence of silver in Sn based solders increases the bulk solder modulus and is generally believed to improve resistance to fatigue from thermal cycles. Increased solder modulus can be advantageous or disadvantageous depending on the desired performance attribute. For example in high strain rate situations, higher modulus of the bulk solders results in lower life time.

A wide variety of leaded and lead-free solders containing different levels of silver has been studied and is in use in electronics industry for a wide range of applications right now. Studies specific to application process, or performance attributes have been conducted and reported in technical and commercial publications. At Cookson Electronics we have investigated a whole range of solder alloys containing various levels of silver for various reasons and for a variety of applications. There is need in the industry to understand the effects of silver presence in solders from various applications perspective. This article will attempt to present a review of the key published results on the silver containing alloys along with results of our internal studies on wave soldering, surface mount and BGA/CSP applications. Advantages and disadvantages of silver at different levels will be discussed. Specifically this report will focus on the effect of silver on process conditions, drop shock resistance, solder joint survivability in high strain rate situations, thermal fatigue resistance, Cu dissolution and effects of silver in combination with other alloy additives. Specific application problems demanding high silver level and other requiring silver level to the minimum will be discussed.



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