Most manufacturers and service providers in the electronics industry are well aware that to meet the RoHS directive they will need to adapt solder processes that use alloy compositions that are free of lead. And by now they know that the alloy composition finding favor for most commercial applications is basically tin with a relatively small percentage (by weight) of silver and less than one percent of copper. This so called ‘SAC’ alloy combination is classified as a near eutectic composition and has proved (for a majority of applications) to be a viable substitute for the lead-bearing eutectic solder traditionally used for electronic assembly. A number of concerns for the end products survivability when processed with the lead-free alloy compositions remain however. While many will find that the SAC solder joint reliability meets the stresses typically experienced for a wide number of use conditions, the higher process temperatures required to complete the joining process can adversely impact product reliability resulting from acute material degradation. One exposure to the lead-free solder process may not be of concern but repeated exposures to high process temperature, typical for more complex assemblies, may severely impact the physical integrity of the resin systems used in the circuit board laminates, as well as the number of passive components and even the molding compounds traditionally used for encapsulating Ics. This paper considers the potential for product failure due to exposure to the higher process temperatures required for lead-free soldering and examines new industry standards for a PCB laminate systems that are also RoHS compliant. Included are options for compatible surface plating and coatings and the reflow solder profiles that have been proposed for soldering with the tin, silver, copper (SAC) alloy compositions.
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