Lead-free solder replacement: Beyond the material substitution

Various studies have identified alternatives for tin-lead solder. Characteristics such as availability, melting point, shear strength, and solderability have led to different alternatives being recommended for different applications. The most critical effect is in reflow soldering, where tin-lead solder has been heated to 220°C, and the recommended temperature for the alternative alloys is 260°C. A different degree of preparation for lead-free technologies exists when comparing board subassemblies with components. Board finishes with lead-free materials have been used for years with varying success. Palladium-based component finishes have also been available, but the greatest concern for components exists in plastic-encapsulated packages. Moisture sensitivity of packages that will be heated 40°C above current processing levels presents the potential of delamination and cracks. CALCE Electronic Products and Systems Center (EPSC) has been investigating the primary issue in the use of lead-free soldering, which is the reaction of currently available components to the higher temperatures during processing. Concern exists for the stability and heat resistance for such components as plastic-encapsulated devices, printed circuit boards, and connectors. In most cases the time and temperature of the new reflow profiles exceed those parameters on the components manufacturer's data sheets. Potential problems that could result include popcorning, cracking, and malfunctioning.