In the component finish selection avoid lead bearing finishes. The lead in the finish will dissolve into the lead-free solder. This will cause the formation of lead intermetallic phases with differing physical properties (such as expansion/contraction differences) and differing melting points. Work is ongoing to determine the long-term effects of small amounts of lead on high reliability electronics. For many consumer electronic assemblies such as mobile phones and household electronics, where the thermal cycling and condition of use are not extreme the inclusion of lead in component finishes has not demonstrated any negative characteristics to the solder joint integrity. As Japan and Europe progress with lead-free assembly numerous component finishes are already available without lead. It is important to work closely with component suppliers to insure the lead finish is lead-free compatible, the component molding plastic is able to withstand the higher temperatures associated with lead-free soldering and also the component’s reliability will not be jeopardized with the higher exposure temperatures. •Some common finishes include:
◦NiPd
◦NiPdAu
◦SnB
◦Sn
◦SnCu
◦SnAg
◦Au
◦AgPt
◦More finishes are originating from Asia
•PBGA
◦ With SnAgCu, some issues need to be investigated
•Flip Chip
◦ Patented indium alloy compatible with SnAgCu
◦ Might be exempt
•Molded Components
◦Concern about higher processing temperatures, components are available that sustain the higher soldering temperatures.
•Component Process Consideration
◦ Work closely with component suppliers
◦ Determine component lead-free finish availability
◦ Select best solderable finish and component finish shelf life
◦ Select components with compatible molded plastics and the ability to sustain the thermal requirements of the lead- free process
◦ Material handling logistics, segregate lead-free finished components from leaded components, if using both a lead-free and a leaded assembly process
◦ Insure the components and component feeders are identified as containing lead-free finishes.
◦ Train purchasing, receiving and assembly personnel on the handling procedures to avoid confusion between leaded and lead-free components during the transition stage.
◦ Identify the soldered assembly as lead-free to insure the proper rework of the lead-free components in-house and in the field.