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Why has lead received so much attention?

Do you consider a solder joint (SMT or thru hole) to be a homogeneous material? If so, do you agree that component lead finish; BGA solder balls; solder applied to SMT pads & thru hole components and PWB/PCB HASL finish all contribute material to the formation of their respective solder joints?

What about backwards compatibility of components, i.e.: can a lead-free component be used in a leaded process?

What lead-free materials should not be used in a lead process?

Q: Why has lead received so much attention?
A: Lead-free solders have higher melting points than traditional tin/lead solder. This therefore requires a higher soldering temperature, which potentially will require significant changes to manufacturing processes. To many customers the elimination of lead is the most important of the changes that RoHS demands.
Lead has been used in solders for hundreds of years because tin/lead solders have a low melting point, are easy to use and give reliable solder joints. Despite extensive research, no lead-free solder has been found which has identical properties. The most useful alternative alloys have higher melting temperature, which can cause damage to laminate and to heat sensitive components. Solder wetting is slower and inferior to tin lead and lead-free solder joints appear dull. As there are no drop-in replacements for tin/lead, manufacturers have a lot of work to develop new lead-free products. Criteria that need to be considered include

• Are components able to withstand the higher temperature?
• Is equipment suitable?
• Will suitable components be available, otherwise a design change may be required
• Will lead-free products be reliable?

Most components were made using tin/lead termination coatings and this also is being changed. Most component manufacturers are switching to tin but wetting characteristics will not be identical to tin/lead and there is a small risk of tin whiskers from electroplated tin coatings.

Q: Do you consider a solder joint (SMT or thru hole) to be a homogeneous material? If so, do you agree that component lead finish; BGA solder balls; solder applied to SMT pads & thru hole components and PWB/PCB HASL finish all contribute material to the formation of their respective solder joints?
A: Yes. Once the solder joint has been created, the tin alloy from the various parts listed above will combine and be one homogeneous material. The only exception would be areas of termination coating that are not covered by solder and so will have their original composition. The authorities in the EU could, in theory, analyze these materials.

Q: What about backwards compatibility of components, i.e.: can a lead-free component be used in a leaded process?
A: Backwards compatibility is a serious issue that should be evaluated on a case-by-case basis. Manufacturers data sheets and Part Change Notifications (PCNs) provide significant data to support compatibility statements

Q: What lead-free materials should not be used in a lead process?
A: The material to avoid in a lead process is bismuth. Bismuth forms a low melting phase with tin and lead and this creates weak unreliable joints