LEAD-FREE
FREQUENTLY ASKED QUESTIONS

Reliability

What is the impact of lead contamination on lead-free joints on pull and shear test results?

For small amounts of lead in SAC alloys, no difference was noticed in pull or shear test data. Gintic Singapore Consortium report showed that up to 2% by weight lead in lead-free SAC joints had no discernable negative impact. However, lead-free terminations soldered with lead-free solders are still considered the most reliable.

Lead in wave soldering however can result in some fillet lifting to occur.

What are the first steps to take to insure a reliable SMT, wave solder process with lead-free solders?

The knowledge base for Lead-free Asembly is still increasing rapidly. Choosing an alloy, which has been studied carefully is essential. SAC solders would fit this category and lots of data now exists; however this is not the case with others. Choosing an alloy, which does not have substantial historical use or limited data will therefore require substantial investment in reliability testing.

Understanding the physical and chemical properties of the lead-free solder alloy is important since many have reduced wetting behavior and higher surface tension. This will enable an engineer to optimize the soldering process to account for these differences and insure a solid solder joint.

Knowing the component finishes and board finishes and what can be expected during soldering will enable proper selection of fluxes designed to solder them. Chose a flux system designed for lead-free.

After consideration is given to equipment compatibility a DOE should be run to determine the best process parameters to achieve good lead-free solder joints.

Proper training will be required since the cosmetics of lead-free joints are different in cosmetics and wetting spread and wetting angles when compared to 63/37 leaded joints.