Solder Reliability Tests

With the advent of lead-free it is essential to evaluate several possible alloy combinations and select the most appropriate substitute for lead-based solder. 

In surface mount technology (SMT) lead is widely used in components, solder paste, and board surface finishes, hence eliminating lead would involves changes to the entire assembly process. 

A complete lead-free transition would require careful modification of several process parameters. Any lead-free alloy replacing lead-based solder should qualify with requirements such as low melting point, adequate wetting characteristics, comparable cost, consistent manufacturability (at the component level and the board level), wide availability, acceptable reliability, ease of reworkability and reparability etc [1].
Several possible combinations for lead-free are available in the market. Most commonly used lead-free solder paste is SAC305. Many alloys in this family typically have melting points ranging from 217°C to 222°C. 

Lead-free solder bumps comprises of combinations such as SAC105, SAC305, SAC405, SnAg, etc. Choosing a combination of lead-free solder bump and lead-free solder paste would
dictate the reliability of the assembly.
Today’s hand held devices are subjected to many stresses and hence requiring them to have to reinforce mechanical strength. For superior protection of solder joints against mechanical strains such as shock, drop and vibration, underfill technology should be adopted. 

Underfill technology aims to ensure that area array packages assembled on PCBs can withstand mechanical and thermal shock [2]. In order to prevent the solder joint strain at corner balls it was decided to underfill only the four corners of the package.

thermal_shock_and_drop_test_smta.pdf