Size effect of Sn3.0Ag0.5Cu solder joint on intermetallic layer growth

In the current study, the size effect of Sn3.0Ag0.5Cu solder joints on intermetallic growth is investigated. Experiments were performed to solder joints with a diameter of 2 mm and the solder thickness ranges from 2 mm to 50 μm. The thickness of intermetallic compound (IMC) of solder joints with different thickness as reflowed are found to be dependent on the size of solder joints. The IMC of small size solder joints as reflowed is thinner than those in the large size solder joints. To probe into the difference of IMC growth during solid state and liquid state thermal aging, IMC of solder joints after thermal aging at 210°C and 300°C is investigated. It finds out that IMC growth rate exhibits clearly size effect and there are different relations between solder joint size and IMC thickness for solid state thermal aging and liquid state thermal aging. IMC thickness of solder joints after thermal aging for different time was measured. For solid state thermal aging under 210°C, there are linear relation between IMC thickness and square root of time and the slope is the square root of IMC growth rate. The larger size solder joint possess larger IMC growth rate. For liquid state reaction conditions, 300°C thermal aging and reflow procedure, there are similar tendency between IMC and solder joint thickness. The IMC growth rate of smaller size solder joints are faster than larger size solder joints under solid state thermal aging, while in liquid state reaction the IMC growth rate of smaller size solder joints are slower than larger size solder joints. Prism-like Cu₆Sn₅ was observed in 2 mm and 1mm thickness size solder joint, respectively, while fewer Cu₆Sn₅ prism was found in 50 μm thickness solder joints.