Experimental Investigation Of The Mechanical Behavior Of IMC In Solder Joints Under Various Strain Rates

At present, application of electronic products in today’s society is becoming morecommon. The electronic packaging provides a stable environment for electronicproducts and components. Every electronic packaging contains a lot of solder joints.Solder joints in electronic packages serve as electrical connections and mechanicalsupports. The solder joint is usually fabricated by the reflow process, in which a liq uidsolder alloy reacts with a solid metal substrate to form a thin layer of intermetalliccompounds （IMC） at the bonding interface. The IMC layer is essential for theformation of a functional and robust metallurgical bond in a solder joint interface.However, an excessively grown IMC layer becomes vulnerable and severely degradesthe mechanical strength of the solder joints. All kinds of electronic products will haveto experience vibration, shock, drop and so on. Therefore, further understanding of theIMC growth and its effect on the mechanical behavior of the solder joints issignificant for the implementation of lead free solders in electronics industry.The samples of Sn0.7Cu/Cu solder joints are made and aged isothermally at150degrees centigrade for0,72,168,288and500hrs. It turned out that with the increaseof aging time, IMC bulge height decreased, center distance between adjacent grainsincreased, IMC continuous part thickness increased, all of which indicates that theIMC and solder interface morphology became flat and IMC average thicknessincreased.The tensile tests of the aged solder joints samples are conducted under thestretching rate of0.012mm/min,1.2mm/min and120mm/min, the strain rates are2×103,2×101and2×10s1.The test results show that, at the strain rate of0.002s-1,the tensile strength of specimens keeps declining with the increasing aging time; at thestrain rate of0.2s-1, the downward trend of the tensile strength of specimens slowsdown with the increase of aging time, at the strain rate of20s-1, the tensile strength ofspecimens fluctuate with the increasing aging time.After tensile test, we observe the fracture by optical microscope and ScanningElectron Microscope （SEM） to research the relationship between fracture mode andsolder tensile strength. Results indicate that, at low strain rate the failure mode ofsolder joints mainly present ductile fracture mode of solders, with the increasing strain rate, the failure modes of solder joints are combined of solder’s brittle fracture andIMC’s ductile fracture, and finally mainly present the form of brittle fracture mode.