Research On Imc Growth Regularity Of Lead-free SnAgCu/Cu Under Multiphase Field Device

With the rapid development of electronic technology, electronics and packaging technology have entered the era of the high density, intelligent, miniaturized development. Electronic products have been widely used in everyday life as well as the high-tech field of aviation, aerospace and other fields. Forced by the increasing environmental pressures, lead-free solder has become an inevitable trend in the development of electronic products. The solder and the substrate have a certain influence on the microstructure of welded joints, while the IMC is a key factor in the reliability of lead-free solder joints, the study of lead-free solder joints on IMC growth variation is very necessary. Using the wide application Sn3.0Ag0.5Cu lead-free solder as the research object, the effects of different soldering time and different conditions of service on IMC growth variation were studied, which is to provide a theoretical basis for improving the reliability of lead-free solder joints. The main contents and conclusions of the text are as follows:The growth and shear strength of IMCs at the interface between Sn-3.0Ag-0.5Cu lead-free solder and Cu substrate during different soldering time were studied. The results show that with the increase of the soldering time, the average thickness of the IMCs increases gradually and the growth index is 0.4, which is a result of the grain boundary diffusion together with crystal diffusion. The growth rate is larger when the soldering time is within 60 s. The Cu3 Sn appears between the Cu6Sn5 and Cu substrate when the soldering time is 180 s. With the increase of the soldering time, the shear strength of solder joint increases firstly, then decreases gradually. This is closely related to the growth behavior of the hard brittle phase Cu6Sn5.Based on the home-made multiphase field device, the IMCs growth behavior changes of Sn3.0Ag0.5Cu/Cu under the 30-150℃ multi-field coupling conditions were studied by comparing quasi-situ with non-situ observation prospective method. The results show that: the thickness of IMC increases with the thermal cycles increasing; At the same time, the initial scallop IMC layer changes into a plane shape.The thickness of the IMC grows faster in 400 cycles by Non-situ observation, When the thermal cycles are more than 400 cycles, the IMCs thickness grows slowly; By quasi-situ observation, when the cycles are less than 200, the IMCs thickness increases slowly, after 200 cycles, the IMCs grow faster, then the IMCs thickness increases slowly after 400 cycles. The shear strength of the sample declines rapidly with the increase of the cycles. In the early thermal cycles, the fracture morphology is mainly based on toughness fracture morphology, it has a tendency to change into brittle fracture with the increase of thermal cycles.Based on the home-made multiphase field device, microscopic morphology and growth of Sn3.0Ag0.5Cu/Cu IMCs under 30-125℃, 30-150℃thermal cycles were studied by the use of quasi-situ observation prospective method. The results show that : with the increase of the thermal cycles, the average thickness of the same IMCs increase gradually. At the same time, it is consistent with the parabola growth and its growth is controlled by diffusion mechanism. The interface compound thickness increases slowly in the intial thermal cycles; When the thermal cycles are more than 200 cycles, the IMCs grow faster, then increases slowly after 400 cycles. The thickness of the IMCs under 30-150℃ thermal cycles grow faster in the same thermal cycles. The IMCs growth has three-dimensional characteristics. Single scalloped Cu6Sn5 in longitudinal direction reduces first, then increases gradually. In the transverse direction, the average width of the same single scalloped Cu6Sn5 increases with the increase of the cycles, The IMCs which is perpendicular to the sample interface have a similar growth pattern.Based on the home-made multiphase field device, an investigation was carried on IMCs growth behavior and thickness of Sn3.0Ag0.5Cu lead-free solder under different thermal cycles with low current density which is 1.0×103A/cm2. The results show that: with the increase of thermal cycles, the thickness of the IMCs grow gradually. In the same thermal cycles, the growth index of anode IMCs and cathode IMCs are 0.59, 0.56, which grows faster than that of no current; At the same time, the growth of Cu6Sn5 is obvious. Under the same experimental conditions, the growth rate of anode IMCs is fastest. This is because chemical diffusion force and electronic wind act together to drive the growth of IMCs at the anode.