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Finite Element Simulation and Experimental Characterization of Shear Fracture Behavior of BGA Structure Sn3.0Ag0.5Cu Solder Interconnects and the Joint Volume Effect

Author: XiaJianMin
Tutor: ZhangXinPing
School: South China University of Technology
Course: Materials Processing Engineering
Keywords: Solder Joint Reliability Shear fracture Volume effect Stress intensity factor Torsional Angular
CLC: TN05
Type: Master's thesis
Year: 2011
Downloads: 115
Quote: 1
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Abstract

With the continuous miniaturization of electronic products, fine pitch interconnect and high-density packaging technology developed rapidly, the volume of the corresponding interconnect solder joints are gradually reduced. Solder joint size is decreasing, however, the microstructure and mechanical properties are changed, showing a significant effect of solder volume (or size). Therefore, the research solder volume decreases due to variation of the microstructure and mechanical properties (ie solder volume effect) is particularly important. The the interconnect solder joints under actual working conditions is mainly exposed to shear stress caused by the different thermal expansion mismatch, and therefore the shear test to better reflect the actual solder joint loading conditions as well as the failure mechanism. In this paper, two-dimensional finite element simulations and experiments carried out in-depth study of different volume (height) BGA the structure Cu/Sn3.0Ag0.5Cu/Cu solder joints under shear load of crack initiation and propagation, fracture paths and fracture mechanism, solder volume (height) of its secondary reflux interface IMC growth and its evolution, fracture strength, fracture morphology and fracture mechanisms. First, based on the volume of solder reflow before and after to maintain the same assumptions combined with minimum energy method, a simple post-reflow solder joint appearance calculated and solder joint height of 0.30 mm and reflux before the ball diameter 0.60 mm as a reference to calculate the different solder joint height (i.e. 0.10,0.15,0.20,0.30 and 0.50 mm) the shape parameters of the interconnect pads and the required size of the solder balls. According to the results, the use of reasonable reflow process, different volume (height) BGA Solder joint specimens were prepared, and the finite element model. Then, the study of the growth and evolution of the solder joints secondary reflux of IMC. The results show that: the thickness of the interface IMC with the reduction in solder joint height increases, and the brazing material in vivo tissue tends to refine. After 1000 hours of aging at 125 ℃ interface IMC thickness increases, the Cu / Cu ₃ Sn and Cu _{3 6} Sn _{AND 5} the interface well Cu ₃ Sn and Cu ₆ Sn ₅ layer Kirkendall voiding and void density is reduced with the solder joint height increases. Dynamic mechanical analyzer (DMA) to test the shear strength of the solder joints of different volume and analyzed by SEM fracture morphology. The results found that the shear strength of the solder joints after aging decline; unaged solder joints under shear cracks, mainly in Cu ₆ Sn ₅ / brazing the material interface near the interface Cu ₆ Sn ₅ initiation and rapid to the solder vivo expansion; However, after 1000 hours of aging at 125 ℃ solder cracks in the Cu ₃ Sn / Cu interface initiation, transfer to the solder vivo expansion and expansion of certain regions within the IMC, higher solder joint height, the greater the expansion area within the IMC. Using the finite element method to simulate the deformation behavior of the solder joints. The research results show that the solder joint fracture path consistent with the distribution of characteristics of high Von Mises plastic strain. Different height pads average elastic, plastic, and the shear strain is less than the nominal deformation. In the case of small strain (less than 5%), the average strain of the solder joints with the solder joint height decreased and increased, larger strain (5%) under reduced height decreases with solder. Only when the solder in the solder joints is plastically deformed, the shearing effect began to spread in the solder joint. Finally purely elastic and visco-plastic fracture behavior of the solder joint. The research results show that different properties of solder joints showed tensile fracture (ie, K _{I led) rather than shear type (ie K _Ⅱ-led) fracture. Preset crack away from the IMC / solder interface position is constant, the same volume of solder joint fracture parameters are similar regardless of the thickness of the interface IMC. IMC thickness, the crack distance interface farther then the stress intensity factor (K _Ⅰ and K _Ⅱ) and twisted Angular (θ) the greater, the direction of crack propagation in Vietnam small crack is more likely to expand in the IMC.}

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