Abstract
To make the light-emitting diode (LED) more compact and effective, the flip chip solder joint is recommended in LED chip-scale packaging (CSP) with critical functions in mechanical support, heat dissipation, and electrical conductivity. However, the generation of voids always challenges the mechanical strength, thermal stability, and reliability of solder joints. This paper models the 3D random voids generation in the LED flip chip Sn96.5–Ag3.0–Cu0.5 (SAC305) solder joint, and investigates the effect of thermal shock load on its mechanical reliability with both simulations and experiments referring to the JEDEC thermal shock test standard (JESD22-A106B). The results reveal the following: (1) the void rate of the solder joint increases after thermal shock ageing, and its shear strength exponentially degrades; (2) the first principal stress of the solder joint is not obviously increased, however, if the through-hole voids emerged in the corner of solder joints, it will dramatically increase; (3) modelling of the fatigue failure of solder joint with randomly distributed voids utilizes the approximate model to estimate the lifetime, and the experimental results confirm that the absolute prediction error can be controlled around 2.84%.
Highlights
As it has advantages of high light efficiency [1], small volume [2], long lifetime [3], rapid response, and being environmentally friendly [4], light emitting diodes (LEDs) have become one of the most popular optoelectronic light sources and have been widely applied in the field of general lighting, displays, and communications, among others [5,6]
The simplified LED model includes the LED chip, SAC305 solder joint, and substrate, whose materials are considered as isotropic
To investigate the reliability of the SAC305 solder joint used in a LED chip-scale packaging (CSP), the 3D modeling of solder joints with randomly distributed voids was firstly established in this study with statistical methods
Summary
As it has advantages of high light efficiency [1], small volume [2], long lifetime [3], rapid response, and being environmentally friendly [4], light emitting diodes (LEDs) have become one of the most popular optoelectronic light sources and have been widely applied in the field of general lighting, displays, and communications, among others [5,6]. Materials 2020, 13, 94 power, heat generation, and packaging density are becoming higher and the operation condition is severer, the demand on the highly reliable LED CSP is dramatically increasing [9,10]. The increase of loads on a LED CSP has put forward more requirements on the reliability of a solder joint, because the fatigue failure of the solder joint under the thermal cycling condition will lead to the failure of whole package. The thermal shock load on the mechanical reliability of the LED flip chip solder joints has always been one of the critical bottlenecks in the development of LED CSP technology [13,14,15]
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