Investigations on High-Power LEDs and Solder Interconnects in Automotive Application: Part I—Initial Characterization

Abstract

Thermo-mechanical reliability is one major issue in solid-state lighting. Mismatches in the coefficients of thermal expansion (CTE) between high-power LED packages and substrates paired with temperature changes induce mechanical stress. This leads to a thermal degradation of LED modules by crack formation in the solder interconnect and/or delamination in the substrate, which in turn increases junction temperature and thus decreases light output and reduces lifetime. To investigate degradation and understand influence of LED package design and solder material, a reliability study with a total of 1800 samples − segmented in nine LED types and five solder pastes − is performed. First of all, in this paper a state-of-the-art review of high-power LED packages is performed by analyzing and categorizing the packaging technologies. Second, the quality inspection after assembly is realized by transient thermal analysis (TTA), scanning acoustic microscopy (SAM) and X-ray. For TTA, a new method is introduced to separate the thermal resistance of the LED package from solder interconnect and substrate by applying the transient dual interface method (TDI) on samples with different solder interconnect void ratios. Further measurement effort is not required. The datasheet values for thermal resistance are verified and the different LED package types are benchmarked. The void ratio of the solder interconnects is determined by X-ray inspection combined with an algorithm to suppress disruptive internal LED package structures. TTA and TDI revealed that initial thermal performance is independent of solder paste type and that voiding is more critical to smaller LED packages. In addition, lower silver proportion in the paste is found to increase voiding. SAM is less sensitive for initial void detection than Xray, but it's applied to monitor crack propagation while aging in combination with TTA. The results of the reliability study, i.e., the crack growth under temperature shock test for the different SAC solders, will be presented in a second independent paper.

X-ray Void Defect Detection in Chip Solder Joints Based on PCB-DeepLabV3 Algorithm

“…The study objects used in this work are nine types of LED chips from seven manufacturers 12 , all packaged using surface mount technology (SMT). The dataset contains a total of 450 LED chips on 20 substrates, with each LED chip mounted on a designated position on the substrate with solder paste brushed on it, and all the LED chips were acquired on a 2D X-ray device using the same settings.…”

“…Nowadays advanced AXI equipment has been commonly used in the integrated circuit industry 11 , with the help of X-ray penetration properties of different substances to successfully image the hidden defects, which is convenient for technicians to check the quality of solder joints. The method proposed in this paper can provide an intelligent modi cation to the existing automatic X-ray inspection 12 equipment. Because AXI equipment still needs technicians to con rm visually, this paper combines the deep learning-based PCB-DeepLabV3 image segmentation algorithm to propose an automated inspection method, which gets rid of the dependence on the technician's experience and greatly improves the inspection e ciency and accuracy in the industrial scenario.…”

Effect of solder void on mechanical and thermal properties of flip-chip light-emitting diode: Statistical analysis based on finite element modeling

“…On the other hand, the thermo-mechanical reliability of these components has been a focal point of research [ [4] , [5] , [6] , [7] , [8] ]. The performance of FCLEDs relies heavily on the material of the FCLED, the interconnecting solder material, and the substrate material of the printed circuit board (PCB).…”

Design and Application of Led Driver Based on Isolated DC-DC Cuk Converter by Comparing Power Led Models

“…[18] realizes adaptive control system considering thermal calibration, [19] designs robust PI controller. [20] investigates thermal degradation of solder interconnection of power LED, [21] examines thermal performance of power LED by experimentally. For high frequency application GaN switch is used in [22].…”