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Thermal analysis of chip-on-flexible LED packages with Cu heat sinks by SnBi soldering

Yang Liu (Department of Materials Science and Engineering, Harbin University of Science and Technology, Harbin, China)
Fenglian Sun (Department of Materials Science and Engineering, Harbin University of Science and Technology, Harbin, China)
Cadmus A. Yuan (Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China)
Guoqi Zhang (DIMES Center for SSL Technologies, Delft University of Technology, Delft, Netherlands)

Microelectronics International

ISSN: 1356-5362

Publication date: 4 January 2016

Abstract

Purpose

The purpose of this paper is to discuss the possibility of using soldering process for the bonding of chip-on-flexible (COF) light-emitting diode (LED) packages to heat sinks. The common bonding materials are thermal conductive adhesives. For thermal performance and reliability concerns, Tin-Bismuth (SnBi) lead-free solder paste was used for the connection of the COF packages and the Cu heat sinks by a soldering process in this study. Meanwhile, the geometrical effect of the SnBi solder layer on the thermal performance was also investigated.

Design/methodology/approach

The effects of the bonding materials and the area of the solder layers on the thermal performance of the LED modules were investigated by finite element simulation and experimental tests.

Findings

The SnBi soldered modules show much lower thermal resistance at the bonding layers than the adhesive-bonded LED module. Vertical heat transfer from the LED chips to the heat sinks is the primary heat dissipation mode for the SnBi soldered modules. Thus, the LED module with local solder layer shows similar LED thermal performance with the full-area soldered module. Meanwhile, the local soldering process decreases the possibility to form randomly distributed defects such as the large area voids and residue flux in the solder layers.

Research limitations/implications

The research is still in progress. Further studies mainly focus on the reliability of the samples with different bonding materials.

Practical implications

COF package is a new structure for LED packages. This study provides a comparison between SnBi solder and adhesive material on the thermal performance of the LED. Meanwhile, the authors optimized the geometrical design for the solder layer. The study provides a feasible bonding process for COF packages onto heat sinks.

Originality/value

This study provides a soldering process for the COF LED packages. The thermal performance of the LED light source was improved significantly by the new process.

Keywords

Acknowledgements

The authors would like to thank the Chinese State Key Laboratory of Solid State Lighting for providing the financial and equipment support. They also thank the Research and Scientific Foundation of Heilongjiang Education Department (No. 12541112) and University Nursing Program for Young Scholars with Creative Talents in Heilongjiang Province (UNPYSCT-2015042).

Citation

Liu, Y., Sun, F., Yuan, C. and Zhang, G. (2016), "Thermal analysis of chip-on-flexible LED packages with Cu heat sinks by SnBi soldering", Microelectronics International, Vol. 33 No. 1, pp. 42-46. https://doi.org/10.1108/MI-04-2015-0034

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Publisher

:

Emerald Group Publishing Limited

Copyright © 2016, Emerald Group Publishing Limited

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