Attachment Quality and Thermal Fatigue Reliability of a Surface Mount Chip Resistor Assembled with a Low Temperature SolderAuthors: Charmaine Johnson, Richard Coyle, Martin Anselm, Lenora Clark, Richard Popowich, Ajitesh Singh Parihar, Tayler Swanson, Jason Fullerton, and Chen Xu
Company: Nokia Bell Laboratories, Rochester Institute of Technology, MacDermid Alpha Electronic Solutions
Date Published: 9/22/2019 Conference: SMTA International
In this study, a daisy chained printed circuit board (PCB) test vehicle was used to evaluate the thermal fatigue reliability of the solder joints of a 2512 chip resistor assembled with a commercial LTS compared to a SAC305 performance baseline. Two PCB surface finishes were included as variables, immersion Ag (IAg) and immersion Sn (ImmSn). ImmSn may have solderability limitations due to Cu-Sn intermetallic (IMC) growth and oxidation resulting from multiple reflow processes or exposure during long term storage. The potential for final finish degradation and loss of solderability were addressed using high temperature storage and reflow preconditioning as additional variables.
Thermal cycling was used to characterize and compare the resistor thermal fatigue reliability with LTS and SAC305, and to assess any effects of surface finish and preconditioning. The interconnect metallurgy and microstructural characterization were compared for all solder alloys and surface finishes and discussed in relation to the thermal cycling results.
Low temperature solder, thermal fatigue reliability, surface finishes, thermal preconditioning
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