The Influence of Printed Circuit Board Thickness on the Thermal Fatigue Reliability of Quad Flat No-Lead PackagesAuthors: Richard Coyle, David Ihms, Neil Hubble, Charmaine Johnson, Jesse deWitt, Jagadeesh Radhakrishnan, Jeffrey Lee, Greg Wu, Ranilo Aranda, and Grace O’Malley
Company: Nokia Bell-Labs, Delphi Technologies, Akrometrix, Intel Corp., IST-Integrated Service Technology, Wistron, FLEX, iNEMI
Date Published: 10/14/2018 Conference: SMTA International
The initial surface mount solder joint assembly quality was documented with x-ray inspection and metallographic cross-sectional analysis using optical and scanning electron microscopy to characterize attachment quality and microstructure. The same metallographic techniques were used for failure mode analysis and for characterizing microstructural evolution during cycling.
The failure data are reported as characteristic lifetime (the number of cycles to achieve 63.2% failure) and slope from a two-parameter Weibull analysis. One of the QFN components showed the expected decrease in reliability with increased board thickness, while the second QFN component had less of a reliability dependence on PCB thickness. The QFN component coefficients of thermal expansion (CTE) were measured using Digital Image Correlation (DIC), and the CTE of each PCB was measured using a thermomechanical analyzer (TMA). Component and PCB warpage were measured using the shadow Moiré warpage measurement technique. The ATC results are discussed in terms of the QFN attributes and the effect of PCB thickness on reliability. Additional QFN components currently are under test and those results will be reported at a future date. Finite element analysis (FEA) has been incorporated into the program to aid in correlating the relationship between the package attributes, PCB properties and thickness, and cycles to failure in each of the test profiles.
Thermal fatigue reliability, thermal cycling, lead-free alloys, QFN, printed circuit board thickness, finite element analysis.
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