SMTA International Conference Proceedings


Author: Pradeep Lall et al.
Company: Auburn University
Date Published: 9/26/2004   Conference: SMTA International

Abstract: Increased use of sensors and controls in automotive applications has resulted in significant emphasis on the deployment of electronics directly mounted on the engine and transmission. Increased shock, vibration, and higher temperatures necessitate the fundamental understanding of damage mechanisms which will be active in these environments. Electronics typical of office benign environments uses FR-4 printed circuit boards. Automotive application typically use high glass-transition temperature laminates such as FR-406 glass/epoxy laminate material (Tg = 164.9°C). In application environments, metal backing of printed circuits boards is being targeted for thermal dissipation, mechanical stability and interconnections reliability.

There have been several studies on electronic reliability for automotive environments [Lall 2003, Syed 1996, Evans 1997, Mawer 1999]. However, none of the previous studies address the damage mechanics of electronics on metal backed substrates. Published data on crack propagation has targeted ceramic BGAs [Darveaux 1992, 1995, 2000] and plastic BGAs on glass-epoxy laminate [Lall 2003]. In this work, the effect of metal-backed boards on the interconnect reliability will be evaluated. Other failure mechanisms investigated include - delamination of PCB from metal backing.

The test vehicle is a metal backed FR4-06 laminate. Metal backings investigated include - aluminum and beryllium copper. Three adhesive have been investigated for metal backing including - arlon, pressure sensitive adhesive and pre-preg. The use of conformal coating for reliability improvement has also been investigated. Component architectures tested include – plastic ball grid array devices, C2BGA devices, QFN, and discrete resistors. Reliability of the component architectures has been evaluated for HASL and electroless Ni/Au finishes.

Crack propagation and intermetallic thickness data has been acquired as a function of cycle count. Reliability data has been acquired on all these architectures. Material constitutive behavior of arlon and PSA has been measured using uni-axial test samples. The measured constitutive behavior has been incorporated into non-linear finite element simulations. Predictive models have been developed for the dominant failure mechanisms for all the component architectures tested.

Key words: Metal-back, Solder Joint, Reliability

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