SMTA International Conference Proceedings


Authors: Andrew Mawer et al.
Company: Freescale Semiconductor, Inc.
Date Published: 9/25/2005   Conference: SMTA International

Abstract: Ball grid array (BGA) packages based on the high coefficient of thermal expansion (CTE) ceramic substrates have previously been shown to provide excellent reliability [1,2]. The glass-filled ceramic, with a room temperature CTE of 12.3 ppm/ºC, has also been found to provide excellent solder joint reliability in Land Grid Array (LGA) form [3,4]. As an LGA, the package is shipped without spheres and the interconnect to the PCB is formed solely by the stencil printed assembly solder [5,6].

LGA eliminates the possibility of spheres being damaged in shipping or handling and resphering for reuse or test is not necessary after removal. The use of Pb-free assembly solder, along with a Pb-free capacitor attach solder interconnect to the LGA substrate, allows the package to be a Pb-free solution.

LGA also has a lower mounted height which may benefit space limited applications and may result in improve delectrical and/or shock performance. This paper outlines a high CTE ceramic LGA SMT assembly process and reliability study that was carried out using SnPb and Pb-free solder pastes. LGAs were assembled to boards with four different stencil thickness and aperture diameter combinations.

Assembly yields and observations for each combination will be reported. Extensive X-ray and crosssectional analyses were carried out to characterize joint geometries and the extent of voiding. The boards were placed into thermal cycling from 0 to 100ºC until >50% failure and post-cycling data and failure analysis results will also be presented.

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