Surface Mount International Conference Proceedings


Author: Robert Larmouth
Company: Teledyne Electronic Tech
Date Published: 4/28/1997   Conference: Surface Mount International

Abstract: Ball Grid Array @GA) packages offer increased I/O density with relatively coarse pitches, when compared to peripheral-leaded SMT packages of the same I/O count. Although the question “Does the lack of a compliant lead in the BGA solder joint reduce reliability?’ continues to be asked, there is evidence of steady industry acceptance of this technology. Micro-BGA technology, one example of chip-scale packaging, is an extension of this technology which allows designers to approach multi-chip module densities while continuing to employ surface mount assembly techniques. The reliability concern, however, is exaggerated since the volume of solder decreases with the finer pitch micro-BGA devices. At the same time, increased use of surface mount on flex circuits, particularly in small form factor products, is demonstrating the ability of flex to mitigate the stress created in a solder joint during thermal excursions. This paper summarizes work being done at Teledyne Electronic Technologies on assemblies employing microBGA packages on both rigid and flexible substrates. These assemblies include BGA pitches down to 0.5mm and pad diameters down to 0.3mm. Solder joint fatigue and/or cracking as a potential failure mechanism is examined, and reliability analysis data is presented as part of an overall assessment of the microBGA technology for use in products in the medical and communications markets. (Keywords: microBGA, flex, SMT-on-Flex, microvia, solder joint reliability, CSP)

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