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30 SMT Magazine • May 2014 Mechanical Reliability A New Method to Forecast Drop Shock Performance abstract In light of the recent technological trends within PCB manufacturing industry, there is an increasing degree of interest in understanding the influence factors of mechanical stress on the durability of mobile devices. In the past, many papers focused on PCB re- liability and the influence factors during drop shock test. In most cases, the potential influ- ence factors in regards to underfill have not been fully investigated. Additionally, there is no clear direction on the influence of the inter- action between solder mask inks and underfill systems. The intent of this article is to identify an accurate method to predict drop test behavior by understanding the surface tension of both the solder mask ink and the underfill material. This could become a significant advantage for improving the reliability of the entire electronic construct. In this paper a method has been ex- amined that can be used to subsequently ana- lyze the reliability of the latest mobile device related materials and design. The prescribed test has been constructed us- ing a cross comparison of pad design, surface finish, solder mask and underfill, measured by drop testing. Based on the resulting data, a method was evaluated to predict and optimize drop test reliability by understanding the sur- face tension of solder mask and underfill (adhe- sion). We are now able to identify specific advan- tages and limitations for different material com- binations, without the need of expensive and time intensive drop tests. In an effort to achieve a broader understand- ing of the entire process and product scope, the feATuRe by Ronald Frosch, Guenther mayr, and manfred Riedler aT&S Shanghai, China

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