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Title: Mechanics of interfacial delamination under hygrothermal stresses during reflow soldering
Authors: Lin, T.Y.
Tay, A.A.O. 
Issue Date: 1997
Source: Lin, T.Y.,Tay, A.A.O. (1997). Mechanics of interfacial delamination under hygrothermal stresses during reflow soldering. Proceedings of the Electronic Technology Conference, EPTC : 163-169. ScholarBank@NUS Repository.
Abstract: Inherent voids or defects at the interface between the die-pad and the plastic encapsulant become sites of stress concentration when the IC package absorbs moisture or undergoes reflow soldering. If the stress intensity factor at the interfacial voids exceeds the critical fracture toughness of the pad-encapsulant interface, delamination will occur which will eventually lead to popcorn cracking. In this paper, the mechanics of interfacial delamination under hygrothermal stress during solder reflow will be discussed. A methodology of computing the resultant total stress intensity factor due to the combined effects of hygro- and thermal stresses will be presented. The methodology will then be applied to study the effect of prebaking on delamination during solder reflow. To verify the methodology, a series of experiments was conducted in which several plastic IC packages were fabricated with a very small defect at the pad-encapsulant interface and preconditioning at 85 °C/85%RH for 168 hours. The packages were then prebaked at 150 °C for varying periods such as half an hour, 6.5 hours and 24 hours before being placed in varying high temperature environments in an oven. Over temperatures ranged from 185 °C to 200 °C. The packages were then examined for delaminations using a scanning acoustic microscope. It was found that when the prebaking period was short, delamination occurred. The methodology developed was applied to predict the minimum period of prebaking to avoid delamination during solder reflow. Good agreement was obtained between predicted and observed values.
Source Title: Proceedings of the Electronic Technology Conference, EPTC
Appears in Collections:Staff Publications

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