Micross

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Increasing IC Leadframe Package Reliability
Keywords: popcorning, leadframe, package
As the conversion of the electronics industry to lead free soldering materials continues, some unexpected negative side effects of higher lead free reflow temperatures have occurred. Defects such as delamination or “popcorning” in surface mount lead frame components have increased significantly since lead free soldering has become mainstream. This can be attributed to the increased reflow temperatures used in PB free reflow processes. Popcorning is a defect that manifests itself as a fracture between the epoxy based encapsulant and the metal, usually copper alloy, leadframe components used to form a surface mount component. This fracture occurs when moisture in the package volatilizes during the reflow process and forces its way through the encapsulation material and leadframe interfaces. The keys to popcorning, or delamination, defect reduction is twofold. The first objective is to enhance the bond between the encapsulant and the copper leadframe materials to form a stronger bond that can resist the vapor pressures induced during reflow. The other objective is to provide a superior bond between the leadframe and encapsulant thus minimizing moisture ingress. New chemical treatment processes have been developed that pre-treat the copper surfaces of the leadframe and significantly enhance the bond between the encapsulant material and the metal leadframe. The chemical treatment process results in micro-roughening of the copper surfaces and at the same time depositing a thermally robust film that enhances the chemical bond between the epoxy encapsulant material and the copper. This paper examines two real life applications and quantifies the defect reduction when comparing standard component manufacturing methods to those that incorporate the aforementioned chemical adhesion promotion process. Components are assembled using both processes and final performance is tested using JEDEC MLS-1 conditioning protocols, acoustic microscopy analysis (SAM), and final yield improvement.
Bruce Lee, OEM Specifications Manager
MacDermid Inc.
Waterbury, CT
USA


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