The Effect of Mixed Gas Ar+H2 Strip Plasma onto the Non-Roughened and Oxidation-Roughened Bare Cu Leadframe Surfaces

Abstract

High power applications have driven the package assembly to design devices into more robust packaging at lower manufacturing cost that could survive stringent reliability tests with no consequent failures such as delamination. For molded packages, the industry slowly shift to non-plated bare Cu leadframes for higher mold adhesion as the organic compound has higher affinity to Cu surfaces. However, the risk of oxide formation on top surface is deemed detrimental especially when exposed to series of heat processes along with material staging time in an uncontrolled environment. Plasma treatment prior mold has been introduced as dry method for isotropic and homogenous cleaning of surface impurities on metal surfaces. Different plasma chemistries are being utilized for different applications on device packaging with varying surface alteration effect. Plasma cleaning has two different mechanisms-through physical sputtering and through chemical reaction. Pure Ar plasma are widely used for surface activation and has prominent sputtering effect which causes micro to submicron surface roughening. However, material redeposition of etched particles from the topmost layer are commonly encountered which causes performance failure such as leakage current. The pure Ar plasma composition could not also completely remove the unwanted oxide layers since inert Ar ion species are highly unreactive and thus has a less effective surface cleaning. On the other hand, the mixed gas plasma chemistry with a certain percent amount of Hydrogen introduces minimal to no surface alteration as the primary reactive Hydrogen radicals react with organic layers producing volatile hydrides byproduct during chemical reaction with oxides thus cleaning the surface and exposing the base metal [1]. The study focused on surface characterization of non-roughened and oxidation-roughened bare Cu leadframes in response of 95:5 $\text{Ar}+\mathrm{H}2$ strip plasma to assess the effectiveness and define optimized parameters for efficient oxide surface cleaning of mixed gas plasma chemistry in response to 0-hour and post reliability mold-to-Cu surface interface delamination and test performance.