Effect of RF plasma process gas chemistry and electrode configuration on the removal of copper lead frame oxidation

Abstract

Copper has a very high affinity with oxygen, and this results in oxidation forming readily on the surface of copper lead frames. Several manufacturing steps in IC packaging require the heating up of the copper lead frames and the high surface temperatures can promote the formation of oxidation on the copper surface. Many studies have shown that lead frame surface oxidation can lead to surface delamination after molding or wire bonding issues. The application of plasma treatment has been proven to be safe and effective solution to address these issues. However, the effectiveness of plasma treatment for removing oxide is dependent on the correct use of recipe parameters, gas chemistry and electrode configuration. In this paper, analytical techniques such as contact angle measurement, high magnification optical inspection and SEM-EDX are carried out on copper lead frames to evaluate the impact of using different plasma gas chemistries and electrode configurations. From the data collected, the plasma treated lead frames show a lower contact angle and reduction in discoloration on the copper surface. It is concluded that the use of Ar/H2 is better than Ar gas chemistry in removing oxide from copper lead frames. Another conclusion is the placement of copper lead frames on ground electrode is showing higher oxide removal rate than the placement on powered electrode. The key take-away from this report is that correct gas chemistry and suitable electrode configuration is necessary to obtain an optimum plasma process that requires a shorter process time and lowers the risk of overtreatment or heat related issues. From a manufacturing perspective, this results in higher production throughputs and better yields.