A Comparison of Passivation Techniques for Corrosion Protection of Metal Core Substrates

摘要

Thin, metal-core substrates as system or package carrier have thermal and electrical performance advantages. Metal for the core has to fit the mechanical needs of the module. Carefully selected Fe/Ni compositions can fulfill custom needs for a system, package or module. But the iron in the Fe/Ni composition is susceptible to corrosion especially under high temperature, humidity, and pressure. Metal-core substrates are typically coated with a dielectric layer before they can be put to use as high performance packaging substrates. One of the methods to assess the reliability of dielectric coated substrates is the IPC test method 2.6.16.1. In this test, samples are subject to highly accelerated stress testing (HAST). HAST is used to evaluate the capability of a dielectric layer to withstand stress induced by moisture and pressure. During such a test, the porosity of the dielectric may cause the moisture to penetrate to the Fe/Ni metal-core and induce corrosion. Corrosion, apart from weakening the integrity of the package, may also affect the adhesion of the dielectric layer. In our investigation, bubbling of the dielectric layer was noticed in the absence of a suitable passivation layer to prevent corrosion of the metal-core.