Fast characterization for moisture properties of moulding compounds: influence of temperature and humidity

Moisture induced failure is a major problem in modern IC technology. When there is moisture present in the moulding compound before the chip is soldered to the printed circuit board, or gets another heat treatment, the moisture expands. With the stresses that are introduced by the expanding compound, the package can crack, causing the failure. If the moisture concentration or the gradient in a material exceeds a critical value, the package breaks in the assembly process or fail during its lifespan due to the moisture. To find this critical value the standard tests, such as the assessment of moisture sensitivity levels (MSL), are useful, because they have proven to simulate real life use. However, for each new moulding compound material, such standard tests are needed, which may take up to 3-6 months of time. It would be more efficient to select these materials in advance, if the moisture behavior is known. If the moisture concentration distribution could be predicted before the final product is made, the time needed to develop a new product can be shorter. At present, no proper methods are available for fast characterization of moisture properties of epoxy materials. Even more, the exact relationships of such properties with temperature and humidity conditions are not exactly known. This paper describes our research to find these relationships. To find the relationships there are a series of tests proposed with varying room humidity´s or temperatures. With the results of these tests and by using a fitting algorithm, the saturation concentration and diffusion coefficient for the compound can be deducted. It also allows us to validate whether the numerical approximation to Fick´s second law is accurate enough to describe the moisture distribution in epoxy materials. Based on the formulas, a set of tests can be defined for fast characterization of epoxy materials to enable efficient material selection that can be used in the early stages of product development. The present stage of research is to validate the formula´s found describing the dependencies of the diffusion coefficient and saturation concentration on humidity and temperature.