Influence of humidity on reliability of plastic packages

Polymers are widely used in microelectronics packaging as e.g. adhesives or encapsulants. Low cost and mass production capabilities are the main advantages of these materials. But like all polymers they cannot provide a hermetical sealing due to their permeability properties. The susceptibility to diffusion of liquids and gases through the polymer and along the interfaces is a drawback for polymers in general, as water or other media inside a microelectronic package might lead to softening and to a decreasing adhesive strength and resulting delaminations close to solder bumps or wire bonds. These delaminations are reducing package reliability by corrupting the package structural integrity and provoking corrosion at the revealed metal interconnects. In addition the absorption of humidity causes a volume increase of the polymer, i.e. swelling, which can also lead to extra package stress which might be especially critical for sensor packages. Also mechanical, thermo-mechanical and electrical properties could be influenced by the absorbed water. Different methods for characterization of humidity absorption, diffusion, permeation, swelling and property changes with respect to microelectronics application have been developed and applied for material characterization and evaluation. The pros and cons of these different approaches are presented and discussed along testing results with relevant examples. The results of the measurement allow supporting miniaturized microsystems packaging by system design concerning packaging concept, geometrical layout as well as material selection and modeling of the package with focus on diffusion, swelling or material degradation and therewith are forecast on the later reliability of the overall system.