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Plastic Molding Compounds
Materials used for encapsulating semiconductor devices are known as plastic molding compounds. Molding compounds are generally composite materials consisting of epoxy resins, phenolic hardeners, silicas, catalysts, pigments, and mold release agents.
Critical properties considered when selecting a molding compound include its glass transition temperature, Tg, moisture absorption rate, flexural modulus/strength, coefficient of thermal expansion, thermal conductivity, and adhesion properties.
There are many types of molding compounds used in the semiconductor industry today. General-purpose molding compounds with relatively high flexural strengths but exert relatively larger stresses to the device may be used for large and thick packages such as the PDIP and PLCC. Low to ultra-low stress molding compounds are preferred for the encapsulation of thin packages. High-thermal conductivity molding compounds, on the other hand, are required to encapsulate high-power devices. Molding compounds used for surface mount devices may have a low moisture absorption rate, or a high flexural strength at board-mounting temperatures, or a combination of both in order to prevent popcorn cracking.
Proper molding compound selection will prevent problems associated with manufacturability, package stress, package cracking, and interfacial delaminations.
Table 1. Formulations of Molding Compounds from Sumitomo Bakelite Co., Ltd.
Table 2. Characteristics of Molding Compounds from Sumitomo Bakelite Co., Ltd.
Table 3. Properties of ARATRONIC 2184 Variants from Ciba-Geigy
See Also: Semiconductor Materials; Encapsulation; IC Manufacturing
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