Encapsulation epoxy molding compounds

Kinjo, N., Ogata, M., Nishi, K. and Kaneda, A. Epoxy Molding Compounds as Encapsulation Materials for Microelectronic Devices. Vol. 88, pp. 1 —48. 

H. Suzuki, T. Moriuchi, and M. Aizawa, Low Mold Stress Epoxy Molding Compounds for Semiconductor Encapsulation, Nitto Electric Industrial Co., Ltd., 1979. 

In this paper we examine moisture sorption in an epoxy molding compound formulation used for semiconductor encapsulation. In particular, we will be concerned with moisture uptake as a function of relative humidity. The effects of temperature, sample thickness, and processing history will be systematically examined for a single commercially important material. 

Epoxy molding compounds, used to encapsulate microelectronic devices, contain bromine to provide flame retardancy to the package. This bromine, typically added as tetrabromo bisphenol-A or its epoxy derivative, has been found to contain many hydrolyzable bromides. These bromides, along with the presence of chloride impurities, are detrimental to the life of the electronic component. Bromine especially has been suspected (proven) to cause wire bond failure when subjected to moisture and/or high temperatures. With the addition of a more thermally and hydrolytic stable bromine compound, flame retardancy does not have to be compromised to increase the device reliability. Stable brominated cresol epoxy novolac, when formulated into a microelectronic encapsulant, increases the reliability of the device without sacrificing any of the beneficial properties of present-day molding compounds. 

Catalysts for Epoxy Molding Compounds in Microelectronic Encapsulation... 

The key to the development of the proper epoxy molding compounds for microelectronic encapsulation is the catalyst in the formulation. In spite of serious limitations in epoxy molding compound performance in sensitive microelectronic devices about ten years ago, the many new developments in catalysts during the last few years have enabled tremendous improvements. However, the exact curing mechanisms of various catalysts in epoxy molding compounds are still not fully understood today. 

The mechanism for organometallics and Lewis acids in phenolic or anhydride cured epoxy molding compounds are still not fully understood. Lewis bases such as imidazoles can be reacted with organic acids to form salts in order to improve latency. Imidazoles are, so far, the most widely accepted as a compatible catalyst family for encapsulating microelectronics. 

Data sheet values. Table 2.27 contains a list of property values for a wide range of epoxy molding compounds— both for the low-pressure encapsulation types and the high-pressure types. 

For epoxy resins used in electronic applications, such as cresol epoxy no-volacs, more powerful polar aprotic solvents such as dioxane or dimethyl for-mamide (DMF) have been used to hydrolyze the difficult-to-hydrolyze HyCls, such as the abnormal chlorohydrins and the organically bound chlorides. The issue here is the inconsistency in results obtained by different methods (78). The presence of ionic hydrolyzable chlorides and total chlorides has been shown to affect electrical properties of epoxy molding compounds used in semiconductor encapsulation (85). For these applications, producers offer high purity grade epoxy resins with low ionic, hydrolyzable and total chloride contents. 

These new type of resins contain minimum amount of chloride and other mobile ions, such as sodium and potassium, and have become widely used in device encapsulation and molding compounds. The incorporation of fused silica as filler in the epoxy system has drastically reduced the thermal coefficient of expansion of these materials which make them more comparable with the IC die attached substrate materials. The incorporation of a small amount of the elastomeric material (such as, silicone elastomer) to the rigid epoxy has drastically reduced the modulus of the material and reduced the thermal stress of the epoxy material This new type of low stress epoxy encapsu-... 

The success of plastic technology in achieving higher rdliability and mass production has led to wider applications in consumer products such as dectronic calculators, radios, televisions, and video recorders and in industrial products such as personal computers, office automation equipment, and computo Today, more tlum 80% of all semiconductor devices are encapsulated by epoxy molding compounds. 

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