Microelectronic 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. 

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. 

Epoxy Molding Compounds as Encapsulation Materials for Microelectronic Devices Table 1. Component materials for plastic packages... 

Epoxy molding compounds in microelectronics encapsulation are usually composed of more than ten kinds of raw materials each of which has its own qtedal fimc-... 

Due to their small feature sizes, microelectronic circuits need protection from environmental hazards such as mechanical damage and adverse chemical influences from moisture and contaminants. Several approaches are currently in use, for example, hermetic encapsulation of the device in sealed metal or ceramic enclosures, application of soft silicone gels as a cover over integrated circuitry, and encapsulation by transfer molding, which is the topic of this report. Both silicone resins and epoxy resins are used for this purpose. As the quality and performance of the epoxy encapsulants improved, the need for the generally more expensive silicone resins diminished. The present work is exclusively devoted to epoxy transfer molding compounds. 

The electronics industry desires improved flame suppressant additives for microelectronic encapsulants due to bromine induced failure. Epoxy derivatives of novolacs containing meta-bromo phenol have exhibited exceptional hydrolytic and thermal stability in contrast to standard CEN resins with conventional TBBA epoxy resins. When formulated into a microelectronic encapsulant, this stable bromine epoxy novolac contributes to significant enhancements in device reliability over standard resins. The stable bromine CEN encapsulant took about 30% more time to reach 50% failure than the bias pressure cooker device test. In the high temperature storage device test, the stable bromine CEN encapsulant took about 400% more time to reach 50% failure than the standard compound. Finally, the replacement of the standard resins with stable bromine CEN does not adversely affect the desirable reactivity, mechanical, flame retardance or thermal properties of standard molding compounds. 

Fundamental characteristics of the molding compound in microelectronics encapsulation to consider are moldability, mechanical and electrical properties, and humidity and heat resistance. These depend significantly on the corresponding charactoistks of the base epoxy resins used. Epoxy resins can be classified rou y into two types structoterminal and structopendant types. Each type includes a variety of epoxy r ns having different chemical structures In these epoxy resins, crosslinking takes place... 

Table 4. Formulation of base epoxy resin for recent molding compounds in microelectronics encapsulation...

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