Glob top

Silicon—Ca.rbon Thermoset. The Sycar resins of Hercules are sihcon—carbon thermosets cured through the hydrosilation of sihcon hydride and sihcon vinyl groups with a trace amount of platinum catalyst. The material is a fast-cure system (<15 min at 180°C) and shows low moisture absorption that outperforms conventional thermosets such as polyimides and epoxies. Furthermore, the Sycar material provides excellent mechanical and physical properties used in printed wiring board (PWB) laminates and encapsulants such as flow coatable or glob-top coating of chip-on-board type apphcations. 

Figure 1 1 Chip-on-board cross-section showing glob-top protection for IC chip.

Several approaches using electrically conductive adhesives instead of solder have been explored and are proving successful. Anisotropic adhesives (See Chapter 1), for example, have been used to connect flex circuits and cables from the separate driver circuits to the panel, avoiding the use of solder connections. More importantly, integrated-circuit chips can be bonded directly to the ITO conductor traces on the panel, a technology called chip-on-glass (COG). IC chips can be flip-chip bonded, then underfilled with a stress-free underfill adhesive if necessary. For protection, the chips may then be encapsulated with epoxy (glob-topped). 

Stress buffer coats are applied to semiconductor devices by two commonly used methods. The first method is termed glob-top coating and involves... 

GTE—glob top enacpsulation, pertains to the glob of encapsulating material used in MCMs. 

Encapsulants are usually characterized as either potting compounds, glob-tops, or underfills, depending on the end use. Potting compounds are materials that are used to protect final assemblies (relays, component terminals, electrical contact assemblies, etc.). Glob-tops and underfills are specifically used for silicon die protection. 

These siloxanes are easily hydrolyzed by ambient humidity and water bound to the substrates to generate transient silanols 77 and 78. Subsequent dehydration initially provides a precursor 79 of crosslinked polydimethylsiloxane network, which is formed by further condensation of the silanol groups. With many variants, this process constitutes the base of the RTV silicones that are mainly used as protection shields in the glob top encapsulation process. Low-stress conductive adhesives have been prepared by the condensation reaction of ethylphenylsila-nediol, l,4-phenylenebis(dimethylsilanol), and trimethylsilyl-terminated poly-diethylsiloxane. When loaded with carbon particles and cured at 180°C, this composition exhibits a volume resistivity of 1.2 X 10 flcm and a thermal conductivity of 2.1 W m K. ... 

Figure 37 General scheme of the die attachment process on copper leadframe before the assembly is encapsulated into an epoxy moulded package (A). Other packaging techniques are the hermetic Cerdip package (B) and glob top encapsulation of surface-mounted...

In terms of fluidics and mechanics, the chip-to-package connection is made by a standard gluing process for which only the duct opening and the seal have to be taken into consideration. The electrical connections are made by wire bonding. The wire bonds are glob-topped for protection against mechanical influences (Fig. 9.2). 

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