Chip protection encapsulation

Electrical Properties. Electrical properties are important for the corrosion protection of chip-on-board (COB) encapsulated devices. Accelerated temperature, humidity, and bias (THB) are usually used to test the embedding materials. Conventional accelerating testing is done at 85°C, 85% relative humidity, and d-c bias voltage. Triple-track test devices with tantalum nitride (Ta2N), titanium—palladium—gold (Ti—Pd—Au) metallizations with 76... 

The commercial integrated circuit (chip) is normally encapsulated in a thermoset plastic molding compound to protect the chip and permit handling and subsequent assembling without loss of circuit integrity. However, the increasing complexity of the chip has... 

Second level—connection of the IC package to the printed circuit board. A key alternate route is direct mounting of the chip on the board, saving one level of interconnection. The chips are protected by the use of gel ("blob top") coatings of polymeric encapsulants applied directly to the IC chip. 

Ea, above and below Tg. Three case studies illustrate the range of applicability of the bending beam setup and factors contributing to the stress state. The first is a comparison of two polymers for interlayer dielectrics PMDA-ODA (pyromellitic acid dianhydride - oxydiamine) and a bis-benzocyclobutene. The second is of a neat epoxy resin commonly used for microelectronics encapsulation (epoxidized ortho-cresol novolac cured with a phenolic novolac). The third is a screen-printable polyimide coating used for protection of the integrated-circuit chip. An outline of our stress model is sketched, and example results are presented. 

Three case studies are examined which illustrate the use of the bending beam stress experiment. The first is a comparison of two polymers for interlayer dielectrics. The second is of a neat epoxy resin commonly used for microelectronics encapsulation. The third is a polyimide coating used for protection of an integrated-circuit 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). 

Epoxy resins are presently the most widely used thermosets in the electronics industry. In "first level" packaging, they are used to encapsulate chips and modules providing environmental and electrical protection. In "second level" packaging, they serve as the mechanical support inside printed circuit (PC) cards or boards as well as dielectrics for the incorporated circuitry. The second level package contains the interconnecting circuitry for the first level packages. 

Underfill. An underfill is then injected into the gap between the chip and chip carrier and then cured to complete the flip chip process. The function of the underfill or encapsulation as it is sometimes referred to is to provide mechanical integrity and environmental protection to a flip chip assembly. Studies have demonstrated that both thermoset and thermoplastic ICAs can offer low initial joint resistances of less than 5 mS2 and stable joint resistances (Au-to-Au flip chip bonding) during all the accelerated reliability testing listed in Table 1. The reliability results have indicated that there is no substantial difference in the performance of thermoset and thermoplastic bumps and both types of polymers apparently offer reliable flip chip electrical interconnections (53). 

Eiometric package—A package where the die is exposed but the interconnections are protected by a window frame and plastic encapsulant. Developed by Harris Corporation (Melbourne, FL) in 1996 for a sensor chip used to recognize a person s fingerprint. 

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