Chip on Board

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. 

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... 

Figure 2. Very soft silicone gels are preferred for encapsulation in post-molded plastic chip carriers (left) and in automotive hybrid packages (center) but are too soft for use as blob top coatings (right) for chip-on-board encapsulation.

Chip on board wafer-level packaged metal-oxide gas sensors on printed circuit board. From Raible et al. (2006). 

Bare die and other chip devices are attached with electrically conductive or nonconductive adhesives to ceramic substrates having defined circuit patterns produced by thin-film vapor deposition and photoetching of metals or by screen-printing and firing of thick-film pastes. With recent advancements in fine-line printed-circuit boards, adhesives are also finding use in attaching bare die to PWBs, a technology known as chip-on-board (COB). 

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

Chip-on-flex is similar to chip-on-board except that the die, chips, or CSPs are wire bonded, flip chip attached, or epoxy connected to a flexible circuit instead of to a rigid interconnect substrate such as a PWB. 

Zou Y, Harris J, Ahmad I, Tucker D, Fathi Z. Comparison of die level stresses in chip-on-board packages processed with conventional and VFM encapsulant curing, IMAPS. In Proc. High-Density Packaging MCM Conf., Denver, CO Apr. 1999. 

Lau JH. Chip on Board. Dordrecht Kluwer Academic Publishers 1994. 

Koh W. Encapsulants for Chip-on-board and Chip Scale Packaging. Dexter Technical Paper Feh. 1996. 

Preforni/Tape bonding Chip-on-board, hybrid or MCM, single-chip (standard and lead-on-chip) Eliminates fluid dispensing, good thickness control Requires die-cut preforms or manual processing... 

Flip-chip in package or flip-chip on board... 

Chip-on board Low MOE, reworkability films Epoxy pastes... 

This technology was recently acquired by National Starch/Ablestik and is finding applications as a laminating resin for printed circuit boards and for chip on board (COB) direct encapsulation of chips, without conventional packaging [31]. 

Zou, Y., Harris, J., Ahmad, I., Tucker, D., and Fathi, Z., Comparison of Die Level Stresses in Chip-on-Board Packages Processed with Conventional and VFM Encapsulant (Turing, IMAPS, Proc. High-Density Packaging andMCM Conf, Denver, CO (Apr. 1999)... 

Lau, id.. Chip on Board, Kluwer Academic Publishers, Dordrecht (1994)... 

---