Flip-chip devices silicon

Lastly, adhesives are used to dissipate stresses that may be generated from thermal excursions, mechanical shock, vibration, or moisture. Specially formulated adhesives are effectively used as underfills for flip-chip devices and ball-grid-array packages to compensate for mismatches of expansion coefficients among the solder, the silicon chip, and the ceramic or plastic-laminate substrate. Low-stress adhesives are also used to attach fragile devices such glass diodes and to dampen stresses due to vibration. 

Electrically conductive adhesives are being used to interconnect flip-chip devices in smart cards resulting in thinner and smaller structures. Flip-chip silicon devices that have been thinned to several mils may be connected to a substrate with silver-filled paste epoxy or with anisotropic film adhesive instead of solder, then embedded and laminated to form a card that is less than 40-mils thick. Requirements for adhesives used in smart cards, in many respects, are more severe than those for other commercial applications. Besides having to withstand high humidity and temperature extremes, smart cards must take the continued abuse of human handling, repeated bending, exposure to human sweat and salt residues, and exposure to ultraviolet radiation from sunlight. 

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