Low-stress adhesives

Adhesives that reduce and dissipate stresses consist of low-modulus elastomeric types. Low-stress adhesives are required in attaching large die, large substrates, and flex circuitry. Low-modulus elastomeric adhesives are also used to attach and fillet large components to dampen vibration and shock. 

First generation of low-stress adhesives (paste and film)... 

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. 

A function of adhesives that is becoming increasingly important is to absorb and dissipate stresses produced in electronic assemblies due to changes in environmental conditions or accelerated testing. The need for stress-absorbing and dissipating adhesives has increased with advancements in microelectronics. Some advancements requiring low-stress adhesives are ... 

High-modulus adhesives are likely to have high bending stresses, high deflections, and low radii of curvature. A comparison of typical and ultra-low-stress conductive adhesives was reported using 250-mil square silicon die (20 mils thick) bonded to 10-mil-thick copper leadframes." A conventional silver-filled adhesive had a deflection of 3 mm and an ROC of 1,070 mm while a low-stress adhesive showed a deflection of 0.01 mm and an ROC >125,000 mm." ... 

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