Viscosity substrate-attach adhesives

Assembly of silicon chips onto substrates with anisotropically conductive adhesives uses specialized equipment, initially developed for ffip-chip solder and TAB inner lead bonding. Heat and pressure are transmitted to the adhesive through a thermode attached to a robotic arm or a high-precision linear translator. Equipment requirements are more demanding than for solder assembly, as no self-alignment can occur. A minimum placement accuracy of 0.0005 in. is required. Coplanarity between the substrate and die is critical one study reports maintaining coplanarity to within 0.00004 in. [19]. The pressure required to achieve interconnection depends on the size of the die, the type of conductive particle used, and the viscosity of the adhesive at the bonding temperature. 

In making an alkyd resin, an excess of the alcohol reagent is commonly used, for reasons of viscosity control. Because alcohols are water-soluble, this excess alcohol means that the coating contains water-soluble material and therefore tends to absorb water and swell [18]. Therefore, aUcyd coatings tend to lose chemical adhesion to the substrates when immersed in water. This process is nsually reversible. As Byrnes describes it, They behave as if they were attached to the substrate by water-soluble glue [18] . AUcyd coatings are therefore not suitable for immersion service. 

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