Rubber aging study hardness

Comparison of ACAs with Hard and Soft Fitters. Kishimoto and coworkers reported (15) ACA pastes using two different fillers Au-coated rubber particles (soft) and nickel particles (hard). The ACAs were used to bond a flip chip with Au plated bumps to a board with copper metallization. With the application of pressure, the soft particles were brought into contact with surface pads and were deformed, which lowered this contact resistance. The hard particles, however, deformed the bumps and pads, and thus were also in intimate contact with the surfaces to help reduce this contact resistance. Their study showed that their choice of both hard and soft flllers in ACA materials had similar voltage-current behavior, and both exhibited stable contact resistance values after 1000 cycles of thermal cycling and 1200 h of 85°C/85% RH aging conditions (15). 

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