Advanced nano-Ag thermal interface material for high thermal flip chip BGA
Flip chip ball grid array (FCBGA) has been found in wild range such as telecommunication, computer, and workstation application because it provided solutions for high speed demand, high input/output (I/0) density, and high electrical performance requirement. In the conventional FCBGA assembly, heat sink was laminated directly onto the chip surface via an epoxy base thermal interface material (TIM) filled with conductive metal particle as silver or aluminum for thermal conduction. For the high power FCBGA device, a sintering type nano-Ag TIM characterized with high thermal conductivity has been demonstrated. In order to achieve intimate sintering contact with the nano-Ag TIM, the Ag finalized multilayer deposited via the direct current (DC) magnetron sputtering was applied onto the surface of chip and heat sink, respectively. The nanolization of Ag particles enabled the Ag to be sintered at low temperature (220 °C). Therefore, continuous heat dissipation paths from the chip to the heat sink could be formed. Test vehicle of 50 × 50mm FCBGA bonded with 19 × 15mm thermal testing die was utilized for thermal performance evaluation, and the thermal resistance of junction-to-case (θ jc) of 0.03 °C /W was achieved. Finally, TIM coverage has been verified via scanning acoustic tomography (SAT) post reliability testing, including 500 cycles of temperature cycling B condition (-55 to +125 °C, liquid-to-liquid), and 96 hours unbiased highly accelerated stress test (130°C, 85% relative humidity) after JEDEC Level 4 preconditioning and three reflow simulations at 245 °C. Meanwhile, high temperature storage life test (150C) for 1000 hours was also implemented. In the end, a realizable manufacturing for high power FCBGA packages with great thermal dissipating characterization has been demonstrated.