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NCP (Non Conductive Paste) for Narrow Gap Flip Chip Package and TSV Package
Keywords: NCP, Non Conductive Paste, Fine pitch and narrpw gap flip chip, TSV
Pre-applied process followed by mounting chip and underfill at the same time is considered as promising underfill process for coming finer pitch and narrower gap flip chip package with Cu pillar and also TSV package with micro bumps. On the other hand, conventional mass reflow could introduce too much stress on low-k chip with advanced node. Pre-applied underfill process can reduce stress on low-k chip by dispersing stress into underfill material at the connection with thermal compression bonding process. One of the challenges of thermal compression bonding process with NCP is trapping material and poor connection at the bonding area. Creeping and voiding are other challenges for NCP. This presentation reports material design of a new NCP, features, and reliability results. Our newly developed NCP material was dispensed smoothly, and didn't cause creeping up on the backside of the chip. While low thixotropic NCP tends to create voids because of easier NCP spreading out when chip is mounted, this NCP material showed good performance in terms of voiding because of high thixotropic index, less spreading out even under heating condition (<80degC) and reduced out gas in this material. We explored appropriate fluxing material inside NCP, optimized filler size and distribution, viscosity, thixotropic index and curing behavior to avoid trapping issue. Cross-section of bonding area showed sufficient solder wetting and this NCP material had excellent connectivity. In addition, this NCP material can be processed in a very short time. The TV underfilled by this NCP material was subjected to reliability tests, and passed 5x reflow test (JEDEC standard preconditioning Level 3), 1000 cycles of temperature cycle test (-55degC to 125degC), and 200 hours of biased HAST test (135degC/85%RH/1.3V).
Hidenori Abe, Engineering Manager
Hitachi Chemical
Cupertino, CA

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