Evaluation for UV laser dicing process and its reliability for various designs of stack chip scale package

Abstract

In the semiconductor market, the trend of packaging for die stacking technology moves to high density with thinner chips and higher capacity of memory devices. Moreover, the wafer sawing process is becoming more important for thin wafer, because its process speed tends to affect sawn quality and yield. ULK (ultra low-k) device could require laser grooving application to reduce the stress during wafer sawing. Furthermore under 75 mum-thick thin low-k wafer is not easy to use the laser grooving application. So, UV laser dicing technology that is very useful tool for Si wafer was selected as full cut application, which has been being used on low-k wafer as laser grooving method. Therefore, this laser full cut application is emerging to respond wafer sawing method for ultra thin wafer as well as thin ULK wafer. Laser full cut application shows higher process speed than diamond blade saw so that there can be the merit for productivity. And quality problems of conventional blade dicing such as top side chipping, back side chipping and lateral crack can be reduced with this technology. In this study, laser full cut application was evaluated whether this would be applicable to mass production and checked its reliability like T/C (temperature cycle) test with various designs of stack chip scale package by comparing result of the conventional diamond blade sawing method. And evaluations on various laser saw systems and processing methods were implemented to compare die breakage strength because its lower value could cause die broken or crack during the die attach or other processes. Also the productivity such as throughput for ultra thin wafer like less than 75um thickness was analyzed to find the best wafer sawing process which is feasible for mass production.