Advanced Die Saw Technology for WLCSP Reliability Enhancement

Abstract

Abstract As consumer and portable devices get thinner and more functionality. Chips which are made by less than 28 nm node wafer with extreme Low-k (ELK) inter metal dielectric material is a trend in order to contain more transistors and to lower power consumption. However, side wall crack (SWC) for WLCSP is one of the major challenges since ELK layer getting brittle. Laser grooving is applied to remove metal before blade saw, but the high temperature during laser grooving usually easily generates HAZ (heat-affected zone) which can induce stress concentration and lower chip strength. The laser ablation also leaves metal-silicon residue (or recast) from the re-deposition of silicon to the groove and surrounding areas. Therefore, SWC (sidewall crack) is a huge potential risk waiting to happen after pick and place, during shipment and during SMT process. In the industry, HAZ size and SWC rate could be reduced by adjusting process parameters, or by exploring new alternatives to eliminate HAZ and silicon recast is one of driving factors of this paper. In this study, plasma etching was applied as surface treatment on the scribe line after laser grooving process with ELK wafer. Plasma could etch HAZ and recast area and expected to increase chip strength and reduce SWC rate. Plasma applied with various process time and power, and different types of mask coating materials were studied. Different plasma gases and effectiveness will be discussed. Conventional blade dicing process will be compared to different plasma etching conditions for mechanical properties of die using 3-point bending test to check die strength, and SEM and OM to verify quality of sidewall of the die. Finally drop test was performed to confirm the reliability enhancement.