Crack Inspection using Activation Station
Small, millimeter length seed cracks represent seed point defects which dramatically reduce mechanical strength of thin wafers or ceramic plates and ultimately lead to breakage and yield loss in production. In-line and off-line inspection of seed cracks can be successfully performed by Activation Station (AS), which is manufactured by Ultrasonic as a stand-alone automated tool or integrated in processing. Typical example of AS application is front-end crack inspection in PV module production prior to individual cells being loaded to a stringer or inspection of wafers after mechanical processing (e.g. grinding). High volume test of the Activation Station in factory statistically documented a reduction of yield loss by as much as 8-10%.
The Activation Station concept is based on delivery of a controlled mechanical stress to bare or processed wafer. Each wafer passes through the AS with settings saved in the tool software as a recipe. After activation, the wafers with cracks are revealed using pressure and optical sensors and sorted out in “Pass” or “Fail” bins. Seed cracks are found in a square size substrate or round shape wafers with >99% accuracy. Additionally, AS allows measuring elastic properties of the substrate serving as automatic in-line quality and process control unit. Activation Station is cost effective flaw inspection tool available for electronic wafer production.
The Activation Station can be integrated with proprietary Resonance Ultrasonic Vibration (RUV) system produced and supported by Ultrasonic Technologies. Activation Station can be used as a stand-alone QC tool. A new AS development allows inspecting solar cell strings after cell soldering to increase a solar module line throughput and yield.