Microvia Formation in 5- $\mu \text{m}$ -Thick Dry-Film Dielectric by Ozone Etch Processes

This paper describes the first demonstration of 20-μm-diameter microvias etched through a 5-μm-thin build-up polymer dielectric, Ajinomoto build-up film GX92, using ozone gas as a massively parallel etch process. This report begins with the demonstration of effective etching of polymer dielectric materials with the ozone gas process. With the use of proper etching masks such as metals or photoresist (PR) layers with openings on top of the dielectric layer, microvias were successfully formed in the dielectric layer. The effect of the different mask materials on the microvia etching rates and via diameters was examined. Microvias with 20 μm diameter and 5 μm depth were achieved with the PR mask with 15-μm openings. After desmear cleaning process, microvias were metallized by electroless and electrolytic copper-plating processes. Thermal shock test between -55 °C and 125 °C was applied to the daisy-chain structures to evaluate the microvia reliability made by ozone etching processes. There was no microvia failure up to 5000 cycles to confirm the reliable interconnection of the formed microvias. The microvia formation process using ozone can create a large number of microvias at once, which is beneficial for large panel application.