Continuous Electroless Seed Layer Deposition in Through-Glass-Vias by Ultrasonic Agitation

This study presents the crucial process of achieving conformal electroless seed layer deposition within blind glass vias. A cost-effective and room-temperature-based ultrasonic machining (USM) method was employed to fabricate blind holes in a glass substrate, demonstrating its viability for large-scale production. During electroless deposition, manual agitation led to nonconformal deposition in blind holes with aspect ratios (ARs) exceeding 1. The nonconformal seed layer results from the entrapment of air within the holes, impeding the uniform distribution of the electroless solution. Ultrasonic agitation was applied to effectively remove trapped air through cavitation induced by pulsating waves. This breakthrough enabled unimpeded access of the electroless solution into the blind holes, resulting in consistent and uniform electroless seed layer deposition. Moreover, the technique was successfully extended to achieve conformal seed layer deposition in a $6\times 6$ array of through holes with an AR of nearly 4.3. This approach resolves the nonconformal seed layer deposition issue and offers a reliable, cost-effective means for fabricating embedded passive devices.