Study on the Novel Fabrication Procedure of Polyimide Multilayer Circuits for a Space Transformer of DRAM Probe Card using Parallel Build-up Process

The space transformer plays a critical role in DRAM probe cards for on-wafer testing of semiconductor chips. Typically, it comprises a multilayer ceramic (MLC) substrate and a multilayer thin film (MTF) circuit based on polyimide. The conventional method of MTF fabrication involves a sequential thin-film build-up process. While this technique can achieve fine conductor lines and small via-holes, it is associated with prolonged delivery times and increased costs due to low yields from circuit defects and layer deformations. In this research, we investigated an innovative parallel build-up process that employs TPI (thermoplastic polyimide)-coated polyimide (PI) films and a Cu-based low-temperature sinterable paste. Via-holes and trenched circuit patterns were generated using laser drilling and scribing methods, followed by filling with a sinterable paste and laminating at temperatures over 270°C in a vacuum press. This approach successfully fabricated MTF composed of a polyimide multilayer circuit board (PI-MCB) with more than 10 dielectric layers, which was integrated onto a 5mm-thick alumina substrate with a spin-coated adhesive layer on its surface by a vacuum press. The results suggest that this novel fabrication procedure is applicable to enhance the MTF manufacturing method of space transformers for DRAM probe cards, offering increased efficiency and cost savings compared to traditional methods.