A feasibility study on manufacturing of embedded capacitors and resistors in multi-layer printed circuit boards

Abstract

Embedding capacitors and resistors into printed circuit boards (PCB) offers many benefits over Surface Mount Technology (SMT) and Through-Hole Packaging (PTH). These benefits include improvement in electrical performance and reliability, and potential cost reduction. Embedded devices also enable signal integrity at speeds over 1 GHz. Also, replacement of surface mounted discrete passives with an embedded passives layer allows for tighter component spacing, fewer via hole counts and a larger routing area. All these are essential for board miniaturization. However, the goals of reliability improvement, space conservation, performance enhancement and solder joint reduction by using embedded passives can only be realized if the PCB fabricator can produce quality boards in a practical production environment in a timely manner. This project investigated the manufacturing of embedded resistors and capacitors on a prototype basis with the possibility of it being extendable to normal mass production. The sequential lamination technique has been applied to form a PCB with embedded passives in this project. To verify the manufacturing capability, samples of integrated planar resistors and buried capacitors were fabricated on specially designed PCB test panels. The results showed that by using the 50 Ohmega-Ply resistivity material, resistors with a 0.5 mm minimum size dimension could be produced with a yield rate of 99%. The average tolerance was below 4% at the resistor core fabrication stage and the embedded resistors after integration showed increments in resistance of around 5% to 20%. In terms of embedded capacitors, the capacitive material namely C-Ply with a capacitance of 0.775 nF/cm2 (5 nF/in2) was used. The results were satisfactory as the measurements showed a maximum average tolerance of 5.7% before integration and a slight improvement to 4.5% after integration. In conclusion, the embedded resistors and capacitors were successfully built with a high yield rate to 99% and the tolerance of embedded resistor and capacitor were maintained at around 5% to 20% before and after PCB lamination.