Professor Yongfeng Lu
Professor Ambrose Wolf
Date of this Version
Farkouh, Raif. “Femtosecond Laser Micromachining of Low-Temperature Co-Fired Ceramic and Glass Fiber Reinforced Polymer Printed Circuit Boards Materials” Master’s Thesis. University of Nebraska-Lincoln, 2017.
Low-temperature co-fired ceramic (LTCC), and glass fiber reinforced polymer (GFRP) printed circuit boards (PCBs) are two materials used for the packaging of electronics. The excellent mechanical and electrical properties of LTCC, combined with the ability to embed passive components offer superior radio frequency (RF) performance and device miniaturization for high-frequency applications. Due to its unique properties, LTCC provides superior performance in applications as diverse as military radar, imaging systems, advanced automotive sensing, telecommunications, and satellites. The use of LTCC in these applications has created a demand for the micromachining of holes, channels, and cavities with specific geometries and structures. Likewise, GFRP PCBs are the backbone of the electronics industry. They work to mechanically support and electrically connect components using conductive tracks, pads and other features etched from copper sheets laminated onto GFRP substrate. Since the electronics industry has been moving toward devices with smaller size and lower cost, there has been an increasing need to drill holes in GFRP PCBs with high quality and efficiency.
Some of the conventional techniques used to machine LTCC and GFRP PCBs are micro punching, mechanical milling, and electrical discharge machining. These techniques can machine some structures on LTCC and GFRP PCBs, but the drawbacks such as geometry-limitation, wear and tear of tools, high-cost, complex equipment, lack of flexibility and crack-tendency limit the application of these techniques. Femtosecond laser micromachining is a comparatively new technique that offers a solution to meet the challenging demand for drilling of LTCC and GFRP PCBs. The unique properties of ultrashort pulse width and the extremely high peak intensity allow fs laser to drill high-quality holes and to minimize thermal and mechanical damage by the term of “cold” ablation mechanism.
In this project, efficient processes for femtosecond laser drilling of LTCC and GFRP PCBs for RF packaging were developed. A high drilling quality with no trace of dross, debris and reacting layer was achieved. The effects of the laser parameters, including pulse energy, scanning speed, focal position, and pitch, on the hole quality, were investigated. A laser polishing process of LTCC was also developed since the reduction of surface roughness is of practical importance for achieving low microwave loss.
Advisors: Yongfeng Lu and Ambrose Wolf