An Investigation of Compound Machining of Ceramic-LPM Package by Ultrafast Laser

Abstract

It is well known that ceramic substrates provide excellent electrical insulation and protection from oxidation/corrosion in addition to idea heat dissipation while allowing heat dissipation through controlled paths, e.g. integrated heat sinks. Low pressure molding (LPM) with polyamide and polyolefin (hot-melt) materials is a process typically used to injection molding for waterproof, to encapsulate and environmentally to protect electronic components. The purpose further than epoxy encapsulation is to protect electronic components with finer pitch against moisture, dust dirt and vibration. There is a special need for SiP (System in Package) application utilizing both ceramic substrate and LPM package materials where ceramic serves as mechanical structure and thermal dissipation path and LPM for high density SMT (Surface Mount) package. The research of this paper is to apply nano UV (Ultraviolet) laser to machine the LPM and ceramic substrate (sapphire, Al 2 O 3 ) and compare the results with nano green laser. The interactions of these two materials with laser are quite different and even conflicting for machining (LPM is ductile and hot-melt while ceramic is brittle), thus proper strategy has to be taken to satisfy needs for both materials. One of the major problem is the re-solidification of LPM material as temperature elevated during laser irradiation. It is necessary to provide a delay time between each laser pulsing. The laser ablation threshold (LAT) of green and UV laser for both materials is also investigated in this paper. The best parameters for processing ceramic substrates are speed 200 mm/s, frequency 95 kHz, delay time 450 ms, when processing LPM speed 700 mm/s, frequency 40 kHz, delay time 250 ms.