Study of Laser Microdrilling for Applications in Microelectronics and Packaging

Advances in microelectronics and packaging require new fabrication techniques such as, e.g., laser microdrilling. In laser microdrilling processes, profile of the heat affected zone (HAZ) and the geometry of the holes strongly depend on settings of the laser parameters such as peak power, pulse length, pulse repetition rate, focal condition, etc. In addition, the processing results are strongly influenced by geometry, dimensions, and material properties of the workpiece. Therefore, it is very critical to model and control the profiles of laser drilled microholes in order to obtain desirable results. This paper presents a study of laser process for drilling of micrometer size holes in thin metal flat stock using a pulsed Nd:YAG laser. Analytical and computational modeling of the temperature distribution is performed and can be used to determine profiles of the HAZs. The effects of different laser parameters on the hole geometry are characterized using optical microscope and scanning electron microscope to investigate the geometry of the holes and surface topography in their vicinity, and it was observed that, the laser power density had the most significant influence on the dimensions of the holes, the number of laser pulses drastically affected the cross sectional profiles of the holes, and the laser pulse length should be carefully chosen for each individual thin metal stock to avoid laser-supported absorption (LSA) by the absorbing plasma which results in the lack of through holes by laser microdrilling. The experimental observations provided practical, useful information in laser microdrilling characteristics and can serve as a guideline on the laser parameters required to drill holes in thin metal stock of a required dimension and cross sectional profile.