Rework of flip-chip populated PCBs by laser desoldering

New packaging concepts for electronic components and assemblies are an essential base for continuing miniaturization. The successful use of flip-chip, chip scale packages and microball grid arrays depends on the availability of suitable rework techniques to minimize refuse by replacing defective components. Laser desoldering of flip chips is a promising precisely controllable alternative to standard repair techniques for removing defective components from the PCB. However, the industrial application of this technology requires the determination of suitable process parameters like laser power, spot diameter and beam feed rate. This paper has twin objectives: firstly, to introduce a new thermal simulation tool based on an efficient strategy for model creation and secondly, to apply this method for a laser desoldering process simulation to reduce the number of experiments needed for the determination of suitable laser parameters. The tool allows us to generate and maintain complex thermal models (including inconstant laser parameters) easily. Moreover, the tool is capable of considering temperature dependent material properties and boundary conditions as required for this application. The experimental investigation, including problems related to the use of underfills during the attachment process and the experimental set-up used for laser desoldering, are described. A comparison between simulation results and those established in experiments is given.