Microprocessing machinability of organic material for semiconductor packaging by 248 nm excimer laser

An organic build-up film is used as the substrate material for a semiconductor multi-die package. However, the miniaturization of the organic build-up film process by the commonly used 355 nm UV laser has almost reached the limit due to its long wavelength. Therefore, to miniaturize the build-up film process, it is necessary to use an excimer laser with a shorter wavelength than the UV laser. In addition, the high photon energy due to the short wavelength of the excimer laser means the thermal effect of the material can be reduced by direct photon absorption. We have developed several types of DUV excimer lasers. One of them is a high power 248 nm excimer laser with free spectrum operation. The 248 nm excimer laser can be applied to the process of organic materials for semiconductor packages. We are developing the processing of organic materials by 248 nm excimer laser. The organic materials are processed directly by the irradiation using the mask by 248 nm excimer laser. We report microdrilling processability of less than 20 mu m diameter for a build-up film using a 248 nm excimer laser. The dependence of the taper angle, processing rate on the fluence for various via hole diameters was evaluated for major commercial build-up films. The results of this study indicate the appropriate selection of build-up film material and excimer laser processing fluence to achieve the processing target diameter and taper angle.