Optical absorption aspects of laser soldering for high density interconnects

In laser soldering, one has direct control over the incident laser pulse energy and duration but only indirect control over the temperature profile of the parts to be soldered. To understand the conversion of incident laser energy into a substrate temperature profile, two processes need to be understood: first, the optical absorption as a function of temperature and, second, the temperature distribution as a function of absorbed energy. The optical absorption aspect is addressed here. A set of total reflectivity measurements for real surfaces of interest is presented along with analytical calculations of the temperature dependence of the optical absorption for both specular and rough surfaces.