The workpiece sample which is a copper printed circuit board (PCB) is mounted on a micro-controlled assembly with double-faced adhesive tape. Here the primary objective is to study the effect of laser cleaning parameters on surface temperature rise and thermoelastic force. The variation of instantaneous temperature rise and thermoelastic force with time using different process parameters (e.g., type of power, focal length, and scanning speed) at a constant absorption coefficient is also investigated, and the best parametric combination have been found out in this experiment. After successful completion of the experimentation, it is observed that the surface temperature increases with the increase in laser power. The maximum temperature rise is observed when the laser power is maximum, and the focal length is minimum. It is further observed that the thermoelastic force increases with the increase in laser power. Maximum thermoelastic force is observed when the laser power is maximum, and the focal length is minimum.
TopIntroduction
Laser cleaning is a method of laser ablation done on the laser milling system where an offset is created to decrease the laser fluence. Due to this the substrate is only heated to reach a temperature near the melting point of the particular material and thus to “flatten” any debris and other recast contaminants on the surface. Any variation from the accurate focal distance causes a decrease in the volume of material removed from the target and this harms the process performance. As this is an undesirable effect, therefore it should be avoided. Hence, an optical sensor system is combined to the machine to determine the distance to the target surface and to modify the laser power output when required, so that a constant material removal rate is sustained.
Chemical and abrasive processing which are traditional cleaning processes is getting near the end of their capability limit as they are both technically and environmentally useless for the severe cleaning requirements.
The dry laser cleaning efficiency for a certified spherical particle (SiO2, 5.0, 2.5, 1.0, and 0.5 μm) is experimentally analyzed from different substrates (Si, Ge, and NiP). The effect of various options (laser wavelength, incident angle, substrate properties, i.e., type of material, surface roughness, etc.) on the cleaning efficiency is presented along with commonly analyzed options (cleaning efficiency versus laser fluence and particle size). The laser cleaning efficiency demonstrates great sensitivity to some of these options (e.g., laser wavelength, angle of incidence, etc.). Partly these properties can be described within the frame of the microelectronics engineering (MIE) theory of scattering. Other effects (e.g., influence of roughness) can be explained along the more complex line, related to examination of the problem “particle on the surface” beyond the MIE theory. The theory of dry laser cleaning, grounded on one-dimensional thermal expansion of the substrate, validates a great sensitivity of the cleaning efficiency on laser pulse shape. For the realistic pulse shape, this theory produces the threshold fluence by the order of magnitude greater than the experimental one. At the same time, the theory which considers the near-field optical enhancement and three-dimensional thermal expansion effects produce the exact values for the threshold.