Design of a micro-scale selective laser sintering system

Micro and nanoscale additive manufacturing methods employing metals and ceramics have many promising applications in the aerospace, medical device, and electronics industries. However, the present state of art metal additive manufacturing tools have feature-size resolutions of greater than 100 μm, which is too large to precisely control the geometrical and dimensional aspects of the parts they produce. The weakness is particularly profound in application of additive manufacturing to the fabrication of fine pitch interconnects in the packaging and assembly of integrated circuits. A new microscale selective laser sintering (μ-SLS) is being developed in this research to improve the minimum feature-size resolution of metal additively manufactured parts by up to two orders of magnitude, while still maintaining the throughput of traditional additive manufacturing processes. This study presents the research towards the development of the μ-SLS system. For use in the μ-SLS system, identification of an appropriate NP source with desirable properties such as uniform shape and size, low degree of agglomeration, low impurities’ levels and low propensity to oxidize is important for achieving good quality sintered parts. An extensive physical, thermal and chemical characterization to identify the NPs to be employed in the system is presented. The study also includes identification of sintering window (fluence/irradiance and exposure duration) for the NPs selected and investigates the effect of bed temperature on the sintering window. The μ-SLS system employs innovative design features such as the use (1) a precision spreader mechanism to spread layers of nanoparticles uniformly and consistently with sub-μm thickness (2) a micro-mirror based optical system to achieve the desired resolution with a large area patterning capability, (3) a 50 mm range high speed precision XY nano-positioner for stepping and patterning with high throughput (4) a heated wafer chuck to allow for elevated sample temperature to minimize residual stresses due to large thermal gradients and (5) a global positioner to shuttle the sample between the coating and sintering stations. Sintering results demonstrating the resolution and large area patterning capability of the system have been included along with future work that can help in optimizing the process parameters for achieving good sintering with the desired throughput