Abstract
One of the biggest challenges in microscale additive manufacturing is the production of three-dimensional, microscale metal parts with a high enough throughput to be relevant for commercial applications. This paper presents a new microscale additive manufacturing process called microscale selective laser sintering (μ-SLS) that can produce true 3D metal parts with sub-5 μm resolution and a throughput of greater than 60 mm3/hour. In μ-SLS, a layer of metal nanoparticle ink is first coated onto a substrate using a slot die coating system. The ink is then dried to produce a uniform nanoparticle layer. Next, the substrate is precisely positioned under an optical subsystem using a set of coarse and fine nanopositioning stages. In the optical subsystem, laser light that has been patterned using a digital micromirror array is used to heat and sinter the nanoparticles into the desired patterns. This set of steps is then repeated to build up each layer of the 3D part in the μ-SLS system. Overall, this new technology offers the potential to overcome many of the current limitations in microscale additive manufacturing of metals and become an important process in microelectronics packaging applications.
Highlights
As the additive manufacturing (AM) technologies are maturing, more and more industries are looking into the possibilities of employing AM as part of their production ecosystems
The solder bumps which have traditionally served as the interconnect between two dies or between the die and a substrate are traditionally manufactured through an electroplating process
This paper presents a new micro-AM process called micro-scale selective laser sintering (μ-SLS) that can be used to fabricate three-dimensional parts with feature resolutions of better than 5 μm with a high throughput that can be employed in a production environment
Summary
Electrohydrodynamic jet printing and direct ink writing cannot produce the types of true 3D structures with overhangs that will be required for the generation of 3D electronics[25,26,27], and other processes such as electrochemical deposition and Laser Chemical Vapor deposition are too slow to be used in high volume production environments[28,29]. Process description The three key steps in the μ-SLS process are: (1) NP bed formation to achieve sub-μm layer thicknesses with good packing density, consistency and repeatability, (2) Sintering of particles to achieve the desired sub-5 μm resolution and high throughput using the optical setup, and (3) High precision sample transfer, alignment motion systems, and metrology design for precise motion of the stage under the optical sub-system. Better process tuning for different sub-systems such as optimizing the slot die coating parameters for better layer thickness uniformity and repeatability, improving the optics for better alignment and smaller spherical aberrations, developing DMD pattern correction schemes for better feature resolutions, and optimizing the sintering irradiance vs exposure duration for different layer thicknesses are some of the short-term future work that need to be completed in order to improve the quality, uniformity, and resolution of the parts produced
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