Abstract
We present a novel pneumatic actuation system for generation of liquid metal droplets according to the so-called StarJet method. In contrast to our previous work, the performance of the device has been significantly improved: the maximum droplet generation frequency in continuous mode has been increased to fmax = 11 kHz (formerly fmax = 4 kHz). In addition, the droplet diameter has been reduced to 60 μm. Therefore, a new fabrication process for the silicon nozzle chips has been developed enabling the production of smaller nozzle chips with higher surface quality. The size of the metal reservoir has been increased to hold up to 22 mL liquid metal and the performance and durability of the actuator has been improved by using stainless steel and a second pneumatic connection to control the sheath flow. Experimental results are presented regarding the characterization of the droplet generation, as well as printed metal structures.
Highlights
The generation of liquid metal micro droplets is a challenging area in the field of microelectromechanical systems (MEMS) technologies
It is applicable in a large field of applications, such as the generation of electrical 2D/3D connections or metal layers in the field of microelectronics or MEMS [1,2], e.g., creation of solder bumps for flip chip bonding, rapid prototyping of electric circuits [3] or 3D prototyping of small metal structures [4,5], e.g., printing of porous masters for thermoforming
The limiting factor is the minimum achievable mass flow through the reservoir outlet tube, which is mainly defined by the actuation pressure that has to be applied to overcome the capillary pressure of the ROT
Summary
The generation of liquid metal micro droplets is a challenging area in the field of microelectromechanical systems (MEMS) technologies. For the droplet generation in DoD mode, short pressure pulses are applied onto the reservoir by opening the pneumatic valve for short periods of time. Each of these pulses enforces a little amount of molten metal inside the nozzle chip, where the just mentioned star-shaped structure in combination with the rinse pressure leads to the generation of single droplets. Devices according to the StarJet method should be suitable for generating liquid metal droplets of many kinds of metals, even with high melt temperatures without suffering from the aforementioned common problems
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