Nozzleless Acoustic Droplet Ejector With Electrically Tunable Droplet Size for Picking and Placing Semiconductor Chips
Journal of Microelectromechanical Systems(2021)
摘要
This paper presents a microfabricated nozzleless acoustic droplet ejector with electrically tunable droplet size as a new tool for
on-demand
picking and placing semiconductor chips for semiconductor packaging. The ejector is based on a 2-mm-thick lead zirconate titanate (PZT) sheet with a planar annular-ring air-cavity acoustic Fresnel lens on top. When driven with sinusoidal pulsed voltage signals of 1.16 MHz, the ejector generates focused ultrasound with 1-mm focal diameter and 5-mm focal depth at 22 mm focal length in sodium polytungstate (SPT) solution. A finite-element-method (FEM) simulation model calculating the acoustic-field-induced fluid motion during the droplet ejection process has been developed, and verified by experiments, in which the device ejects SPT droplets whose diameter is from 850 to 2,
$490~\mu \text{m}$
, controlled by the driving pulse width and voltage. The ejected droplets are able to carry 400-
$\mu \text{m}$
-thick square silicon chips with side length from 700 to 3,
$100~\mu \text{m}$
. A polyester channel-embedded guiding cover for semi-automatic loading of silicon chips to the ejection site is designed to avoid manual placement of the silicon chips. With the proof-of-concept system, we demonstrate ejecting silicon chips out of SPT surface onto a nearby paper, assembling them into arrays with good repeatability. [2020-0337]
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关键词
Acoustics,Lenses,Liquids,Transducers,Silicon,Electrodes,Atmospheric modeling
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