A Basic Ink-Jet Setup
This document is intended as a primer for first time users of ink-jet dispensing technology. It is written with the assumption that at least the ink-jet dispensers are purchased from MicroFab Technologies. The document discusses the needs of the “low temperature” dispensers and several approaches to fulfill them. The “high temperature” devices are only sold with their associated printhead and are not discussed here.
Basic Ink-Jet Setup (PDF version of the entire information)
The dispensers manufactured by MicroFab are actuated piezoelectrically. An annular piezoelectric (PZT) element, poled radially, is bonded to a glass tube with an integrated nozzle and orifice. The glass tube is mounted in a protective housing and, at the supply end, bonded to a fitting.
The main function of the drive electronics is to generate the signal that is applied to the piezoelectric actuator. The simplest option is the positive only trapezoidal signal showed when discussing the principle of operation, and is further referred to as “unipolar”. More complex signals can include a negative pulse (or “echo”) as shown in figure to the right. This signal is referred to as “bipolar”.
If using one of MicroFab’s integrated printheads, the specific implementation takes care of the reservoir and connection of the reservoir to the microdispensing device. This section only applies if the microdispenser was purchased separately and the user is setting it up on his own.
Backpressure Control & Purging
If the liquid/air interface is withdrawn inside the tapered area of the nozzle, the actuation does not have enough energy to move the fluid forward and eject it from the orifice. If the liquid forms a “pool” on the orifice face (left image in the figure to the left) around the orifice, the energy input might be too low to form a drop. For a drop-on-demand ink-jet system to operate, the solution/liquid to be dispensed needs to be flush with the orifice. To maintain the fluid flush at the orifice during operation, the surface tension and hydrostatic pressure forces need to balance.
During drop formation it is useful to observe the drops being generated to get an idea of the drop characteristics (diameter, velocity and directionality) and for troubleshooting (identification of clogging or air bubble presence). High speed cameras could be used for this purpose, but they are expensive and require special illumination. Drop observation can be achieved in a more cost effective manner using synchronized illumination.
The low temperature devices in the MJ family (-AB, -AT, -ABP, -ATP, -ABL and -AL) can be mounted into MicroFab's printhead assemblies. Alternately, they can be mounted into customer designed fixtures. All low temperature devices are usually held by the cylindrical section in a small clearance hole using a nylon set screw to prevent deformation. A feed through for the wires must be a part of the mounting fixture. The wires come out at the center of the cylindrical section of each device type.
The described set-up consists of the basic equipment that will allow the user to generate drops, to observe the drop formation and to optimize drop generation. It can be used to evaluate various solutions for dispensing, which is necessary during the formulation of ink-jettable materials. In most cases, the generated droplets need to be deposited on a substrate that has to be moved under the dispenser.