Dispensing of Adhesives
GeSiM’s standard piezoelectric micropipettes/microdispensers can dispense liquids with viscosities of about 5 mPa·s (5 cP). Slightly higher viscosities may work but this must be tested for each liquid.
Adhesives often have high viscosities. There are two ways to dispense them: the design of the microdispenser can be optimized for higher viscosities or the viscosity is reduced by heating. GeSiM microdispensers should not be heated to more than 120 °C, i.e., the viscosity of the liquid should not exceed 5 mPa·s at 120 °C.
Droplet velocities and diameters were measured with a microscope under stroboscopic illumination. Spot arrays were dispensed after mounting the heatable dispenser to the GeSiM Nano-PlotterTM . A special Z-head can carry up to four dispensing or pick-and-place tools using four independently movable (optionally: rotating) Z-axes. The distance between Z-axes is 22 mm.
The UV-curable adhesives OG169 and UVO-114 (Epoxy Technologies) could be dispensed (viscosities at room temperature: 82 mPas and 300 - 700 mPas, resp.) Fig. 1 depicts the dependence of droplet velocity and diameter on the excitation voltage for UVO-114; the inset of Fig. 1 shows a picture of a single droplet of adhesive in front of the dispenser nozzle.
|Fig. 1: Droplet velocity (blue) and diameter (red) vs. excitation voltage at 90 °C for UVO-114.|
Fig. 2 shows an array of single epoxy spots on glass. The spot size of about 200 µm and can be varied using different piezo settings. Although the viscosity of OG169 is much lower than that of UVO-114, it needs a higher temperature for dispensing.
|Fig. 2: Array of UVO-114 with a spot diameter of ~ 200 µm on a glass slide.|
A number of liquids (e.g. glycerol) were successfully tested. In the case of two-component epoxies, the individual components must be dispensed using two different microdispensers. Mixing and curing of the epoxy then takes place on the substrate, one example being 301-2 from Epoxy Technologies.
A more detailed description on this topic is found on our download page.