Adhesive Applications

MicroFab is using ink-jet printing methods for data-driven fabrication of a wide variety of components and devices. Materials used include optical adhesives, UV-curing polymers, index-tuned thermoplastic formulations and other specialty bonding materials. MicroFab's patented high temperature printheads are used to dispense adhesive materials at temperatures up to 220°C. By varying the process parameters, dot arrays, fine lines, and areas can be printed with dimensions ranging from 10s of micrometers to several millimeters with precision levels of just a few microns.

The advantage of inkjet micro-dispensing is the precise control of location, single dispense volume, distribution of the material over the area, and line width. The level of precision printing control allows one to explore the following applications:

• MEMS, and small flat panel displays glass sealing where thin and narrow bond lines are critical.
• Micro-optics element attachment to very small components.
• Filling vias where precision and speed is critical.
• Medical devices, curved surfaces, MEMS components that require non-contact adhesive dispensing to prevent damaging and/or contaminating the devices.
• Applications that require printing both conductive and non-conductive bonds on the same part.
• Printing glass frits for glass bonding application.
• Deposition of underfill material with uniform or variable density for packaging.

Examples of adhesive dispensing are shown in the following images.

Left - Adhesive lines of varying width and thickness deposited with a single dispenser by using different print patterns. Center - Adhesive dots of varying sizes (smallest 80um in diameter) printed with the same device to adjust the local the material density. Right - Wafer bonding.

Dots of UV curing polymer of varying sizes - lateral view.

Adhesive / Bonding Material Types

Materials used for bonding could be in one of the following categories:

• Thermoplastic / Thermosetting / Hot-Melt
• Cyanoacrylates
• Epoxy
• UV Cures
• Silicones
• Acrylics
• Urethane

Materials in all above categories were dispensed/printed using Ink Jet Micro-dispensing. Off-the-shelf materials from suppliers such as Norland, Henkel, Locktite, Ablestik, Dymax, Panacol, 3M, etc. are available and were and can be used in ink-jet systems.

Many commercial adhesive products are readily suitable for ink jet deposition, while others need some adjustment. Viscosity and rheology are fluid characteristics important from an ink-jetting perspective. Based on the shear rate achieved in the dispenser orifice, 50cPs is considered a practical limit for the fluid viscosity (as dispensed). Commercial adhesives with higher viscosities can be brought in the operational range of ink-jet dispensers, by heating or by dilution.

The use of the MicroFab’s high temperature printheads allows heating of the dispensed material up to 220ºC. Adhesives with viscosities in the 100-200cPs range can have their viscosity lowered in an acceptable range by heating to about 100ºC. Dilution with compatible solvents also reduces the viscosity. After dispensing the solvent evaporates leaving behind only the adhesive.

Left - PolymerJet heated printhead. Right - Low-cost table-top ink-jet printing platform.

In cases where adhesion is not the only requirement, the commercially available materials can be modified to increase their thermal or electrical conductivity by filling with metal particles, carbon nanotubes, or ceramic particles.

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