Photopolymerizable Compositions for Encapsulating Microelectronic Devices in High-Speed Manufacturing
Composite materials are typically comprised of two-phase materials. There is a continuous binder (matrix) phase and a stronger or stiffer (discontinuous) reinforcement material phase. To achieve high speeds in manufacturing, reaction injection molding (RIM) techniques have been employed widely.
However, resins (e.g., unsaturated polyesters, epoxies, vinyl esters) have become popular for a wide array of applications. Resin transfer molding (RTM) has been developed for low-volume production and involves a mechanical pumping apparatus to transfer catalysts and reactive resins from holding tanks into a closed mold containing a reinforcement material. Modification of the RTM process to produce thick polymeric (0.1 to 0.5 cm) or composite parts at high speeds would be very valuable for an array of emerging resin-containing applications.
Description of Technology
The present invention is versatile, allowing use of many of the monomer systems conventionally used in forming composite parts, such as RTM. The invention decouples the mold filling operation from the initiation of the reaction by using an alternative process to produce thick polymeric or composite parts. A photopolymerizable composition is used including a photoinitiator and light intensity gradient to cure resin areas to a desired thickness. The result is a composite part or polymeric part with similar strength and other characteristics indicative of the type of polymer system currently used.
The invention eliminates the need for high pressures or external heating of the mold or die, improves energy efficiency, and would provide the following benefits:
- Less expensive: Alternatives to achieve rapid curing rates in high speed in RIM require expensive molds and pumping systems.
- Faster and less cumbersome: Avoid mold-filling problems associated with high operating pressures to fill the mold. Also avoid poor resin impregnation into the preform or other reinforcement material.
- Higher manufacturing yield: Eliminate potential compromise of reinforcement materials like displacement and compression during curing of resin flow into the mold. Eliminate or reduce downtime associated with cleaning transfer lines of resin gelation.
- Reduce damaged to parts during manufacturing: Decrease or eliminate wire sweep or damage to the device during encapsulation.
- Less labor intensive than hand layup process: Produce similarly thick and complex parts from composites as produced by hand layup methods but without the time consuming manual steps associated with this customized process.
An array of manufacturing processes could benefit from the invention including coating composite materials in electronics and dental compositions.
Alec Scranton, Kiran Baikerikar, Bharath Rangarajan
For Information, Contact:
Michigan State University