LIFT Your 3D Printing Application

A major focus at Photonics West 2015 was 3D additive manufacturing. There were sessions on laser additive processing, digital light fabrication, and MOEMS devices. In all sessions, there were papers about systems, materials processing and applications. Here are a few of the papers that caught my attention.

Two photon fabrication was the most commonly reported technique, it is the only way to fabricate complex 3D subwavelength structures of interest in photonics. It works by using the simultaneous absorption of two long-wavelength photons to excite a short-wavelength sensitizer. This only happens at the microscope focus of a very high intensity pulsed laser. The focal point is scanned around building a 3D structure.

The most popular materials are hybrid ceramics that are organic photo-materials, supplied by Microresist GmbH, which convert to ceramics after patterning. The possibility of using thiol-enes was also reported, these are intriguing materials with very high transparency and are easily surface functionalized with bio- active species. This opens the door to very interesting , patterned bio-lattice- matrices .

Julia Greer from Cal Tech showed the amazing strength-to-weight ratios of a nanoscale hierarchical structures. The Eiffel Tower is a great example of a hierarchical structure. A web of a web of girders is used to create the main structural elements of arching legs that meet at the top. The Cal Tech team created miniature Eiffel Tower-like designs, then coated them with nanolayers of ceramic or metal. These nanostructures had completely unpredictable properties, some became very brittle, other highly elastic. They all had remarkable strength to weight ratios. The essential idea is that materials properties change at the nanoscale, and that super strength-to-weight materials could have very interesting applications particularly for flying objects.

High-power pulsed laser systems also are very effective ablation systems. Several authors reported on using Digital Mirror Devices (DMD) to allow micro patterning by ablation. Managing power at the DMD is critical in these applications, they need to deliver around 1 J cm² in a 0.1 nano-second pulse, and a repetition rate at KHz rates. A group from U Southampton showed 200nm features, which can act as diffractive optics for security marking.

An alternative ablation-like strategy is called Laser Induced Forward Transfer (LIFT). A transfer film is coated on a transparent substrate. A high intensity laser illuminates a pattern through the back of the substrate, and ablation of the interface with the transfer film, pops a piece of the transfer film which then lands on a target surface placed a few um’s away.

Schematic of LIFT and examples of pattern placement.

The first surprising feature was the excellent edge of the popped features, nice and smooth with no raggedness. The second surprising feature was that a wide arrange of materials from solids to viscous paste have been transferred. There were numerous examples of PCB sized features being transferred.

Then there was a paper from the Office of Naval Research that showed popping ICs from a tape and then popping interconnects down. They were demonstrating a complete replacement for pick and place assembly.

No one showed 3D printing using LIFT, but it is easy to see how a roll of film could be mounted above the 3D product and a patterned layer popped down. A commercial group, Aurentum GmbH, has developed a demonstration of record high writing speeds with LIFT. The Naval research team has demonstrated the use of DMD for LIFT.

The potential limitation is obviously pattern placement. The SEM images suggest that placement of +/- 2 to 5 μm across a 100 um gap is practical.

The interest in 3D printing continues to grow, and is enabling all sorts of new devices. It will not be long before the barrier to commercial progress will be speed, speed and speed. It is not often that a completely new patterning technique comes along. LIFT has the potential to make a significant impact at >10 μmgeometries. As an integrated assembly and interconnect process, it could be a game changer. As a technology for 3D printing, LIFT could reduce the time between scans, that is currently limited by the required to settle the liquid layer.