Paul Hartmann heads the Institute of Surface Technologies and Photonics at Joanneum Research in Austria since 2010. As an LED expert he is still involved in the R&D activities of the reasearch group for “Light and optical technologies” of the Institute. He is also member of the board of the national platform Photonics Austria.
After obtaining a diploma in Solid-State Physics (1991, TU Graz, Austria) and a Ph.D. in Experimental Physics (1995, Univ. Graz) he joined AVL medical instruments (1991-2000) and later Roche Diagnostics in Graz (2000-2005) as development engineer for new technologies and for product development of in-vitro point-of-care medical devices.
From 2005 to 2010 he was Head of R&D and Head of Research of Tridonic Jennersdorf, which is part of the Zumtobel group.
Aerosol Jet Printing: A Promising Technology for LED Packaging
Modern LED packaging technologies have to satisfy the demand for integrating an ever increasing number of components (LED dice, photo diodes, sensors, etc.) into a module to comply with customer’s expectations, such as high light intensity, dynamical color temperature- and light intensity control and high product reliability, while targeting low production costs. State-of-the-art packaging of LED dice based on chip-on-board (COB) technology comprises some shortcomings both of the manufacturing process and tolerances but also with regard to potential sources of failures. For instance, (i) electrical contacting of LED chips with a conductive die-attach poses the risk of short circuits due to lack of volume control of the glue. (ii) The connection of face-up-mounted contact pads is usually based on wire bonding, with the wire bonds encapsulated in a silicone layer for mechanical protection. For white light generation, phosphor particles are typically added to this silicone layer or droplet, forming a color conversion element (CCE). The extreme thermal conditions LEDs experience in particular in general lighting applications lead to heavy stress of the bonded wires exerted by surrounding silicone due to different thermal expansion coefficients. (iii) Similarly, state-of-the-art manufacturing technologies and the design of the CCE itself need to be carefully optimized to support superior white light quality and good heat dissipation.
Therefore, there is a clear need for alternative packaging processes. A promising technology in this regard, which offers the potential for a proper system configuration and integration in many aspects of module packaging, is additive manufacturing. This technology has gained some attention during the last years due to its material and cost saving potential. First attempts of fabricating electrical interconnects of LED modules by ink-jet printing have already been reported. However, the need for high currents in LED operation for lighting applications requires low resistivity of the electrical interconnects and therefore a comparatively large cross section of the structures, which limits the use of ink-jet printing. Disadvantages of this approach are the required low viscosity of the ink and limitations in particle size leading to low content of solids. Caused by the required small distance between nozzle and substrate a mounted LED die may further obstruct the nozzle.
Aerosol-jet printing has demonstrated many advantages over ink jet printing. With this technology it is possible to print highly viscous inks containing particles up to a diameter of 1 μm and to deposit more material during a single printing step. Based on these technological advantages circuits with a higher ampacity can be realized. Since Aerosol-jet printing also allows for a much higher distance between nozzle and substrate it is possible to manufacture modules with a much higher integration density of dice.
Based on test samples and test structures, in this contribution the potential of Aerosol-jet printing in various aspects of LED module packaging will be discussed, ranging from the deposition of the die-attach material, wire bond replacement by printed electrical interconnects to aspects and new concepts for CCE deposition and integration.