Innovative process development for LEDs dome shaping without molding

The industry of white LEDs is today an established reality. By the variety of applications, the size of the manufacturing plants, the massive aspect of the production, and also the increasing number of actors. Even with this ground factors, the lighting of the world with LEDs has not still reached the maturity that the former technological competitors have reached (quality of light over time, reliability, optimized price...). One of the leading factors to increase the maturity of white LEDs is the packaging and a good control of the final encapsulation step. Among LED packaging technologies, the encapsulation of the LED package building process is still a challenge because it is not just a protection as for the other active or passive electronic components. The encapsulation product has to be as most transparent as possible for a given wavelength (blue for most of GaN LEDs) or for visible light in general for white LED with a phosphor conversion layer. The other main function is the shape of the encapsulation dome which is critical for light extraction and beam shaping specifications. In addition to these main functions, the polymer used for this operation must be stable over time, with no yellowing and a good adhesion to the die, as any delamination will create a decrease of light extraction. Our study covers a wide exploration of dome shaping processes in order to comply all the challenges written above with a volumetric dispensing based technology. To master the geometric shape of the dome with the right aspect ratio (height over radius) and taking into account the thickness of the die to encapsulate, ray-tracing simulations have been performed. The results have been then applied to automatic dispensing equipment with heating on bottom. These experiments concern both single dies on a dedicated substrate as well as LED mounted on substrate with multiples chips in order to build a PCB for luminaire applications. At this level of the study, the dispersion measurements have shown a value lower than 8% for volume deposition thanks to the use of an automatic tool for dispensing.