Light-emitting diodes (LEDs) are the product of choice for many commercial and industrial lighting applications. Due to increasing power densities, alternative mounting solutions are being evaluated in order to achieve the lowest junction temperatures and lowest thermal resistances. Previous papers have explored the benefits of using a thick film system as opposed to a traditional Metal Core Printed Circuit Board (MCPCB). The advantage of being able to directly insulate a heat sink eliminates additional MCPCB layers and mechanical attachment that can decrease the thermal conductivity of the module and increase cost. Lower thermal resistance results in higher performing LED modules at a lower cost and a longer lifetime. A process has been developed and evaluated where an ultra-low temperature co-fired ceramic (ULTCC) tape will be laminsated directly on to an aluminum heat sink in order to electrically isolate the substrate. The green tape will then have a silver conductor applied to it and fired in one step. Using a tape system as opposed to an ink system creates many advantages. The tape system allows for processing in cavities, which is beneficial for recessed lighting and three-dimensional substrates. The co-firing silver conductor reduces the number of firing steps, leading to less dimensional variation of the heat sink and lower processing costs. This paper will discuss the material solutions, processing requirements, and reliability data for a completely co-fired ULTCC system on aluminum.

An increased interest in low temperature polymer thick film products has become apparent due to the rise of the printed electronics market. The specifications for these products are becoming more demanding with expectations that the low temperature products should perform at a level that is typically reserved for their high temperature counterparts; including solderability with lead free solders, high reliability and strong adhesion. Traditionally, it has only been possible to use leaded solders for soldering to polymer based thick film conductors. Over the last 15 years environmental concerns and legislation have pushed the industry towards a lead free approach. The shift to lead free solders, while beneficial, provides new challenges during processing. The high temperatures required for a lead-free soldering process yield a naturally harsher environment for polymer thick film pastes. In the past these conditions have proven too harsh for the pastes to survive. The polymer thick film discussed in this document aims to address some of these concerns for a highly reliable and easy to process polymer thick film paste. Due to the poor leaching characteristics of polymer thick films, at elevated temperatures, the predecessors of this paste typically soldered at low temperatures with leaded solders. The goal of this paper is to present a low temperature paste that is compatible with a variety of substrates and readily accepts lead-free solder. This paper will discuss a newly formulated low temperature curing (150°C – 200°C) RoHS and REACH compliant paste that shows excellent solderability with SAC305 solder. The paste was evaluated using a dip soldering method at 235°C–250°C on a variety of substrates. The data presented includes solder acceptance, adhesion data, thermal analysis and SEM analysis.