Evolution of lumens per watt efficacy has enabled exponential growth in light-emitting diode (LED) lighting applications. However, heat management is a major challenge for an LED module design due to the necessity to conduct heat away from the LED chip. Elevated chip temperatures cause adverse effects on LED performance, lifetime, and color. This paper compares the thermal performance of high-power LED modules made with two types of circuit boards: novel substrates based on insulated aluminum material systems (IAMSs) technology that inherently allows using thermal vias under the LEDs and traditional metal core printed circuit boards (MCPCBs) commonly used with high-power LED applications. IAMS is a thick-film insulation system developed for aluminum that cannot handle temperature higher than 660°C. The coefficient of thermal expansion of IAMS pastes is designed to match with aluminum, which minimizes any bowing. The thermal via underneath the LED enables excellent thermal performance. More than 7°C reduction in LED junction temperature at 700-mA drive current and 27% reduction in the total thermal resistance from the LED junction to the bottom of the substrate were demonstrated for the IAMS technology when compared with MCPCB. When considering only the thermal resistance of the substrate, reductions of around 70% and 50% were obtained. This versatile and low-cost material system has the potential to make LEDs even more attractive in lighting applications.

This paper presents Thick Printed Copper (TPC) as substrate technology for High Brightness LEDs, which features a strongly improved reliability combined with a significant cost advantage over incumbent technologies for High Brightness LED substrates. The advantages of TPC over Direct Bonded Copper (DBC) and Direct Plated Copper (DPC) substrates will be demonstrated by thermal shock test results and a demonstration of the versatile design options. The good thermal performance of TPC is demonstrated by comparative Finite Element Modelling of TPC and DBC substrates. A detailed review is given discussing the different copper to ceramic bonding mechanisms, which prevent void formation and are responsible for the excellent thermo-mechanical reliability

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.

The thick film paste manufacturers are expected to produce conductors which are lead and cadmium free, yet have excellent fired film properties and the same performance and properties as the cadmium and lead containing formulations. The fired film surface of these conductors must be defect free (i.e. imperfections, pills, agglomerates) after multiple firing steps and must perform on dielectric as well as substrates from different suppliers. Typically, the thick film gold conductors are used in high reliability applications such as medical devices, military applications, and high frequency circuits, which require robust performance at high and low temperatures, in chemically aggressive environments, or extremely humid conditions. As circuits decrease in size and become more complex, the thick film gold properties become increasingly critical. The challenge is to develop an alternative gold conductor formulation, which can print and resolve fine features (down to 4 mil lines and spaces) as well as have the ability to be etched for higher density circuit designs (down to 1–2 mil lines and spaces). Gold conductors are typically used in conjunction with other high temperature thick films so good performance after multiple firings was also a targeted requirement. Heraeus has been proactive for the past decade in the development of thick film products that are both RoHS (lead and cadmium free) as well as REACH compliant. This paper discusses the experiments that were performed in order to understand the contribution of gold powder, organic and inorganic system to improve the fired film performance. These formulations were compared against existing gold conductors including the high performance gold conductor options as well as other available standard gold conductor options. Thin wire bonding trials including both gold and aluminum wire are used to compare influences of raw materials which includes high volume wire bonding reliability including failure modes and aged wire bond adhesion at elevated temperature exposures (300°C) for extended periods of time. In order to analyze fired film morphology and link this up to wire bond performance, SEM images of the conductor surface and cross sections were conducted. These studies resulted in a newly developed thick film gold conductor paste for use in a wide variety of applications. We present wire-bonding data with gold and aluminum wire and reliability results on both 96% Al2O3 ceramic substrates as well as on top of standard dielectrics.

In the recent few years, high power electronic becomes one of the fastest growing market segments of semiconductor industry, because of the strong demand of high energy conversion efficiency and low energy loss, for the green environment protection. The major applications are motor drivers, UPS, PV inverters, hybrid/electric vehicle, rail traction and wind turbines…etc. Those applications are typically operating at very high voltage (> 200V) and high current (> 50A), and also need to operate under high temperature and harsh environment. Therefore, the circuit boards for such applications must achieve outstanding characteristics in terms of electrical, thermal, and mechanical performance, in order to provide reliable functionality during operation. Ceramics are no doubt the unique material that can offer excellent performance to survive at such operation conditions, and can be used as the core material of the circuit board for power modules. Therefore, in order to further understand the advantages and disadvantages of each ceramic technology, such as DBC, DPC, and thick film substrates, a comprehensive comparison study on reliability, thermal, and electrical performance were discussed.