In a wide variety of high-tech applications, the modules have the task of managing electricity. That is to say, they optimally adjust the power output to the demand. This is the job of semiconductor chips within the electronic assembly. The chips are installed in power modules with the aid of various materials and components from assembly and connection technology. With the continuing development of these technologies, the requirements are also increasing: Ever smaller chips have to be able to handle ever larger power loads, for one thing. At the same time, new areas of application are continually emerging within increasingly complex overall systems that are expected to be extremely reliable. Automobile manufacturers expect the automotive supply industry to provide products with a lifespan of at least 15 years or 250,000 km, for example.
Sinter Technology: Intelligent Module Design Thanks to Optimized Temperature Sensors
Intelligent module design and the introduction of sinter technology play a crucial role in the performance (component density) of power electronic chips. In power electronics modules, sinter technology is increasingly becoming the first choice for assembly and connection technology. Sintered connections have clear advantages over traditional solder connections in regard to heat dissipation (i.e., optimized cooling) and electrical conductivity—especially if the chips are also sintered. In applications such as IGBT modules, this allows for higher electrical loads and therefore higher temperatures, thus enabling very effective operation. A precise, flexible, resilient and, above all, long-lasting sensor solution is important in order to operate the systems in the optimal temperature window.
With a newly developed platinum temperature sensor from Heraeus, only minimal substrate surface is necessary, resulting in optimum space requirements. The mounting of the sensor, which is only 3.1 x 1.5 mm, is potential-free and therefore allows placement very close to the chip, i.e., the actual heat source, without the use of special strip conductors on the substrate. If sintering is the general procedure, no additional mounting or positioning steps are necessary and sintering is carried out during the die attachment process. The typical cleaning process after soldering (removal of remaining soldering flux) is no longer required as the result of using sinter technology.
Because of the intelligent chip design, with electrically isolated functional surfaces for picking up signals and for transmitting heat, the substrate does not need to be specially structured for the temperature chip. As a result, there is greater freedom during the design phase of module construction.
Changes in the position of the temperature chip after the design freeze no longer represent a hurdle, because placement on the metalized surface can be freely selected. The optimal position directly next to the heat source (the die) is now only limited by the space required, which is very small, with dimensions of length 3.1 x width 1.5 x height 0.51 mm.
The highly robust, tried-and-true platinum thin-film construction provides long-term stability along with maximum precision. The standardized characteristics make the layout process easier and are defined and extremely stable over the entire operating range. Depending on the assembly and connection technology selected (which sinter materials and bonding wires are used), temperatures up to 300 °C are possible on the chip side.
Advantages of the Sinter Chip
During the process of positioning the power die on the substrate, the sinter chip is also placed on the substrate and is then sintered with the other components in a single step. The silver sintering process can be carried out with or without pressure and must be chosen depending on the customer’s plant and requirements. Delivery on a wafer frame is particularly helpful for this process; it allows materials to be handled with standard “pick and place” equipment and eliminates the need for additional devices. In addition, on a wafer frame, the temperature chips are optimally protected from damage, soiling and oxidation, facilitating optimized production.
General use of sinter technology eliminates the need for previously used solder connections, and expensive cleaning processes to remove soldering flux become obsolete. As a result, production expenses and the risk of insufficient cleaning are considerably reduced.
Author: Martin Bleifuß, Heraeus Sensor Technology