Power modules serve a wide and diverse range of purposes. For some applications, power density is a key factor. For others, efficiency or price may be the sticking point. But for all applications, reliability is a top priority.
Modules with solid baseplates made of copper or aluminum silicon carbide are commonplace. Cost concerns have also given rise to a new breed of module without a baseplate. The Figure shows a flow 0 module without a baseplate using direct bonded copper (DBC), and a flow 2 module with a baseplate.
Flow 0 direct bonded copper without a baseplate (upper)
and flow 2 with a copper baseplate (lower)
DBC substrates have proven their merits in power electronic applications over many years. The advantages of DBC substrates are many: They can handle high temperatures and current. Their coefficient of thermal expansion (CTE) is a good match for that of silicon. They isolate high voltages and show low capacitance between the front and back sides.
When several aluminum oxide DBC substrates are used, they are often soldered to an additional baseplate. For some large modules equipped with a rectifier, brake, and an inverter, the rectifier and brake are soldered to one substrate, and the inverter IGBTs and freewheeling diodes to another.
AlSiC (aluminum silicon carbide) baseplates are often used for traction applications in place of copper plates. The materials have very different physical properties, with the CTE and thermal resistance being the key factors.
This article looks as various thermal and reliability aspects of power modules with and without baseplates, including:
●The coefficient of thermal expansion
●The reliability of different approaches
●The influence of thermal spreading
“Modules without a baseplate: a reliable and cost-effective solution ” includes cross-section diagrams, microphotographs, and numerical tables to explain the situation, and is presented as a pdf document.