Intelligent Power Modules and Insulated Metal Substrate Technology

In applications where high temperatures need to be dissipated through the printed circuit board (PCB), a highly popular choice that provides highly efficient cooling is the use of Insulated Metal Substrate (IMS) technology. IMS-based PCBs use aluminium as the material for the metal core and are ideal for thermal management of circuits. A key example of IMS technology in use today is in power modules, as well as in high-power LED applications.

 

Insulated Metal Substrate Technology

A leader in the power electronics arena with a strong reputation for performance and reliability is ON Semiconductor. In 1969, the company first developed its Insulated Metal Substrate Technology (IMST®), which can enable the assembly of passive and active components as well as ICs to form electronic circuits such as power-output, control and peripheral circuitry on plates of aluminium that offer high thermal conductivity. The company uses IMST in its range of Intelligent Power Modules (IPMs). The composition of IMST is shown in figure 1.

 

Figure 1 – Composition of IMST

 

The IMST technology features a high-thermal-conductivity aluminium substrate covered with an insulating layer and topped with copper foil for electrical routing. A feature of the technology is the absence of ceramic layers as an insulator or mechanical substrate, therefore offering significantly better grounding than ceramic-based hybrids. The technology is also highly effective against EMC/EMI noise, which is due to distributed capacitance generated from insulation resin between the aluminium metal substrate and the copper foil pattern. In addition, use of the technology leads to increased robustness to mechanical and temperature stress cycling and a better thermal coefficient match with silicon.

 

Bonding

One issue is that solder joints can become a problem at the substrate/component (passive or die) interface of the IPM. However, the company uses ‘over moulding’ as a method to reinforce mechanical cohesion, reducing the risk of mechanical stress at the solder joint and thereby delivering higher reliability. In the IMST process, bare semiconductor chip devices such as power transistors, ICs and diodes are connected to copper foil patterns that form the circuits using ultrasonically bonded aluminium wires. The bonding technology uses aluminium wires with diameters from 30 to 500µm, with size determined according to current flow and also their purpose, for example as jumper or grounding wires.

 

Figure 2 – IMST bonding schemes

 

IMS technology allows the integration of passive devices, active components (bare die or packaged), ASICs and sensors into a single module as shown in figure 3. Following the moulding process, several pin forming schemes are possible including vertical SIP, bent SIP and DIP.

 

Figure 3 – IMS technology integration

 

Market

According to recent market research, motor driver inverters represent almost 50% of the inverter market with growth projections over the next five years of more than 50%. Market requirements are demanding ever higher performance in motor drives, together with higher efficiency, reduced noise reduction higher reliability, which is driving demand for IMS technology. The power modules market is shown in figure 4. The market for wideband gap devices based on gallium nitride (GaN) or silicon carbide (SiC) remains a small proportion of the market today.

 

Figure 4 – Market for power modules (product technologies addressed by ON Semiconductor are in green)

 

Conclusions

As a leading maker of discrete power components, ON Semiconductor offers a high level of vertical integration in the manufacture of its IPM family from active embedded components such as power MOSFETs, power IGBTs, diodes and ICs up to fully packaged modules. Suitable for applications including industrial, white goods and automotive motor control, the company’s IPM technology is cost effective, reliable and offers high efficiency and low noise emissions and meets a wide range of requirements in the power market from 300W up to 5-6kW.

The STK series of motor-driver ICs from ON Semiconductor is now available from RS Components.