Posted on 17 December 2012

Comparison of Power Modules with or without a Base Plate


Some comparisons of power modules with or without a baseplate are rather inaccurate since they compare the two technologies by examining a module with base plate to begin with and then simply removing the base plate to perform the comparison. Of course, both design variants must be constructed by totally different methods. Both technologies have advantages and disadvantages which are briefly described below.


Power modules with base plate

Such modules are charaterised by the use of few large chips with good heat spreading through the base plate.


  • Mechanically more robust during transport and assembly
  • Larger thermal mass, lower thermal impedance within the range of 1 s

Disadvantages of modules with soldered or bonded chips (IGBT modules):

  • Higher thermal resistance chip / heat sink Rth(j-s) , because base plate bending requires a thicker layer of thermal paste
  • Reduced slow power cycling capability, since the large-area base plate solder pads are susceptible to temperature cycles
  • Higher internal terminal resistances (r cc’-ee’ ), since, for thermo-mechanical reasons, the design is based on small ceramic substrates that require additional internal connectors
  • Increased weight

Power modules without base plate

Such modules use smaller chips and achieve thermal spreading on the heat sink thanks to heat sources which are better spread.


  • Lower thermal resistance; because layers are omitted, even contact with the heat sink results in thinner thermal paste layers
  • Improved thermal cycling capability; because of removal of solder fatigue in base plate soldering (because there is no base plate)
  • Smaller chips; lower temperature gradient over the chip means a lower maximum temperature and less stress under power cycling conditions
  • Few large ceramic substrates with low terminal resistance


  • No heat storage
  • Processable chip size is limited, resulting in more parallel connections
  • Increased requirements for thermal paste application

Eliminating the thermo-mechanical stress between base plate and ceramic substrate, rather than connecting several small substrates soldered onto a common base plate into one circuit with the aid of additional connection elements, enables very large ceramic substrates to be used in modules with no base plate (Figure 1).

Large DBC substrate

Figure 1. Large DBC substrate (115 mm x 80 mm), equipped with the chips of a 350 A / 1200 V IGBT three-phase bridge and angle connectors

The most important thing is that the ceramic substrates are not completely rigid, but can be bent a little without breaking. This ensures that, when pressure is applied, the substrates can properly adapt to heat sinks that are not ideally even. The crucial point here is that insulating substrate is not pressed onto the heat sink at the corners only but at many different points, e.g. in the centre and along the periphery, and also next to and in between the chips. This ensures good adaptation of the DBC substrate to the heat sink surface. As a result, the thermal paste - which makes the contact with the heat sink - may be much thinner (about 20…30 μm) than for conventional modules which are only pressed onto the heat sink with screws at the corners or at the edges.

Base plate bending and thermal paste requirements

Figure 2. Base plate bending and thermal paste requirements regarding thickness for a conventional module (left) and a module in SKiiP® technology (right)

For these standard modules, thermal paste thickness must be 70 μm to 120 μm in order to prevent air bubbles between the module and heat sink surfaces which will never be ideally planar. This much thinner thermal paste layer results in a lower static thermal resistance in power modules without a base plate than in standard modules. The transient resistance of SKiiP® modules, however, is slightly higher in the time range between 0.1 s and 1 s.


For more information, please read:

Heat Transfer in Power Semiconductor Devices

Sintering Technology

Power Electronics Packaging Technology

Pressure Contact Connection Technology

The Road to the Next Generation Power Module – 100% Solder Free Design


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