FOLDED LEADFRAME SOLUTION TO REDUCE INTERCONNECTIONS IN A 3 PHASE POWER CONVERTER SYSTEMFOLDED LEADFRAME SOLUTION TO REDUCE INTERCONNECTIONS IN A 3 PHASE POWER CONVERTER SYSTEM
Original Publication Date: 2001-May-17
Included in the Prior Art Database: 2001-May-17
AbstractFOLDED LEADFRAME SOLUTION TO REDUCE INTERCONNECTIONS IN A 3 PHASE POWER CONVERTER SYSTEM
FOLDED LEADFRAME SOLUTION TO REDUCE INTERCONNECTIONS IN A 3 PHASE POWER CONVERTER SYSTEM
by Fabien Malacarne
The packaging of automotive power electronics is facing very challenging times, in particular with the advent of 42V applications requiring more and more power.
A typical 42V application is the Integrated Starter Alternator Damper system (ISAD). The heart of the system is a powerful electrical motor directly on the crankshaft and replacing the conventional alternator, starter and flywheel. Different motor technologies are possible, but a 3-phase asynchronous motor has many advantages and has been selected by many system suppliers.
Then the associated power electronics is made of half-bridge modules switching high currents (up to 600A) in the windings of the motor. Considering the current performance of power MosFet's, a total power of 5kW and the use of 4 MosFet's and 6 diodes per half-bridge module, up to 6 half-bridge modules per phase need to be assembled in parallel between the 2 battery connections. Each of these modules must also be connected to the controller board.
Therefore the interconnections between all those elements become a real challenge. It is especially true in an automotive environment where the solution must be reliable, cost effective, compact and modular.
The heart of the solution is a leadframe on a reel (see figure 1). Power MosFet's and diodes are eventually soldered on this leadframe and then wirebonded. The leadframe can be either insert moulded before dies assembly or transfer moulded after dies assembly.
But the leadframe is designed in such a way that the battery connections are the 2 side rails of the leadframe. The low current pins (to be eventually connected to the controller board) are also designed in such a way that, once folded, the leadframe provides a succession of half-bridge modules in parallel (between the battery connections) with all the signal pins on the same side (see figure 2). Then those pins can be wave soldered directly on the controller printed circuit board. Only one additional bus bar is required to connect together all module's phase tabs for each one of the 3 phases.
This folded leadframe solution provides optimised interconnections from die to system: the wirebonds quantity is reduced to its minimum (only from dies to leadframe) and no connector is added. In automotive terms, it means reliability and cost effectiveness. It is also compact and modular: the number of half-bridge modules in each folded structure can indeed be optimised to suit the required system power.
Figure 1 Leadframe schematic (flat structure)
Figure 2 Folded structure