Projects

Scalable low-inductive molded power module

Molding technology has been established as an encapsulation technology for power modules, but each module is encapsulated in a product-specific, single cavity and all contacts are in one plane, which requires subsequent forming of the signal pins. Fraunhofer IZM is introducing the encapsulation of power modules by compression molding. The process offers the advantage of using a height-flexible molding tool for the simultaneous encapsulation of multiple heterogeneous devices with different widths and/or thicknesses. In addition, less encapsulation material is used as compression molding is a runnerless process.

Compression molding is an established process for the encapsulation of bare dies. Our current project, however, aims to encapsulate more complex devices, requiring the process to be adapted for increased thickness and exposure of lateral power connects. The targeted power module is an AMB-based switching cell with two or four semiconductors, offering low inductive switching through 3D shaped power contacts and a suitable isolation distance between DC+ and DC-. The signal pins are guided to the module top side, where a plated redistribution layer enlarges the small gate and source contact areas to allow them to be connected by spring contacts.

In terms of module design, a skilled power connector design and the direct metallized mold surface allow a very low inductive switching cell and a very low inductive driver connection for faster and more stable switching behavior. Power scaling of the half-bridge module can easily be realized by implementing more chips in parallel; the manufacturing sequence is hardly affected by scaling.

On the manufacturing side, the encapsulation process has been extended to broader applications, namely heterogeneous devices and increased thickness. There is no need for a dedicated molding tool for each module size as required for transfer molding. Process adaptation comprises:

• Mold film wrinkle/crack behavior for tool depths up to 6 mm
• Lading & melting of ten times the typical encapsulant load

Encapsulation by compression molding of heterogeneous devices does not require the dedicated mold tooling required by transfer molding.