The study includes an analysis of the improvement in terms of mass, cost and voltage which could
be appropriate for next generation of the EPC. This study also includes a market overview about materials and processes in order to make a leap frog especially in the coating/moulding of HV
module with a focus on European products and processes. The potting used up to now for the high voltage modules of the EPC (voltage up to 8500 V during technological qualification) sustains three main constraints:
- the electrical insulation of the EPC,
- the mechanical and thermo mechanical performance and integrity of the module,
The change of implementation of the EPC HV module will offer the opportunity to study a new design for the module.
The step in technology that we need is an improvement of the insulation technology of the HV module; indeed, the present PCB containing as much as possible SMD for cost reduction with a
surrounding moulding materials, our actual insulation material, has the following main drawbacks :
The module has to evolve on two inseparable aspects, the implementation and the material. To reduce the mass and the thermo-mechanical management inside the module, we wanted to
drastically reduce the thickness of the potting. The introduction of thin coating requires new materials and the associated implementation. Several ways of investigations have been explored:
- Dipping of the module using a traditional material: the dipping can be made by layer with intermediate gelation phase between two steps. The number of layers must be optimised to meet the mechanical, electrical, mass constraints.
- Deposit from the gaseous phase in addition with a further protection. A typical material for that is the Parylene with the deposition developed.
- Deposit of a thin layer of product by spray gun, the layer can be pre-cured between two depositions. Such a deposition imposes some specific characteristics like the viscosity and the pot life.
- Use of the prototyping techniques could allow us to obtain "tailored" moulds. The mould would follow closely the shapes of the modules limiting that way the resin quantity and constraints (local moulding).
Based on the encouraging results of Phase 1, we decided to use the local moulding by the dam and fill deposition process by using an automatic dispensing machine. The Phase 1 activities have
permitted to put into evidence the main advantages of this technology. The goal of the Phase 2 was to identify the adequate machine/process in order to be validated in a representative EPC circuitry regarding environmental constraints.
During Phase 2, the trade-off of the machine market, performances, parameters, and automation aspects have been studied. Machine experimental parameters have also be deeply defined and
validated on simplified test samples specially designed for this application before starting the design and the development and the manufacturing of the new HV module.
After the definition of the dispensing machine parameters, a technological evaluation has been performed on the new HV module architecture.
The selected technology has been merged in the premises of a completely new HV module architecture containing, a part of current HV1 functional module including some HV diodes and HV
capacitors technology, HV interconnections, new insulation material to validate the heart of a future EPC. This architecture will allow us to work at 15kV DC.
The analysis and the development of the new HV module have been realized taken into account the new constraints introduced by the new implementation, and based on the conclusions of the Phase1.
After their manufacturing; altogether 3 identical HV modules have been tested with success in the frame of this technological evaluation regarding EPC environmental constraints (with a special focus on mechanical, vacuum, thermo mechanical and electrical life test constraints).