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Advanced GaN packaging

Final Report Summary - AGAPAC (Advanced GaN packaging)

Executive summary:

AGAPAC is an important project for Europe: the market for gallium nitride (GaN) transistors is expected to have a strong growth, with main turnover in third-generation (3G) base station, satcom and military. This project targets packaging for space applications to enable Europe to maintain a strong position in the highly competitive space industry. Up to 25 High-power amplifier (HAP) packages have been produced by Egide according to TAS design. These packages have been found hermetic according to space standards.

State-of-the-art results have been obtained for L band HPA, putting forward the strong impact of base plate material to be used into RF power modules. Up to 65 % power added efficiency with up to 180 W Radio frequency (RF) power in L band has been obtained with no tuning on several power module using diamond silver base plate material The gain in power added efficiency is about 10 points for same design implemented into CuW standard micropackage.

Tremendous thermal advantage obtained representative HPA implemented onto commercial CuW, Cu / Mo / Cu macro composite and AGAPAC diamond silver produced by Plansee have confirmed the excellent electrical results obtained.

Selection of high thermal conductivity material with other European source than Plansee has been performed with technological and thermal evaluation of the selected material.

Project context and objectives:

Reducing size and, in parallel, increasing power capabilities of electronic devices in a spacecraft is of immense importance for the overall performance of any satellite. As the power density increases, it is of critical importance to have packaging technologies available, which can transport the generated heat to the surrounding environment and keep the temperature of the device within its specified limits.

For power packages, it is compulsory to provide at the same time minimised thermal resistance and high protection to all devices and circuits with respect to contaminations, mechanical aggressions, radiations and electromagnetic perturbations.

GaN technology has recently made a remarkable breakthrough in the world of microwave electronics with the announcement of commercially available transistors from 5 to over 200 W at microwave frequencies. Originating from a major industrial transistor vendor in Japan but also from Europe and the United States, equipment manufacturers and especially those related to space applications strongly believe that time has now come for a rapid insertion of GaN electronics into their systems.

Apart from the reliability concerns that still need to be addressed specifically for space use, these GaN power transistors will roughly increase power density by more than an order of magnitude for large devices compared to present solutions (from 0.5 to 5 W / mm for space applications including de-ratings). Consequences will directly impact packaging technology for which the thermal resistance needs to be significantly reduced if the advantages obtained at die level are to be maintained at its highest at the module and equipment level.

AGAPAC, which aims to address this critical challenge for space satellite applications. This item is identified on the ESA roadmap (Ref: ESTEC / AC / 418-20, ESA-IPC 2006) for GaN component strategy but is not funded by the European Space Agency (ESA).

AGAPAC core objective is to establish a space compatible European supply chain for packaging solutions of GaN HEMTs and GaN MMICs to cover the need for GaN-based HPAs for space applications.

More precisely, the AGAPAC project technical objectives are to:

- extend beyond state-of-the-art for high thermal dissipation composites (up to 600 W / mK) using materials based on diamond solutions as well as on carbon nano-fibres, compatible with hybrid micropackage manufacturing technologies;
- develop a space compatible power hybrid able to withstand up to 150 W of RF power in L band, with minimal junction temperature elevation. Note that power modules used in space commercial flights have a maximum RF power of 40 W in L band.

AGAPAC has also brought together actors and industry from material science (in Spain and Austria), thermal and mechanical analyses (United Kingdom and France), with the packaging industry (France), and GaN device manufacturing (Germany) around the needs of major space actors in Europe.

To realise this project's objectives, the partners have defined sub-objectives that directly relate to 7 Work packages (WPs) targeting:

- WP1: Requirements and GaN components.
- WP2: Thermal and thermo-mechanical simulation and characterisation.
- WP3: High-conductivity material development.
- WP4: Package development.
- WP5: HPA module assessment.
- WP6: Use and dissemination.
- WP7: Management.

Project results:

AGAPAC is an important project for Europe: the market for GaN transistors is expected to have a strong growth, with main turnover in 3G base station, satcom and military. This project targets packaging for space applications to enable Europe to maintain a strong position in the highly competitive space industry. Up to 25 HPA packages have been produced by Egide according to TAS design. These packages have been found hermetic according to space standards.

State-of-the-art results have been obtained for L band HAP, putting forward the strong impact of base plate material to be used into RF power modules . Up to 65 % power added efficiency with up to 180 W RF power in L band has been obtained with no tunning on several power module using diamond silver base plate material. The gain in power added efficiency is about 10 points for same design implemented into CuW standard micropackage.

Tremendous thermal advantage obtained representative HPA implemented onto commercial CuW, Cu / Mo / Cu macro composite and AGAPAC diamond silver produced by Plansee have confirmed the excellent electrical results obtained.

Selection of high thermal conductivity material with other European source than Plansee has been performed with technological and thermal evaluation of the selected material. 2 packages have been proposed and implemented with two material base plate coping with Plansee discontinuation of production and patented RF F / T from TAS (AGAPAC FUTURE packages).

In addition to initial project objectives and thanks to ESA support, multifactor tests have been implemented with representative test structure supplied by Egide. It shows that RF feedthrough has been tested until 450 W without multipactor discharge. Preliminary technology assessment of the AGAPAC micropackages have been performed according to TAS standards. No failures could be reported with HPA module mounted into representative SSPA structure after 500 thermal cycles (-55, 125 degrees of Celsius) showing the robustness of the AGAPAC micropackage versus space environment.

Innovative non-destructive testing means such as three-dimensional (3D) X-ray tomography has been used and have been proven to be useful to determine voids into HPA module.

Lately, the dissemination is being at the level of high quality results obtained by the consortium as AGAPAC will be again present at the main event in the field in Europe (European microwave conference in Amsterdam, October 2012) and in North America (international microwave symposium in Montreal Canada, June 2012) with many other reported in past years in relevant conferences.

Potential impact:

The AGAPAC project has involved several engineers, technicians and operators within TAS. Since the start of the project, one women engineer that has participated at the AGAPAC proposal, has been hired in TAS in permanent position. She has not been directly involved into the technical work, but work load generated by AGAPAC has allowed to hire her in the same team leading AGAPAC.

Thanks to AGAPAC, outside technical achievements that were outstanding, we have built inside the consortium strong link among the consortium which gave rise of other collaborations, enhancing the European integration of its advanced Research and development (R&D). Finally, AGAPAC has also been for TAS an important milestone toward the widespread of European GaN technology including power packages for RF power amplifier into space subsystem. Next stage is to prepare for flight demonstration of such technology.

The AGAPAC project has involved the work of numerous engineers and technicians at Egide. No formal specific gender balance has been set up for the project, however the statistics of the company show already an interesting contribution to tend towards equality principles, and AGAPAC has been integrated in this movement.

Indeed even if external and internal management of the project were ensured by male persons, the major developments in the field of HTCC ceramic were managed and made by women, as well as all the RF simulation activities, a part of the package design work and a part of the plating development work. In total, at least half of the development work in AGAPAC has been made by women in Egide. This work has allowed them to comfort their respective position and to develop their expertise in the different domains involved. The AGAPAC project has contributed maintaining all the skills at Egide in R&D field, and provides perspectives of increase in employment within 2 or 3 years thanks to the new technological bricks developed.

AGAPAC has also reinforced Egide's visibility, position, and expert reputation in the field of high-end packages, especially for space applications.

Plansee's silver-diamond-composite was introduced as baseplate material for high power RF applications. The material passed space qualification with excellent results so that applications manufacturers gained confidence in that material also for other thermal management applications. Successful implementation of metal-diamond-composites into leading edge technology can facilitate dissemination of this promising material technology and thereby support other suppliers and start-ups like RHP in this field. The contribution to AGAPAC has strengthened the position of Plansee as a European based provider of innovative thermal management products. Further business development in this field can secure and generate new employment within the EU.

The new developed semiconductor technology GaN is now used for first devices commercially available. The qualification was finished successfully in December 2011 and first customers are testing the devices for their application. But for high power applications most customer request packaged devices with more output power than available today. To develop and design such devices the outcomes of AGAPAC is of high interest and secure the employment. For the development of suitable package solutions for customers UMS intend to increase the staff.

The participation of UMS at AGAPAC enables us to increase the visibility in this emerging market even when the technology was not qualified and thus not available for customer.

Tecnalia has been visible in the thermal management field through its continued investigation of materials for thermal management materials as well as its role as a member of the technical committee of one of Europe's key thermal management conferences (IMAPS France). AGAPAC has enabled Tecnalia to continue its fundamental research in nano particle filled metal matrix composites (which has provided further research opportunities outside of the current research field particularly in tribological applications), as well as providing the basis for expansion into other nano-based fields of investigation (carbon nanofibre and carbon nanotube related).

This continued development has enabled security of employment for existing staff as well as new employment for additional staff members linked to the fundamental research upon which the Tecnalia participation in AGAPAC is based.

The involvement of Tecnalia (and its change in role within the consortium) has clearly led to the involvement of a new actor (namely RHP technology) within the project. This was achieved due to their product range but also due to the previous development work carried out with Tecnalia in previous EU funded and private client funded projects.

AGAPAC was the key factor in the development of the 3D X-ray activities in CNES lab. In fact challenges brought by AGAPAC in term of new material have pushed us to purchase new equipment in order to be able to characterise developed materials. This 3D X-ray activity started under the pressure of AGAPAC has also impacted job and commercial activities in our lab shared with companies (public / private partnership and / or CNES spin-off). Company NOVAMEMS is now proposing a full service on this new technology with an increase of 10 % of its turnover. Spin-off INTRASPEC has introduced 3DXray techniques in its magnetic microscopy offer: a permanent job has been secured.

The University of Bristol trained during AGAPAC a wide range of researchers that contributed to the AGAPAC programme, including two female researchers (one EC, one non-EC), contributing to the training of a qualified work force for the United Kingdom's and European Commission (EC)'s economy. Further benefits arose in development novel experimental techniques and simulation approaches that will provide the basis for future employment, in part related to enable proposal applications such as to the European Space Agency (ESA), EC ENAIC and UK TSB and EPSRC.

As described in D6.1 TAS has shown a clear exploitation of the project results with a presentation of its business plan for L band SSPA which includes the production of very HPA module which will need solution like developed in AGAPAC. One main point is to secure a European supply chain for very high thermal conductivity material compatible with packaging constraints as requested in space satellites. Dissemination of knowledge has been done by TAS as reported into D6.2 in major microwave events (European microwave, International Microwave Symposium) but also in dedicated workshop internal or external (ESA, CNES).

As described in D6.1 the work performed within the Agapac consortium is a first step towards the extension of Egide's RF power package productline. It also strengthens Egide's position as a key European player in high end hermetic packages. Beyond the R&D done under the AGAPAC programme, the first designs based on technology bricks coming out of the Agapac project are under discussion with several end customers. With a series production projected for 2014 / 2015.

After the decision to discontinue the diamond composite operations in 2009 Plansee made great efforts to find an investor who is able to successfully continue this technology. Several companies had seriously indicated their interest but finally none of the potential transfer partners was in the position to fund the transfer and further development of the technology. Plansee still maintains the patent portfolio of the diamond-composite technology for possible licensing and transfer options. The resumption of the operations is conceivable if a sustainable business case can be identified.

In the frame of AGAPAC project UMS sub-contracted a model development including electro-thermal effects of power bars with great gate periphery. This enables UMS to go forward with the technology development towards higher power density and more powerful devices, taking into account thermal constraints or new materials like the AGAPAC AgD base plate. From the reliabilitiy point of view it is important to have a possibility to lower the channel temperature at very high output power level, especially for space application.

The use of our power bar with 36 mm gate periphery for L band application is also of high interest for UMS. This gives us and the potential customer TAS-F a deep view inside what could be reached in terms of output power and efficiency.

Internally, Tecnalia (formerly Inasmet) has used its Intranet and website continuously to inform all staff members of ongoing projects. Details of the AGAPAC project have been posted as well as further details within Inasmet newsletters.

Quarterly meetings continue to be held to discuss ongoing projects within the Transport Division of which one of the focus groups is aimed at material developments for use in electronics and packaging applications. These focus groups are attended by staff members, heads of departments, as well as the head of division. These provide a forum for the presentation of key projects (including results / problems / future targets) and also enable an exchange of ideas across related work groups.

Externally, Tecnalia (Inasmet) has been responsible for the development of the project website which will be maintained for at least the next three years during which time it will be available to continue to present the findings of the project. Tecnalia has also been involved with several presentations particularly including the annual IMAPS (France) European advanced technology workshop on micropackaging and thermal management. This has been attended by at least one of the AGAPAC partners throughout the project. At each of the last four workshops (2009 to 2012) a presentation has been made by either Thales (2009 and 2012) or Tecnalia (2010 and 2011) to either present the project structure and intended goals, or the actual project results. Tecnalia is a member of the technical committee of this workshop and has worked to ensure that the AGAPAC project has been presented to as many of the workshop attendees as possible over the four years. Future presentations to this workshop remain possible and the call for papers for 2013 will shortly be sent out to the industry.

GaN power devices (provided by UMS) are candidate for an introduction into the European preferred parts list (EPPL) mastered by ESA for spacecraft. The use of such a device comes together with the development of a package, able to meet the requirements in matter of dissipative performance while keeping a level of reliability compatible with telecommunication satellite. This work was done in the collaborative study AGAPAC. AGAPAC offers a strong basis where main difficulties have been solved despite the fact that the base plate material source is not secured. During the project progress CNES was asked by French Department of Defence (DGA), a substantial end user of such a product, to provide results of AGAPAC. A dedicated meeting with TAS / CNES (open to AGAPAC partners) will be organised to present the AGAPAC results, to DGA and other potential users. This presentation will be done in the frame of the CNES think tank?structure called Centre de Competence Technique du CNES (CCT).

List of websites: www.agapac.eu
d7-6v2-publishable.pdf