Final Report Summary - FAMOBS (Frequency Agile Microwave Bonding System)
Executive Summary:
A microwave processing system – the Frequency Agile Microwave Bonding System (FAMOBS) – has been developed to enable rapid bonding of thermosetting materials. The overall objective of the FAMOBS project was to provide a productivity gain for the benefit of small and medium-sized companies in Europe specialized in assembly of microelectronics, optoelectronics, medical devices and micro systems.
In microtechnology a variety of thermosetting polymer materials is applied. Such materials are dispensed in a liquid form and are heated with the intent to cure them. Conventional processes often take several hours to bring the material up to temperatures which result in a significant rate of cure. An alternative approach to curing thermosetting polymers is the use of microwave energy, which has been shown to cure such materials in substantially shorter times.
The project started in November 2008 and the duration was 36 months. The technical part were to be carried out within the first 24 months, while the last twelve months were designated for dissemination and exploitation activities.
The project started with work package one. Content was the acquisition and specification of requirements for the novel bonding system imposed by potential suppliers and customers. Furthermore the characterization methods necessary to check the prior specified parameters were described.
The focus of work package two was the modeling, simulation and design of the microwave curing process. The main goals were to understand the curing process and to find optimum process parameters. A complex coupled mathematical model has been developed. The application of numerical methods (finite element analysis) on this model allows detailed analysis of the curing process and the resulting product. The model was fitted to the empirical results using particle swarm optimization methods. The model can be applied to predict the reliability of the microwave-processed products.
Within the third work package the microwave oven was further developed. Main goal was to produce an oven which can be mounted onto a precision placement machine. The oven had to be modified in many ways. It was optimized mechanically to be lighter and smaller. A pyrometer was integrated in order to enable closed-loop control of the temperature. Furthermore the shape and the material composition were optimized using numerical methods. The result was a microwave oven with a far more homogeneous energy distribution.
The characterization of the assembly process is the purpose of work package four. The electrical and mechanical characteristics of the paste materials were measured. Particular focus was set on the influence of the microwave fields on the paste materials. The microwave oven was found to be able to cure the examined pastes to one hundred percent degree of cure. The obtained results were also implemented into the mathematical model from work package two.
The FAMOBS demonstration system was designed and set up within work package 5. Three representative products were defined. A highly flexible system, which is allows assembling the products using the FAMOBS system was specified, designed and realized. The FAMOBS system could be applied within a completely automated assembly process with no detrimental effects evident. The system has a process accuracy of less than 10µm and does thus allow a flip-chip assembly.
Within work package six a series of trials was performed using the prior set-up test equipment. A series of pull and shear tests was done to determine the mechanical properties of the microwave-cured materials. No significant differences between microwave and convectionally cured materials were evident. To identify a possible effect of the microwave cure onto the reliability of microelectronic components, a series of HALT and HAST tests was performed. The microwave-cured samples showed a significantly improved reliability compared to the oven cured samples. The obtained results and end-user feedback were used to design an optimum manufacturing solution.
The dissemination and exploitation of project results is the focus of work package seven. The consortium has been very present in the scientific community: 17 conference contributions and two journal papers have been published so far. The project member organizations promote the project and its results regularly on events, in magazines, newsletters and on the internet. A leaflet and a questionnaire have been prepared for quick and comprehensive communication between the consortium and interested parties. A homepage (www.famobs.eu) which provides project information has been set up. It also serves as a platform for the internal distribution of project results.
The final goal of the Famobs project will be achieved through collaborations within a very strong consortium based on a team with outstanding scientific, engineering and manufacturing qualifications. The consortium consists of 15 European leading companies (ACI ecotec (D), Kepar Electronics (E), Seho Systems GmbH (D), Industrial Microwave Systems (UK), RF Com Ltd. (UK), Freshfield Microwave Systems Ltd. (UK) and Ribler GmbH (D)), associations (Camero di Commercia di Milano (I), Innovhub (I), Mikrosystemtechnik Baden-Württemberg (D), ARIES (RO) and National Microelectronics Institute (UK)) and research institutions (Heriot-Watt University Edinburgh (UK), University of Greenwich (UK), Eesti Innovatsiooni Instituut (Estonia), Fraunhofer IPA (D)).
Project Context and Objectives:
Microelectronics packaging often utilizes thermosetting polymer materials such as encapsulants, underfills or electrically conductive adhesives. Initially thermosetting polymers are liquid or paste like and are hardened through a cure process. Heating is required to initiate or expedite this cure process. Electromagnetic energy at microwave frequencies (1-30 GHz) was shown to be able to heat up polymer material significantly faster than conventional heating methods, revealing a potential to reduce packaging process running costs.
FAMOBS (Frequency Agile Microwave Bonding System) aims to enable rapid processing of individual components on a board assembly. In addition to the decrease in process time, the system enables package-specific processes such as flip-chip underfill cure, encapsulation and possibly rework to be performed.
The objectives of the project are:
- Understanding of the behaviour of the paste material needed for bonding and packaging the component as the paste has been cured. The mechanical and electrical characteristics of the paste material will need to be modelled and optimised to ensure optimum bonding and minimum degradation to the component when it is cured. This activity will be exploited to support the development and manufacture of the miniaturised microwave oven and lead the development of new paste and adhesive materials.
- New knowledge in the setting up of optimum parameters using industrial samples and prototype equipment. In particular, the electrical characteristic of the paste materials as a function of temperature and frequency of operation will be measured providing unique data for paste manufacturers. Isotropic conductive adhesive (ICA) curing, lead-free solder re-flow and encapsulation material will be the assembly media that will be studied. Surface mount technology (SMT) and direct flip attach (DCA) techniques will use these assembly technologies.
- New knowledge concerning the quality and reliability of assembly process in terms of technical properties of the bonds, reduced process time and cost of ownership of the equipment and process.
Project Results:
Specification and Characterisation:
The relevant applications for the FAMOBS technology have been described and assessed. The main part of the applications are in the microelectronics sector, but also optoelectronics, microsystem technology or medical technology can be thought of.
The set of applications enabled the derivation of process requirements. This has been performed with respect to existing standards and the state of the art. The FAMOBS technology is able to excel conventional technologies in certain aspects. Those have been identified.
In order to evaluate the process, a set of physical parameters has been chosen and described. Furthermore appropriate test methods and the necessary equipment have been described.
The knowledge of the relevant applications and process requirements allow the RTD performers to work focused towards goals, which are relevant to the industry. Together with the necessary test methods the developments can be evaluated. All in all a foundation for the development of a FAMOBS system has been set.
Modeling, Simulation and Design:
A fully coupled multidomain FDTD-UFVM has been developed for analysis of the FAMOBS process. The model is at the cutting-edge of numerical modeling capability and has advanced modelling capabilities in the area of microelectronics assembly. Application of this model to the FAMOBS process has shown that the process is feasible, within the bounds of the assumptions made. A literature review of the curing capabilities of the microwave ovens is also presented for understanding the capabilities of the FAMOBS oven. A number of computer simulations have been conducted. A low order cavity excitation has been considered in the first instance in order to develop and understanding of the relationships introduced through the theory. Various modal resonances have been simulated using integrated electromagnetic solver. The oven design has been successfully proven to provide heating of encapsulant samples to temperatures well above the glass transition temperature (typically 125°C) and with moderate input power levels (up to 35W). A method of optimising the strength of the electromagnetic fields has been developed based on insertion of a low loss dielectric 'wafer' material, placed between the main or bulk dielectric and the air section. Furthermore, a good understanding has been obtained with regards to the 'design trade-offs' when designing an open-ended oven to a particular specification. This understanding will be extended to meet the end user specifications and with some practical demonstration experiments. And a method of characterising the complex permittivity of encapsulant materials has been developed based on a commercially available, dielectric probe component from Agilent Technology. Complex permittivity from 0.5GHz to 18GHz and versus temperature has been published within the literature. The data generated has made a major contribution to the input data requirements of the multi-physics model developed by the University of Greenwich. The model allows the user to simulate the change in electromagnetic fields, temperature gradients, the degree of cure and the change in the degree of stress within a component.
The polymer cure modeling is one part of the FAMOBS numerical multi-physics model. A challenge of the project was to fit the experimentally obtained data to an appropriate polymer cure model. Thus, an optimization algorithm, based on a particle swarm optimization method, to capture the cure kinetics of the polymer materials was developed.
Using the multi-physics model, the mechanical behaviour of assembled QFN devices during thermal cycling was simulated. Based on the simulation results the impact of changes to the CTE and Modulus of the polymer material that may result from the microwave cure process was assessed.
Development of improved cavity oven:
A series of improved cavity oven prototypes so as to tailor the oven for efficient curing of the microelectronic chips and for easier integration with the pick and placement machine have been developed. The various prototypes can be broadly outlined as
1. Finalising the improved oven with dielectric insert for efficient heating of the microelectronic chips
A ten-fold increase in the heating rate (temperature increase per second) has been achieved when compared with the previous generation of the cavity oven. Ten-fold reduction of curing time was demonstrated with respect to convection oven.
2. Improved oven with a pyrometer integrated for ease of temperature control
A novel mechanical and electromagnetic design was designed. A new design for integration with the pick and placement machine was implemented. An integrated IR pyrometer was engineered for temperature sensing and thereby to achieve a temperature profile based curing of materials.
3. Improved metamaterial based oven
Improved metamaterial based oven has been successfully fabricated, tested and compared with the normal oven. It is the first time that FSS has been used for such an application. The temperature profile is more uniform with the FSS oven when compared with the normal oven. This has resulted in uniform curing of the materials.
All of these new generation improved oven prototypes have resulted in the efficient curing of the microelectronic chips with improved reliability when compared with the conventional curing process. Also, these prototypes have resulted in adaptable sub systems that can be integrated with the pick and placement machine.
Characterisation of Assembly Process:
Different curing strategies for the processing of different materials were designed. The different materials were cured and post cure analysis like DSC, FTIR and ageing analysis were performed. It has been established that pulsing technique tends to control the temperature of the curing material quite accurately. The measuring temperature curves do not follow the predicted cure temperature models based on the conventional heating techniques and so fast cure, optimum cure and long cure temperature profiles have been developed for the microwave curing of encapsulant materials.
1. Successful temperature profile based curing has been achieved with the new integrated oven
a. A novel pulsing technique developed to control the temperature of the curing material quite accurately.
b. The pulsing technique is combined with selective VFM (Variable frequency microwave) technique where in the frequency is hoped between selective modes only for efficient coupling of power to the material of insert .
c. An optimized control algorithm has been developed in coordination with Fraunhofer IPA for temperature profile based controlled curing of the materials.
d. Hot spots and thermal runaway problems are avoided with controlled curing.
2. Characterization of the cured specimens
a. A number of test material specimens have been cured using the fast, optimized and long cure temperature profiles at HWU.
b. Some of the cured samples were sent to EII for DSC and FTIR analysis.
c. DSC, Attenuated Total Reflectance Fourier-Transform Infrared (ATR-FTIR) analysis and Dynamic Mechanical Analysis (DMA) were performed also at HWU on a number of test samples.
d. The analysis have shown ~99.2% degree of cure for the fast cure profile and the FTIR analysis showed Tg, of 113oC for a sample cured at 150oC for 90 seconds
e. For the corresponding convection oven cured sample the degree of cure was found to be approximately 70% for the same duration of cure
f. The ATR-FTIR analysis showed no significant difference between the conventionally and microwave cured samples.
g. Thermal ageing analysis performed on fully conventional and microwave cured samples showed similar ageing behavior for both samples at a given temperature under Tg.
h. These post cure properties of the encapsulant material are closely related to the reliability and thus these experimental investigations have resulted in establishing the temperature dependent pulsing based microwave power control profiles to cure the materials for encapsulation of microelectronic chips for reliability analysis.
i. HWU also assisted in encapsulation of the microelectronic chips to be sent for the reliability analysis
j. The reliability analysis have shown improved reliability when compared with the conventionally cured microelectronic chips
Design and Set-Up of Famobs Equipment:
Sample products and the assembly system have been described. Three products have been chosen for the testing and validation phase. The complexity of the products was chosen to increase within the testing phase.
The demonstration system has been set up on the base of an existing precision placement machine. The system is modular from the mechanical and control point of view. This way it can be easily adapted to process changes and the change-over times are this way reduced. The control system was tailor-made for the requirements of FAMOBS. The microwave system was modified in order to be smaller, lighter and to allow closed-loop control of the temperature. Two main setups of the assembly system have been designed and the “encapsulation”-setup was already realised and tested successfully. This was performed during the first 18 months of the project.
As the solid-state microwave source was not available within the first period, the first demonstrator was realized using laboratory equipment. The solid-state microwave source offers a lot more possibilities and is much closer to an industrially exploitable system. The new Famobs system has new control, which is more robust and more reliable and can be directly integrated onto the moving part of the machine. The integration of the solid state components and the aspired flip-chip set-up required major changes of the system. Especially major mechanical changes were necessary, but also the control system had to be adapted. The resulting system with the integrated solid-state based Famobs system, has the necessary accuracy for flip-chip assembly and integrates all required processes in one machine, which is a major advantage compared to existing SMT lines for small to medium lots.
HWU assisted Fraunhofer IPA in designing the chip holder for efficient curing of the microelectronic chips in the FAMOBS prototype equipment. A study with the rotating type RF connector for mechanical conformity of the RF cables while movement in the pick and place machine has been undertaken. This exercise has resulted in a flexible and compact FAMOBS oven system to be integrated with the pick and placement machine. HWU also assisted Fraunhofer IPA and Freshfield in evaluating the microwave power requirements, the frequency tuning capability, the pulsing capability and establishing the mechanical dimensions of the microwave source.
Validation and Testing:
Shear tests, pull tests and visual inspection have been performed with three different materials to compare the mechanical properties of Famobs-oven cured materials to convection oven cured materials.
The material properties of EO1080 and CE3103WLV do not differ significantly, while Ribler 386 becomes much more elastic after microwave cure. The results indicate that the Famobs oven can be applied for EO1080 and CE3103WLV. The elastic properties of Ribler 386 indicate a possible use for special applications, e.g. in vibrating systems.
A series of assembly trials has been performed. The results show a positioning accuracy of ±9µm at 4 sigma. The system is thus able to perform state-of-the-art flip-chip assembly processes.
The productivity gain of the Famobs system in comparison to a conventional assembly system is dicussed and compared for a flip-chip use case. For a single assembly, a three-fold decrease of assembly time was identified.
Reliability testing was performed on QFN integral circuit packages using Henkel EO1080 composite material as a sealant. Three different microwave curing profiles and one conventionally cured sample batches were tested using HAST and thermal cycling testing. Test results showed that microwave cured samples had 1.5 times higher reliability than conventional oven cured samples thus showing that FAMOBS technology is actually better than expected by simulation results.
Based on FAMOBS system description, simulation and test results main guidelines for future technology users were described. The document shows necessary calibration procedures, list of composites that have been proven to be curable using FAMOBS process and composite selection criteria for microwave curing. Also for tested composites the best thermal profiles for highest reliability were given.
Potential Impact:
The results of the project were very successful and are described in detail before. There is potential for the results to be applied to a variety of industrial applications. The results so far have mainly been disseminated at conferences worldwide where interest from the relevant community was raised. However, positive feedback was achieved at industrial trade shows as well.
Apart from various leaflets and posters to be used by all partners a professional video about the FAMOBS system has been created as well. This video is available for all partners to be used for a variety of dissemination activities such as:
• website of all partners
• industrial trade shows
• project and product presentations
• conferences and scientific events
The key parts of the developed technology are covered by 2 inventions concerning the overall control system and the micro wave cavity. This confidential knowledge will give the consortium and owners of the rights a competitive advantage in the market and will support the impact of this developed technology in the market and for the associations.
Impact will be created through the exploitation of the technology via a selected technology provider from the industrial microwave field.
The associations being the owners of the rights will give a licence to a commercial technology provider. According to the exploitation plan this will be a SME from the project consortium.
In order to get the technology closer to the market and provide an industrial demonstrator or prototype further project activities are planned using national funding schemes such as funding via TSB in UK. As same key partners are from the UK (NMI, RfCom, HWU) this is the preferred route. The prototype activity will involve an industrial end user from the NMI membership.
In line with the prototype activity further commercialisation will be taken forward by the technology provider that takes on the licence. The framework for a licence agreement has been established. To support the consortium and cooperation of the consortium partners beyond the project a Joint Ownership Agreement has been drafted.
Further development work towards an industrial prototype already has started through a further project under the the EUMINAfab platform and is based on the results from the FAMOBS project.
List of Websites:
Website: www.famobs.eu
Contact details:
Dr. Guenter Hoercher
Guenter.Hoercher@ipa.fraunhofer.de
A microwave processing system – the Frequency Agile Microwave Bonding System (FAMOBS) – has been developed to enable rapid bonding of thermosetting materials. The overall objective of the FAMOBS project was to provide a productivity gain for the benefit of small and medium-sized companies in Europe specialized in assembly of microelectronics, optoelectronics, medical devices and micro systems.
In microtechnology a variety of thermosetting polymer materials is applied. Such materials are dispensed in a liquid form and are heated with the intent to cure them. Conventional processes often take several hours to bring the material up to temperatures which result in a significant rate of cure. An alternative approach to curing thermosetting polymers is the use of microwave energy, which has been shown to cure such materials in substantially shorter times.
The project started in November 2008 and the duration was 36 months. The technical part were to be carried out within the first 24 months, while the last twelve months were designated for dissemination and exploitation activities.
The project started with work package one. Content was the acquisition and specification of requirements for the novel bonding system imposed by potential suppliers and customers. Furthermore the characterization methods necessary to check the prior specified parameters were described.
The focus of work package two was the modeling, simulation and design of the microwave curing process. The main goals were to understand the curing process and to find optimum process parameters. A complex coupled mathematical model has been developed. The application of numerical methods (finite element analysis) on this model allows detailed analysis of the curing process and the resulting product. The model was fitted to the empirical results using particle swarm optimization methods. The model can be applied to predict the reliability of the microwave-processed products.
Within the third work package the microwave oven was further developed. Main goal was to produce an oven which can be mounted onto a precision placement machine. The oven had to be modified in many ways. It was optimized mechanically to be lighter and smaller. A pyrometer was integrated in order to enable closed-loop control of the temperature. Furthermore the shape and the material composition were optimized using numerical methods. The result was a microwave oven with a far more homogeneous energy distribution.
The characterization of the assembly process is the purpose of work package four. The electrical and mechanical characteristics of the paste materials were measured. Particular focus was set on the influence of the microwave fields on the paste materials. The microwave oven was found to be able to cure the examined pastes to one hundred percent degree of cure. The obtained results were also implemented into the mathematical model from work package two.
The FAMOBS demonstration system was designed and set up within work package 5. Three representative products were defined. A highly flexible system, which is allows assembling the products using the FAMOBS system was specified, designed and realized. The FAMOBS system could be applied within a completely automated assembly process with no detrimental effects evident. The system has a process accuracy of less than 10µm and does thus allow a flip-chip assembly.
Within work package six a series of trials was performed using the prior set-up test equipment. A series of pull and shear tests was done to determine the mechanical properties of the microwave-cured materials. No significant differences between microwave and convectionally cured materials were evident. To identify a possible effect of the microwave cure onto the reliability of microelectronic components, a series of HALT and HAST tests was performed. The microwave-cured samples showed a significantly improved reliability compared to the oven cured samples. The obtained results and end-user feedback were used to design an optimum manufacturing solution.
The dissemination and exploitation of project results is the focus of work package seven. The consortium has been very present in the scientific community: 17 conference contributions and two journal papers have been published so far. The project member organizations promote the project and its results regularly on events, in magazines, newsletters and on the internet. A leaflet and a questionnaire have been prepared for quick and comprehensive communication between the consortium and interested parties. A homepage (www.famobs.eu) which provides project information has been set up. It also serves as a platform for the internal distribution of project results.
The final goal of the Famobs project will be achieved through collaborations within a very strong consortium based on a team with outstanding scientific, engineering and manufacturing qualifications. The consortium consists of 15 European leading companies (ACI ecotec (D), Kepar Electronics (E), Seho Systems GmbH (D), Industrial Microwave Systems (UK), RF Com Ltd. (UK), Freshfield Microwave Systems Ltd. (UK) and Ribler GmbH (D)), associations (Camero di Commercia di Milano (I), Innovhub (I), Mikrosystemtechnik Baden-Württemberg (D), ARIES (RO) and National Microelectronics Institute (UK)) and research institutions (Heriot-Watt University Edinburgh (UK), University of Greenwich (UK), Eesti Innovatsiooni Instituut (Estonia), Fraunhofer IPA (D)).
Project Context and Objectives:
Microelectronics packaging often utilizes thermosetting polymer materials such as encapsulants, underfills or electrically conductive adhesives. Initially thermosetting polymers are liquid or paste like and are hardened through a cure process. Heating is required to initiate or expedite this cure process. Electromagnetic energy at microwave frequencies (1-30 GHz) was shown to be able to heat up polymer material significantly faster than conventional heating methods, revealing a potential to reduce packaging process running costs.
FAMOBS (Frequency Agile Microwave Bonding System) aims to enable rapid processing of individual components on a board assembly. In addition to the decrease in process time, the system enables package-specific processes such as flip-chip underfill cure, encapsulation and possibly rework to be performed.
The objectives of the project are:
- Understanding of the behaviour of the paste material needed for bonding and packaging the component as the paste has been cured. The mechanical and electrical characteristics of the paste material will need to be modelled and optimised to ensure optimum bonding and minimum degradation to the component when it is cured. This activity will be exploited to support the development and manufacture of the miniaturised microwave oven and lead the development of new paste and adhesive materials.
- New knowledge in the setting up of optimum parameters using industrial samples and prototype equipment. In particular, the electrical characteristic of the paste materials as a function of temperature and frequency of operation will be measured providing unique data for paste manufacturers. Isotropic conductive adhesive (ICA) curing, lead-free solder re-flow and encapsulation material will be the assembly media that will be studied. Surface mount technology (SMT) and direct flip attach (DCA) techniques will use these assembly technologies.
- New knowledge concerning the quality and reliability of assembly process in terms of technical properties of the bonds, reduced process time and cost of ownership of the equipment and process.
Project Results:
Specification and Characterisation:
The relevant applications for the FAMOBS technology have been described and assessed. The main part of the applications are in the microelectronics sector, but also optoelectronics, microsystem technology or medical technology can be thought of.
The set of applications enabled the derivation of process requirements. This has been performed with respect to existing standards and the state of the art. The FAMOBS technology is able to excel conventional technologies in certain aspects. Those have been identified.
In order to evaluate the process, a set of physical parameters has been chosen and described. Furthermore appropriate test methods and the necessary equipment have been described.
The knowledge of the relevant applications and process requirements allow the RTD performers to work focused towards goals, which are relevant to the industry. Together with the necessary test methods the developments can be evaluated. All in all a foundation for the development of a FAMOBS system has been set.
Modeling, Simulation and Design:
A fully coupled multidomain FDTD-UFVM has been developed for analysis of the FAMOBS process. The model is at the cutting-edge of numerical modeling capability and has advanced modelling capabilities in the area of microelectronics assembly. Application of this model to the FAMOBS process has shown that the process is feasible, within the bounds of the assumptions made. A literature review of the curing capabilities of the microwave ovens is also presented for understanding the capabilities of the FAMOBS oven. A number of computer simulations have been conducted. A low order cavity excitation has been considered in the first instance in order to develop and understanding of the relationships introduced through the theory. Various modal resonances have been simulated using integrated electromagnetic solver. The oven design has been successfully proven to provide heating of encapsulant samples to temperatures well above the glass transition temperature (typically 125°C) and with moderate input power levels (up to 35W). A method of optimising the strength of the electromagnetic fields has been developed based on insertion of a low loss dielectric 'wafer' material, placed between the main or bulk dielectric and the air section. Furthermore, a good understanding has been obtained with regards to the 'design trade-offs' when designing an open-ended oven to a particular specification. This understanding will be extended to meet the end user specifications and with some practical demonstration experiments. And a method of characterising the complex permittivity of encapsulant materials has been developed based on a commercially available, dielectric probe component from Agilent Technology. Complex permittivity from 0.5GHz to 18GHz and versus temperature has been published within the literature. The data generated has made a major contribution to the input data requirements of the multi-physics model developed by the University of Greenwich. The model allows the user to simulate the change in electromagnetic fields, temperature gradients, the degree of cure and the change in the degree of stress within a component.
The polymer cure modeling is one part of the FAMOBS numerical multi-physics model. A challenge of the project was to fit the experimentally obtained data to an appropriate polymer cure model. Thus, an optimization algorithm, based on a particle swarm optimization method, to capture the cure kinetics of the polymer materials was developed.
Using the multi-physics model, the mechanical behaviour of assembled QFN devices during thermal cycling was simulated. Based on the simulation results the impact of changes to the CTE and Modulus of the polymer material that may result from the microwave cure process was assessed.
Development of improved cavity oven:
A series of improved cavity oven prototypes so as to tailor the oven for efficient curing of the microelectronic chips and for easier integration with the pick and placement machine have been developed. The various prototypes can be broadly outlined as
1. Finalising the improved oven with dielectric insert for efficient heating of the microelectronic chips
A ten-fold increase in the heating rate (temperature increase per second) has been achieved when compared with the previous generation of the cavity oven. Ten-fold reduction of curing time was demonstrated with respect to convection oven.
2. Improved oven with a pyrometer integrated for ease of temperature control
A novel mechanical and electromagnetic design was designed. A new design for integration with the pick and placement machine was implemented. An integrated IR pyrometer was engineered for temperature sensing and thereby to achieve a temperature profile based curing of materials.
3. Improved metamaterial based oven
Improved metamaterial based oven has been successfully fabricated, tested and compared with the normal oven. It is the first time that FSS has been used for such an application. The temperature profile is more uniform with the FSS oven when compared with the normal oven. This has resulted in uniform curing of the materials.
All of these new generation improved oven prototypes have resulted in the efficient curing of the microelectronic chips with improved reliability when compared with the conventional curing process. Also, these prototypes have resulted in adaptable sub systems that can be integrated with the pick and placement machine.
Characterisation of Assembly Process:
Different curing strategies for the processing of different materials were designed. The different materials were cured and post cure analysis like DSC, FTIR and ageing analysis were performed. It has been established that pulsing technique tends to control the temperature of the curing material quite accurately. The measuring temperature curves do not follow the predicted cure temperature models based on the conventional heating techniques and so fast cure, optimum cure and long cure temperature profiles have been developed for the microwave curing of encapsulant materials.
1. Successful temperature profile based curing has been achieved with the new integrated oven
a. A novel pulsing technique developed to control the temperature of the curing material quite accurately.
b. The pulsing technique is combined with selective VFM (Variable frequency microwave) technique where in the frequency is hoped between selective modes only for efficient coupling of power to the material of insert .
c. An optimized control algorithm has been developed in coordination with Fraunhofer IPA for temperature profile based controlled curing of the materials.
d. Hot spots and thermal runaway problems are avoided with controlled curing.
2. Characterization of the cured specimens
a. A number of test material specimens have been cured using the fast, optimized and long cure temperature profiles at HWU.
b. Some of the cured samples were sent to EII for DSC and FTIR analysis.
c. DSC, Attenuated Total Reflectance Fourier-Transform Infrared (ATR-FTIR) analysis and Dynamic Mechanical Analysis (DMA) were performed also at HWU on a number of test samples.
d. The analysis have shown ~99.2% degree of cure for the fast cure profile and the FTIR analysis showed Tg, of 113oC for a sample cured at 150oC for 90 seconds
e. For the corresponding convection oven cured sample the degree of cure was found to be approximately 70% for the same duration of cure
f. The ATR-FTIR analysis showed no significant difference between the conventionally and microwave cured samples.
g. Thermal ageing analysis performed on fully conventional and microwave cured samples showed similar ageing behavior for both samples at a given temperature under Tg.
h. These post cure properties of the encapsulant material are closely related to the reliability and thus these experimental investigations have resulted in establishing the temperature dependent pulsing based microwave power control profiles to cure the materials for encapsulation of microelectronic chips for reliability analysis.
i. HWU also assisted in encapsulation of the microelectronic chips to be sent for the reliability analysis
j. The reliability analysis have shown improved reliability when compared with the conventionally cured microelectronic chips
Design and Set-Up of Famobs Equipment:
Sample products and the assembly system have been described. Three products have been chosen for the testing and validation phase. The complexity of the products was chosen to increase within the testing phase.
The demonstration system has been set up on the base of an existing precision placement machine. The system is modular from the mechanical and control point of view. This way it can be easily adapted to process changes and the change-over times are this way reduced. The control system was tailor-made for the requirements of FAMOBS. The microwave system was modified in order to be smaller, lighter and to allow closed-loop control of the temperature. Two main setups of the assembly system have been designed and the “encapsulation”-setup was already realised and tested successfully. This was performed during the first 18 months of the project.
As the solid-state microwave source was not available within the first period, the first demonstrator was realized using laboratory equipment. The solid-state microwave source offers a lot more possibilities and is much closer to an industrially exploitable system. The new Famobs system has new control, which is more robust and more reliable and can be directly integrated onto the moving part of the machine. The integration of the solid state components and the aspired flip-chip set-up required major changes of the system. Especially major mechanical changes were necessary, but also the control system had to be adapted. The resulting system with the integrated solid-state based Famobs system, has the necessary accuracy for flip-chip assembly and integrates all required processes in one machine, which is a major advantage compared to existing SMT lines for small to medium lots.
HWU assisted Fraunhofer IPA in designing the chip holder for efficient curing of the microelectronic chips in the FAMOBS prototype equipment. A study with the rotating type RF connector for mechanical conformity of the RF cables while movement in the pick and place machine has been undertaken. This exercise has resulted in a flexible and compact FAMOBS oven system to be integrated with the pick and placement machine. HWU also assisted Fraunhofer IPA and Freshfield in evaluating the microwave power requirements, the frequency tuning capability, the pulsing capability and establishing the mechanical dimensions of the microwave source.
Validation and Testing:
Shear tests, pull tests and visual inspection have been performed with three different materials to compare the mechanical properties of Famobs-oven cured materials to convection oven cured materials.
The material properties of EO1080 and CE3103WLV do not differ significantly, while Ribler 386 becomes much more elastic after microwave cure. The results indicate that the Famobs oven can be applied for EO1080 and CE3103WLV. The elastic properties of Ribler 386 indicate a possible use for special applications, e.g. in vibrating systems.
A series of assembly trials has been performed. The results show a positioning accuracy of ±9µm at 4 sigma. The system is thus able to perform state-of-the-art flip-chip assembly processes.
The productivity gain of the Famobs system in comparison to a conventional assembly system is dicussed and compared for a flip-chip use case. For a single assembly, a three-fold decrease of assembly time was identified.
Reliability testing was performed on QFN integral circuit packages using Henkel EO1080 composite material as a sealant. Three different microwave curing profiles and one conventionally cured sample batches were tested using HAST and thermal cycling testing. Test results showed that microwave cured samples had 1.5 times higher reliability than conventional oven cured samples thus showing that FAMOBS technology is actually better than expected by simulation results.
Based on FAMOBS system description, simulation and test results main guidelines for future technology users were described. The document shows necessary calibration procedures, list of composites that have been proven to be curable using FAMOBS process and composite selection criteria for microwave curing. Also for tested composites the best thermal profiles for highest reliability were given.
Potential Impact:
The results of the project were very successful and are described in detail before. There is potential for the results to be applied to a variety of industrial applications. The results so far have mainly been disseminated at conferences worldwide where interest from the relevant community was raised. However, positive feedback was achieved at industrial trade shows as well.
Apart from various leaflets and posters to be used by all partners a professional video about the FAMOBS system has been created as well. This video is available for all partners to be used for a variety of dissemination activities such as:
• website of all partners
• industrial trade shows
• project and product presentations
• conferences and scientific events
The key parts of the developed technology are covered by 2 inventions concerning the overall control system and the micro wave cavity. This confidential knowledge will give the consortium and owners of the rights a competitive advantage in the market and will support the impact of this developed technology in the market and for the associations.
Impact will be created through the exploitation of the technology via a selected technology provider from the industrial microwave field.
The associations being the owners of the rights will give a licence to a commercial technology provider. According to the exploitation plan this will be a SME from the project consortium.
In order to get the technology closer to the market and provide an industrial demonstrator or prototype further project activities are planned using national funding schemes such as funding via TSB in UK. As same key partners are from the UK (NMI, RfCom, HWU) this is the preferred route. The prototype activity will involve an industrial end user from the NMI membership.
In line with the prototype activity further commercialisation will be taken forward by the technology provider that takes on the licence. The framework for a licence agreement has been established. To support the consortium and cooperation of the consortium partners beyond the project a Joint Ownership Agreement has been drafted.
Further development work towards an industrial prototype already has started through a further project under the the EUMINAfab platform and is based on the results from the FAMOBS project.
List of Websites:
Website: www.famobs.eu
Contact details:
Dr. Guenter Hoercher
Guenter.Hoercher@ipa.fraunhofer.de