Quasi-ambient bonding to enable cost-effective high temperature Pb-free solder interconnects
Lead Research Organisation:
Loughborough University
Department Name: Wolfson Sch of Mech, Elec & Manufac Eng
Abstract
There is an increasing demand for electronics that can operate at temperatures in excess of 200 degrees C, well above the maximum operating temperature of traditional silicon microelectronics. Key application areas are in the power, automotive, aerospace and defence industries. Electronic devices capable of operating at such high temperatures are now available. However, new methods are also needed for integrating these devices into circuits and systems, and in particular for attaching them, both mechanically and electrically, to circuit boards and heatsinks.
At present high-temperature devices are typically attached by soldering using high-melting-point, lead-rich solders. However, there is a strong environmental imperative to reduce the use of lead in all electronics, so this cannot be accepted as a long-term solution. Alternative solutions employing gold-rich solders or sintered nano-silver pastes can be used, but these are expensive and can suffer from reliability issues. Low-cost, lead-free high-temperature solder alloys are also available; however, these tend to require significantly higher soldering temperatures and longer processing times, leading to slower production and higher thermal load on the devices during soldering.
This project will explore the use of quasi-ambient bonding (QAB) with reactive nanofoils as a route to lowering the process time and thermal load during packaging of high-temperature electronic devices. Reactive nanofoils are multilayer materials comprising alternating layers of two elements (typically nickel and aluminium) that react exothermically i.e. with the release of heat. Once the reaction is triggered, it is self-propagating and spreads throughout the foil. If the foil is sandwiched between two parts that are pre-coated with solder, the heat generated can be used to melt the adjacent solder layers momentarily and form a permanent bond. The heating is intense, but occurs over a short timescale, so that while the local temperature can reach up to 1500 degrees C, heating is confined to a narrow region around the foil, with negligible temperature rise occurring elsewhere.
Up to now, quasi-ambient bonding applications have used traditional lower-temperature solders. In this project we will extend the application of QAB to a range of low-cost, lead-free high-temperature alloys. The primary aim will be to develop bonding processes tailored for applications in high-temperature power electronics and optoelectronics. We will also explore the use of QAB for sealing of hermetic packages which is another key area where low cost and low thermal load can be an advantage. The processes developed will be evaluated in terms of bonding strength and in-service reliability, and benchmarked against alternative processes based on lead- and gold-based solders.
Alongside the process development and evaluation, we will carry out extensive modelling and characterisation aimed at gaining an improved understanding of the QAB process. Developments to date have been mainly empirical, and fundamental aspects of the process remain poorly understood. QAB is fundamentally different from traditional soldering because of the very short timescale over which the process takes place. In order for it to become established in mainstream electronics manufacturing, the potential detrimental effects of residual stresses and microstructural defects incorporated into QAB bonds need to be fully understood.
The proposed research has the potential to provide a low-cost, sustainable joining technology for electronics manufacturing that can continue to meet the operating temperature requirements of high-temperature electronics for many years to come. At the same time it will yield new fundamental insights into processes involving rapid solidification of complex alloys that will be of wide interest to the materials science and manufacturing research communities.
At present high-temperature devices are typically attached by soldering using high-melting-point, lead-rich solders. However, there is a strong environmental imperative to reduce the use of lead in all electronics, so this cannot be accepted as a long-term solution. Alternative solutions employing gold-rich solders or sintered nano-silver pastes can be used, but these are expensive and can suffer from reliability issues. Low-cost, lead-free high-temperature solder alloys are also available; however, these tend to require significantly higher soldering temperatures and longer processing times, leading to slower production and higher thermal load on the devices during soldering.
This project will explore the use of quasi-ambient bonding (QAB) with reactive nanofoils as a route to lowering the process time and thermal load during packaging of high-temperature electronic devices. Reactive nanofoils are multilayer materials comprising alternating layers of two elements (typically nickel and aluminium) that react exothermically i.e. with the release of heat. Once the reaction is triggered, it is self-propagating and spreads throughout the foil. If the foil is sandwiched between two parts that are pre-coated with solder, the heat generated can be used to melt the adjacent solder layers momentarily and form a permanent bond. The heating is intense, but occurs over a short timescale, so that while the local temperature can reach up to 1500 degrees C, heating is confined to a narrow region around the foil, with negligible temperature rise occurring elsewhere.
Up to now, quasi-ambient bonding applications have used traditional lower-temperature solders. In this project we will extend the application of QAB to a range of low-cost, lead-free high-temperature alloys. The primary aim will be to develop bonding processes tailored for applications in high-temperature power electronics and optoelectronics. We will also explore the use of QAB for sealing of hermetic packages which is another key area where low cost and low thermal load can be an advantage. The processes developed will be evaluated in terms of bonding strength and in-service reliability, and benchmarked against alternative processes based on lead- and gold-based solders.
Alongside the process development and evaluation, we will carry out extensive modelling and characterisation aimed at gaining an improved understanding of the QAB process. Developments to date have been mainly empirical, and fundamental aspects of the process remain poorly understood. QAB is fundamentally different from traditional soldering because of the very short timescale over which the process takes place. In order for it to become established in mainstream electronics manufacturing, the potential detrimental effects of residual stresses and microstructural defects incorporated into QAB bonds need to be fully understood.
The proposed research has the potential to provide a low-cost, sustainable joining technology for electronics manufacturing that can continue to meet the operating temperature requirements of high-temperature electronics for many years to come. At the same time it will yield new fundamental insights into processes involving rapid solidification of complex alloys that will be of wide interest to the materials science and manufacturing research communities.
Planned Impact
A primary aim of this proposal is to expand the range of industrial applications for quasi-ambient bonding (QAB) technology. This will be of direct benefit to a range of stakeholders:
1) UK Industry and Economy:
The potential industrial importance of this technology is demonstrated by the wide range of industrial partners who attended our grant application planning meeting in March 2017 and who have provided letters of support. The new technology that is at the heart of this proposal is urgently needed to address the increasingly stringent regulations on the use of toxic metals such as Pb. Currently available lead-free technologies are expensive and/or liable to failure (with associated cost implications). Also, they will not be able to support increasing operating temperatures in the longer term. The QAB process that is at the heart of this proposal has the potential to overcome these challenges, allowing UK industry to stay at the forefront of technological progress in a wide range of applications. The industrial partners on this project cover the whole microelectronics supply chain including materials suppliers, technology providers, testing & qualification and end users in the optoelectronics and high-temperature/harsh environment electronics sectors.
2) Environment and Society:
The elimination of heavy metals such as Pb from electronics is highly desirable from an environmental perspective, reducing the potential for toxic pollutants going into landfill. This proposal will enable the cost effective substitution of Pb-solders with non-toxic alternatives in a wide range of applications. In addition, QAB has the potential to provide shorter production times for microelectronic components and hence improved efficiency and reduced energy consumption. Streamlining of the production process and reducing raw material costs (compared to Au and Ag based solder materials) has the advantage of substantial cost saving. Such cost savings allow UK industry to sustain a highly skilled workforce. In addition, the expansion of this to a wider range of industrial applications provides opportunities for job creation.
3) Project Staff:
This project is only achievable due to the collaboration of three academic groups with different scientific expertise (materials, manufacturing and microsystem engineering). The academics and postdoctoral researchers working on this project will benefit from regular meetings with the other academic partners and opportunities to travel to other groups to perform experiments. They will also interact with the industrial partners so gain directly relevant industrial knowledge and experience. This combined expertise will help to facilitate greater academic-industrial integration to the benefit of both parties. The project will also train a number of highly employable and skilled postdoctoral workers with the necessary expertise to work across disciplines or to transition to industry as they desire.
4) Academia:
This proposal will improve our fundamental understanding of QAB through detailed characterisation and innovative in situ materials characterisation. For example, the new test rigs for synchrotron X-ray diffraction measurements have potential for academic application in any high speed phase transformation process, and as such will be of interest to those working on cutting edge materials characterisation, synchrotron beamline development or high speed imaging. The work on ignition by electromagnetic induction heating will also yield new results relevant to a wide range of other applications.
1) UK Industry and Economy:
The potential industrial importance of this technology is demonstrated by the wide range of industrial partners who attended our grant application planning meeting in March 2017 and who have provided letters of support. The new technology that is at the heart of this proposal is urgently needed to address the increasingly stringent regulations on the use of toxic metals such as Pb. Currently available lead-free technologies are expensive and/or liable to failure (with associated cost implications). Also, they will not be able to support increasing operating temperatures in the longer term. The QAB process that is at the heart of this proposal has the potential to overcome these challenges, allowing UK industry to stay at the forefront of technological progress in a wide range of applications. The industrial partners on this project cover the whole microelectronics supply chain including materials suppliers, technology providers, testing & qualification and end users in the optoelectronics and high-temperature/harsh environment electronics sectors.
2) Environment and Society:
The elimination of heavy metals such as Pb from electronics is highly desirable from an environmental perspective, reducing the potential for toxic pollutants going into landfill. This proposal will enable the cost effective substitution of Pb-solders with non-toxic alternatives in a wide range of applications. In addition, QAB has the potential to provide shorter production times for microelectronic components and hence improved efficiency and reduced energy consumption. Streamlining of the production process and reducing raw material costs (compared to Au and Ag based solder materials) has the advantage of substantial cost saving. Such cost savings allow UK industry to sustain a highly skilled workforce. In addition, the expansion of this to a wider range of industrial applications provides opportunities for job creation.
3) Project Staff:
This project is only achievable due to the collaboration of three academic groups with different scientific expertise (materials, manufacturing and microsystem engineering). The academics and postdoctoral researchers working on this project will benefit from regular meetings with the other academic partners and opportunities to travel to other groups to perform experiments. They will also interact with the industrial partners so gain directly relevant industrial knowledge and experience. This combined expertise will help to facilitate greater academic-industrial integration to the benefit of both parties. The project will also train a number of highly employable and skilled postdoctoral workers with the necessary expertise to work across disciplines or to transition to industry as they desire.
4) Academia:
This proposal will improve our fundamental understanding of QAB through detailed characterisation and innovative in situ materials characterisation. For example, the new test rigs for synchrotron X-ray diffraction measurements have potential for academic application in any high speed phase transformation process, and as such will be of interest to those working on cutting edge materials characterisation, synchrotron beamline development or high speed imaging. The work on ignition by electromagnetic induction heating will also yield new results relevant to a wide range of other applications.
Organisations
- Loughborough University (Lead Research Organisation)
- UNIVERSITY OF NOTTINGHAM (Collaboration)
- Indium Corporation (Collaboration)
- Manufacturing Technology Centre (MTC) (Collaboration)
- Teer Coatings Ltd (Collaboration)
- TT Electronics (Project Partner)
- Oclaro (United Kingdom) (Project Partner)
- Indium Corporation (United States) (Project Partner)
- Tribus-D (Project Partner)
- Dynex Semiconductor (United Kingdom) (Project Partner)
- Datalink Electronics (Project Partner)
- Manufacturing Technology Centre (United Kingdom) (Project Partner)
Publications
Liu L
(2022)
Interfacial reaction between Sn-Ag solder and electroless Ni-Fe-P diffusion barriers with different internal microstructure
in Materials Research Bulletin
Jiang H
(2022)
Defect formation and mitigation in Cu/Cu joints formed through transient liquid phase bonding with Cu-Sn nanocomposite interlayer
in Microelectronics Reliability
Liang S
(2022)
Preferential growth of intermetallics under temperature gradient at Cu-Sn interface during transient liquid phase bonding: insights from phase field simulation
in Journal of Materials Research and Technology
Liu C
(2022)
Self-propagating exothermic reaction assisted Cu clip bonding for effective high-power electronics packaging
in Microelectronics Reliability
Chen Y
(2022)
Transient liquid phase bonding with Ga-based alloys for electronics interconnections
in Journal of Manufacturing Processes
Liang S
(2022)
Investigation of thermal effect on solidification in Sn/Cu interconnects during self-propagating exothermic reaction bonding
in Microelectronics Reliability
Jiang H
(2022)
Rapid formation of intermetallic joint using Cu-Sn nanocomposite interlayer based on patterned copper nanowire array
in Materials Letters
Su Y
(2023)
Statistical effects of pore features on mechanical properties and fracture behaviors of heterogeneous random porous materials by phase-field modeling
in International Journal of Solids and Structures
Description | Numerous new conceptual ideas have been inspired from the on-going research activities, including 1) using nanocomposite interlayers to achieve high temperature interconnects, e.g. for die attach or substrate attach; 2) QAB high melting point alloys (e.g. brazing alloys) through surface functionalization. |
Exploitation Route | By closely working with industrial collaborators and by targeting the exact industrial cases to demonstrate the impacts. |
Sectors | Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Education,Electronics,Energy,Manufacturing, including Industrial Biotechology,Transport |
Description | The project industrial collaborators have expressed their great interest in exploitation of the potential research findings, and will support from various angles to make use of the technologies to be developed. We have recently expanded the potential uses of the QAB process for bonding DBC substrate with baseplate of the power modules for minimising the CTE mismatch with the existing industrial collaborators. Our findings have also been used to provide the guidance to power electronics industry in their design, packaging and integration of power modules, particularly aligned with wide-band Gap (WBG) devices (e.g. SiC, GaN). We anticipate that the industry may take up the developed processes and apply to the manufacturing of future generation power electroncis. |
First Year Of Impact | 2019 |
Sector | Aerospace, Defence and Marine,Education,Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology,Transport |
Impact Types | Societal,Economic |
Title | Advanced simulation tool for QAB bonding process analysis |
Description | Phase field models has been established to underpin the fundamental understanding of relevant phenomena associated with QAB bonding and performance of bonded structures, e.g. void formation, incurred residual stress, and their effects on reliability of the bonds. |
Type Of Material | Improvements to research infrastructure |
Year Produced | 2020 |
Provided To Others? | No |
Impact | The notable impacts include: i) provide detailed SPER bonding process in terms of liquid-solid interfacial interactions/reactions; ii) quantitively evaluation of internal voids and their formation, as well as resultant residual stresses; ii) the tool may be applicable to the potential applications to enable understanding the phenomena of multi-scale and multi-phase interactions in the manufacturing. |
Title | Flip chip bonder |
Description | We have developed a flip chip bonder suitable for quasi-ambient bonding which has in-built capability for nanofoil ignition by exposure to infrared radiation from a pulsed fibre laser. The tool allows bonding to be carried out under precisely controlled conditions (pre-heating, bonding force, alignment including coplanarity). |
Type Of Material | Improvements to research infrastructure |
Year Produced | 2020 |
Provided To Others? | Yes |
Impact | This tool will be one of the primary sources of experimental data in the EPSRC project EP/R031770/1 (Quasi-ambient bonding...). |
Title | In-house constructed and modified bonding tool |
Description | A bonding rig has been developed capable of applying precise loads and preheating sample before self-propagating NanoFoil bonding. A procedure for bonding has been developed consisting of stacking NanoFoil between two preformed solder foils and then inserting this sandwich between the components/devices to be bonded. During reactive bonding, the structure is heated with a hot plate. Following this, precise loads can be applied to the NanoFoil, component stack. The loading head includes a damper system to spread the load and maintain loading during bonding. Typical reaction conditions are (<10MPa) with a preheat temperature (<200°C), we have found these parameters to enhance the wetting and filling abilities of solder alloys (primarily (SAC) solder). Thus far all reactions have taken place in air and been ignited through contact with a sharp copper probe supplied with direct current (DC). Upon ignition the NanoFoil combusts generating considerable heat, melting the neighbouring solder layers resulting in bonding of the components. The heating is sufficiently localised such that the components are cool within a few seconds. |
Type Of Material | Technology assay or reagent |
Year Produced | 2019 |
Provided To Others? | No |
Impact | This self-constructed/modified bonding rig with incorporated preheating, pressure and electrical ignition can produce bonded structures suitable for industrial validation with industrial components of a range of sizes and requirements. |
Description | ISCF-DER Challenge centre partnership |
Organisation | Manufacturing Technology Centre (MTC) |
Country | United Kingdom |
Sector | Private |
PI Contribution | As an academic partner within the consortium the team has contributed invariably in the preparation of the relevant technical attributes to the DER centre biding team. |
Collaborator Contribution | Our partner had been working and co-ordinating the application and the relevant activities. |
Impact | The panel interview has be conducted by UKRI, and the result will be confirmed shortly by this week. |
Start Year | 2020 |
Description | ISCF-DER Challenge centre partnership |
Organisation | University of Nottingham |
Department | Nottingham Clinical Trials Unit (NCTU) |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | As an academic partner within the consortium the team has contributed invariably in the preparation of the relevant technical attributes to the DER centre biding team. |
Collaborator Contribution | Our partner had been working and co-ordinating the application and the relevant activities. |
Impact | The panel interview has be conducted by UKRI, and the result will be confirmed shortly by this week. |
Start Year | 2020 |
Description | QAB process development |
Organisation | Indium Corporation |
Country | United States |
Sector | Private |
PI Contribution | We have carried out process development on SPER (self-propagating exothermic reaction) nanofoils provided by Indium Corp, exploring new processing regimes. |
Collaborator Contribution | Indium Corp have provided the nanofoil materials and guidance on established processing regimes. |
Impact | The work has yielded new information on the useable parameter space for QAB (quasi-ambient bonding) with SPER nanofoils. The results will be published in due course. |
Start Year | 2019 |
Description | Teer coating limited |
Organisation | Teer Coatings Ltd |
Country | United Kingdom |
Sector | Private |
PI Contribution | We provide a business need for potentially using the equipment, expertise and technology of Teer coatings limited. |
Collaborator Contribution | Teer coating offered some trials to develop novel surface coatings for bonding. |
Impact | Currently planning various experimental trials. |
Start Year | 2022 |
Description | IMAPS-UK presence and engagement |
Form Of Engagement Activity | A magazine, newsletter or online publication |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Industry/Business |
Results and Impact | IMPAS-UK 2020 February newsletter reported our current research activities which can be connected to this work. |
Year(s) Of Engagement Activity | 2018,2019,2020 |
Description | Industrial demonstrations |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Industry/Business |
Results and Impact | Working directly with project partners to demonstrate the uses of the technology using the benchmark components and materials. |
Year(s) Of Engagement Activity | 2018 |
Description | Interviews and discussion with potential undergraduate students |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Undergraduate students |
Results and Impact | Each Department Open Day (~15 dates per year) involves visits for 60-100 school pupils who are potential or actual university applicants. Prof Haigh regularly interviews candidates for these events. In 2020/2021 these have been operating online. |
Year(s) Of Engagement Activity | 2019,2020,2021 |
URL | https://www.manchester.ac.uk/study/undergraduate/courses/2021/09895/meng-materials-science-and-engin... |
Description | Research seminar with Prof. Johan Liu from Chalmers University of Technology Sweden |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Industry/Business |
Results and Impact | Prof. Johan Liu gave a lecture about the application of graphene in electronic package. Research group members have got helpful inspiration from his research experience. We shared our research progress and discussed with Prof. Johan Liu afterwards. |
Year(s) Of Engagement Activity | 2019 |