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Akbari, S., Lövberg, A., Tegehall, P.-E., Brinkfeldt, K. & Andersson, D. (2019). Effect of PCB cracks on thermal cycling reliability of passive microelectronic components with single-grained solder joints. Microelectronics and reliability, 93, 61-71
Open this publication in new window or tab >>Effect of PCB cracks on thermal cycling reliability of passive microelectronic components with single-grained solder joints
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2019 (English)In: Microelectronics and reliability, ISSN 0026-2714, E-ISSN 1872-941X, Vol. 93, p. 61-71Article in journal (Refereed) Published
Abstract [en]

Lead-free tin-based solder joints often have a single-grained structure with random orientation and highly anisotropic properties. These alloys are typically stiffer than lead-based solders, hence transfer more stress to printed circuit boards (PCBs) during thermal cycling. This may lead to cracking of the PCB laminate close to the solder joints, which could increase the PCB flexibility, alleviate strain on the solder joints, and thereby enhance the solder fatigue life. If this happens during accelerated thermal cycling it may result in overestimating the lifetime of solder joints in field conditions. In this study, the grain structure of SAC305 solder joints connecting ceramic resistors to PCBs was studied using polarized light microscopy and was found to be mostly single-grained. After thermal cycling, cracks were observed in the PCB under the solder joints. These cracks were likely formed at the early stages of thermal cycling prior to damage initiation in the solder. A finite element model incorporating temperature-dependant anisotropic thermal and mechanical properties of single-grained solder joints is developed to study these observations in detail. The model is able to predict the location of damage initiation in the PCB and the solder joints of ceramic resistors with reasonable accuracy. It also shows that the PCB cracks of even very small lengths may significantly reduce accumulated creep strain and creep work in the solder joints. The proposed model is also able to evaluate the influence of solder anisotropy on damage evolution in the neighbouring (opposite) solder joints of a ceramic resistor.

Keywords
Anisotropy of tin grains, Finite element modelling, Lead-free soldering, Passive components, PCB cracking, Anisotropy, Ceramic materials, Cracks, Creep, Electronics packaging, Finite element method, Mechanical properties, Microelectronics, Printed circuit boards, Resistors, Soldering, Thermal cycling, Accelerated thermal cycling, Microelectronic components, Printed circuit board (PCBs), Thermal and mechanical properties, Thermal cycling reliability, Lead-free solders
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-37331 (URN)10.1016/j.microrel.2019.01.006 (DOI)2-s2.0-85059773183 (Scopus ID)
Note

 Funding details: VINNOVA, 2015-01420; Funding details: Swedish Insitute, SI; Funding text 1: This work has been conducted within the Swedish national project "Requirements, specification and verification of environmental protection and life of solder joints to components" supported by the Swedish Governmental Agency for Innovation Systems (Vinnova) under contract 2015-01420 .

Available from: 2019-01-22 Created: 2019-01-22 Last updated: 2019-01-22Bibliographically approved
Brinkfeldt, K., Wetter, G., Lövberg, A., Tegehall, P.-E., Andersson, D., Goncalves, J., . . . Kwarnmark, M. (2018). Feasibility of PCB-integrated vibration sensors for condition monitoring of electronic systems. In: ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems, InterPACK 2018: . Paper presented at ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems, InterPACK 2018, 27 August 2018 through 30 August 2018.
Open this publication in new window or tab >>Feasibility of PCB-integrated vibration sensors for condition monitoring of electronic systems
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2018 (English)In: ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems, InterPACK 2018, 2018Conference paper, Published paper (Refereed)
Abstract [en]

The increasing complexity of electronics in systems used in safety critical applications, such as for example self-driving vehicles requires new methods to assure the hardware reliability of the electronic assemblies. Prognostics and Health Management (PHM) that uses a combination of data-driven and Physics-of-Failure models is a promising approach to avoid unexpected failures in the field. However, to enable PHM based partly on Physics-of-Failure models, sensor data that measures the relevant environment loads to which the electronics is subjected during its mission life are required. In this work, the feasibility to manufacture and use integrated sensors in the inner layers of a printed circuit board (PCB) as mission load indicators measuring impacts and vibrations has been investigated. A four-layered PCB was designed in which piezoelectric sensors based on polyvinylidenefluoride-co-trifluoroethylene (PVDF-TrFE) were printed on one of the laminate layers before the lamination process. Manufacturing of the PCB was followed by the assembly of components consisting of BGAs and QFN packages in a standard production reflow soldering process. Tests to ensure that the functionality of the sensor material was unaffected by the soldering process were performed. Results showed a yield of approximately 30 % of the sensors after the reflow soldering process. The yield was also dependent on sensor placement and possibly shape. Optimization of the sensor design and placement is expected to bring the yield to 50 % or better. The sensors responded as expected to impact tests. Delamination areas were present in the test PCBs, which requires further investigation. The delamination does not seem to be due to the presence of embedded sensors alone but rather the result of a combination of several factors. The conclusion of this work is that it is feasible to embed piezoelectric sensors in the layers of a PCB.

Keywords
Automobile electronic equipment, Automobile manufacture, Condition monitoring, Electric sensing devices, Integrated circuit manufacture, Microsystems, Piezoelectric devices, Piezoelectric transducers, Piezoelectricity, Printed circuit manufacture, Safety engineering, Soldering, Electronic assemblies, Physics of failure models, Piezoelectric sensors, Polyvinylidene fluorides, Printed circuit boards (PCB), Prognostics and health managements, Safety critical applications, Self-driving vehicles, Printed circuit boards
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-36610 (URN)10.1115/IPACK2018-8386 (DOI)2-s2.0-85057248348 (Scopus ID)9780791851920 (ISBN)
Conference
ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems, InterPACK 2018, 27 August 2018 through 30 August 2018
Available from: 2018-12-06 Created: 2018-12-06 Last updated: 2018-12-21Bibliographically approved
Lövberg, A., Tegehall, P.-E., Akbari, S. & Andersson, D. (2018). On the formation and propagation of laminate cracks and their influence on the fatigue lives of solder joints. In: 2018 19th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2018: . Paper presented at 19th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2018, 15 April 2018 through 18 April 2018 (pp. 1-13).
Open this publication in new window or tab >>On the formation and propagation of laminate cracks and their influence on the fatigue lives of solder joints
2018 (English)In: 2018 19th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2018, 2018, p. 1-13Conference paper, Published paper (Refereed)
Abstract [en]

Lead-free solder joints have been shown to increase the risk for crack formation in the PCB laminate under the solder pads. As such cracks propagate during thermal cycling, they decrease the strain imposed on the solderjoint by acting as strain relief. In accelerated thermal cycling, these joints have been found to remain virtually undamaged even after a very high number of cycles. If these cracks do not form or propagate to the same extent under milder cycling conditions, typical of service conditions, it may lead to an overestimation of the fatigue life of the solder joints in accelerated testing. In this work, the extent of strain relief and the influence of grain orientations on the initiation and propagation of these cracks are investigated through FE-modelling and compared to what has been experimentally observed for cross-sections of solder joints moulded in epoxy resin with added fluorescent agent and inspected using UV-light and electron backscatter diffraction. Due to the strong anisotropy of lead-free solder joints, the stress transferred to the laminate will vary significantly depending on grain orientation. The presence of these laminate cracks adds another layer of uncertainty to the already complex SnAgCu system, where the strong effects of anisotropy, the continuously evolving secondary precipitate coarsening and its interaction with the recrystallisation process govern the damage evolution. If these effects are not properly accounted for, the interpretation of thermal cycling or modelling and simulation results may be strongly misleading.

National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34020 (URN)10.1109/EuroSimE.2018.8369923 (DOI)2-s2.0-85048886876 (Scopus ID)9781538623596 (ISBN)
Conference
19th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2018, 15 April 2018 through 18 April 2018
Available from: 2018-07-04 Created: 2018-07-04 Last updated: 2018-08-20Bibliographically approved
Wünscher, H., Steinke, A., Ortlepp, T., Grönqvist, H., Tegehall, P.-E., Lidström, O., . . . Lagerkvist, P. (2018). Supervision unit for harsh environments. In: : . Paper presented at Conference of Smart Systems Integration 2018 - 12th International Conference and Exhibition on Integration Issues of Miniaturized Systems ; Conference Date: 11 April 2018 Through 12 April 2018; Conference Code:138405 (pp. 522-525). Mesago Messe Frankfurt GmbH
Open this publication in new window or tab >>Supervision unit for harsh environments
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2018 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Mesago Messe Frankfurt GmbH, 2018
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:ri:diva-35555 (URN)2-s2.0-85054865286 (Scopus ID)
Conference
Conference of Smart Systems Integration 2018 - 12th International Conference and Exhibition on Integration Issues of Miniaturized Systems ; Conference Date: 11 April 2018 Through 12 April 2018; Conference Code:138405
Available from: 2018-11-02 Created: 2018-11-02 Last updated: 2018-11-12Bibliographically approved
Andersson, D., Tegehall, P.-E. & Wetter, G. (2018). The impact of conformal coatings on the environmental protection of PCBassemblies and the reliability of solder joints. In: : . Paper presented at 2018 IMAPS Nordic Conference on Microelectronics Packaging (NordPac), June 12-14, Oulu, Finland.
Open this publication in new window or tab >>The impact of conformal coatings on the environmental protection of PCBassemblies and the reliability of solder joints
2018 (English)Conference paper, Oral presentation only (Other academic)
National Category
Other Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34840 (URN)
Conference
2018 IMAPS Nordic Conference on Microelectronics Packaging (NordPac), June 12-14, Oulu, Finland
Available from: 2018-08-15 Created: 2018-08-15 Last updated: 2019-03-07Bibliographically approved
Lövberg, A. & Tegehall, P.-E. (2018). The Stress State of BGA Solder Joints Influenced by the Grain Orientations of Neighboring Joints. In: : . Paper presented at ECTC Conference, May 29 – June 1, San Diego (pp. 882-889). , Article ID 8429649.
Open this publication in new window or tab >>The Stress State of BGA Solder Joints Influenced by the Grain Orientations of Neighboring Joints
2018 (English)Conference paper, Published paper (Refereed)
National Category
Other Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34837 (URN)10.1109/ECTC.2018.00136 (DOI)2-s2.0-85048853670 (Scopus ID)
Conference
ECTC Conference, May 29 – June 1, San Diego
Available from: 2018-08-15 Created: 2018-08-15 Last updated: 2019-03-07Bibliographically approved
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-8556-0925

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