Fatigue Cycling of Electrical Interconnects Dispensed on Flexible Substrate (original) (raw)

Reliability of screen-printed conductors and resistors during fatigue cycling on flexible substrate

International Symposium on Microelectronics, 2019

Scalable printing of conductor and resistor components has revolutionized the field of flexible electronics by enabling a myriad of low cost highly conformable devices. Flexible electronic devices need to exhibit reliable performance under strenuous mechanical deformations to be adopted in applications such as human and asset monitoring. The reliability of the devices is in turn affected by the microstructure of the materials, manufacturing processes, and conditions of use. In this research, the mechanical behavior and microstructural properties of stretchable silver conductor and stretchable carbon conductor inks on flexible substrate are studied. The test vehicles (such as 4- point probe structures are screen printed on thermoplastic polyurethane (TPU) and cured in a convection oven. The quality of the printed traces including the resolution and thickness profile are measured by Confocal Laser Scanning microscope. The microstructure of the sample including particle/nanoparticles m...

Fatigue Analysis and Optimization of Flexible Printed Circuits

2006

Flexible printed circuits (FPC) are widely used in various electronic packages to interconnect high-performance devices. In case of dynamic applications mechanical reliability of FPCs is becoming a serious issue as complexity of the devices grows and miniaturization trend continues. For many of such applications, failures of FPCs can lead to serious consequences. Fatigue data on FPCs are not commonly available in published literature. One way to obtain such data is to combine fatigue test results from standard or proprietary FPC dynamic testers with Finite Element Analysis (FEA) based simulations. This paper describes first results of a research project on development of an automated procedure of fatigue life assessment of FPCs by FEA combined with fatigue and optimization analysis. Two goals have been pursued with development of the methodology: to enable quick modeling and FEA of FPCs by electrical or mechanical designers who are not familiar with FEA technology and ABAQUS softwar...

Cyclic endurance reliability of stretchable electronic substrates

Microelectronics Reliability, 2011

Stretchable electronic circuit boards have been developed based on three different technologies. Such substrates serve to connect rigid interposers or electronic components. The conducting traces have a meandering shape and consist of Cu-foil or screen-printed Ag-paste. These conducting traces are attached to or embedded in polyurethane, polydimethylsiloxane, or breathable non-woven stretchable substrate material. The long-term endurance behavior of this novel type of boards is studied by cyclic elongation at strain ranges of up to 20% and monitoring the electrical connectivity. The main failure mode in the Cu-foil based technologies is fatigue of the conducting traces and can be described in terms of the Manson-Coffin relation. Indications for high-cycle fatigue were found. The screen-printed conductors on nonwoven substrates fail by breaking of the connection between the metallic grains. The application areas are electronic monitoring systems that need to be placed directly on the skin, or conformable systems for curved surfaces.

Characterization of Bending, Crease, Aging, and Immersion Effects on Flexible Screen-Printed Silver Traces

IEEE Transactions on Components, Packaging and Manufacturing Technology, 2019

Printed flexible electronics have been of great interest in the electronics industry in recent years since this technology can be used to replace existing rigid printed circuit boards and open new application domains. Several use cases for flexible substrates involve mechanical bending and creasing as well as exposure to liquids. Hence, there is a need for the characterization of the reliability of the silver races on flexible substrates under such conditions. In response, ASTM standard tests were used to quantify the effects of repeated bending and creasing on the resistance change of commercially used silver inks screen printed onto flexible substrates. Three distinct ink/substrate combinations were investigated in terms of bending and crease testing up to 10,000 cycles. Traces with and without dielectric encapsulant were exposed to the water immersion and the simulated sweat tests for up to 2,500 hours of exposure. The effects of mechanical stress and liquid exposure on the surface morphology and oxidation species was analyzed and corroborated with the electrical results.

The Effect of Lamination on Printed Silver Tracks for Plastic Circuits

2012

Circuits in Plastic (CiP) is an electronic systems manufacturing technology with cost and environmental advantages. Flexible and CiP circuits both require conductive tracks on plastic. In CiP silver tracks are screenprinted on thin film, thermally cured and the film is hot laminated to a plastic substrate with components to form the circuit. As both the curing step and the lamination step requires elevated temperatures, the option of using a single temperature step for both processes was investigated. Standard length tracks of varying widths were printed on a 1.6 mm thick polycarbonate substrate with a SMT resistor. The circuit was sealed by laminating a 0.1 mm thick cover sheet using controlled temperature and pressure. Dog-bone tensile tests were used to assess the reliability and limits of connections. The electrical contacts on the substrate and components remained intact until the specimens were extended beyond 3%. This has proved to be a robust circuit manufacturing technique.

Reliability testing on stretchable electronics : printed conductors under strain

2019

The aim of stretchable electronics research is to develop stretchable circuit boards and devices that can replace today's hard and rigid circuit boards and devices. Stretching would allow for more comfortable, flexible and stretchable devices. The aim of this thesis is to investigate the properties of printed conductors on a stretched substrate, the requirements for testing, and to produce a device for stretch testing which meets desired requirements. The properties of the printed conductor are influenced by the used fabrication technique and the drying times, as well as materials such as printing ink and substrate. The properties affect the reliability and durability of the conductor, for example, failure mechanisms such as cracking and delamination of the conductor. Requirements for the test device is 1 % accuracy as a standard for the measuring instrument, which was achieved for the measuring instruments in this thesis. With the test apparatus implemented in the thesis, the s...

Experimental and Analytical Studies on the High Cycle Fatigue of Thin Film Metal on PET Substrate for Flexible Electronics Applications

IEEE Transactions on Components, Packaging and Manufacturing Technology, 2011

This paper addresses the behavior of thin-film metal coated flexible substrates under high cyclic bending fatigue loading. Polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are widely used substrates in the fabrication of microelectronic devices. Factors affecting the fatigue life of thin-film coated on a flexible PET substrates were studied, including thin-film thickness, film material, bending radius, temperature, and humidity. A series of experiments for sputter-deposited copper and aluminum coated on a PET substrate were conducted. Electrical resistance and crack growth rate were monitored during the experiments at specified time intervals. In addition, a finite element model was built to simulate the bending of thin-films on flexible substrate structure. Layered shell elements were used in the model. Stress intensity and stress distribution across the film were obtained and compared with the experiments. Initial results of copper-coated PET showed a great agreement between the model and the experimental results. Index Terms-Flexible electronics, flexible substrates, high cyclic bending fatigue, thin films.

Bending machine for testing reliability of flexible electronics

2017 IMAPS Nordic Conference on Microelectronics Packaging (NordPac), 2017

A novel bending machine has been designed and tested. It enables flexible electronics to be subjected to repeated bending with constant radius and tension. In-situ electrical characterization can give accurate analysis of lifetime distributions if sufficiently many samples are ran to failure, allowing reliability prediction models to be developed. Four sets of test samples with different combinations of substrate, routing, interconnect technology and components were examined. A poor level of reliability was observed when using anisotropic conductive paste to form interconnects, whereas a significantly higher level of reliability was observed when using a bismuth-tin solder paste. The assembly of larger components resulted in shortened time to failure, whereas increasing the bending radius prolonged the observed lifetimes.

Electrical Reliability of a Film-Type Connection during Bending

Electronics, 2015

With the escalating demands for downsizing and functionalizing mobile electronics, flexible electronics have become an important aspect of future technologies. To address limitations concerning junction deformation, we developed a new connection method using a film-type connector that is less than 0.1 mm thick. The film-type connector is composed of an organic film substrate, a UV-curable adhesive that deforms elastically under pressure, and electrodes that are arranged on the adhesive. The film-type connection relies on a plate-to-plate contact, which ensures a sufficient contact area. The electrical reliability of the film-type connection was investigated based on changes in the resistance during bending at curvature radii of 70, 50, 25, 10, 5, and 2.5 mm. The connection was bent 1000 times to investigate the reproducibility of the connector's bending properties. The tests showed that no disconnections occurred due to bending in the vertical direction of the electrode, but disconnections were observed due to bending in the parallel direction at curvature radii of 10, 5, and 2.5 mm. In addition, the maximum average change in resistance was less than 70 milliohms unless a disconnection was generated. These results support the application of the new film-type connection in future flexible devices.