Printed Circuit Board Substrate Research Articles

Sustainable printed circuit board substrates based on flame-retarded PLA/flax composites to reduce environmental load of electronics: Quality, reliability, degradation and application tests

The present paper introduces a novel, sustainable approach to produce an eco-friendly Printed Circuit Board (PCB) substrate; a substitute for traditional substrates, to significantly reduce e-waste. We present the prepreg technology, the road to actual circuit assembly with application studies, life cycle analysis (LCA), and sustainability analysis. The flame-retarded prepregs and resulting PCB assemblies were based on polylactic acid (PLA), the structure is reinforced with flax textiles. After copper lamination, subtractive PCB production was performed, and thermal and mechanical reliability was investigated in the case of both laminated and bare substrates. Steps of surface roughness, peel and thermal analysis followed. After a new set of assemblies, the post-assembly analysis was extended with further shear strength analysis on the soldered components and mass analysis regarding thermal processes. The evaluation showed that PLA/Flax substrates provide reliable structural performance up to 200 °C in the reflow soldering process; this allows limited but stabilized application possibilities with specific eco-friendly lead-free solders. A basic blinker circuit and a field programmable gate array (FPGA)--based design was produced and tested; the latter has the general complexity of a commercial circuit. A vol% and wt% analysis extended our discussion with a reduction of harmful components in waste in the range of 90%, which is a disruptive and significant result. Life cycle analysis (LCA) quantified the ecological impact of the assembly, highlighting a significant ease on environmental load (∼10%) for the total assembly. Finally, a qualitative degradation study was introduced to the prepared samples to investigate short-term stability with mechanical-, colour-, mass- and scanning electron microscopy (structure) analysis. Early results show that the boards can withstand the harsh environment of a composting bin for a few days, but in the time of a few weeks, degradation starts, pointing to eventual decomposition. The work directly connects with multiple sustainability development goals.

Innovating in-situ characterization: a comprehensive measurement system for measuring the ZT and the contact resistance of vertical thermolegs exploiting the vertical transfer length method

In order to optimize their system design and manufacturing processes, it is crucial to undertake a thorough electrical and thermal characterization of micro thermoelectric generators (µTEGs). To address this need, a highly advanced and fully integrated in-situ measurement system has been developed. The main objectives of this system are to (1) enable the measurement of ZT and thereby of all thermoelectric (TE) properties of thermolegs made from powder-based TE materials and (2) at the same time accurately measure the contact resistance between the TE material and the electrical contacts. The µTEG fabrication concept used in this study is based on copper-cladded printed circuit board (PCB) material as a substrate, using the Cu layers for easy contact formation. In a first step, an innovative measurement concept, based on a distinctive vertical rendition of the well-established transfer length method, has been realized, allowing for the in-situ measurement of contact resistance between the TE material and the copper conductors on the PCB substrate. This enables a comprehensive assessment of the impact exerted by the applied force and temperature during e.g. a hot-pressing step for compacting the powder-based thermolegs during the manufacturing process. In a second step, a comprehensive measurement platform, referred to as the ZT-Card, has been devised to facilitate the evaluation of all relevant TE material properties—Seebeck voltage, electrical conductivity and thermal conductivity (all measured in vertical cross-plane orientation)—inherent to a highly miniaturized thermoleg. Additionally, the ZT-Card also allows for the assessment of contact resistance between the copper contacts and the TE material. Successful testing of this measurement system inspires confidence in the capabilities of the platform and will aid in future µTEG development.

Polyphenylene oxide/boron nitride–alumina hybrid composites with high thermal conductivity, low thermal expansion and ultralow dielectric loss

AbstractTraditional integrated circuit (IC) packaging materials and printed circuit board substrate materials suffer from several limitations including low thermal conductivity, high coefficient of thermal expansion (CTE), and poor dielectric properties. Although significant efforts have been made to enhance these properties, achieving a single composite system with simultaneous high thermal conductivity, extremely low CTE, and dielectric loss remains a formidable task. In this study, we propose a hybrid polymer composite system that addresses these challenges. Our approach involves utilizing a thermosetting polyphenylene oxide (PPO) as the resin matrix, while incorporating boron nitride (BN) sheets with high thermal conductivity and alumina (Al2O3) spheres with favorable fluidity as fillers. To optimize the composite properties, the filler surfaces are modified using dopamine and silane coupling agents, ensuring proper interface control. The composites exhibit significant improvements in thermal conductivity, reduced dielectric loss and CTE, while maintaining excellent processibility. Specifically, with a composition of 25 vol% BN and 25 vol% Al2O3, the thermal conductivity of the composite reaches 2.18 W·m−1 K−1, surpassing neat PPO resin by a factor of 10.9. Simultaneously, the CTE decreases from 2.27% to 1.18% between 50 and 260°C, and the dielectric loss reduces from 0.0024 to 0.0011 at 10 GHz, as compared to neat PPO resin.Highlights The reported novel hybrid composite offers a promising solution to the limitations of traditional IC packaging materials. The reported hybrid composite exhibits significantly improved thermal conductivity, ultralow dielectric loss, and reduced coefficient of thermal expansion, while maintaining excellent processibility. The thermal conductivity of the composites reaches 2.18 W·m−1 K−1, surpassing that of the neat resin by a factor of 10.9, meanwhile the dielectric loss is as low as 0.0011 at 10 GHz, which is extremely difficult to achieve simultaneously for thermosetting polymer composites. Synergetic effects were realized with the hybridization of fillers with different dimensionality, and proper filler surface modification.

Magneto‐electric dipole antenna array for 77 GHz automotive radar

AbstractA 1 × 4 magneto‐electric dipole (ME dipole) antenna array for 77 GHz automotive radar is proposed. The ME dipole is fed by a fork‐shaped microstrip line coupling through a dog‐bone slot. To meet the requirements aimed at automotive radar applications, the beamwidths of the proposed antenna are well‐designed. Specially, a method of adding passive elements on both sides of the array is proposed to increase the 3 dB beamwidth from ±34° to ±52° in azimuth. Additionally, in elevation, a 3 dB beamwidth of ±10° is achieved by designing the spacing between array elements. Moreover, based on low‐loss printed circuit board substrates, radiation efficiency of the proposed array can reach approximately 90% at 77 GHz. Furthermore, a 4 × 4 array is established by arranging four 1 × 4 subarrays spacing 1.95 mm (half a free‐space wavelength at 77 GHz) to study the interactions between subarrays for multiple input multiple output scenarios. A 1 × 4 and a 4 × 4 antenna prototypes are fabricated and measured to validate the correctness of this design. The results show that the proposed antenna is an eligible candidate for the medium‐ and short‐range automotive radars.

Monomer ratio‐controlled polyimides with enhanced dielectric properties and thermal stabilities through crosslinking network

AbstractPolyimides (PI) are considered as one of the most used materials for flexible printed circuit board substrates because of their excellent thermal stabilities, outstanding mechanical properties, and great dielectric properties. Dielectric constants (Dk) of common commercial PIs, however, are still above 3.0 (at 10 GHz), which is still substandard for high‐frequency applications. In this study, we develop thermally stable PIs with enhanced dielectric properties by structural design and crosslinking. Stiff aromatic 2,2′‐bis(trifluoromethyl)benzidine (TFMB) and soft aliphatic dimer diamines (DDA, priamine), including priamine 1074 (DDA‐1) and priamine 1071 (DDA‐2), are used as the diamines, and cyclobutanetetracarboxylic dianhydride (CBDA) is used as the dianhydride. By adjusting the ratio of the diamines, a series of PIs (PI‐1–PI‐5) with high thermal stabilities and low‐Dk values are synthesized. Among these PIs, PI‐4 synthesized by diamines with the ratio of TFMB:DDA‐1:DDA‐2 = 85:10:5, possesses relatively good performances. Therefore, PI‐4 is further chosen to be thermally crosslinked. By changing the contents of the crosslinker, triallyl isocyanurate (TAIC), crosslinked PIs (CPIs) are synthesized. The resulting CPIs have a significant improvement in thermal properties, dielectric properties, and mechanical strengths. Especially, for the CPI‐4‐30, in which 30% of TAIC is used, the glass transition temperature (Tg) increases by 20°C, the Dk decreases from 2.62 to 2.41, and the ultimate tensile strength boosts from 91.65 to 115.16 MPa. The CPIs with low Dk and high Tg values may have great potential as substrate materials for broad applications, such as microelectronics and integrated circuit packages.

A Green Conformable Thermoformed Printed Circuit Board Sourced from Renewable Materials.

Printed circuit boards (PCBs) physically support and connect electronic components to the implementation of complex circuits. The most widespread insulating substrate that also acts as a mechanical support in PCBs is commercially known as FR4, and it is a glass-fiber-reinforced epoxy resin laminate. FR4 has exceptional dielectric, mechanical, and thermal properties. However, it was designed without considering sustainability and end-of-life aspects, heavily contributing to the accumulation of electronic waste in the environment. Thus, greener alternatives that can be reprocessed, reused, biodegraded, or composted at the end of their function are needed. This work presents the development and characterization of a PCB substrate based on poly(lactic acid) and cotton fabric, a compostable alternative to the conventional FR4. The substrate has been developed by compression molding, a process compatible with the polymer industry. We demonstrate that conductive silver ink can be additively printed on the substrate's surface, as its morphology and wettability are similar to those of FR4. For example, the compostable PCB's water contact angle is 72°, close to FR4's contact angle of 64°. The developed substrate can be thermoformed to curved surfaces at low temperatures while preserving the conductivity of the silver tracks. The green substrate has a dielectric constant comparable to that of the standard FR4, showing a value of 5.6 and 4.6 at 10 and 100 kHz, respectively, which is close to the constant value of 4.6 of FR4. The substrate is suitable for microdrilling, a fundamental process for integrating electronic components to the PCB. We implemented a proof-of-principle circuit to control the blinking of LEDs on top of the PCB, comprising resistors, capacitors, LEDs, and a dual in-line package circuit timer. The developed PCB substrate represents a sustainable alternative to standard FR4 and could contribute to the reduction of the overwhelming load of electronic waste in landfills.

An ultrawideband antenna with two independently tunable notch bands

This paper presents a planar CPW-fed Ultrawideband (UWB) antenna with two independently tunable notch bands. The proposed design consists of a modified Rhombus-shaped monopole structure that is integrated with a dual band-stop filter based on hexagonal split ring resonators (HSRR). The antenna is capable of suppressing multiple frequency bands within ultrawideband range (3.1–11 GHz) such as WLAN and X-band downlink satellite communication frequency bands with an independent tunable mechanism to fulfill the on-demand band rejection. The frequency reconfigurability of the two notch bands is obtained by loading the hexagonal filter arms with two varactor diodes (for each band). Details of antenna design steps and reconfigurability mechanism are illustrated. The notch band element is explained using equivalent circuit model and surface current distribution at lower and higher notch frequency bands. A prototype of the proposed design is printed on the RO4003C (ϵr = 3.55) substrate printed circuit board (PCB) and tested to authenticate the performance. The proposed antenna volume is 21.5 ▪ 48 ▪ 1.524 mm3 and demonstrates an omnidirectional radiation pattern in E and H planes with an average gain of 3.7 dBi across the operational passbands, while a sharp reduction in gain of -6.8 dBi and -3.5 dBi is achieved at the lower and higher notch bands, respectively. Continuous tuning is achieved experimentally from 5.08 to 5.77 GHz and 7.75 to 8.52 GHz for the lower and higher notch bands, respectively. Excellent agreement is observed between the simulated and measured results. Application areas include radio-frequency identifications, ground-penetrating radar, and wireless communications.

Analysis of Tempering Effects on LDS-MID and PCB Substrates for HF Applications

Mechatronic Integrated Devices or Molded Interconnect Devices (MID) are three-dimensional (3D) circuit carriers. They are mainly fabricated by laser direct structuring (LDS) and subsequent electroless copper plating of an injection molded 3D substrate. Such LDS-MID are used in many applications today, especially antennas. However, in high frequency (HF) systems in 5G and radar applications, the demand on 3D circuit carriers and antennas increases. Electroless copper, widely used in MID, has significantly lower electrical conductivity compared to pure copper. Its lower conductivity increases electrical loss, especially at higher frequencies, where signal budget is critical. Heat treatment of electroless copper deposits can improve their conductivity and adhesion to the 3D substrates. This paper investigates the effects induced by tempering processes on the metallization of LDS-MID substrates. As a reference, HF Printed Circuit Boards (PCB) substrates are also considered. Adhesion strength and conductivity measurements, as well as permittivity and loss angle measurements up to 1 GHz, were carried out before and after tempering processes. The main influencing factors on the tempering results were found to be tempering temperature, atmosphere, and time. Process parameters like the heating rate or applied surface finishes had only a minor impact on the results. It was found that tempering LDS-MID substrates can improve the copper adhesion and lower their electrical resistance significantly, especially for plastics with a high melting temperature. Both improvements could improve the reliability of LDS-MID, especially in high frequency applications. Firstly, because increased copper adhesion can prevent delamination and, secondly, because the lowered electrical resistance indicates, in accordance with the available literature, a more ductile copper metallization and thus a lower risk of microcracks.

Power Law Creep Behavior Model of Third Generation Lead-Free Alloys Considering Isothermal Aging

Abstract In realistic applications, the solder joint is continually subjected to thermal-mechanical stress due to the difference in the coefficient of thermal expansion between the printed circuit board substrate and the electronic packaging components. Creep and fatigue processes were the most common causes of failure in electronic assemblies. Under isothermal aging, creep deformation becomes more prominent. The aged microstructure was recognized by intermetallic coarsening and the appearance of intergranular fracture generated by dynamic recrystallization in the bulk solder joint. In this study, the influence of Bi content on the creep behaviors of solder joints was investigated under various aging conditions. Three lead-free solder alloys, including SAC305, SAC-3Bi, and SAC-6Bi, are tested at room temperature. For each alloy, preliminary micro-indentation tests were conducted to define three stress levels for distinct aging conditions. After each test, displacement versus time data was gathered. A novel approach based on an empirical model was developed to systematically examine the development of the steady-state creep rate. A power dependency prediction model was developed to investigate the relationship between creep strain rate and stress levels. The steady-state creep rate of SAC305 is significantly higher than that of SAC-Bi alloys owing to the presence of bismuth (Bi) in the solid solution at room temperature. The creep properties showed less variation after 100 h of aging. SAC-Bi alloys showed less coarsening of the intermetallic compounds precipitates after aging than SAC305. In the SAC-Bi solder alloys, combinations of precipitate and solid solution hardening mechanisms were observed, while Ag3Sn particles were the dominant strengthening mechanism in the SAC305 alloy system.

Copper from Waste Printed Circuit Boards Was Effectively Bioleached Using Newly Isolated Microorganisms and Subsequently Recovered by Microbial Fuel Cell

Two newly isolated bacterial strains were isolated from activated sludge and identified as Coniochaeta fodinicola (C. fodinicola) and Talaromyces barcinensis (T. barcinensis) by 16S rDNA. C. fodinicola and T. barcinensis were used to bioleach the copper from the waste printed circuit boards (WPCBs) powder, which was obtained by crushing and sorting the printed circuit board substrate after removing components. Results showed that the minimum and maximum Cu2+ leaching rates for C. fodinicola leaching were 3.9% and 89.2%, respectively. The minimum and maximum Cu2+ leaching rates for T. barcinensis leaching were 20.6% and 89.0%, respectively. The bioleaching solution was used as the cathode liquid of a dual chamber microbial fuel cell (MFC), and an X-ray diffraction (XRD) pattern displayed that the Cu2+ in the bioleaching solution was reduced to copper using biological electricity generation.

Concept and Process Development Using Ex Situ Fabricated High-Density Interconnect Plugs for Circuit-Board Embedded Magnetic Components

Magnetic circuit components have long been the largest and most difficult components to miniaturize. Printed circuit board (PCB) fabrication methods cannot achieve small diameter, high aspect-ratio vias for high winding turn numbers to achieve high inductance, and microelectronics methods cannot achieve the high-quality and thick ferrite core materials. In this paper, we present an alternative breakthrough method of printed circuit fabrication to significantly reduce the effective via diameter for embedded magnetic devices, boosting the inductance per unit area. To reduce the effective via diameter, high-density via plugs are ex-situ fabricated and shaped, and then embedded into PCB substrate in the same process as standard magnetic core embedding. The structure of the plug is such that precise placement within the substrate, or alignment to the plug with the winding pattern, is not necessary. Devices presented in this paper use via plugs with an effective diameter of 40 μm and a theoretically unlimited aspect ratio, though refinements in the plug fabrication process are expected to reduce the via diameter down to 10μm. The process is experimentally demonstrated with a 14-turn racetrack shaped transformer; novel diagnostic methods using magneto-optic garnet films to image current paths are also demonstrated.

D-Band Air-Filled Substrate Integrated Waveguide (AFSIW) and Broadband Stripline to AFSIW Launcher Embedded in Multi-Layer PCBs

We report <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$</tex-math> </inline-formula> -band air-filled substrate integrated waveguides (AFSIWs) with solid copper sidewalls fabricated inside a multi-layer printed circuit board (PCB) with broad wall width of 1.6 mm and cavity height of 300 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m. Measurements show a loss of 0.07–0.08 dB/mm across 115–155 GHz. This result is the first demonstration of an AFSIW above 100 GHz in a low-cost mass manufacturable PCB and has the lowest loss compared to reported planar PCB lines or substrate integrated waveguides (SIWs) in PCBs and Interposers. We also introduce a broadband stripline to the AFSIW launcher using a broad wall transverse slot which offers ease of manufacturability over existing transitions having a measured insertion loss of 1.1 dB and 27% bandwidth. The combination of a low-loss AFSIW and wideband launcher allows both striplines and AFSIWs to coexist in the same multi-layer PCB.

A novel approach of fabricating low-cost high temperature printed circuit board substrate based on poly(ether-ketone)/fly ash composites

A novel approach of fabricating low-cost high temperature printed circuit board substrate based on poly(ether-ketone)/fly ash composites

Powder production from recycled low-density polyethylene waste and doum palm nuts for light weight engineering application: A circular economy approach

The circular economy approach has been established as a possible solution to the increasing menace of hazardous waste materials. Despite the advances in science and technology, the world still struggles with the disposal and management of low-density polyethylene (LDPE) waste. This study presents the potential of recycled waste LDPE known as “pure water sachets” (PWS) and doum palm nut (DPN) as raw materials for lightweight structural engineering applications. Powder samples were produced from the different compositions of PWS and DPN heated in a controlled environment. The heating temperatures ranged from 250 to 350 o C while the holding time was 60, 90, and 120 minutes. The fixed mass of each powder sample was compacted into cylindrical pellets, only G and H samples had sufficient strength to be handled after compaction. Sample G is a compact from the powder with 40% DPN, 60% PWS, heated to 350 o C for 60 minutes while sample H is from the powder with 60% DPN and 40% PWS, heated to 350 o C for 90 minutes. The micrographs showed that sample G was more homogeneous than sample H and contained fewer voids. F-TIR analysis conducted on the samples shows C-H functional group at 2915 and 2845 cm -1 , 1460 cm -1 , and 700 cm -1 which is similar to low-density polyethylene. The X-ray diffraction analysis conducted on the fabricated samples shows that the doum palm nut sample had an amorphous feature while the samples G and H show a semi-crystalline feature. The sample G had a density of 1.0 g/cm 3 and a hardness value of 10.2 HV making it useful for Printed circuit board substrates. • This study is concerned with taking advantage of the vast amount of plastic and agro-waste and recycling to develop compatible powder for lightweight engineering applications e.g. printed circuit board substrates. Doum palm nut (DPN) and waste pure water sachet were processed into powder using different heating temperature regimes and different holding times. The chemical, mechanical and thermal behavior of the compacted powder was investigated.

A customizable cost-effective design for printed circuit board-based nanolayered gold screen-printed electrode: From fabrication to bioapplications.

Screen-printed electrodes (SPEs) are promising candidates for fabricating biosensing platforms in the laboratory and industry due to the various advantages they involve. The primary method for fabricating SPEs is 2D printing. However, commercial SPEs have some limitations due to the specific ports and connections they require, inflexible design, high prices, and decreased efficiency after a short time. This article introduces high performance, feasible, and cost-effective gold SPEs based on the combination of printed circuit board substrate (PCBs) and sputtering methods for electrochemical biosensing platforms. First, we discuss a general gold SPE development procedure that helps researchers to develop specific designs. The final developed version of SPEs was characterized in the second step, showing positive performance in electrochemical parameters because of the optimization of design and fabrication steps. In the study's final phase, SPEs were used to fabricate a simple platform for breast cancer cell detection as a proof of concept without using any linker or labeling step. The designed immunosensor is very simple and cost-effective, showing a linear calibration curve in the range of 10 - 2× 102 cellsmL-1 (R 2 = 0.985, S/N = 3). This research can be used as a reference for future studies in SPEs-based biosensors because of the flexibility of its design and the accessibility of the manufacturing equipment required.

Research on the Reliability of a Core Control Unit of Highway Electromechanical Equipment Based on Virtual Sensor Data.

The printed circuit board (PCB) is the core control unit of electromechanical equipment. In order to determine the influence of the coupling vibration caused by vehicle–road interaction on the PCB reliability of roadside electromechanical equipment, first, the dynamic load of the vehicle tire is solved by establishing the dynamic model of a vehicle road. Then, the acceleration response data generated by road vibration are obtained by solving the road finite element model. Finally, the power density spectrum of the acceleration response is taken as input excitation, and the deformation response of the PCB under vehicle–road coupling vibration is analyzed. The experimental results show that when the vehicle is driving close to the roadside, the vibration caused by vehicle–road coupling will lead to a large deformation of the PCB, and the deformation value reaches 0.170 mm, which can cause structural damage to the PCB. This shows that the vehicle–road coupling vibration can affect the reliability of the roadside electromechanical equipment; thus, the optimal design of the PCB layout is created. After optimization, the first-order modal frequency of the PCB is increase by 5.4%, which reduces the risk of the components breaking away from the PCB substrate.

Rapid calculation method to evaluate thermal management of LED systems based on an improved multi-layer model

An improved laminated structure model of LED systems is proposed. Besides the light-emitting diode (LED) chip, printed circuit board (PCB) substrate, heat sink, etc, additional interface layers are applied to model the non-ideal surface of thermal interface materials (TIMs). And a rapid calculation method is developed for temperature-related calculations. Through comparisons, the method is proved to be valid, and the execution time can be greatly reduced. It is found that the air gap at the TIM surface does hinder heat conduction but the effect is not obvious. The influence of LED chips on system thermal management is comprehensively analyzed. For a single LED chip, the junction temperature shows a linear relationship with its thermal resistance and heat power. The chip size, as well as the aspect ratio between the chip and the PCB substrate, has great effects on the junction temperature. For a multi-chip array, the impact of the chip quantity is suggested to be considered combined with the chip layout. The mutual thermal interaction among LED chips is of most concern, which will become more serious with an increasing number of chips. The work provides a rapid and flexible evaluation method for thermal management of LED systems.

Sparse 2-D PZT-on-PCB Arrays With Density Tapering.

Two-dimensional (2-D) arrays offer volumetric imaging capabilities without the need for probe translation or rotation. A sparse array with elements seeded in a tapering spiral pattern enables one-to-one connection to an ultrasound machine, thus allowing flexible transmission and reception strategies. To test the concept of sparse spiral array imaging, we have designed, realized, and characterized two prototype probes designed at 2.5-MHz low-frequency (LF) and 5-MHz high-frequency (HF) center frequencies. Both probes share the same electronic design, based on piezoelectric ceramics and rapid prototyping with printed circuit board substrates to wire the elements to external connectors. Different center frequencies were achieved by adjusting the piezoelectric layer thickness. The LF and HF prototype probes had 88% and 95% of working elements, producing peak pressures of 21 and 96 kPa/V when focused at 5 and 3 cm, respectively. The one-way -3-dB bandwidths were 26% and 32%. These results, together with experimental tests on tissue-mimicking phantoms, show that the probes are viable for volumetric imaging.

Novel Planar Strain Sensor Design for Capturing 3-Dimensional Fingertip Forces from Patients Affected by Hand Paralysis.

Assessment and therapy for individuals who have hand paresis requires force sensing approaches that can measure a wide range of finger forces in multiple dimensions. Here we present a novel strain-gauge force sensor with 3 degrees of freedom (DOF) designed for use in a hand assessment and rehabilitation device. The sensor features a fiberglass printed circuit board substrate to which eight strain gauges are bonded. All circuity for the sensor is routed directly through the board, which is secured to a larger rehabilitative device via an aluminum frame. After design, the sensing package was characterized for weight, capacity, and resolution requirements. Furthermore, a test sensor was calibrated in a three-axis configuration and validated in the larger spherical workspace to understand how accurate and precise the sensor is, while the sensor has slight shortcomings with validation error, it does satisfy the precision, calibration accuracy, and fine sensing requirements in orthogonal loading, and all structural specifications are met. The sensor is therefore a great candidate for sensing technology in rehabilitation devices that assess dexterity in patients with impaired hand function.

Machine learning aided modelling of thermomechanical fatigue of solder joints in electronic component assemblies

Printed board assemblies, i.e. components soldered on printed circuit boards (PCBs), are exposed to thermal cycles responsible for fatigue cracking of solder joints as a result of thermal expansion mismatch between the constituting elements. Advanced finite element simulations are performed using a traction–separation law to represent the cracking process and a temperature-dependent elasto-viscoplastic model for the joint response. Predictions are successfully assessed towards machine learning processed experimental data. In particular, the high sensitivity of thermal ageing reliability to geometric dimensions and solder joint thickness is properly captured. Additional parameters, related to the PCB substrate, are also studied, opening new avenues towards design optimization.