Conductivity Of Resin Research Articles

Molecular-scale investigation on relationship between thermal conductivity and the structure of crosslinked epoxy resin

Epoxy resins are widely used as matrix resins in many fields due to their excellent physical and mechanical properties. However, their low thermal conductivities restrict their applications, especially in electronic packaging. In this work, nonequilibrium molecular dynamics (NEMD) simulations were used to investigate the relationship between thermal conductivity and epoxy resin structure. Three systems, diglycidyl ether of bisphenol A (DGEBA)/4,4’-diamino diphenyl sulfone (4,4’-DDS), DGEBA/diethylene triamine (DETA), and tetraglycidyl diamino diphenyl methane (TGDDM)/4,4’-DDS, were simulated based on our previous crosslinking algorithm. The thermal conductivity of DGEBA/4,4’-DDS increased with the degree of crosslinking, which is due to increases in new thermal pathways through crosslinking bonds. The sequence of thermal conductivities was found to be TGDDM/4,4’-DDS > DGEBA/DETA > DGEBA/4,4’-DDS which was quantitatively validated with our experimental measurements, consistent with the sequence of crosslink density. To explore the microscopic mechanism governing thermal conductivity, separate heat transfer modes were investigated, revealing that the thermal conductivity contribution of bonded interactions dominates over that of non-bonded interactions for all three systems. This finding verifies that introducing crosslinking bonds dominantly contributes to higher thermal conductivity in epoxy materials. Our research provides suggestions for large scale manufacture of higher thermal conductive epoxy resins.

An HTS Model Magnet for MRI Systems Equipped With Electrically Conductive Epoxy Resin for Quench Protection

We have been developing conduction-cooled HTS magnets wound with REBCO-coated conductors for MRI systems, with the aim of developing 9.4 T MRI magnets for whole-body and brain imaging. One of the key technologies to implement the REBCO coil is quench protection and we proposed a quench protection method using electrically conductive epoxy resin. The electrically conductive epoxy resin is attached to the edge of the winding. When the coil voltage rises unintentionally, the excessive current can be automatically bypassed from turn to turn through the electrically conductive epoxy resin. In order to verify the effectiveness of this method with a large-scale coil that has higher stored energy, an HTS MRI model magnet equipped with conductive epoxy resin was designed and fabricated. The magnet has a REBCO multicoil composed of 100 single pancakes whose inner diameters are 500 mm. The total conductor length is 31 km, and the total inductance is 91 H. The central magnetic field is 3 T at 142.7 A, and the size of the homogeneous magnetic field region is 200 mm diameter spherical volume (DSV). This paper presents the design, fabrication of the REBCO multicoil, and test results of the HTS MRI model magnet in a conduction-cooled configuration.

Achieving High Thermal Conductivity in Epoxy Resin Composites by Synergistically Utilizing Al2O3 Framework and BN Sheet as Fillers

AbstractThe application of high thermal conductive Epoxy resin (EP) is an efficient way to improve the heat dissipation in electronic device. In this work, the thermal conductivity of EP is significantly improved by synergistically utilizing Al2O3 framework (AF) and boron nitride sheet (BN) as fillers. The polyurethane foams with different pore sizes are used to prepare AF for the first time. The microstructure characterization demonstrates the successful preparation of AF/EP and AF‐BN/EP with different AF pore size. The thermal conductivity of AF/EP is superior to that of Al2O3/EP composites with randomly distributed Al2O3 nanoparticles. The smaller pore of AF is beneficial to achieving a greater thermal conductivity in AF/EP composites. Especially, by combing BN with AF can further improve the thermal conductivity of AF‐BN/EP composites. The optimal value of 1.18 W m−1 K−1 (5.42 times high than pure EP) is obtained for 60 ppi‐AF‐20 wt% BN/EP composite. Besides, the dielectric property shows that by combining of AF and BN increases the permittivity, as well as low dielectric loss. The high thermal conductivity and excellent dielectric property are simultaneously achieved by synergistically utilizing AF and BN fillers, the resultant EP composites have great potential to be used in electronic devices.

Electrically conductive carbon fiber reinforced plastics induced by uneven distribution of polyaniline composite micron-sized particles in thermosetting matrix

We developed electrically conductive carbon fiber reinforced plastic (CFRP) for lightning strike protection by infusing carbon fiber (CF) woven fabric with a low viscosity liquid conductive thermosetting resin, providing a conductivity in the thickness direction of the CFRP of above 0.1 S/cm. The novel CFRP fabrication method uses a styrene derivative based thermosetting resin liquid dispersion including newly designed micron-size polyaniline (PANI)/dodecyl benzene sulfonic acid (DBSA) based composite particles. The dispersion liquid showed low viscosity and no viscosity increase at room temperature, and could penetrate into CF woven fabric and undergo a cross-linking reaction after heating to around 120 °C. Nine-layered stacked sheets were hot-pressed to make solid laminated composites with 50 vol% CF. The cross-section in the thickness direction was analyzed by optical microscopy, scanning electron microscopy, and electron probe microanalysis to determine the distribution of PANI/DBSA particles and CF per unit area. It was found that PANI/DBSA particles were located between the binding of the plain-woven CF, and showed a conductivity of 0.5 S/cm in the thickness direction, even when the PANI amount was as small as 4 wt%.

Thermally conductive polymer composites for thermal management of electric machines: A modeling and experimental study

With ever-increasing drive to improve the power output of electric machines and reduce heat accumulation based insulation failure, efficient thermal management is highly desirable. Increasing thermal conductivity of impregnation resin is critically important for thermal dissipation in electric machines. In this work, we investigated how the improvement in thermal conductivity of impregnation resins could benefit the heat dissipation of electric machines. To this end, a two-dimensional (2D) finite element analysis (FEA) was conducted, which revealed that increasing the thermal conductivity of impregnation resins to 0.6–0.8 W·m−1·K−1 could significantly decrease the winding temperature. Meanwhile, epoxy-based composites with different thermally conductive fillers were synthesized. The effect of filler type/loading on thermal conductivity and viscosity were investigated. After systematically measuring the thermal conductivity and viscoelastic properties of these composites, a “viscosity-thermal conductivity” correlation was plotted to sort out candidate resin for impregnation trials. In addition, impregnated prototypes comprising enamel wires and both neat epoxy resin and thermally conductive composite impregnation resins were fabricated. Under both natural and forced convection, the epoxy/BN composite resin was shown to be effective in reducing the core temperature of prototype by 9.1–18.6 °C compared with neat epoxy-impregnated prototype. The results indicated that thermally conductive polymer composites had the potential to greatly improve thermal management of electric machines. The findings in this work provide insights and guidelines for future development of thermally conductive impregnation resins.

Effect of Temperature on the Charge Transport Behavior of Epoxy/Nano-SiO2/Micro-BN Composite.

Thermally conductive epoxy resin composites are widely used as electrical equipment insulation and package materials to enhance heat dissipation. It is important to explore the dielectric properties of the composites at high temperatures for the safe operation of the equipment. This paper investigated the charge transport behavior of an epoxy/nano−SiO2/micro−BN composite at varied temperatures by combined analysis of the TSDC (thermally stimulated current), conduction current, complex permittivity and space charge distribution between 40 and 200 °C. The results show that ionic space charge accumulation was significantly suppressed in the composite at high temperatures. The conduction current increased gradually with temperature and manifested a remarkable shift from electron charge transport to ion charge transport near the glass transition temperature (Tg). The real and imaginary permittivity showed an enormous increase above Tg for both the epoxy resin and the composite. The conduction current and permittivity of the composite were remarkably reduced in comparison to the epoxy resin. Therefore, the ionic process dominated the high temperature dielectric properties of the epoxy resin and the composite. The nano–micro fillers in the composite can significantly inhibit ion transport and accumulation, which can significantly enhance the dielectric properties of epoxy resin. Thus, the nano–micro composite has a strong potential application as a package material and insulation material for electronic devices and electrical equipment operated at high temperatures.

Photo curable resin for 3D printed conductive structures

In this study, a new resin formulation method was developed to fabricate 3D printed conductive structures via digital light processing (DLP) 3D printing technology. Metal fillers, such as silver-coated copper flakes (AgCu) and silver nanoparticles (AgNP), were tested for conductive resin formulation. With low UV shielding and printing derivation, AgCu was selected as the conductive filler, and mixed with a photo curable acrylic resin. To resolve the sedimentation problem of metal fillers, carbon nanotubes (CNT) were added as a thickening agent to provide a supportive network to stop the metal fillers from settling. With the CNT addition, AgCu up to 70 wt% can be well dispersed in the acrylic resin with both fluidity and suspension stability. The resin can be printed into 3D metal circuitry structures with a conductivity up to 1000 S/cm without sintering. Multi-material stereolithography was also performed to produce conductive circuitry within insulation materials. The sectional view showed great connections between multiple layers of printed conductive tracks. Through-hole vias and blind vias were also built with great quality to demonstrate the capability of this conductive resin formulation.

Constructing three‐dimensional boron nitride network for highly thermally conductive epoxy resin composites

AbstractConstruction of heat conduction channels in polymer matrix plays a key role in thermally conductive composite. In this work, three‐dimensional (3D) boron nitride (BN) framework was successfully fabricated by decomposing the sacrificial material. The resultant 3D‐BN framework with honeycomb‐like structure was further infiltrated with liquid epoxy resin. With the aid of thermally conductive pathways formed by the 3D‐BN framework, the maximum thermal conductivity of EP/3D‐BN composites reaches 3.53 W/m·K with 55.85 vol% BN, which is 17.6 times larger than that of pure EP. The EP/3D‐BN composites demonstrate strong capability to dissipate the heat during heating and cooling processes. This work provides a facile method for developing thermal conductive composites applied in thermal management for electronics.

Miniaturization and Thermal Design of a 170 W AC/DC Battery Charger Utilizing GaN Power Devices

This paper presents the design and analysis of a high-density two-stage battery charger for mid-power applications like small electric vehicles and high-performance laptops utilizing gallium nitride (GaN) power devices. In addition to adherence of maximum junction temperatures, a thermal analysis is carried out for in-housing operation, which is particularly critical for fanless wall chargers. Design measures include calorimetric semiconductor selection, half-bridge miniaturization, thermally conductive epoxy resin and reference-based convection modeling for thermally optimized component placement using 3D-stacking. Furthermore, the remaining optimization potential of the charger is estimated by virtual prototyping. A 170 W hardware prototype is developed and tested, achieving a two-stage power section efficiency of 95.4% with a maximum switching frequency of 550 kHz. This results in a power density in open-housing operation of 1.6 kW/dm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> . Using epoxy resin, copper and graphite heat spreaders, an in-housing operation power density of 1.1 kW/dm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> is achieved with minor reduction of output power due to surface temperature constraints.

Single droplet 3D printing of electrically conductive resin using high aspect ratio silver nanowires

The incorporation of silver nanowires (Ag NWs) in digital light processing (DLP) 3D printing enables the fast production of electrically conductive composites. The polyvinylpyrrolidone (PVP)-free polyol synthesized Ag NWs, in particular, exhibits high aspect ratio and requires less time in both synthesis and post processing as opposed to the conventional hydrothermal method. In this study, Ag NWs were synthesized in less than 30 min using the PVP-free polyol method. Long and thin pentagonal Ag NWs synthesized at 170 °C had the highest aspect ratio of around 1000 among the three temperatures examined. The as-synthesized Ag NWs were mixed directly with the liquid thermoplastic polyurethane (TPU) resin to produce electrically conductive resin. The optimum Ag NW loading was determined based on their printability and electrical performance. In order to achieve high precision and material utilization efficiency, a modified 3D printing process was proposed to fabricate a controllable 3D structure with single droplet of electrically conductive resin. A 3D printed structure with 1.3 wt% Ag NWs loading exhibited the highest electrical conductivity of 14 mS/cm. Additionally, the curing speed of the electrically conductive resin was enhanced by 450% with the introduction of 10 phr of photoinitiator. The 3D printed structure with the optimized electrically conductive resin formulation was able to light up an LED with 3.5 V applied and the IV characteristic revealed that the printed structure exhibited conductivity in the range of conductive materials (R = 13.7 kΩ). • High aspect ratio silver nanowires were successfully synthesized under 30 min via a PVP free polyol method. • An electrically conductive 3D printing resin was formulated with high aspect ratio silver nanowires as the nanofillers. • The modified 3D printing process greatly improved the utilization efficiency of the electrically conductive resin.

Femtosecond Laser 3D-printing of Conductive Microelectronics for Potential Biomedical Applications.

Development of soft and conductive micro devices represents a demanding research topic in various biomedical applications, particularly organic bioelectronics. Among various fabrication methods, two-photon polymerization (2PP) using a wide range of photocurable inks is a promising 3D printing technique for construction of structures in submicron resolution. Herein, we introduce a novel conductive photosensitive resin by using poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and poly(ethylene glycol) diacrylate), and fabricate 3D conductive polymeric microstructures via 2PP. In the developed resin, presence of PEDOT:PSS significantly enhances the electrical conductivity of microstructures (~ 10 orders of magnitude).Clinical Relevance- Conductive microdevices based on the PEDOT:PSS-doped resin open new avenues in a broad range of biomedical research areas including neural interfaces, biosensors, and bioelectronics.

On Demand Electrochemical Peroxide Generation for Disinfection

Novel technologies with limited earth support are required to enable habitation in microgravity spacecraft habitats such as International space station (ISS). One area of particular need for the interstellar travel community is cleaning/sanitizing supplies to meet personal hygiene requirements, which is currently accomplished through the use of pre-packaged, disposable, wetted wipes. These items represent an appreciable carry-along mass and disposal/replacement burden requiring ground support. Therefore, a system is desired that could utilize onboard utilities to create disinfecting solutions to eliminate storage/disposable problems of the wetted wipes and further reduce the astronaut’s dependence on earth-based supplies.Faraday Technology Inc. is addressing this challenge by demonstrating an electrochemical technology which utilizes on-board supplies of air and water for on demand generation of hydrogen peroxide. This concept is based on the electrochemical reduction of oxygen to hydrogen peroxide by two electron transfer reactions which proceeds as [O2 + 2H+ + 2e- → H2O2 or O2 + 2H2O + 2e- → H2O2 + 2OH-][i]. Hydrogen peroxide is well-established disinfectant with non-toxic decomposition products (viz., O2 and H2O), that is safe enough for human contact to be sold commercially as a 1-5 w/w% solution, which makes it an ideal disinfecting solution for closed space environments.Previously, Faraday has demonstrated electrochemical generation of 3 w/w% hydrogen peroxide in a ‘H-cell’ electrochemical laboratory set-up utilizing a sodium sulfate electrolyte[ii]. Following on, Faraday designed and constructed an electrochemical sub-scale reactor for generating >1 w/w% hydrogen peroxide in RO water enabled by ion conductive resin[iii]. The next step was to understand the effects of zero-gravity on the hydrogen peroxide reactor. The electrochemical reactor and components were assembled in a zero-gravity test setup. Optimized conditions from ground-based performance data were implemented during the zero-gravity flight test. The flight tests indicated there were no adverse effects of zero-gravity on the performance of the hydrogen peroxide generation system vis-à-vis ground operation[iv]. In order to facilitate use of low conductive DI water stream available aboard the International Space Station (ISS), Faraday modified the reactor design by utilizing anion exchange membrane (AEM) within the sub-scale reactor, which reduced flooding and improved reactor stability (Figure 1)[v]. The modified sub-scale reactor was used to demonstrate the potential of generating >2 w/w% hydrogen peroxide in very low conductivity electrolytes such as DI and pure oxygen. On-going activities at Faraday are defining the effects of capsule air and contaminants in the DI water on performance of the sub-scale reactor. The system is also being scaled to deliver 1L of ~2% w/w% hydrogen peroxide for disinfectant applications from DI water feed-stream with air as a feed source[v]. This system eliminates the need to ferry disinfectant wipes to manned space capsules and is a critical enabling technology for future moon-based missions and beyond. Acknowledgements: Financial support of NASA Contracts NNX16CA43P, NNX17CJ12C, and 80NSSC20C0070 is acknowledged.

Ice-Prevention and De-Icing Capacity of Epoxy Resin Filled with Hybrid Carbon-Nanostructured Forms: Self-Heating by Joule Effect

In this study, CNTs and graphite have been incorporated to provide electrical conductivity and self-heating capacity by Joule effect to an epoxy matrix. Additionally, both types of fillers, with different morphology, surface area and aspect ratio, were simultaneously incorporated (hybrid CNTs and graphite addition) into the same epoxy matrix to evaluate the effect of the self-heating capacity of carbon materials-based resins on de-icing and ice-prevention capacity. The self-heating capacity by Joule effect and the thermal conductivity of the differently filled epoxy resin were evaluated for heating applications at room temperature and at low temperatures for de-icing and ice-prevention applications. The results show that the higher aspect ratio of the CNTs determined the higher electrical conductivity of the epoxy resin compared to that of the epoxy resin filled with graphite, but the 2D morphology of graphite produced the higher thermal conductivity of the filled epoxy resin. The presence of graphite enhanced the thermal stability of the filled epoxy resin, helping avoid its deformation produced by the softening of the epoxy resin (the higher the thermal conductivity, the higher the heat dissipation), but did not contribute to the self-heating by Joule effect. On the other hand, the feasibility of electrically conductive epoxy resins for de-icing and ice-prevention applications by Joule effect was demonstrated.

Ultrathin Semi-Interpenetrating Network Membranes Based on Perfluorinated Sulfonic Acid Resin and Polydivinylbenzene with Declined Hydrogen Crossover for Proton Exchange Membrane Fuel Cell

Ultrathin semi-interpenetrating proton exchange membranes (SIPN PEMs) comprised of conductive perfluorinated sulfonic acid resin (PFSA) and cross-linked polydivinylbenzene (PDVB) have been fabricated. The SIPN PEMs containing both conductive and cross-linked components exhibited better mechanical stability and electrochemical properties than recast PFSA. The SIPN-3 membrane with the lowest IEC 0.8493 mmol g−1 among the three SIPN PEM samples, however, showed the highest proton conductivity, 0.083 S cm−1, and a comparatively low swelling ratio of 10.12% at 80 °C in deionized water. At the same time, the unique structure and lower thickness endowed the membranes with outstanding fuel cell performance due to the decreased proton transfer resistance. The results show that SIPN-3 with 964.6 mW·cm−2 power density was obtained, and the gas crossover current density was only 1.34 mA·cm−2, which was lower than that for the recast PFSA (1.5 mA·cm−2) and Nafion® NC700 (2.75 mA·cm−2). Thus, constructing a semi-interpenetrating network is certified to enhance properties of the membrane prominently, which has the potential to be applied in PEMFC.

Simulated lightning strike investigation of CFRP comprising a novel polyaniline/phenol based electrically conductive resin matrix

Traditional carbon fiber reinforced plastics (CFRPs) have been reported to exhibit lower electrical conductivity in the through-thickness direction, and have since paved the path for developing new resin systems to improve the through-thickness electrical conductivity and functionality of CFRP laminates. This study designs and investigates a novel Polyaniline (PANI)/Phenol resin, which possesses high electrical conductivity and mechanical strength. The CFRP manufactured by this PANI/Phenol resin with an addition of up to (~23.30%) phenol resulted in 0.6 S/cm through-thickness conductivity and demonstrated flexural strength and modulus values of 477 MPa and 59.2 GPa, respectively. We further evaluate the effectiveness of lightning strike protection of PANI/Phenol-based conductive CFRP laminates with a simulated lightning strike test. In essence, this research reports on PANI/Phenol-based CFRP's effectiveness as a material for lightning suppression without applying traditional metal-based lightning strike protection (LSP) systems.

Physics-informed neural network for modelling the thermochemical curing process of composite-tool systems during manufacture

We present a Physics-Informed Neural Network (PINN) to simulate the thermochemical evolution of a composite material on a tool undergoing cure in an autoclave. In particular, we solve the governing coupled system of differential equations – including conductive heat transfer and resin cure kinetics – by optimizing the parameters of a deep neural network (DNN) using a physics-based loss function. To account for the vastly different behaviour of thermal conduction and resin cure, we design a PINN consisting of two disconnected subnetworks, and develop a sequential training algorithm that mitigates instability present in traditional training methods. Further, we incorporate explicit discontinuities into the DNN at the composite-tool interface and enforce known physical behaviour directly in the loss function to improve the solution near the interface. We train the PINN with a technique that automatically adapts the weights on the loss terms corresponding to PDE, boundary, interface, and initial conditions. Finally, we demonstrate that one can include problem parameters as an input to the model – resulting in a surrogate that provides real-time simulation for a range of problem settings – and that one can use transfer learning to significantly reduce the training time for problem settings similar to that of an initial trained model. The performance of the proposed PINN is demonstrated in multiple scenarios with different material thicknesses and thermal boundary conditions.

Highly thermally conductive 3D BN/MWCNTs/C spatial network composites with improved electrically insulating and flame retardancy prepared by biological template assisted method

Boron nitride/multiwalled carbon nanotubes/carbon (BN/MWCNTs/C) networks were prepared via a rape pollen (RP) biological template assisted strategy. The highly thermally conductive epoxy resin (EP) composites were prepared by impregnating EP into the 3D BN/MWCNTs/C networks. Fourier transform infrared spectra and X-ray photoelectron spectroscopy analyses indicated that the successful modification of BN (m-BN) and the interaction between RP, carboxyl functionalized MWCNTs (c-MWCNTs) and m-BN. Scanning electron microscopy images clearly present the network morphology constructed by MWCNTs connected to m-BN. Thermogravimetric analyzer curves determine the mass concentration of m-BN in EP-based composites. The thermal conductivity (K) reached 1.84 W/(m·K) in the composites at a BN content of 21.3 wt%, displaying a significant enhancement of 868% compared with pure EP. The enhanced K is attributed to the effective connection of BN by the MWCNTs covered on the surface of RP. Meanwhile, the composites exhibit a tensile strength of 39.2 MPa, electrically insulating with a volume electrical resistivity about 9.17 × 1010 Ω cm and good flame retardancy.

Improved Copper-Epoxy Adhesion by Laser Micro- and Nano-Structuring of Copper Surface for Thermal Applications.

The objective of this work is the enhancement of metal-to-metal bonding to provide high thermal conductivity together with electrical insulation, to be used as heat sinks at room and cryogenic temperatures. High thermal conductive metal (copper) and epoxy resin (Stycast 2850FT) were used in this study, with the latter also providing the required electrical insulation. The copper surface was irradiated with laser to induce micro- and nano-patterned structures that result in an improvement of the adhesion between the epoxy and the copper. Thus, copper-to-copper bonding strength was characterized by means of mechanical tensile shear tests. The effect of the laser processing on the thermal conductivity properties of the Cu/epoxy/Cu joint at different temperatures, from 10 to 300 K, is also reported. Using adequate laser parameters, it is possible to obtain high bonding strength values limited by cohesive epoxy fracture, together with good thermal conductivity at ambient and cryogenic temperatures.

Discharge Behaviour and Modelling of a 1.5T REBCO Magnet With Quench Tolerant Coils Impregnated with Conductive Epoxy.

We have designed and built a small, conduction cooled, 1.5 T high-temperature superconductor (HTS) magnet. The magnet coils have been wet-wound with a novel conductive epoxy resin system to achieve a derivative of the no-insulation coil winding method. The epoxy is filled with copper powder to reliably set the turn-to-turn contact resistivity and diamond powder to accurately space the coil turns apart, as well as match the filled epoxy thermal contraction rate to that of the HTS. The magnet is designed to act as a test bed to measure sudden discharge rates and hence validate models of coil behaviour using the filled epoxy system we have developed. A lumped-element electrical model was used to predict the coil contact resistivity needed to bring the magnetic field of the 1.5 T magnet down to a near-zero level within 0.5 s. The conductive epoxy blend was tuned to give a contact resistivity of 1 × 10-6 Ω m2, based on previous measurements of coil contact resistivity at 77 K. Once the magnet was wound and tested at 40 K, we found the magnet's sudden discharge time constant was 500 ms rather than 69 ms as was predicted from the 77 K measurements. The discrepancy was traced to the temperature dependence of the contact resistivity. With further testing of the individual coils this was accounted for and the model adjusted. The predicted discharge time was 2 s, in good agreement with the measured sudden discharge time of the magnet.

Sudden Discharging and Overcurrent Simulations of REBCO Coils Coated With Conductive Epoxy Resin

In 2011, a no-insulation (NI) winding technique was first proposed. Rare-Earth Barium Copper Oxide (REBCO) pancake coils using the NI winding technique are promising to generate an ultrahigh magnetic field, because the NI winding technique drastically enhances the thermal stability. When a local hot spot appears on a turn of the NI REBCO pancake coil, the enforced current can bypass into the adjacent turns to suppress the Joule heat generation. Recently, different types of REBCO coils to enhance the thermal stability by escaping the current flow from a local hot spot have been researched and developed. A few years ago, a REBCO single pancake coil whose upper surface was coated with conductive epoxy resin was proposed as one kind of NI winding techniques. The high thermal stability of conductive-epoxy-resin-coated (CERC) REBCO single pancake coil was demonstrated through an overcurrent test. However, the current behavior in the coil is still unclear. Therefore, we have newly developed an equivalent circuit model for CERC REBCO pancake coils. The sudden discharging and overcurrent tests were simulated for CERC REBCO pancake coils, and the resistance parameters were varied to investigate the coil stability.