Epoxy Mold Research Articles

Features of Applying Cast Epoxy Insulation and Compositions Based on It for High-voltage Equipment

Features of Applying Cast Epoxy Insulation and Compositions Based on It for High-voltage Equipment

Aging of epoxy cast insulation with different voltages and environmental stresses

Aging of epoxy cast insulation with different voltages and environmental stresses

Design and Architecture Definition for Advanced 3D Fan-Out Wafer-Level Packaging

Advanced 2.5D/3D wafer-level fan-out packaging technologies have been studied widely in literature and industry in recent years. Miniaturization, reduction in manufacturing costs, improvement in performance, and lower power consumption using packaging technologies drive increase in interconnect density and pitch scaling. Heterogeneous systems in package used in advanced packaging often include a combination of silicon, epoxy underfill or mold compounds, and organic or inorganic passivation or redistribution layers. This heterogeneity poses challenges with manufacturability, process selection, package architecture, and test vehicle design. The coefficient of thermal expansion mismatch, wafer warpage, and wafer yield are some of the critical process challenges. Delamination of silicon side wall or passivation to epoxy underfill or mold compound, joint fatigue are critical reliability challenges. This article explores various processes and reliability challenges with 3D wafer-level fan-out packaging and provides package design and architecture guidelines to overcome these failure modes. Stacked die-to-wafer test vehicles have been used for data collection. Different assembly materials, processes, and tooling have been evaluated to define comprehensive design rules.

The sensitivity analysis of geometric parameters on the power cycling reliability of bond wires

Considering the reliability of the bond wire comes as the main factor determining the reliability of power devices at present, and the geometric parameters of the bond wire have an in-negligible effect. A Finite Element (FE) simulation model based on a discrete device with TO-247 package and a single bond wire is established in this paper, and the influences of the geometric parameters are analyzed, which include the joint length L, the diameter D, and the aspect ratio λ. Then to understand the influence degree of the parameter on the reliability, the sensitivity analysis of these geometric parameters is carried out based on the sobol' method, using the Monte Carlo method for estimating the sensitivity index. The results show that increasing the joint length L, the diameter D and the aspect ratio λ all have a negative impact on the bond wire reliability, while a positive influence is presented by increasing the aspect ratio λ in the case without epoxy mold compound (EMC). This is because of the EMC's protective effect which inhibits the bond wire's thermal expansion. The aspect ratio λ is the most sensitive parameter of the three geometric parameters since it has the largest total sensitive index.

Experimental Method to Measure High-Temperature Hygroscopic Swelling in Epoxy Mold Compounds and Dielectric Build-Up Films

Experimental Method to Measure High-Temperature Hygroscopic Swelling in Epoxy Mold Compounds and Dielectric Build-Up Films

Study on the Effect of Recycled Brass-Filled Epoxy Mould Inserts for Rapid Tooling

Rapid Tooling able to produce complex prototypes directly from three-dimensional CAD software using materials such as polymer, wax, and paper, but it is typically used for low-volume production. The current technology uses epoxy filled with metal fillers such as aluminum or copper to enhance the mechanical properties of rapid tooling molds. This study aims to investigate the effect of using recycled brass filler mixed with epoxy resin as mold inserts for Rapid Tooling in injection molding applications. An optimal ratio of brass filler particles will be evaluated to determine the best physical and thermal properties for the mold inserts. Significantly, this study will encourage the use of recycled materials such as metal waste from machining to offer great help in environmental sustainability.

Coffee ring-free inkjet printing using UV-curable quantum dot-acrylate solution for high resolution displays

We report the coffee ring-free inkjet printing using a UV curable quantum dot (QD)-acrylate coating solution. The main objective of this study is to utilize UV curable acrylate monomers to prevent formation of coffee rings and hence to obtain uniform QD patterns using inkjet printing. For the UV curing reaction, cyclohexylmethacrylate (CHMA) was selected as the acrylate monomer, 1-[4-(phenylthio)phenyl]-1,2-octanedione 2-(o-benzoyloxime) (OXE-01), 2-isopropylthioxanthone (ITX), and 2,2-dimethoxy-2-phenylacetophenone (DMPA) were tested as photoinitiators (PIs), and pentaerythritol triacrylate (PETA) was used as a crosslinker. When the QDs were used with CHMA monomers without UV curing, inkjet printing resulted in the formation of coffee rings or cracks during monomer evaporation. However, UV curing with ITX as a PI produced inkjet droplets with uniform surfaces owing to the balance between evaporation and UV curing rates. By optimizing the compositions of the monomer, PI, and crosslinker, we successfully obtained uniform QD patterns on the micrometer scale using inkjet printing. We also demonstrated that this technique could be applied to inkjet printing of the 400 ×100 μm patterned epoxy molds. These results will be useful for the inexpensive and rapid fabrication of high-resolution QD displays using inkjet printing.

Development of a facile, versatile and scalable fabrication approach of solid, coated, and dissolving microneedle devices for transdermal drug delivery applications

Nowadays, microneedles as novel transdermal delivery systems are interested in scientists for biomedical applications. This work aims to present a Cascade Microneedle Molding Technique (CMMT) for the reusable fabrication of polydimethylsiloxane (PDMS) molds to produce microneedle devices. To produce a positive master mold from epoxy resin, a negative PDMS mold was first fabricated. PDMS can be molded, and microneedles can be fabricated using this epoxy mold in a scalable and cost-effective manner. These molds were used to manufacture solid, coated, and dissolving microneedles, which were characterized comprehensively. Microneedle morphology and geometry were evaluated using Scanning Electron Microscopy (SEM). The mechanical integrity and ability to insert the microneedle device into the skin were assessed using compression strength analysis and force-displacement measurements. Drug penetration through animal skin was evaluated for Rhodamine B (RhB) loaded microneedles. The depth of needle insertion was also visualized using histological analysis while the spatial distribution of released cargo was determined by using confocal microscopy. Taken together, CMMT offers a simple, rapid, cost-effective, and scalable method for mass-producing microneedles with remarkable properties compared to direct 3D printing or laser ablation.

Effect of Mold Materials Used During Hot Embossing on Feature Fidelity for Microfabrication in Cyclic Olefin Polymer (COP) Substrate

During the transition from research to market, the fabrication of microfluidic devices in thermoplastic substrates is inevitable. For short production runs of several hundred products, hot embossing is the typical method before moving on to a typically more expensive injection molding process for higher production volumes. In this work, we investigated the effect of mold material used during hot embossing on feature fidelity for microfabrication in cyclic olefin polymer (COP) substrate. Specifically, we designed a simple flow-focusing microfluidic device and fabricated three different molds using silicon wafer by deep reactive ion etching (DRIE), aluminum filled high temperature epoxy by soft lithography and aluminum by CNC milling. We performed hot embossing experiments with 2mm thick COP substrates and these three different molds using automatic bench top Carver hot press. Finally, we characterized the hot embossed substrates by optical and scanning electron microscopy. Fabrication results demonstrate that the mold material plays a big role in feature fidelity. Among the mold materials used, silicon substrate performed the worst based on defects after demolding. Epoxy and aluminum molds were similar in terms of microfabricated feature defects in the substrate which could be mostly attributed to their coefficient of thermal expansion (CTE). A mold material with a CTE closer to the thermoplastic will result in much better feature fidelity.

Thermal runaway and induced electrical failure of epoxy resin in high‐frequency transformers: Insulation design reference

AbstractSolid‐state transformers (SSTs) have applications in medium‐voltage direct current (MVDC) grids and compact power systems. High‐frequency transformer (HFT) is the core component of SSTs. High levels of high frequency high dv/dt voltage stresses challenged the integrity of the galvanic insulation of HFTs. However, dielectric thermal runaway and resultant electrical failure mechanisms in epoxy resin (EP) cast insulation remain unclear. Dielectric heating of EP across varying voltages, frequencies, rising edges, duty cycles and DC biases were measured and corroborated by simulation. The thermal runaway threshold mainly depends on the tangency point of the loss generation and heat dissipation curves below the glass transition temperature. Observations reveal that thermal runaway does not directly cause breakdown; instead, thermal decomposition above 200°C triggers discharge and eventual failure. Simulations demonstrate that temperature rise mainly depends on the average field within the electrode region and inter‐segment and inter‐layer distances within the HFT winding definitively impact insulation thermal runaway. By applying different criteria for MV and high‐voltage (HV) transformers, the reference electric fields for insulation design with unfilled and filled EP were obtained. For instance, limiting dielectric heating below 5 K at 50 kHz necessitates an RMS average field less than 0.44 V/mm, which is much lower than dry‐type transformer conventions. The authors prove the necessity of re‐evaluating the permissible field strength in HFT insulation design.

Mode I Fatigue and Fracture Assessment of Polyimide-Epoxy and Silicon-Epoxy Interfaces in Chip-Package Components.

Semiconductor advancements demand greater integrated circuit density, structural miniaturization, and complex material combinations, resulting in stress concentrations from property mismatches. This study investigates the failure in two types of interfaces found in chip packages: silicon-epoxy mold compound (EMC) and polyimide-EMC. These interfaces were subjected to quasi-static and fatigue loading conditions. Employing a compliance-based beam method, the tests determined interfacial critical fracture energy values, (GIC), of 0.051 N/mm and 0.037 N/mm for the silicon-EMC and polyimide-EMC interfaces, respectively. Fatigue testing on the polyimide-epoxy interface revealed a fatigue threshold strain energy, (Gth), of 0.042 N/mm. We also observed diverse failure modes and discuss potential mechanical failures in multi-layer chip packages. The findings of this study can contribute to the prediction and mitigation of failure modes in the analyzed chip packaging. The obtained threshold energy and crack growth rate provide insights for designing safe lives for bi-material interfaces in chip packaging under cyclic loads. These insights can guide future research directions, emphasizing the improvement of material properties and exploration of the influence of manufacturing parameters on delamination in multilayer semiconductors.

Effect of high-frequency pulse voltage parameters and DC bias on breakdown of epoxy cast insulation

Effect of high-frequency pulse voltage parameters and DC bias on breakdown of epoxy cast insulation

Influence of material thickness and hatching strategies on laser cutting of epoxy mold composites

Glass-filled composites are used for overmolding of electrical components due to their good electrical isolation properties. Laser cutting is a preferred technology to remove excess mold material to achieve a low surface roughness and reduce tool wear. Hatching strategies improve the laser-cutting process of carbon fiber-reinforced polymers toward lower cutting times and a more homogeneous cut surface. The impact of hatching strategies on epoxy mold compounds has been so far unknown as the laser-cutting strategy was based on multiple single passes in previous studies. This work investigates the effects of hatching strategies such as perpendicular hatching, parallel hatching, and a single line, including the influence of material thickness and filler content regarding the cutting time, kerf taper angle, and heat-affected zone, using a 50 W short-pulsed fiber laser for different highly filled epoxy mold compounds. Results show that the use of a hatching strategy is required to cut workpieces at thicknesses of 4 mm or higher due to the sieving size of the filler. Perpendicular hatching needs to be chosen when the aim is a minimal cutting time. The kerf taper angle at the top of the cut is below 4° while hatching leads to a more pronounced kink of up to 25° occurring toward the bottom of the cut. Meanwhile, an increase in filler concentration leads to an increase in cutting time, because of higher thermal conduction, while no effect on the kerf taper angle or the heat-affected zone can be identified.

Accuracy of fit for cobaltchromium bar over two implants fabricated with different manufacturing techniques: an in-vitro study

ObjectiveThe purpose of the invitro research was to compare the fit of Cobalt Chromium customized bar fabricated with different manufacturing processes cast metal bar, milled bar and 3D printed bar using scanning electron microscope.Materials and methodsClear epoxy resin molds were prepared. In each mold two parallel implants with a 14 mm distance from each other were embedded. Thirty Co-Cr custom bars were constructed and were divided equally into three groups: Group (I) (Co-Cr conv), group (II) milled bar (Co-Cr milled), and group (III) printed bar (Co-Cr print). The marginal fit at implant-abutment interface was scanned using scanning electron microscope (SEM).ResultsThere was a significant difference between the three studied groups regarding marginal misfit the between implant and fabricated bars with p-value < 0.001. The highest value of micro-gap distance was found in Co-Cr conventional group (7.95 ± 2.21 μm) followed by Co-Cr 3D printed group (4.98 ± 1.73) and the lower value were found in Co-Cr milled (3.22 ± 0.75).ConclusionThe marginal fit of milled, 3D printed and conventional cast for Co-Cr alloy were within the clinically acceptable range of misfit. CAD/CAM milled Co-Cr bar revealed a superior internal fit at the implant-abutment interface. This was followed by selective laser melting (SLM) 3D printed bar and the least fit was shown for customized bar with the conventional lost wax technique.

Rapid tooling of composite aluminium filled epoxy mould for injection moulding of polypropylene parts with small protruded features

Abstract Rapid tooling evolved from rapid prototyping is a novel method for developing prototype tooling rapidly using various additive manufacturing techniques. Traditional injection moulding is unsuitable for low-volume production because of the high initial cost. This study is focused on a rapid tooling approach for producing an injection mould insert for the low-volume production of plastic components. A plastic injection mould insert is designed, developed using composite aluminium filled epoxy with minute protruded features and tested on a vertical injection moulding machine as a rapid tool for low-volume production of plastic components. The composite aluminium filled epoxy (CAFE) mould insert is prepared using a wax master from silicon rubber mould prepared using a stereolithography master. Experiments are performed to determine the optimum mixing ratio of epoxy: aluminium powder for making the composite aluminium filled epoxy injection mould. The mould insert prepared was tested for the injection of polypropylene components on a vertical injection moulding machine and analyzed for dimensional accuracy. The analysis of dimensional accuracy and viability of minute features on the injected parts shows promising results for up to 30 injected parts. The injection of parts after 30 pieces resulted in increasing mould erosion and pitting, causing mould damage at the 36th injection shot. The experimental finding supports the feasibility of using the composite aluminium filled epoxy injection mould for low-volume production of the parts; however, the surface finish is inferior. The life of the mould is expected to give better results with a higher surface finish. It is also exposed that using mould release agents improves the life of the composite aluminium-filled epoxy injection mould.

“Generating a eco friendly reinforced composite using human hair and analyzing it for commercial use”

This paper delves into the development and characterization of natural hair fiber-reinforced polymer composites, with a focus on their physical and mechanical attributes. Composite materials encompass ceramic matrix composites (CMC), metal matrix composites (MMC), and polymer matrix composites (PMC), with PMC being favored for its cost-efficiency and ease of production, notably employing thermoplastic polymers for recyclability. Natural fibers are gaining traction, especially in the automotive industry across Asia and Europe, due to their low density and environmental friendliness. Human hair stands out as a reinforcing material owing to its impressive tensile strength, sustainability, abundance, and keratin content. The paper addresses challenges linked to natural fibers in composites, including moisture resistance and dimensional availability. The research involves creating composites using human hair fibers, epoxy resin (polypropylene), and specific molds, varying hair fiber percentages. Detailed methodology covers materials, equipment, mold prep, specimen prep, and mathematical modeling. Tensile, flexural bending, and impact strength tests reveal insights into composite mechanics. Hair fiber additions strengthen the polymer matrix, particularly at 5 to 15 weight percentages, though flexural strength diminishes compared to non-reinforced composites. Higher hair fiber percentages enhance hardness. In conclusion, this study showcases human hair fiber's potential as a reinforcement in polymer composites, emphasizing the need for further exploration of matrix-fiber adhesion to boost composite performance. These findings contribute to the growing interest in natural fiber composites for sustainable and economical applications.

An ultrasonic phantom for cortical and cancellous bone

There is interest in developing ultrasonic techniques for diagnosing osteoporosis. Many techniques perform measurements at skeletal sites such as the heel, hip, and spine where the bone tissue consists of a non-porous outer layer of cortical bone that surrounds a porous interior region of cancellous bone. The goal of the present study was to develop an ultrasonic phantom that simulates this tissue configuration. A block of polymer open cell rigid foam (OCRF) was partially embedded in a thin layer of clear epoxy casting resin to create the phantoms. The resulting phantoms were 40mm × 40 mm × 20 mm with one 40 mm × 40 mm face embedded in ∼3mm of resin. Ultrasonic measurements were performed to characterize the speed of sound and attenuation of the resin and the OCRF separately and together, as configured in the phantom. Backscatter measurements were also performed. The resulting specimens can be used to investigate how non-normal incidence of an ultrasonic wave on the bone cortex may produce errors in these measurements.

A Novel Approach for Characterizing Epoxy Mold Compound High Temperature Swelling

In this paper, a novel method for measuring hightemperature material swelling of an epoxy mold compound is explored. This work attempts to extend the swelling characterization beyond the capability of typical commercial tools. The approach uses a high-pressure chamber to maintain a saturated liquid environment for the specimen. Digital image correlation is used to measure in-situ strain change in the specimen due to hygro-thermal expansion. The results show moisture-induced swelling increases with temperature and is significant compared with thermal expansion. Results are compared against other measurement methods and published data. This has yielded good fundamental learnings for the novel concept and identified areas for future work.

Moisture absorption and desorption in epoxy mould compounds: Characterization of Fickian and non-Fickian behaviours in complex packages

This works analyses the moisture absorption and desorption in three different mould compounds used in QFN packaging technology. Moisture diffusion during accelerated tests is replicated on different sample type: bulk material, empty QFN strips and empty QFNs to examine the diffusion modes. The temperature-dependent diffusion parameters are characterised using the Dual stage model. The combination of a Fickian and a non-Fickian behaviour of this model fits perfectly the diffusion results in a bulk resin sample. However, the diffusion parameters in the case of the QFN strips and packages suggest a non-negligible diffusion along the interfaces. The desorption analyses in these QFN samples show residual moisture. We suspect the presence of residual moisture at the leadframe/moulding interfaces. The desorption at standard industrial temperatures highlights anomalies, suggesting a critical thermal aging phenomenon.

Obtaining thermal resistance of mold compounds using a package structure model with a heat-generating test element group: Comparison of the thermal conductivity and glass transition temperature of epoxy mold compounds

Epoxy mold compounds (EMCs) with thermal conductivity of 0.8–4 W/m∙K and a glass transition temperature (Tg) of 150–270 °C were prepared using epoxy resins with various network structures and SiO2 and Al2O3 fillers. The test structure was fabricated using a heat-generating test element group (TEG) chip and an EMC in which the thermal conductivity and Tg varied. The TEG chip has two types of measurement pad: one for sensing the surface temperature and the other for heating the chip surface. The thermal resistance of the package structure model decreased from 14 °C/W to 4 °C/W from 0.8 to 4 W/m∙K, with the thermal conductivity of the mold compound having the same Tg. The thermal resistance of the package structure model decreased from 7.5 °C/W to 5.5 °C/W by increasing the Tg of the mold compound having the same thermal conductivity from 150 °C to 270 °C. Control over the thermal conductivity of the EMCs appeared to have a greater effect than the Tg on the thermal resistance of the package structure model using a TEG. The liquid EMC with a thermal conductivity of 4 W/m∙K provided the lowest thermal resistance (4 °C/W) among the EMCs examined.