Novel conductive adhesives for surface mount applications

Electrically conductive adhesives (ECAs) have been explored as a tin/lead (Sn/Pb) solder alternative for attaching encapsulated surface mount components on rigid and flexible printed circuits. However, limited practical use of conductive adhesives in surface mount applications is found because of the limitations and concerns of current commercial ECAs. One critical limitation is the significant increase of joint resistance with Sn/Pb finished components under 85°C/85% relative humidity (RH) aging. Conductive adhesives with stable joint resistance are especially desirable. In this study, a novel conductive adhesive system that is based on epoxy resins has been developed. Conductive adhesives from this system show very stable joint resistance with Sn/Pb‐finished components during 85°C/85% RH aging. One ECA selected from this system has been tested here and compared with two popular commercial surface mount conductive adhesives. ECA properties studied included cure profile, glass transition temperature (T_g), bulk resistivity, moisture absorption, die shear adhesion strength, and shift of joint resistance with Sn/Pb metallization under 85°C/85% RH aging. It was found that, compared to the commercial conductive adhesives, our in‐house conductive adhesive had higher T_g, comparable bulk resistivity, lower moisture absorption, comparable adhesion strength, and most importantly, much more stable joint resistance. Therefore, this conductive adhesive system should have better performance for surface mount applications than current commercial surface mount conductive adhesives. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 399–406, 1999     

Novel flexible electrically conductive adhesives from functional epoxy,flexibilizers, micro‐silver flakes and nano‐silver spheres for electronic packaging

In this study, five different flexibilizers were added into a matrix resin to improve the flexibility of electrically conductive adhesives (ECAs). The flexible ECAs were fabricated from the matrix resin and electrically conductive fillers. Their curing was fixed at 150 °C for 30 min. Of the five flexibilizers, 1,3‐propanediol bis(4‐aminobenzoate) (PBA) had the best effect on the electrical, mechanical and thermal properties of the ECAs. During curing, PBA reacted with the functional epoxy in the matrix resin. The soft ether segments in PBA were grafted into the crosslinked epoxy network to form an orderly spaced mesh structure. This led to high‐temperature stability, with the pyrolysis temperature being above 350 °C. Flexible ECAs with a 10% weight ratio of PBA in the matrix resin had the best properties. Their viscosity and bulk resistivity were the lowest. Their flexibility and electrical conductivity were the highest. They also had low storage modulus which could effectively dissipate or reduce the residual shear stress generated by the mismatch of thermal expansion coefficient between chip and substrate. Their impact strength was the lowest, and the toughening effect was so significant that the improvement was about 48% compared to ECAs. © 2013 Society of Chemical Industry     

Study on the properties of conductive adhesives in various curing manners for MCM applications

In this work, the properties of solvent and solvent-free electrically conductive adhesives (ECAs) in four curing manners and after solder reflows are investigated for multi-chip module applications. The curing behaviors and thermal degradation of solvent and solvent-free ECAs are also studied by differential scanning calorimeter and thermogravimetric analysis, respectively. The bulk resistivity of ECAs in four curing manners is significantly different, even if they are cured at the same temperature and time. The conductive trends of solvent and solvent-free ECAs are also different. The good and poor conductive properties of solvent ECA are obtained at curing temperature starting from room temperature and setting temperature, respectively. However, the results of solvent-free ECA are opposite. All the bulk resistivity and the coefficients of thermal expansion of solvent and solvent-free ECAs tend to decrease after solder reflows. The reasons are studied by thermomechanical analyzer, thermogravimetric analysis, topography and deformation measurement, and scanning electron microscopy.     

Environmental aging effects on thermal and mechanical properties of electrically conductive adhesives

This article investigates environmental aging effects on thermal and mechanical properties of three model electrically conductive adhesives (ECAs). A combination of several experimental techniques including thermogravimetric analysis (TGA), water uptake measurements, dynamic mechanical analysis (DMA), and stress-strain dogbone testing has been utilized throughout this study. Samples were aged at 85°C and 100% RH for periods of up to 50 days, and some of the samples were dried at 150°C after aging. Results obtained on aged samples with and without drying suggest that the conductive adhesives may have experienced both reversible and irreversible effects during environmental aging. Both plasticization, which is reversible, and further crosslinking and thermal degradation, which are irreversible, are indicated upon exposure of ECAs to the hot/wet environment.     

MXene fillers and silver flakes filled epoxy resin for new hybrid conductive adhesives

The addition of V₂CT_x two-dimensional materials as auxiliary fillers in conductive adhesives can increase the contact area between conductive particles inside the matrix effectively reducing the resistivity of epoxy resin conductive adhesives. The V₂CT_x/Ag/rGO/MWCNTs fillers inside the epoxy resin will connect more Ag-clad Cu particles to form a conductive pathway, but its excessive content will be aggregated inside and thus increase the resistivity of the conductive adhesive. The volume resistivity of ECAs increases from 4.4 × 10⁻⁶ Ω m to 1.15 × 10⁻⁵ Ω m when the V₂CT_x/Ag/rGO/MWCNTs content of 0.1% increases to 0.34%. The Ag-clad Cu particles are interconnected inside the epoxy resin to form an electron transfer network. Inside the epoxy resin substrate Ag-clad Cu particles and V₂CT_x/Ag/rGO/MWCNTs interconnects to form a larger conductive network, so that the conductive adhesive shows good conductive properties.     

Electrical and mechanical properties of electrically conductive adhesives from epoxy,micro-silver flakes,and nano-hexagonal boron nitride particles after humid and thermal aging

In this study, we incorporated micro-silver flakes and nano-hexagonal boron nitride (BN) particles into a matrix resin to prepare electrically conductive adhesives (ECAs). The humid and thermal aging results under a constant relative humidity level of 85% at 85 °C revealed that the aged ECAs containing 3 wt% of nano-hexagonal BN particles had high reliability. The contact resistance was low and the shear strength high. Nano-hexagonal BN particles have a good effect on the reliability of ECAs that can be used to improve the properties of ECAs.     

Effect of nanoparticles on the performance of thermally conductive epoxy adhesives

Microsized or nanosized α‐alumina (Al₂O₃) and boron nitride (BN) were effectively treated by silanes or diisocyanate, and then filled into the epoxy to prepare thermally conductive adhesives. The effects of surface modification and particle size on the performance of thermally conductive epoxy adhesives were investigated. It was revealed that epoxy adhesives filled with nanosized particles performed higher thermal conductivity, electrical insulation, and mechanical strength than those filled with microsized ones. It was also indicated that surface modification of the particles was beneficial for improving thermal conductivity of the epoxy composites, which was due to the decrease of thermal contact resistance of the filler‐matrix through the improvement of the interface between filler and matrix by surface treatment. A synergic effect was found when epoxy adhesives were filled with combination of Al₂O₃ nanoparticles and microsized BN platelets, that is, the thermal conductivity was higher than that of any sole particles filled epoxy composites at a constant loading content. The heat conductive mechanism was proposed that conductive networks easily formed among nano‐Al₂O₃ particles and micro‐BN platelets and the thermal resistance decreased due to the contact between the nano‐Al₂O₃ and BN, which resulted in improving the thermal conductivity. POLYM. ENG. SCI., 50:1809–1819, 2010. © 2010 Society of Plastics Engineers     

Processing and shape effects on silver paste electrically conductive adhesives (ECAs)

Various amounts of silver flakes and dendrites were used as conductive fillers in an electrically conductive adhesive (ECA) resin with DPM, BCA and xylene as diluent to help uniform distribution of filler particles in the matrix. Due to the fact that the higher the temperature, the higher the shrinkage rate of the polymer resin and, consequently, the larger the connecting area in-between fillers, a better curing condition for processing silver filled ECA was found to be a relatively higher curing temperature. The mechanism of conductivity achievement in conductive adhesives was analyzed by comparing processing conditions, resistivity and microstructures. In addition, the influence of adding nano-sized silver particles on the resistivity of the conductive adhesives was also investigated and the addition of nano-sized silver particles resulted in a lower percolation threshold for ECAs.     

Solvent presence and its impact on the lap-shear strength of SDS-decorated graphene hybrid electrically conductive adhesives

The mechanical bonding strength of electrically conductive adhesives (ECAs), as well as the impact of residual solvent on the bonding strength was investigated between a copper clad FR-4 surface and conductive adhesives using Lap-shear testing. Both solvent-free and solvent-assisted formulations with various filler concentrations of silver (Ag) and sodium dodecyl sulfate (SDS)-decorated graphene (Gr(s)) in epoxy matrices were prepared and compared. It was found that the introduction of 0.75 wt% Gr(s) in solvent-free formulations increased the Lap-shear strength (LSS), while the combination of ethanol solvent and SDS in solvent-assisted formulations significantly decreased the LSS. In addition, it was found that increasing the Ag content generally lowers the LSS for both the solvent-free and solvent-assisted formulations. By examining the structure and interface of both formulations using optical microscopy, surface profilometry and SEM, we found that the solvent-assisted formulations exhibit more voids at the surface of the paste and more bubble formation throughout the material compared to the solvent-free formulations. Therefore, the significant drops of LSS in solvent-assisted Gr(s)-filled formulations may be attributed to the formation of bubbles at the micron range during the curing process.     

High performance electrically conductive adhesives from functional epoxy,micron silver flakes,micron silver spheres and acidified single wall carbon nanotube for electronic package

To develop high performance electrically conductive adhesives (ECAs), bi-modal ECAs were prepared by a matrix resin, micron silver flakes and micron silver spheres, and tri-modal ECAs were prepared by a matrix resin, micron silver flakes, micron silver spheres and acidified single wall carbon nanotube (ASWCNT). With the increase of nano silver spheres, the bulk resistivity of bi-modal ECAs decreased firstly and then increased while tri-modal ECAs' bulk resistivity firstly increased and then decreased with the increase of ASWCNT due to different electrically conductive channels were formed in them. After aged for 500 h under humid and thermal cycle of constant humidity level of 85% relative humidity at 85 °C, the contact resistance shift of bi-modal ECAs was more than 20% and that of tri-modal ECAs was less than 15% showing tri-modal ECAs had lower and more stable contact resistance. The humid and thermal surroundings had bad effect on the mechanical properties of bi- and tri-modal ECAs, after aged for 500 h, they both were reduced about 50–65%. And a bi-modal ECAs and a tri-modal ECAs were optimized and investigated in detail which can be used in electronic packaging.     

Self‐healing Ag/epoxy electrically conductive adhesive using encapsulated epoxy‐amine healing chemistry

In this study, a dual‐microcapsule epoxy‐amine self‐healing concept is used for electrically conductive adhesives (ECAs). It provides the ECA samples with the ability to recover mechanical and electrical properties automatically. Epoxy and amine microcapsules were prepared and incorporated into silver/epoxy ECAs. The healing efficiency and bulk resistivity of the undamaged, damaged, and healed specimens were measured, respectively. The optimal loading of the epoxy and amine microcapsules is 6 wt % (weight ratio 1.05), and the bulk resistivity of the healed specimens is 3.4 × 10^?3 Ω cm. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41483.     

抗静电环氧树脂胶粘剂的制备与性能研究

以导电碳黑和银粉为导电填料制备了抗静电环氧树脂(EP)胶粘剂,考察了导电填料的种类和用量对胶粘剂导电性能和力学性能的影响。研究结果表明,导电填料的种类对胶粘剂导电性能和力学性能的影响显著不同;以导电碳黑作为导电填料时,当w(导电碳黑)=5.0%时EP胶粘剂开始具备抗静电能力,当w(导电碳黑)≈7.1%时胶粘剂的体积电阻率发生突跃式下降;而以银粉作为导电填料时,当w(银粉)=0～38%时EP胶粘剂不具备抗静电能力。EP胶粘剂的拉伸强度和剪切强度随着导电碳黑用量的增加呈线性下降的趋势,而随着银粉用量的增加则呈线性上升的趋势。     

Sintering behavior and effect of silver nanoparticles on the resistivity of electrically conductive adhesives composed of silver flakes

In this paper, silver nanoparticles with size of 30–50 nm were synthesized by reducing silver nitrate with sodium borohydride and sodium citrate and using PVP as an adsorption agent in the ethanol solution. The experimental results indicate that the morphologies and sintering behaviors of both kinds of silver nanoparticles are impacted by glutaric acid and sintering temperature. The electrically conductive adhesives (ECAs) filled with micro-sized silver flakes and silver nanoparticles as hybrid fillers were fabricated and the electrical properties were investigated based on the fraction of the silver nanoparticles of the total of silver flakes and the curing temperature, etc. The incorporation of the untreated/treated silver nanoparticles into the polymer matrix with 65?wt% silver filler the resistivity increased in almost all cases, especially the high fraction and the low curing temperature. The curing temperature has influence on the resistivity of the ECAs filled with micro-sized silver flakes and the silver nanoparticles due to the sintering of the silver nanoparticles. The addition of 10% treated silver nanoparticles into the ECAs with 60?wt% silver fillers, the resistivity is slightly lower than that of the ECAs with micro-sized silver flakes. In the system of the ECAs with the high loading of silver fillers, the untreated/treated silver nanoparticles have little effect on the electrical conductivity. The results suggest that the morphology and distribution of silver fillers are the key to affect the conductivity of ECAs when nanoparticles are included in the system.     

Use of cyanoacrylate adhesives in dermal lesions: a review

Sutures have traditionally been considered the preferred choice for the mechanical closure of tissue injuries. However, suturing implies an additional trauma to the wound. The search for a quick, painless method with good aesthetic results has prompted a number of publications and studies that have evaluated the effectiveness of synthetic tissue adhesives (cyanoacrylate adhesives) and other biological sealants (fibrin glue and others) as an alternative to standard suturing. The therapeutic applications covered by the literature on cyanoacrylate-based adhesives are most varied. This literature review seeks to show the evolution over time of the methods and results obtained by scientific research on the use of biological adhesives for dermal closure, by collecting existing data on aspects relative to cyanoacrylates and their application on dermal lesions from papers published over the past 50 years. Such a review is novel in the existing literature. In recent decades, the use of cyanoacrylate-based adhesives for the closure of dermal lesions in different surgical areas has spread thanks to the positive results reported by the vast majority of the studies. New avenues for tissue adhesive production are being explored currently. The prospects for these adhesives are positively appraised, though potential disadvantages and contraindications must be borne in mind.     

ENVIRONMENTAL AGING EFFECTS ON THERMAL AND MECHANICAL PROPERTIES OF ELECTRICALLY CONDUCTIVE ADHESIVES

This article investigates environmental aging effects on thermal and mechanical properties of three model electrically conductive adhesives (ECAs). A combination of several experimental techniques including thermogravimetric analysis (TGA), water uptake measurements, dynamic mechanical analysis (DMA), and stress-strain dogbone testing has been utilized throughout this study. Samples were aged at 85°C and 100% RH for periods of up to 50 days, and some of the samples were dried at 150°C after aging. Results obtained on aged samples with and without drying suggest that the conductive adhesives may have experienced both reversible and irreversible effects during environmental aging. Both plasticization, which is reversible, and further crosslinking and thermal degradation, which are irreversible, are indicated upon exposure of ECAs to the hot/wet environment.     

Effects of the aluminum filler content on moisture diffusion into epoxy adhesives in distilled water and sea water

Epoxies are the most common of high‐performance structural adhesives, especially in automotive and aircraft manufacturing. In a variety of industrial applications, epoxy adhesives are required to have enhanced thermal conductivity. The normal method of changing this property is to add to the epoxy a filler of higher conductivity than the continuous phase. Although the improvement in the thermal properties of adhesives by the addition of metal fillers is obvious, their influence on water sorption characteristics of adhesives is not clear. It was the objective of this study to shed light on these aspects, which are lacking in the literature. The emphasis was placed on determining the moisture sorption behavior of aluminum‐powder‐filled epoxy adhesives under complete immersion in distilled water and sea water. Moisture diffusion tests show that the addition of aluminum filler into epoxy decreases the total amount of water intake at saturation in both fluids. However, there appears to be no significant effect of the aluminum filler content on the moisture diffusivity in epoxy adhesive specimens in either distilled water or seawater. It has also been determined that the adhesives adsorb a larger amount of water upon exposure to distilled water than when exposed to seawater, whereas the moisture diffusion rate in the adhesive immersed in seawater is higher than that in distilled water. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1165–1171, 2005     

示温粘接涂层用胶粘剂的研究进展

胶粘剂在示温粘接涂层的成膜性、变色性等方面起着重要作用。在简要介绍胶粘剂对示温粘接涂层作用的基础上,重点介绍了近年来国内外各类胶粘剂[包括环氧树脂(EP)、酚醛树脂(PF)、有机硅树脂、醇酸树脂(AK)、氟碳树脂和丙烯酸酯类胶粘剂等]在示温粘接涂层中的研究现状,并对其发展趋势作了展望。     

Effect of Ti3C2Tx/Ag MXene fillers on the electrical conductivity of Ag-coated Cu conductive adhesives

In this paper, we prepared ECAs (electrical conductive adhesives) with high electrical conductivity by using Ag-coated copper powder and M − II (Ti₃C₂T_x/Ag powder) as conductive filler. M-Ⅰ (Ti₃C₂T_x) and M-Ⅱ were prepared by acid etching and hydrothermal methods, respectively, and the electrochemical properties of M-Ⅱ and the effects of different contents of M-Ⅱ on the conductivity of ECAs were investigated. M − II has a unique reticular structure which helps to create conductive pathways, and its high specific surface area provides a large number of active sites for charge storage, resulting in increased electrical conductivity. The experimental results show that the best conductivity is achieved when the M-Ⅱ powder content is 1.2%, with a volume resistivity of 4.84 × 10⁻⁶ Ω m, at which time the Ag-coated Cu powder content is 69.8%. It has been shown in many studies that only when Ag-coated copper powder content is 70%–80%, the resistivity reaches about 10⁻⁶ Ω m. This work showed that adding a small amount of M − II and reducing the amount of Ag-coated copper powder could maintain the high electrical conductivity of ECAs.     

单组分室温固化环氧建筑胶粘剂的研究动向

环氧建筑胶粘剂是一类应用非常广泛的建筑结构胶。本文结合应用实际,简述了单组分室温固化环氧建筑胶包括湿气固化型建筑胶粘剂、丙烯酸改性环氧建筑胶粘剂、单组分环氧乳液胶粘剂等的研究进展,并着重介绍了以酮亚胺为固化剂的建筑胶的几个典型研究案例。