Dispersed acrylate rubber-modified epoxy resins for electronic encapsulation

A process was developed to incorporate stable dispersed acrylate rubber particles in an epoxy resin matrix which greatly reduces the stress of cured epoxy resins for electronic encapsulation application. The effect of the alkyl group of the acrylate monomer on the phase separation of resultant elastomers from epoxy resin was investigated. The dispersed acrylate rubbers effectively reduce the stress of cured epoxy resins by reducing the flexural modulus, while the glass transition temperature (T_g) was hardly depressed. Electronic devices encapsulated with the dispersed acrylate rubber-modified epoxy molding compounds have exhibited excellent resistance to the thermal shock cycling test and resulted in an extended device use life.     

Characterization of reworkable high-temperature adhesives for MCM-D application

The need to have a high-temperature adhesive that can withstand temperatures in excess of 350°C for MCM-D silicon substrate process application, yet which can be reworkable at slightly high temperature ∼ 400°C for the removal from the glass pallet, is important. A novel, reworkable, high-temperature adhesive based on polyimide–amide–epoxy (PIAE) copolymer was developed and investigated using modulated differential scanning calorimetry (MDSC), thermal gravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR) and solid-probe pyrolysis mass spectroscopy (MS). Compared with commercial polyimide–amide (PIA) adhesives, FTIR spectra reveal that the thermally degradative ester groups contribute to the reworkability of the PIAE adhesive at a specific temperature (400°C), yet they remain thermally stable at a lower working temperature (350°C). FTIR spectrum comparison of the residuals of PIAE and PIA are similar after exposure to 400°C. MS spectra of outgassed products identify that the components of radical fragmentation from PIAE are due to polymeric chain degradation at 400°C, while only volatile trace water and N-methyl pyrolidone (NMP) are evolved from the commercial PIA adhesive. TGA results suggest a complementary explanation for the variation of total ion current (TIC) curves on these two adhesives. MDSC curves further verify that the reworkable PIAE adhesive is a copolymer. Furthermore, a reasonable thermal degradation mechanism is presented on the adhesive reworkability. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 997–1005, 1999     

导热环氧灌封胶的研制

以环氧AG-80为主体树脂,端羧基液体丁腈橡胶与1,6-已二醇二缩水甘油醚的反应产物为活性增韧稀释剂,纳米AlN为导热填料,缩胺-105为固化剂制备导热灌封胶。实验结果表明,每100份环氧树脂中活性增韧稀释剂为20份时,灌封胶的力学性能、耐热性能良好;纳米AlN的质量分数为12％,灌封胶的热导率达到0．85W／m·k,可满足使用要求。     

导热型环氧复合材料的研究进展

介绍了导热型环氧复合材料导热性能和导热机理。并综述各类导热环氧复合材料的研究进展,在此基础上讨论提高复合材料导热性能的途径。     

Physical study of room‐temperature‐cured epoxy/thermally reduced graphene oxides with various contents of oxygen‐containing groups

In this study, the effects of different oxygen‐containing group contents in thermally reduced graphene oxides (TRGs) for enhancing the physical properties of epoxy nancomposites was examined. The epoxy/TRG nanocomposites (ETNs) were prepared by a room temperature curing method in the presence of TRGs containing different oxygen‐containing groups and were then characterized by Fourier transform infrared spectroscopy. TRG contents with higher oxygen‐containing group contents (ca 33%) were found to show better dispersion capability in the epoxy matrix than TRGs with lower oxygen‐containing group contents (ca 11%) based on morphological observations by transmission electron microscopy. The better dispersion capability of TRGs with higher oxygen‐containing group contents in ETN membranes was found to lead to significantly enhanced mechanical strength, thermal stability and thermal conductivity based on measurements of dynamic mechanical analysis, tensile tests, thermogravimetric analysis and by the transient plane source technique. © 2014 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry     

Study on synthesis of polyurethane‐epoxy composite emulsion

The stable polyurethane‐epoxy composite emulsion with the epoxy‐amine oligomer (DEA‐EP) and the epoxy resin oligomer has been prepared by step‐growth polymerization and controlled crosslinking technique. The emulsion forming transparent films can be cured at room temperature with trimethylolpropane tris (1‐ethyleneimine) propionate (TMPTA‐AZ). The DEA‐EP structure and its reaction with urethane prepolymers were proved by Fourier transform infrared spectra (FTIR). The studies on particle size, the particle size distribution, viscosity, and the films' transmittance (Tr) indicated that both trimethylol propane (TMP) and DEA‐EP contributed to improving the resin blends' compatibility and reducing the viscosity. The epoxy resin content can increase up to 20.0 wt % (based on the total content of the polyurethane and epoxy resin) and the emulsion was still stable. The data from the tensile test experiments showed that with the epoxy content increasing, the tensile strength (σ_b) and Young's modulus were proportionately raised, but the elongation at break (ε_b) decreased. Tensile tests also revealed that introducing TMPTA‐AZ as an outside‐crosslinker can increase the tensile strength. By adding 0.3 wt % of TMPTA‐AZ, the ε_b reduced from 429% to 371% and the σ_b increased from 4.4 to 13.73 MPa; by adding 1.8 wt % of TMPTA‐AZ, ε_b of the film was 67% of ε_b of the film with 0.3 wt % of TMPTA‐AZ, but its σ_b was 24.77 MPa and 180% of σ_b of the film with 0.3 wt % of TMPTA‐AZ. The cured films possessed excellent water and toluene resistance: water uptake (48 h, 3.1%; degree of curing: 70%), toluene uptake (210 h, 8%. degree of curing: 70%). Better properties of the composite emulsion will confer it as a potential application in low volatile industrial coatings. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Clay‐reinforced epoxy nanocomposites

Epoxy/clay nanocomposites were prepared using a conventional diglycidyl ether of bisphenol A (DGEBA) epoxy, cured with diethyltoluene diamine (DETDA). The nanocomposites were characterized by dynamic mechanical analysis. A modest increase in glass transition temperature and significant increase in storage modulus were achieved as a result of incorporation of clay. The formation of nanocomposite was confirmed by wide‐angle X‐ray analysis. The higher impact strength of the nanocomposite compared the DGEBA matrix was explained in terms of with the morphology observed by SEM. © 2003 Society of Chemical Industry     

Mechanical properties and morphology of epoxidized soyabean‐oil‐modified epoxy resin

Epoxidized soyabean oil (ESO) has been used to toughen epoxy resin cured with an ambient temperature hardener. The ESO was prepolymerized before blending with epoxy resin to obtain modified networks having various concentrations of ESO. The modified networks were also made by blending the ESO with epoxy resin by a one‐stage process. All the modified networks were characterized for their thermal, flexural and impact properties, and compared to the parent epoxy network. The optimum properties were obtained at 20 parts per hundred grams of resin (phr) of ESO. The impact behaviour is explained in terms of morphology observed by scanning electron microscopy. © 2001 Society of Chemical Industry     

Rheology Study of Wafer Level Underfill

Summary: As a special epoxy resin material used in the electronics packaging, wafer level underfill (WLU) is studied using a chemorheology approach to provide a fundamental understanding of its reaction dependent rheology behaviors. In this work, the relationship between the molecular weight ( ) and the viscosity of the epoxy resins at fixed temperatures has been established. Subsequently an Arrhenius‐Erying equation was used to fit the relationship between viscosity and temperature for given molecular weight epoxies. By combining the two relationships, the viscosity could be modeled as a function of temperature and molecular weight. To obtain the viscosity change of the WLU during the reflow process, the molecular weight change of the underfill was calculated from the degree of curing through the kinetics modeling. A semi‐empirical model was developed to predict the viscosity of the underfill as a function of time and temperature during the curing process. Modeled predictions were compared with experimental data under isothermal and ramping temperatures during curing experiments. The model showed good agreement with the experiments in the early stage of curing reaction. The critical viscosity of the underfill for solder wetting was obtained by wetting experiments, which can be used as the criteria to determine the flowability of the wafer level underfill.

Data fitting of the viscosity model at isothermal condition.     

Toughening of epoxy resin using acrylate‐based liquid rubbers

Carboxyl‐terminated poly(2‐ethylhexyl acrylate) (CTPEHA) liquid rubbers of different molecular weights and functionalities (LR‐1 to LR‐6) were synthesized by bulk and solution polymerization techniques. The liquid rubbers were characterized by nonaqueous titration, vapor pressure osmometry, and gel permeation chromatography. The CTPEHA oligomers were prereacted with the epoxy resin, and the modified epoxy networks were made by curing with an ambient‐temperature curing agent. The impact properties of the modified epoxy networks were evaluated, and the effects of molecular weight, functionality of the liquid rubber, and ductility of the matrix on the impact strength of the modified networks were investigated. The morphology of the toughening behavior was analyzed using a scanning electron microscope. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 716–723, 2000     

Development and electrical conductivity behavior of copper‐powder‐filled‐epoxy graded composites

This article reports the development and direct‐current (dc) conductivity behavior of copper‐powder‐filled‐epoxy graded composite. Copper‐powder‐filled‐epoxy composites with 10 wt % copper powder and epoxy resin were developed. dc conductivity measurements were performed on the graded composites with an electrometer in the temperature range of 28–146°C. The dc conductivity decreased with an increase in the distance in the direction of the centrifugal force, and this showed the formation of a graded structure. The dc conductivity increased as the copper powder content increased. Two‐phase conduction occurred in all the copper‐filled‐epoxy graded samples. The activation energy calculated with an Arrhenius equation for one sample was 0.88 eV, and this was mainly due to conduction electronic. Another sample had an activation energy of 1.33 eV. Three samples exhibited ionic conduction. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of silane oligomers containing vinyl and epoxy group for improving the adhesion of addition-cure silicone encapsulant

Two types of silane oligomers containing vinyl and epoxy group (PTGM and PTGE) as adhesion promoters were synthesized by the reaction of trimethylolpropane monoallyl ether with 3-glycidoxypropylmethyldimethoxysilane and 3-glycidoxypropylmethyldiethoxysilane, respectively. Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy, and gel permeation chromatography were used to characterize their chemical structures. The effect of adhesion promoters on properties of addition-cure silicone encapsulant (ASE) with lots of alumina (Al₂O₃) particles as thermally conductive fillers was investigated. The results showed that PTGM and PTGE could significantly improve both the adhesive strength and mechanical properties of ASE. The viscosity of ASE with no more than 3.0 phr PTGM and PTGE was below 5000 mPa s so that they were suitable for encapsulating process. Observation using scanning electron microscopy revealed that PTGM and PTGE could improve the dispersion of Al₂O₃ particles in silicone rubber matrix and enhance the bond between the particles and the matrix.     

Study of dynamically cured PP/MAH‐g‐PP/talc/epoxy composites

In the present study, an epoxy resin was dynamically cured in a polypropylene (PP)/maleic anhydride–grafted PP (MAH‐g‐PP)/talc matrix to prepare dynamically cured PP/MAH‐g‐PP/talc/epoxy composites. An increase in the torque at equilibrium showed that epoxy resin in the PP/MAH‐g‐PP/talc composites had been cured by 2‐ethylene‐4‐methane‐imidazole. Scanning electron microscopy analysis showed that MAH‐g‐PP and an epoxy resin had effectively increased the interaction adhesion between PP and the talc in the PP/talc composites. Dynamic curing of the epoxy resin further increased the interaction adhesion. The dynamically cured PP/MAH‐g‐PP/talc/epoxy composites had higher crystallization peaks than did the PP/talc composites. Thermogravimetric analysis showed that the addition of MAH‐g‐PP and the epoxy resin into the PP/talc composites caused an obvious improvement in the thermal stability. The dynamically cured PP/MAH‐g‐PP/talc/epoxy composites had the best thermal stability of all the PP/talc composites. The PP/MAH‐g‐PP/talc/epoxy composites had better mechanical properties than did the PP/MAH‐g‐PP/talc composites, and the dynamically cured PP/MAH‐g‐PP/talc/epoxy composites had the best mechanical properties of all the PP/talc composites, which can be attributed to the better interaction adhesion between the PP and the talc. The suitable content of epoxy resin in the composites was about 5 wt %. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

E‐beam‐cured layered‐silicate and spherical silica epoxy nanocomposites

This research demonstrates that an epoxy nanocomposite can be made through electron beam (e‐beam) curing. The nanofillers can be two‐dimensional (layered‐silicate) and zero‐dimensional (spherical silica). Both the spherical silica epoxy nanocomposite and the layered‐silicate epoxy nanocomposite can be cured to a high degree of curing. The transmission electron microscopy (TEM) and small‐angle X‐ray scattering of the e‐beam‐cured layered‐silicate epoxy nanocomposites demonstrate the intercalated nanostructure or combination of exfoliated and intercalated nanostructure. The TEM images show that the spherical silica epoxy nanocomposite has the morphology of homogeneous dispersion of aggregates of silica nanoparticles. The aggregate size is ～ 100 nm. The dynamic mechanical analysis shows that the storage modulus of the spherical silica nanocomposite has been improved, and the glass transition temperature can be very high (～ 175°C). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

High‐performance biobased epoxy derived from rosin

Great achievements have been made in the research of biobased thermoplastic polymers, but the progress concerning thermosetting resins has been minor. In particular, research on high‐performance thermosetting polymers from renewable feedstock has not been reported elsewhere. A novel biobased epoxy was synthesized from a rosin acid. Its chemical structure was confirmed using ¹H NMR, ¹³C NMR and Fourier transform infrared spectroscopy. The results indicated that the rosin‐based epoxy possessed high glass transition temperature (T_g = 153.8 °C), high storage modulus at room temperature (G′ = 2.4 GPa) and good thermal stability. A rosin‐based epoxy with excellent properties was achieved. The results suggest it is possible to develop high‐performance thermosetting resins from renewable resources. Copyright © 2010 Society of Chemical Industry     

Fracture properties of epoxy/poly(styrene‐co‐allylalcohol) blends

The epoxy/polystyrene system is characterized by a poor adhesion between the constituent phases, which determines its mechanical properties. The adhesion can be improved via blends based on epoxy resin and random copolymers, poly(styrene‐co‐allylalcohol) (PS‐co‐PA). In this work, the influence of PS‐co‐PA content and the good adhesion between the phases on the tensile properties and the fracture toughness achieved through instrumented Charpy tests have been investigated. The tensile strength and the deformation at break showed an increase in the PS‐co‐PA content while the Young's modulus remained the same. The tensile fracture surfaces revealed that the improvement of these magnitudes was mainly due to a crack deflection mechanism. Also, the fracture toughness of the blends was superior to that of the pure epoxy resin. The main operating toughening mechanism was crack deflection. The fractographic analysis showed that ～ 80% of the particles were broken, and the crack tended to divert from its original path through the broken PS‐co‐PA particles. The remaining particles were detached from the epoxy resin, and the holes left suffered plastic deformation. Analytical models were used to predict successfully the toughness due to these mechanisms. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Mechanically robust,electrically and thermally conductive graphene-based epoxy adhesives

This study develops a facile approach to fabricate adhesives consists of epoxy and cost-effective graphene platelets (GnPs). Morphology, mechanical properties, electrical and thermal conductivity, and adhesive toughness of epoxy/GnP nanocomposite were investigated. Significant improvements in mechanical properties of epoxy/GnP nanocomposites were achieved at low GnP loading of merely 0.5?vol%; for example, Young’s modulus, fracture toughness (K_1C) and energy release rate (G_1C) increased by 71%, 133% and 190%, respectively compared to neat epoxy. Percolation threshold of electrical conductivity is recorded at 0.58?vol% and thermal conductivity of 2.13?W m^?1 K^?1 at 6?vol% showing 4 folds enhancements. The lap shear strength of epoxy/GnP nanocomposite adhesive improved from 10.7?MPa for neat epoxy to 13.57?MPa at 0.375?vol% GnPs. The concluded results are superior to other composites or adhesives at similar fractions of fillers such as single-walled carbon nanotubes, multi-walled carbon nanotubes or graphene oxide. The study promises that GnPs are ideal candidate to achieve multifunctional epoxy adhesives.     

High‐performance liquid chromatography‐mass spectrometry of epoxy resins

The application of liquid chromatography coupled to mass spectrometry (LC‐MS) for the analysis of epoxy resins is shown in two examples. Electro spray (ESI) and atmospheric pressure chemical ionization (APCI) are compared with respect to the ionization of diglycidylether of bisphenol A‐based (DGEBA) epoxy resins. By‐products in a typical modified solid DGEBA‐based epoxy resin and in a new weatherable crosslinker for powder coating applications are characterized and discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 913–925, 1999     

Controlled degradation of epoxy networks: analysis of crosslink density and glass transition temperature changes in thermally reworkable thermosets

The characteristics of networks formed in cured ‘reworkable’ epoxy thermosets capable of controlled thermal degradation were studied. Dynamic mechanical thermal analysis, swelling measurements, and glass transition temperature measurements were used to obtain information regarding the time and temperature dependence of the crosslink densities of these materials. By applying isothermal conditions, networks containing up to 36 mol% non-degradable components could be completely degraded, i.e. progress from a network of infinite molecular weight to a finite one with zero crosslink density. Percolation theory was used to facilitate the interpretation of these results. The degradation behavior of the reworkable thermosets were well-described by gel degradation theory, i.e. the reverse of the gelation process, and the experimental results were in good agreement with calculated values obtained by replacing the extent of reaction, p, in Macosko and Miller's branching theory with the extent of degradation, 1−p.     

Acrylate‐based liquid rubber as impact modifier for epoxy resin

Carboxyl‐terminated poly(2‐ethyl hexyl acrylate) (CTPEHA) having various molecular weights were synthesized by bulk polymerization in the form of liquid rubber. The liquid rubbers (LR‐1 to LR‐4) were characterized by ¹³C‐NMR spectroscopic analysis, nonaqueous titration, and vapor‐pressure osmometry (VPO). The liquid rubber having the lowest molecular weight (M?_n = 3600) was prereacted with the epoxy resin and the modified epoxy networks were made by curing with an ambient temperature curing agent. The modified epoxy networks containing different concentrations of CTPEHA were evaluated with respect to their thermal and impact properties. The optimum properties were obtained at about 10–15 phr of CTPEHA concentration (phr stands for parts per hundred parts of epoxy resin). Fracture surface analysis by scanning electron microscopy (SEM) indicated the presence of a two‐phase microstructure. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1792–1801, 2001