Enhanced adhesion of silica for epoxy molding compounds (EMCs) by plasma polymer coatings

Silica for epoxy molding compounds (EMCs) was coated via plasma polymerization using an RF plasma (13.56 MHz) as a function of the plasma power, gas pressure, and treatment time. The monomers utilized for the plasma polymer coatings were 1,3-diaminopropane, allylamine, pyrrole, 1,2-epoxy-5-hexene, allyl mercaptan, and allyl alcohol. The EMC samples were prepared from biphenyl epoxy resin, phenol novolac, triphenyl phosphine, and plasma polymer-coated silica, and the loading of silica was controlled to 60 wt%. The EMC samples were cured at 175°C for 4 h and subjected to T_g, CTE, and water absorption measurements. The adhesion of silica to epoxy resin was evaluated by measuring the flexural strength of EMC samples and the fracture surfaces were analyzed by SEM. Plasma polymer coatings were also characterized by FT-IR and coating thickness measurements. The plasma polymer coating of silica with 1,3-diaminopropane and allylamine enhanced the flexural strength of EMC samples (167 and 165 MPa), compared with the control sample (140 MPa), and exhibited a higher T_g, a lower CTE, and lower water absorption. The enhanced properties with 1,3-diaminopropane and allylamine plasma polymer coatings can be attributed to the amine functional groups in the plasma polymer coatings.     

Adhesion of nylon-6 to triazine trithiol-treated metals during injection molding

Abstract —An examination was made of the adhesion of nylon-6 resin to treated metals such as phosphor bronze, brass plates, and electronickel platings during injection molding. No adhesion to any of these metals was noted to occur under ordinary injection molding conditions and an aqueous solution of 1,3,5-triazine-2,4,6-trithiol mononatrium (TTN) was thus used to induce adhesion. Following treatment with aqueous TTN solution under optimal conditions, nylon-6 adhered tightly to all the above metals under ordinary injection molding conditions. The TTN treatment led to the formation of surface films containing metal salts of 1,3,5-triazine-2,4,6-trithiol (TT). Conditions were made optimal with regard to time, temperature and TTN concentration. Adherent films were generally formed when bronze and brass were treated for short periods, at low temperature, and at low TTN concentration, although this was not the case with nickel plating. There was no adhesion to nickel plating even for a prolonged treatment time, high temperature, and high TTN concentration. Adherent and non-adherent films did not differ in the chemical structures of the metal salts of TT but they did differ in morphology. Good adhesion was noted in the case of TT-metal salts present at low density on the metal surface. Some films readily reacted with amino compounds under conditions similar to those generally used for the injection molding of nylon. The adhesion was concluded to be due to the formation of interfacial bonds during injection molding.     

Metal–Plastic Adhesion in Injection-Molded Hybrids

Polymer–metal hybrids are replacing steel structures in many applications. Combining metals and plastics is, however, complicated because they have very different physical and chemical characteristics. This study characterizes plastic–metal adhesion in insert-injection-molded hybrids. Diaminofunctional silane was used as a coupling agent between thermoplastic urethane and stainless steel. Before silane treatment, various surface treatments, including electrolytic polishing and different oxidation treatments, were applied to the steel inserts to understand better the bonding between silane and steel. The effects of the surface treatments and silane application on plastic–metal adhesion were studied by means of contact angle measurements, adhesion tests, and microscopic characterizations. Electrolytic polishing and oxidation of the steel inserts significantly improved the silane bonding to the steel insert, and consequently the plastic adhesion to steel.     

Study of heat of reaction between plasma-polymer-coated silica fillers and biphenyl epoxy resin

Silica fillers were coated by plasma polymer coatings of 1,3-diaminopropane, allylamine, pyrrole, 1,2-epoxy-5-hexene, allyl mercaptan and allyl alcohol using RF plasma (13.56 MHz). The coated fillers were then mixed with biphenyl epoxy, phenol novolac (curing agent) and/or triphenylphosphine (catalyst), and subjected to DSC analyses in order to elucidate the chemical reaction between functional moieties in the plasma polymer coatings and the epoxy resin. For comparison, samples were also prepared with liquid monomers, biphenyl epoxy, phenol novolac and/or triphenylphosphine. In addition, silicon wafers were coated by plasma polymerization and analyzed by FT-IR. Only the samples with 1,3-diaminopropane and allylamine plasma-polymer-coated silica fillers showed heat of reaction peaks when they were mixed with biphenyl epoxy resin, while these samples as well as the sample with pyrrole plasma-polymer-coated silica fillers exhibited heat of reaction peaks when mixed with both biphenyl epoxy and phenol novolac (curing agent). However, all plasma polymer samples exhibited heat of reaction peaks when they were mixed with biphenyl epoxy, phenol novolac and triphenylphosphine. The samples with liquid monomers showed a similar behavior, but the peaks appeared in the lower temperature range.     

Study of adhesion failure due to molding compound additives at chip surface in electronic devices

Today the microelectronics market requires devices with failure levels approaching zero. To attain this goal all production processes must be subjected to extreme quality control. Molding is one of the most critical assembly processes in power plastic packages. This is related to the complexity of phenomena which may occur at the interfaces involved in this process. This paper reports an adhesion study of epoxy-phenolic molding compounds to the most relevant surfaces encountered in power devices assembled in plastic packages such as copper oxide-hydroxide, nickel oxide-hydroxide, aluminium oxide-hydroxide, and silicon 'nitride'. The study was carried out by combining delamination (scanning acoustic microscopy) and pull strength data with the interface chemistry studied using ESCA. Different adhesion failure mechanisms were found to be operative in these systems. These mechanisms are related to either the chemical nature and thickness of the inorganic layer or the segregation of various additives such as wax, polyoxyalkylene ethers, and alkylsiloxanes, contained in the molding compound.     

Moisture absorption and wet-adhesion properties of resin transfer molded (RTM) composites containing elastomer-coated glass fibers

Transient water sorption studies were carried out at constant temperature (45 °C) to assess the hydrolytic stability and wet-adhesion properties of glass fiber/epoxy composites having different sizings. Lower effective diffusivity values correlated with improved overall mechanical performance in relation to the control (unsized) samples, and revealed the importance of changing the surface energy characteristics of glass fibers by using distinctively hydrophobic pure polymers. Admicellar polystyrene and styrene-isoprene coatings formed over the inorganic reinforcement appear to create an interface with much higher resistance to moisture attack than the organosilane/matrix interface in composites with commercial sizing. This fact was corroborated by comparing their effectiveness in property retention, which showed the mechanical property (e.g. ultimate tensile strength, stiffness and interlaminar shear strength) increased with respect to the uncoated composites in the dry state as well as after water saturation. Poor wet-adhesion properties of commercial sizings in humid conditions could perhaps be attributed to higher contents of inert material present in these coatings. Fractography analysis was consistent with the previous observations regarding catastrophic failure in composites without coating, and suggested that interfacial debonding, extensive fiber pullout and matrix crazing were the major contributors to the overall failure mechanism. Failed surfaces of both commercial and elastomer-coated composites also showed areas with fiber pullout, but in this case, matrix residues remained on the fiber surfaces, yielding a much rougher appearance. Good fiber-matrix adhesion, particularly in admicellar-coated composites, was also revealed by the presence of hackles and more tortuous failure paths.     

Dimple-type failures in a polymer/roughened metal system

Roughening of metal surfaces frequently enhances the adhesion strength of polymers to metals by mechanical interlocking. When a failure occurs in a polymer/roughened metal system, the failure is prone to be cohesive within the polymer. In a previous work, an adhesion study on a polymer (epoxy molding compound, EMC)/roughened metal (brown-oxide-coated copper-based leadframe) system was carried out, and the correlation between the failure path and adhesion strength was investigated. In the present work, an attempt to explain why such failure paths occurred was made under the assumption that microvoids were formed in the EMC, as well as near the roots of the CuO needles during the compression-molding process. A simple adhesion model developed from the theory of fiber reinforcement of composite materials was introduced to explain the adhesion behavior and thereby explain the formation of failure paths. It is believed that the adhesion model developed in the present work can be used to explain the adhesion behavior of other similar polymer/roughened metal systems.     

Plasma polymerization coating of silica fillers for Epoxy Molding Compounds (EMCs)

Silica fillers for Epoxy Molding Compounds (EMCs) were modified via plasma polymerization coating of acrylonitile, acrylic acid and dimethyl phosphite with RF plasma (13.56 MHz). The resulting samples were characterized by DSC, FT-IR and contact angle measurements. EMC samples were prepared from silica fillers, biphenyl epoxy resin, phenol novolac and triphenyl phosphine, and cured at 175°C for 4 h. Flexural strength of the EMC samples was evaluated in a 3-point bending mode with an Instron 5567 at a crosshead speed of 1 mm/min both at RT and 250°C, and failure surfaces were analyzed by SEM. Some samples were exposed to 121°C, 2 atm pressure and 100% RH for 12, 24 and 32 h, and then to 250°C for 10 min prior to testing at RT. Plasma polymer coating of silica with acrylonitrile greatly improved the flexural strength of EMC at RT as well as at 250°C, followed by acrylic acid and dimethyl phosphite. Exposing EMC samples to 121 °C, 2 atm pressure and 100% RH for 32 h decreased the flexural strength by 13% when the silica was coated with acrylonitrile plasma polymer, compared to the 21% decrease in the control sample. Plasma polymer coating of silica also increased the Tg of the EMC, and lowered water absorption and CTE in the rubbery region. Therefore, enhanced properties by plasma polymer coating of silica with acrylonitrile or acrylic acid can be attributed to nitrile or carboxylic acid groups, as confirmed by FT-IR, which can react with epoxy groups in the base resin, as evidenced by DSC analysis.