High temperature capability resins

Epoxy-phenolic adhesives are made by blending epoxy resins with phenolic resins to improve the high-temperature capabilities of the standard epoxy resins. Developed in the early 1950s, they were the first high-temperature epoxy adhesives to become commercially available.2,3... 

Ordered polymer films made from poly benzthiazole (PBZT) and poly benzoxazole (PBO) can be used as substrates for multilayer printed circuit boards and advanced interconnects to fill the current need for high speed, high density packaging. Foster-Miller, Inc. has made thin substrates (0.002 in.) using biaxially oriented liquid crystal polymer films processed from nematic solutions. PBZT films were processed and laminated to make a substrate with dielectric constant of 2.8 at 1 MHz, and a controllable CTE of 3 to 7 ppm/°C. The films were evaluated for use in multilayer boards (MLBs) which require thin interconnect substrates with uniform controllable coefficient of thermal expansion (CTE), excellent dielectric properties, low moisture absorption, high temperature capability, and simple reliable processing methods. We found that ordered polymer films surpass the limitations of fiber reinforced resins and meet the requirements of future chip-to-chip interconnection. 

The SiOC matrix was prepared using the Blackglas 493-type preceramic resin. The Nextel 312 fabric was an AF-10 5H satin weave (600 denier tows, 275 g/m areal weight). Nextel 312 is the lowest cost ceramic fiber with acceptable strength and high temperature capability that is commercially available. The boron nitride interface layer on the Nextel 312 fibers was produced by the previously described high temperature nitridation process. 

Polyethylene glycol (200) dibenzoate n. C6H5C0(0CH2CH2)40C0-C6H5. a plasticizer compatible with cellulose acetate butyrate, ethyl cellulose, polymethyl methacrylate, polystyrene, and vinyl resins. Its major application is with phenol-formaldehyde resins in laminating applications, to improve flexibility without loss of electrical properties and high-temperature capability. 

Epoxy. The most widely used matrices for advanced composites are the epoxy resins even though they are more costly and do not have the high-temperature capability of the bismaleimides or polyimide the advantages listed in Table 2.32 show why they are widely used. 

The commercially important properties of Et>-Nb copolymers include low density, high transparency and low color, high moisture barrier and low moisture absorption, low optical distortion, excellent feature replication, resistance to polar solvents, high purity, shatter resistance, good biocompatibiUty, extremely low dielectric loss, high temperature capability, and compatibility with polyethylenes. The resins also have the low shrinkage and warpage typical of amorphous polymers. 

For example the DuPont ThermX polyester tolerates high temperatures and is based on poly(cyclohexylene-dimethylene terephthlate) chemistry. It has the chemical resistance, dimensional stability and processability of such polyesters as PET and PBT but with a melting point of 285 °C compared with PET (255 °C) and PBT (225 °C). DuPont claims that ThermX complements its other very high thermally capable Zenite TCP and Zytel HTN (high temperature Nylon) resins in applications which call for higher thermal capabilities than those of PBT, PET and PA66. ThermX,... 

A comparison of the high temperature capability of the four principal thermosetting resins is given in Figure 4.14. 

Time, temperature and load are important in assessing high temperature capability of a resin. For structural applications, phenolics have clear... 

PEEK and epoxy have similar properties in flexural fatigue and it is from a consideration of other properties such as high temperature capability, processability or cost that specific advantages might accrue to one or other resin system. 

Sihcon carbide fibers exhibit high temperature stabiUty and, therefore, find use as reinforcements in certain metal matrix composites (24). SiUcon fibers have also been considered for use with high temperature polymeric matrices, such as phenoHc resins, capable of operating at temperatures up to 300°C. Sihcon carbide fibers can be made in a number of ways, for example, by vapor deposition on carbon fibers. The fibers manufactured in this way have large diameters (up to 150 P-m), and relatively high Young s modulus and tensile strength, typically as much as 430 GPa (6.2 x 10 psi) and 3.5 GPa (507,500 psi), respectively (24,34) (see Refractory fibers). 

A substantial effort in our laboratory has been directed toward the synthesis and characterization of acetylene-terminated (AT) matrix resins. The most significant feature and driving force for the effort is that the thermal induced addition reaction provides a moisture Insensitive cured product. This technology offers a wide variety of thermoset resins for various high temperature applications. Backbone structural design for use temperature capabilities, processing characteristics and mechanical performance has demonstrated the versatility of the AT type systems. 

Electrical Properties. Polysulfones offer excellent electrical insulative capabilities and other electrical properties as can be seen from the data in Table 7. The resins exhibit low dielectric constants and dissipation factors even in the GHz (microwave) frequency range. This performance is retained over a wide temperature range and has permitted applications such as printed wiring board substrates, electronic connectors, lighting sockets, business machine components, and automotive fuse housings, to name a few. The desirable electrical properties along with the inherent flame retardancy of polysulfones make these polymers prime candidates in many high temperature electrical and electronic applications. 

Epoxy Coreactants. One of the most successful epoxy coreactant systems developed thus far is an epoxy-phenolic alloy. The excellent thermal stability of the phenolic resins is coupled with the valuable adhesion properties of epoxies to provide an adhesive capable of 371°C short-term operation and continuous use at 175°C. The heat resistance and thermal-aging properties of an epoxy phenolic adhesive are compared with those of other high-temperature adhesives in Fig. 15.5. Epoxy-phenolic adhesives are generally preferred over other high-temperature adhesives, such as the polyimides and polybenzimidazoles, because of their lower cost and ease of processing. 

---