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New Materials: Thermal Interfaces, Encapsulants, Adhesives, and More
July 21, 2009 |Estimated reading time: 5 minutes
— Victrex, Huntsman, Wacker Chemie, Dymax, and other companies introduced new materials for electronics assembly, from underfills to thermal greases, glass-filled polymers, halogen-free resins, silicone rubbers, encapsulants, and more.
Potting and Encapsulation for ElectronicsSEMICOSIL UV is a room-temperature-curing silicone rubber that only crosslinks after irradiation with UV light for potting electronic components, circuit boards, and photovoltaic components. It is a one- and two-component UV-active system based on polyorganosiloxanes, characterized by a long shelf life and rapid processing. SEMICOSIL UV does not release any by-products as it cures. Curing rate can be controlled by appropriate selection of the elastomer, UV dose and process temperature. This can be summed up by the 10x10x10 rule of thumb for SEMICOSIL UV: irradiate with UV for ten seconds, then allow to cure for ten minutes, to produce a silicone sealing that withstands a ten-kilogram load on an area of 4 cm2. At room temperature, SEMICOSIL UV has short activation and curing times. It suits automotive and power electronics, sensor technology, and photovoltaics.
Plasticizer-free, transparent silicone gel WACKER SilGel 612 is an addition-curing silicone elastomer that vulcanizes at room temperature to yield a transparent, plasticizer-free gel. The gel crosslinks on the component to produce a permanently elastic silicone layer, protecting components from the environment. Its low Young's modulus suits sensitive devices, such as bonded integrated circuits (ICs). Fragile devices can be protected against damage even under severe temperature cycling. Moisture and corrosion protection suits solar cells, sensors and electronic devices in car electronics modules, high-performance rectifiers, and optoelectronic applications. The product can be applied in automated mixing and metering equipment during mass production. SilGel 612 does not require pre-treatment of glass surfaces; the silicone gel bonds by adhesion. It is transparent, does not yellow, and is highly weather- and heat-resistant. WACKER, www.wacker.com.
Chip Encapsulants DYMAX Multi-Cure 9001-E Series encapsulants cure in seconds for moisture and abrasion resistance and thermal cycle protection of electronic and microelectronic assemblies. The materials are all one part, so no mixing is required and viscosity is consistent. Various viscosities are available for different geometries. Multi-Cure 9001-E series materials have high ionic purity and are solvent- and isocyanate-free. A low modulus minimizes stress on wire bonds. Material exposed to light will cure in seconds, while any shadowed areas will cure upon heat exposure. The encapsulants contain no sharp, abrasive mineral or glass fillers. Adhesion to Polyimide, PET, flexible printed circuits, FR4 and ceramic boards is good, protecting glob top, chip-on-board (COB) applications, and ICs in flex circuits. DYMAX Corporation, www.dymax.com.
Thermally Conductive GreaseA thermally conductive grease that does not pump out, LORD TC-501 Grease replaces greases used as thermal interface materials (TIMs) between the heat spreader and the heat sink (commonly known as TIM2). TC-501 Grease, a silicone TIM, provides high thermal conductivity and low thermal resistance. Proprietary technology prevents pump-out. It suits applications in packages that cannot go through a cure profile required normally by non-grease TIMs. LORD Corporation, www.intelligentgrease.com.
CSP/BGA UnderfillHysol UF3800 is a room-temperature, fast-flowing, low-temperature-cure, reworkable CSP/BGA underfill designed for use in modern handheld communication and entertainment devices. The lack of a substrate pre-heat requirement combined with Hysol UF3800's faster flow and low-temperature quick curing enables manufacturers to reduce energy costs, eliminate capital equipment expenditure associated with heaters, and improve throughput rates. The material's chemistry offers a relatively high glass transition temperature (Tg) and stable electrical performance under temperature humidity bias (THB). It is a halogen-free material that meets the current accepted industry standard of less than 900 parts per million (ppm) chlorine (Cl) and bromine (Br). Henkel Corporation, www.henkel.com/electronics.
UV-cure Coating125-17 is a screen-printable, solvent-resistant, flexible, ultraviolet-curable coating. The blue dielectric is used as a protective insulating layer as well as a crossover layer for polymer thick-film conductive inks in printed circuit applications. This coating is compatible with substrates including polycarbonate, polyester, polyimide, glass, and ITO-sputtered surfaces. The printed void-free coating is resistant to humidity, temperature fluctuations, and solvents. This product is designed for use with a variety of CMI conductive silver and carbon inks. Applications of 125-17 include membrane switches, flex circuits, touch screen applications, and other printed circuitry. Creative Materials Inc., www.creativematerials.com.
Nano ResinA nano-toughened, high-temperature epoxy adhesive, Araldite EP1000 A/B epoxy adhesive is a two-part, thixotropic paste with a convenient 2:1 mix ratio and low viscosity that accommodates easy handling. The epoxy is supplied in dual-barrel cartridge mixing kits for waste-free application. Araldite EP1000 A/B cures at ambient temperature to 100°C. It achieves a stable maximum glass transition temperature after gelling at room temperature followed by a mild heat cure and requires no autoclave cycling. Once cured, Araldite EP1000 A/B has high lap shear strength and good peel strength. It maintains more than 90% of its shear strength after exposure to aviation fuels and hydraulic fluids and retains 25–30% of its physical properties at temperatures of up to 150°C). Huntsman Advanced Materials, www.huntsman.com.
Nickel-filled AdhesiveDuralco 122 nickel-filled adhesive and casting epoxy is formulated to provide a low-cost alternative to silver-filled electrically conductive epoxies. It suits manufacturing and repairing of flexible circuits, solder replacement, bonding semiconductors, EMI shielding, thermistors, wire tacking, heating elements, assembling, electronics, etc. This two-part epoxy is mixed by hand and cures at room temperature (75°F) in 16 to 24 hours or can be fast cured in 10 minutes at 200°F. For optimum conductivity, adhesion and strength, post cure at 250°F for 2 hours. It bonds well to glass, ceramics, plastics, metals (steel, stainless, aluminum, lead), and dissimilar materials. The epoxy is resistant to moisture, chemicals, and solvents. COTRONICS CORPORATION, www.cotronics.com.
Thermally Conductive Mounting TapeKeratherm KL 90 thermally conductive, double-sided adhesive tape provides 1.4 W/mK of thermal conductivity for heat transfer from hot components to heatsinks. Thermal impedance is 208°C-mm2/W. Keratherm KL 90 tape comprises a ceramic-filled acrylic adhesive film. A fiberglass-reinforced version, KL 91, is available for applications requiring higher levels of ruggedness, peel strength, and conformability to irregular surfaces. Both Keratherm KL 90 and KL 91 mounting tapes are silicone-free. If necessary, the tapes can be cleanly removed using a thin-edge blade. Keratherm KL 90 double-sided adhesive tape is supplied on 400-mm-wide rolls, and is also available in custom die-cut shapes. Its standard material thickness is 0.300 mm. MH&W International, www.mhw-thermal.com.
Harsh-environment PolymersVICTREX ST polymer, part of the VICTREX PEEK product family, is designed for demanding environments, specifically in applications requiring a combination of high temperature, mechanical performance, and dimensional stability. The new polymer launches with two grades: VICTREX ST STG45 polymer (an unfilled grade) and VICTREX ST ST45GL30 polymer (a glass-filled grade). Properties include purity, electrical resistance, chemical resistance, dimensional stability, and low permeability/moistures. VICTREX STG45 has good mechanical performance especially from 150° to 200°C. VICTREX ST45GL30 features a heat distortion temperature of 380°C. VICTREX ST polymer is a metal replacement option for many types of applications such as gears, seals, rings, valve plates, wire coating, disk drive carriers, connectors and test sockets. Victrex Polymer Solutions, a division of Victrex plc, www.victrex.com.