New PCB Fabrication Materials
April 20, 2010 |Estimated reading time: 7 minutes
-- These new materials include eco-friendly FR polymers, ultra-fine PCB substrate yarns, thermally enhanced substrates, halogen-free LCPs, as well as flex circuit materials.
PCB Substrate Yarns
Ultra-fine yarns for use in PCB substrates are designed to meet miniaturization and increased functionality requirements, enabling thinner laminates for higher layer counts and greater circuit density. Glass fabric reinforcement must become even thinner and this requires finer glass yarns. The small number of fine-diameter filaments comprising the yarn make it thin. The C1200 yarn, which is used to produce fabric style 1037, consists of 100 filaments of 4.5-µm diameter. BC 1500 yarn, used to produce fabric style 1027, consists of 100 filaments of 4-µm diameter. BC 3000 yarn, currently under development, will contain only 50 filaments of 4-µm diameter. Used as a reinforcement and dielectric, the ultra-fine yarn is woven into fabric and then laminated with epoxy resin and copper foil to produce copper-clad laminate (CCL). The yarn’s E-Glass composition enables good electrical insulation and provides thermo-mechanical stability to the PCBs. Reinforcement with glass fiber fabrics reportedly results in excellent dimensional stability, reducing warpage. Ultra-fine yarn suits rigid-flex PCBs. The fine diameter of ultra-fine yarns is conducive to very thin circuits that may involve some degree of flexing or bending. Another emerging market for ultra-fine yarn is mobile communications base stations that require very high layer count boards and a high degree of functionality in a given space. AGY, www.agy.com
Thermally Conductive PCB Substrate
The Tlam SS LLD is a versatile, thermally-enhanced PCB substrate system designed for heat dissipation in bright and ultra-bright LED module applications. The thermally conductive PCB substrate provides 8-10 times the heat dissipation as compared to conventional FR4-based PCBs; a key ability in keeping components cool. A copper circuit layer and aluminum or copper base plate are bonded together with an LLD dielectric, which is essential to the high-performance of the PCB substrate. The dielectric can fit, and is processed through, standard FR4 print-and-etch operations without various parameter modifications. These dielectrics provide electrical isolation, thermal transfer, and an adhesion layer for the substrate. The enhanced Tlam SS LLD substrate improves thermal transference from the heat source to the heat sink through PCBs, reducing the thermal stress placed on the PCB. The Tlam SS LLD boards are processed through standard pick-and-place surface mount technology (SMT) and manual wire bond operations. Standard constructions are made with one or two ounce copper and 0.040" (1 mm) or 0.059" (1.5 mm) thick aluminum, grade 5052; 0.040" (1 mm) or 0.062" (1.6 mm) thick aluminum, grade 6061; with a copper base available. Laird Technologies, Inc., http://www.lairdtech.com
High-temperature, Halogen-free LCP
The Vectra G Series is cost-competitive halogen-free liquid crystal polymer (LCP) grades with processing characteristics that avoid issues commonly encountered by electrical and electronic manufacturers that use challenging flame-retardant, high-temperature nylons to mold components. Vectra G131 and G331 are glass- and mineral-filled LCPs designed to meet demanding lead-free soldering and halogen-free requirements and avoid corrosion and maintenance issues. The Vectra G Series is inherently flame resistant, UL94 V-0, and halogen-free without the need of flame-retardant additives. The 35% glass-filled Vectra G131 and 35% mineral- and glass-filled Vectra G331 from Ticona are potential drop-in solutions for small FR, HT nylon parts. In addition, both Vectra G grades offer E/E component manufacturers the opportunity to achieve excellent dimensional stability in thin-wall parts, even at higher temperatures — more than 260°C. They are designed to outperform traditional FR, high temperature (HT) polyamides (nylons) and thermoplastic polyesters (PBT) that require lead-free soldering resistance. The series have a faster molding cycle that FR, HT nylons, with no flash and mold deposit. They are lead-free reflow capable and have no moisture-related blister issues vs. FR, HT nylons. Tool life is extended due to non-corrosive properties in water-heated molds. The materials are 25% regrind (UL listing pending). Ticona, the engineering polymers business of Celanese Corporation, www.ticona.com and www.celanese.com
Non-brominated, Non-chlorinated Flame Retardant PC Film
The Lexan polycarbonate (PC) film technology Lexan EFR delivers non-brominated, non-chlorinated flame retardance (FR) at thinner gauges than flame-retardant polypropylene (FRPP). It enables electrical/electronics (E/E) OEMs to create flatter, lighter-weight notebook computers and other electronic devices while significantly reducing material costs, giving them a competitive advantage. The new Lexan EFR film is a top-choice environmental solution that increases the ability of global E/E manufacturers to go beyond current environmental directives by voluntarily eliminating halogenated additives in their products. Lexan EFR polycarbonate-based film offers flame retardance without the use of brominated or chlorinated additives thus meeting the requirements of the European Union’s Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE 2006) directives. These new materials have a full listing in the Underwriters Laboratory (UL) yellow card system. According to UL 94, Lexan EFR film, in clear and opaque versions, delivers V-0 performance above 380 microns; VTM-0 flame resistance performance down to 125 microns for translucent and 100 microns for opaque materials; and complies with TCO-99 eco label requirements. Compared to FRPP, Lexan EFR film reduces shrinkage by a factor of three, provides significantly higher puncture resistance and tensile strength. These properties make it feasible to use very thin gauges of Lexan EFR film to replace thicker FRPP film without sacrificing performance. Not only do thinner gauges help designers create slimmer and lighter-weight consumer electronics, but down-gauging also lowers total costs by reducing the amount of material required. The new film also provides low moisture absorption, high thermal performance (glass transition temperature of 170ºC) and excellent dielectric strength. Target applications for this material include insulation for printed circuits, PCB, disk drive, keyboard, inverters and adaptors, die-cut spacers, labels and overlays. Electromagnetic interference/radio frequency interference (EMI/RFI) shielding is another important benefit provided by Lexan EFR film. Lexan EFR film can be fabricated using thermoforming, embossing, clean-edge die cutting, scoring and bending. The product is available globally in matte/polish and velvet/matte finishes and various gauges between 100 and 762 microns. SABIC Innovative Plastics is a wholly owned subsidiary of Saudi Basic Industries Corporation (SABIC), www.sabic-ip.com
Teflon/Kapton Flexible Circuit Materials
A high-performance laminate for PCBs, DuPont Pyralux TK flexible circuit material is a CCL and bonding film system formulated with DuPont Teflon fluoropolymer film and Kapton polyimide film for high-speed digital and high-frequency flexible circuit applications. DuPont Pyralux TK delivers a low dielectric constant (DK), low loss tangent, low moisture tolerance, and tight thickness tolerance; there is no glass in the construction of Pyralux TK. With a dielectric constant (DK) of 2.3 to 2.7, and loss dissipation factor (DF) of 0.002 or 0.003 depending on the film construction, Pyralux TK suits high-speed flex applications, including microstrip and stripline controlled impedance constructions. The clad dielectric is a proprietary layered composite of Teflon and Kapton films, available in a variety of copper foil weights. Standard foils are 18 and 35-µm rolled annealed (RA) copper. Pyralux TK bonding film is also a layered dielectric, made with Teflon and Kapton films. The bonding film contains a Teflon film with a lower lamination temperature than the clad. The Teflon in the bonding film is also available separately as a sheet adhesive. Thin (2 to 4 mil) DuPont Pyrlaux TK is available in laminate thicknesses of 50, 75 and 100 µm. Bondply thicknesses are available in 75 or 100 µm. DuPont also plans to offer a Pyralux TK sheet adhesive in 12, 25, and 50 µm. DuPont Circuit & Packaging Materials (CPM), http://www.DuPont.com
Direct Write Lithography System for High-volume PCB Production
The new direct-write digital imaging technology for PCB production, MLI-2027 direct-write lithography system, uses standard “Non-LDI” resists. Sanmina-SCI Corporation has accepted the first production tool after completing beta testing, validation, and qualification of the Maskless MLI-2027 equipment at their San Jose, CA facility. Based on its patented Gray Level Imaging (GLI) technology, the MLI-2027 offers high printing speed on conventional dry film resists with real-time distortion correction. Maskless Lithography, www.maskless.com
Silver Conductive Inks
These silver conductive inks are formulated for use in printed electronics, to meet the need for low-cost processing in touchscreens and OLEDs. The new screen printable inks include: DuPont 7723, a low temperature firing silver ink suitable for printing on glass, and DuPont 9169, a low temperature curing Ag ink designed for flexible substrates. DuPont Microcircuit Materials, http://mcm.dupont.com.
Eco Brominated Fire Retardant
A recyclable, eco-friendly, brominated fire safety product, GreenArmor will be marketed under the “Earthwise Fire Safety and Polymers” brand name for commercial use in late 2010. GreenArmor will be an eco-friendly solution compared to many flame retardants currently on the market, while maintaining the premium performance product attributes. GreenArmor is non-bioaccumulative and recyclable, organic-based rather than mineral-based. It is a polymer, which means the chemical is too large to be absorbed by the body or animal life. GreenArmor exists in a pelletized form rather than in powder form. The product’s stable nature enables efficient recycling of the plastics it is used in. Albemarle, http://earthwiseinside.com/
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