Injection molding circuit board

Newer resins include polysulfone, polyethersulfone, polyetherimide, and polyetherketone. Some of these newer materials are high temperature thermoplastic, not thermoset, resins. They are being promoted for the design of injection-molded printed circuit boards in three-dimensional shapes for functional appHcations as an alternative to standard flat printed circuit boards. Only semiadditive or fully additive processing can be used with these devices. 

Ultem PEI resins are amber and amorphous, with heat-distortion temperatures similar to polyethersulfone resins. Ultem resins exhibit high modulus and ate stiff yet ductile. Light transmission is low. In spite of the high use temperature, they are processible by injection mol ding, stmctural foam mol ding, or extmsion techniques at moderate pressures between 340 and 425°C. They are inherently flame retardant and generate Httie smoke dimensional stabiUties are excellent. Large flat parts such as circuit boards or hard disks for computers can be injection-molded to maintain critical dimensions. 

The use of thermoplastics and their selective metal plating opens a new dimension in circuit carrier design to the electronics industry 3D molded interconnect devices (3D MIDs). MIDs are injection-molded thermoplastic parts with integrated circuit traces. They provide enormous technical and economic potential and offer remarkably improved ecological behavior in comparison to conventional printed circuit boards which they wiU, however, complement, not replace. 

Processes developed for the injection molding of circuit boards include PCK Technology s mold-n-plate process uses two shots, the first being one of catalytic resins, to form paths on plastic parts that are then processed in a copper bath to form circuitry. Special grades of polysulfone, polyethersulfone, and polyarylsulfone are used for the process. In the in-mold metallization process, various conductive, resistive, capacitive, or inductive components are embedded directly into the plastic part in the tool. 

MAJOR APPLICATIONS A wide variety of injection-molded automotive parts such as housings, connectors, switches, relays, thrust washers, sphne liners, valve seats, bushings, piston rings and seals, wear rings, ball bearings, rollers, thermal insulators, etc. laminated parts such as printed circuit boards, honeycomb core, radomes, etc. 

Aromatic Polyesters Engineering thermoplastics prepared by polymerization of aromatic polyol with aromatic dicarboxylic anhydride. They are tough with somewhat low chemical resistance. Processed by injection and blow-molding, extrusion, andftiermoforming. Drying is required. Used in automotive housings and trim, electrical wire j acketing, printed circuit boards, and appliance enclosures. 

The use of high temperature thennoplastics for electronic applications is of considerable and growing interest because of the enhanced thermal and electrical properties of these materials. One such material is GE s Ultem polyetherimide which can be injection molded as well as extruded. This latter property is important for utilizations such as flexible circuits where a pliable film is required. The inherent physical properties of the polymer can be enhanced through the addition of fillers. A potential disadvantage, however, is that the nascent translucence of the polyetherimide is eliminated. Visual clarity may be desirable in certain applications such as automatic climate control systems wherein an LED must be read through a patterned circuit board. In addition, neat polymer material may be desirable because of its improved flow properties relative to filled polyetherimide. 

A review (16) and a book (17) on the chemistry and properties of poly(ether ketones) have been published. PEEK is present in the market also in reinforced grades (glass or carbon fibers) as well as in yams or in powder for coatings. Fibers are marketed by ICI imder the trade name Zyex. PEEK found application in the transport, teletronics, and aerospace sectors, with the fabrication of injection-molded engineering components and circuit boards. PEEK materials have also foimd a place in medical technologies. For this purpose, their biological and toxicological safety has been certified (14). 

Wolf, M. Injection Molding Three-Dimensional Circuit Boards. Kunststoffe, pp. 20-22, Feb. 1989. 

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