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52 The PCB Magazine • September 2016 The use of epoxy resin as a component of base materials (also referred to as laminate, cop- per-clad laminate, or "CCL") is well known, but it may be allowed to highlight the basics of FR-4 base material construction: The Manufacture of Laminate and Prepreg (Bondply) The resin (in our case epoxy) is typically a thermoset resin. Resin and curing agent(s) are premixed and dissolved in low boiling solvents (ketones, esters, alcohols) and placed in a trough through which a continuous glass fabric cloth is guided. The dissolved resin, and dispersed fillers as may be the case, coat the glass fabric which travels up a "treating tower" through different temperature zones were the resin is thermally, partially cured to form the "prepreg." The sol- vent is evaporated and the dry prepreg is then rolled up into large rolls, cut up into sheets and then "laid-up" by sandwiching it between copper sheets that have been cut from a large roll of copper foil. Several of these packages are placed into the chambers of a lamination press where the copper clad laminate is formed by fully curing the resin and bonding it to the copper in a process-specific time/temperature/ pressure profile. After the lamination process, the large CCL pieces are routed into smaller panels. The edges of the panels may be beveled for cleaner processing. Circuitized panels (in- nerlayers) may then by laid up to multilayers by alternating prepreg layers with innerlayers, topping the multilayer with a "cap foil" of cop- per. These multilayer lay-ups are separated by separation sheets and inserted into a multilayer press where the prepreg softens, conforms to the adjacent copper, bonds, and fully cures dur- ing the press cycle. After multilayer lamination, the multilayers are taken apart (broken down), their edges are cleaned, and multilayer process- ing continues (drilling, through-hole metalliza- tion, outerlayer circuitization, etc.). Material Suppliers for the Fabrication of Laminate The materials used in the manufacture of laminate come from a broad supplier base. There are less than 10 suppliers of glass fiber worldwide (source; PLUS 4/2012, pg. 809) and fewer glass weave suppliers. The production of glass fiber is very energy intensive and requires the periodic shutdown and re-cladding of fur- naces which can cause 6–9 months of produc- tion loss. The best known glass weave supplier is probably Asahi-Schwebel. Resins are supplied by Nan Ya Plastics Corp., Hexion Specialty Chemicals, Dow Chemicals, The Sanmu Group, Hitachi, Mitsubishi Gas, Huntsman, and oth- ers. Specialty resins are supplied by a number of small customizing/compounding specialty chemical suppliers. Fillers come from a large supplier base. High-performance fillers are mostly supplied by Japanese companies (e.g., spherical, surface-coated silica fillers). Copper foil suppliers include Circuit Foil Luxembourg (now part of the Doosan Group, South Korea), Oak-Mitsui (part of Mitsui Mining & Smelting), Shanghai Metal Corp., Circuit Foil Corp., USA (became Yates, now JiangXi Copper Yates Cop- per Foil Co. Ltd.). A Closer Look at the Epoxy Supply Chain One can go further upstream in the supply chain for epoxy resin and assess the availabil- ity and quality of resin building blocks such as epichlorohydrin (and its raw material allyl chloride), Bisphenol A (and its raw materials ac- etone and phenol), as well as the various curing agents. But for the purpose of this little study I am resisting the temptation to trace the materi- als back to the proverbial "fire and coal" origin. It is typical that the value-added steps of PCB fabrication and their inherent know-how reside with different companies, so that a chain of companies, forming various alliances, are in- volved in the transformation of basic material building blocks such as resins, reinforcement materials, curing agents, flame retardants, and copper to the final products such as copper-clad laminate, prepreg, dielectric film, or bondply. Exceptions to this market model are few (e.g., Nan Ya's vertically integrated FR-4 production). Thus, it is important for a resin supplier to this market to link up in some form to a formulator (i.e., compounder and customizer of dielectrics) to fully understand material requirements de- rived from processing techniques, OEM needs, end-uses, and to have access to specifications and test methods and facilities. In many cases EPOXY: SUPPLY CHAIN AND USE IN ELECTRONICS

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