Reading time ( words)
Recently, I reviewed the new 7th Edition of the Printed Circuits Handbook, which for the first time, includes a section on “Managing the Printed Circuit Supply Chain” (Part 2, Chapters 3–8 by Tim Rogers, including a contribution by Happy Holden). I was delighted to see this important issue addressed explicitly for the first time in this handbook since it is essential to the commercial success of PCB manufacture. The viability of a supply chain infrastructure has many aspects: evaluation and selection of suppliers, contract manufacture considerations, design for manufacturability, data formatting and exchange, process and quality control, auditing, testing, inspection, performance management, proximity of suppliers, warehousing, and many more.
Coming from the material and processing side of PCB fabrication, I tried to find a suitable and important material example to dig into, and I picked one of the most ubiquitous materials used in electronic packaging, namely epoxy resin. Needless to say, the above mentioned chapter on supply chain management cannot cover such a specific example but must focus on higher level issues. So I did my own digging. Since I planned to invest a limited time into this little study, I have to apologize for the somewhat anecdotal character of my findings and the fact that some supplier information may not be up to date due to recent mergers, acquisitions, name changes or other vagaries of the market place.
The use of epoxy resin as a component of base materials (also referred to as laminate, copper-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 solvent 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 (innerlayers) may then by laid up to multilayers by alternating prepreg layers with innerlayers, topping the multilayer with a “cap foil” of copper. 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 during the press cycle. After multilayer lamination, the multilayers are taken apart (broken down), their edges are cleaned, and multilayer processing continues (drilling, through-hole metallization, 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 furnaces which can cause 6–9 months of production 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 others. 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 Copper Foil Co. Ltd.).
Editor's Note: This column originally appeared in the September 2016 issue of The PCB Magazine.