PCB007 Magazine

PCB-Feb2014

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46 The PCB Magazine • February 2014 by Michael Carano omG electronic chemicalS llc Oxide vs. Oxide Alternative Chemistry for High-Performance Resin Systems, Part 1 c o l u m n trouble iN your taNk Introduction By now a good percentage of the PCB fabri- cation world has graduated to the use of oxide alternative as a means for enhancing the inter- laminar bond strength between copper circuitry and the resin system. However, conventional brown or black oxide systems, as these are com- monly called, have continued to serve the in- dustry well. Indeed, frequent visits to Asia have shown me that oxide chemistry is alive and well. So before dedicating the next few columns to oxide alternative chemistry, it would be ap- propriate to present the current state of conven- tional oxide. I can honestly say that the death of conventional-reduced oxide has been greatly exaggerated. Oxide vs. Oxide Alternative Anyone involved in PCB fabrication during the last 25 years should understand that stan- dard oxide treatment of innerlayers to enhance bond strength between the copper and resin has served the industry well. Oxidation of the copper surfaces for multilayer board fabrication was borrowed from the general metal finishing industry. Basically, it is a simple process best characterized as the controlled anodic oxida- tion of copper in an alkaline medium. To re- fresh the memory, the purpose of the oxidation step serves a two-fold purpose: (1) passivation of the copper surface and (2) enhancement of bond strength between the resin and copper. Look at this as the copper oxide crystals provid- ing a high surface area on the copper so that the resin can flow through oxide crystals and provide a heat-resistant bond (Figure 1). With respect to passivation, the concern is that when B-stage resins and unpassivated copper surfaces are bonded together under high heat and pres- sure conditions, water can be a by-product of this reaction. With moisture now in the bond line, the water can vaporize, thus weakening

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