PCB007 Magazine

PCB-Mar2014

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March 2014 • The PCB Magazine 103 This reaction consumes one mole of perox- ide, one mole of sulfuric acid and one mole of copper metal and produces one mole of cop- per sulfate and two moles of water. The posi- tive voltage indicates that this reaction is spon- taneous and the relatively high voltage of this chemical system further indicates that virtually every molecular collision of peroxide with cop- per will result in a reaction (when the acid is in excess). This means that the number of col- lisions per second controls the reaction rate. So the higher the peroxide concentration, agita- tion, and temperature, the faster the reaction will go. The reaction above indicates that there is no gas produced by the reaction, yet when boards are etched with peroxide one can visu- ally see gassing at the board surface. This means that the reaction is not 100% efficient and that some peroxide reacts at the surface by sponta- neously breaking down. This is an important consideration when comparing the chemical usage of oxide alternatives with conventional oxide processes. Figure 1 illustrates the differences in the two innerlayer treatment processing systems. OXIDE VS. OXIDE ALTERNATIVE CHEMISTRY, PART 2 continues Oxide coatings bond by resin wet-out and encapsulation of surface topography—depen- dant on the resin flow. The resin as it cures then forms a bond between the resin treated copper surface. Organo-metallic component of oxide alternative facilitates resin wet-out of surface; in addition, chemical and mechanical bonding occurs. In a future Trouble in Your Tank, we will ex- plore the performance characteristics of oxide alternatives. PCB References 1. "What's Happening with Multilayer Bond- ers," K.H. Dietz, Circuitree Magazine, March 1998. 2. U.S. Patent # 5,691,130. Figure 1: comparison between oxide alternatives (left) and conventional reduced oxide (right). michael carano is with omg electronic chemicals, a devel- oper and provider of processes and materials for the electronics industry supply chain. to read past columns, or to contact the author, click here.

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