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42 The PCB Magazine • January 2017 modules for PCB processing. The advantage of the cone nozzle is its high liquid volume deliv- ery. However, fan nozzles provide higher impact (impingement). This is highly effective especial- ly when developing finer lines and spaces. The author wrote in a previous column[2] that high impingement fan type nozzles work very well in the aqueous development for the removal of resist and developing solution residues from the copper surface and the exposed sidewalls of the resist. A clean removal of all residues from the copper surfaces and sidewalls is required for defect-free plating and to insure the circuit trace is as uniform as possible. In addition, rinsing after developing with a minimum of 70°F water temperature is most effective in removing these alkaline residues. Figure 3 shows incomplete development due to either low pH, inadequate rinsing or insufficient developing/rinsing spray pressures. And finally, proper maintenance of the spray nozzles in both the developing and rins- ing chambers is necessary to ensure nozzles re- main clean and free of resist residues. An ex- ample of what plugged nozzles will lead to is shown in Figure 4. At this point, the operator needs to suspend the operation and either replace the nozzles or at the very least clean the machine and nozzles. Summary To deliver a high-reliability printed circuit board, engineers must not overlook or take for granted aspects of the process that have great impact on the end result. Certainly, most opera - tors and engineers worry about controlling the wet chemistry of the plating process and imag- ing fundamentals such as exposure. Yet, they are often surprised and disappointed that the qual- ity of the finished product is not meeting strin- gent quality requirements. Further examination will find that other aspects of the process often overlooked were not sufficiently controlled and maintained. Thus, it only makes sense that in addition to wet chemistry, other factors such as resist developing, rinsing and nozzle mainte - nance, resistances in the plating cell, and agi- tation and filtration will contribute to overall quality. Ignore these at one's peril. PCB References 1. GABE, D.R., 2006. "Process Agitation: from air bubbling to eductor jetting," Transac- tions of the Institute of Metal Finishing, 84 (2), pp. 67–78. 2. Primary Imaging for Pattern Plating, Part 2: Development, The PCB Magazine, June 2016. Michael Carano is VP of technol- ogy and business development for RBP Chemical Technology. To reach Carano, or read past columns, click here. ACID COPPER PLATING—UNDERSTANDING WHAT'S OFTEN TAKEN FOR GRANTED Figure 3: Developer/resist residues remaining on sidewall and surface. (Source: IPC-9121 Process Effects Handbook) Figure 4: Plugged nozzles in developer chamber. Note uneven developing patterns on the test panel. (Source: RBP Chemical Technology)