Metal Finishing Guide Book

2013

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PROCESS FEATURES Figure 6: Cross section of 0.5-mm through-hole after 6× solder shock test. Surface Appearance. Fine-grained deposits were obtained from this electrolyte. Plated copper was smooth and leveled inside the hole. No thin copper at the knee of the holes was observed. In addition, no plating folds or thin areas inside the through-hole were measured. Plating thickness was consistent throughout the barrel of the hole. Microdistribution: Through-Holes. The throwing power of the plating electrolyte is very important for plating throughholes. Poor throwing power can result in non-uniform copper thickness in the hole, which will result in poor component contact. The microdistribution was the measurements of the amount of copper plated in the center of the hole as a percentage of the copper thickness on the board surface, as shown in Figure 1. The microdistribution values were calculated using the following equation: Microdistribution = [(C + D)/2 á 100]/[(A + B + E + F)/4] Figures 2 and 3 show the data for microdistribution obtained at various current densities and temperatures. Good distribution values were measured across a wide current density range. Bath performance was consistent across temperatures ranging 24–35°C. Tensile Strength and Elongation. Tensile strength and elongation of plated copper were measured in accordance with IPC TM-650 Test Methods Manual, 2.4.18.1. The results from the measurements are demonstrated in Figures 4 and 5. Plating at all conditions meet IPC specifications. According to the results, increasing current density increases tensile strength, whereas increasing current density lowers elongation. Through-Hole Reliability: Thermal Characteristics. Solder shock resistance testing per IPC TM-650 2.6.8 was used to study the thermal characteristics of plated boards. Solder shock conditions were 10-second float at 288¼C for six times. The thermal integrity was excellent for all of the tested through-hole sizes. Neither corner cracks nor barrel cracks were observed, as shown in Figure 6, across the temperature range studied. Process Control. The additives are easily controlled using conventional CVS analysis, but Hull cell tests can also be used to control bath performance. The additive consumption changes insignificantly with the temperature increase, and the organic additive can be mixed together for auto-dosing during plating. Equipment. Air/no air solution agitation were studied, and eductor nozzles were used. There was no difference in the appearance properties of the plated copper with respect to air agitation or the eductor nozzles. 248

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