Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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barrel of the hole. Figure 6: Cross section of 0.5-mm through-hole after 6× solder shock test. Microdistribution: Through-Holes. The throwing power of the plating electrolyte is very important for plat- ing through-holes. Poor throwing power can result in non-uniform cop- per thickness in the hole, which will result in poor component contact. The microdistribution was the measurements of the amount of cop- per 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 val- ues were calculated using the following equation: Microdistribution = [(C + D)/2 · 100]/[(A + B + E + F)/4] Figures 2 and 3 show the data for microdistribution obtained at various cur- rent densities and temperatures. Good distribution values were measured across a wide current density range. Bath performance was consistent across tempera- tures ranging 24–35°C. Tensile Strength and Elongation. Tensile strength and elongation of plated cop- per 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 cur- rent density lowers elongation. Through-Hole Reliability: Thermal Characteristics. Solder shock resistance test- ing per IPC TM-650 2.6.8 was used to study the thermal characteristics of plat- ed boards. Solder shock conditions were 10-second float at 288ºC 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. CONCLUSIONS A new process has formulated for high-volume rigid PWB production, one that 170

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