This paper analyzes the differences in plated through hole fill performance between the regular OSP and Pb-free OSP PCB surface finish chemistries in a Pb-free wave solder process. The variables studied include two board thicknesses - 93mil and 125mil, three hole sizes - pin plus 16, 24 and 40mils, internal Cu layer connections - single and three plane layer connections, two pin shapes - circular and rectangular and two reflow atmospheric preconditions -^sNitrogen and Air. A SnPb control was included for the 93mil thick test board. The bare PCBs were initially subjected to 220°C and 240°C peak reflow process twice for the SnPb and Pb-free wave soldering samples, respectively. This was followed by a wash process before wave soldering. The Pb-free wave soldering results indicated that the Pb-free OSP performed better than the regular OSP chemistry by 15% under air and 40% under nitrogen reflow preconditioning. In Pb-free wave soldering, the air preconditioning resulted in better hole fill than nitrogen. Board to board variation of hole fill was much lower in the Pb-free OSP chemistry compared to regular OSP. Plated through hole size of 40mils and 16mils, larger than the pin diameter proved to be best and worst designs for the 125mil PCB, respectively. The SnPb control almost had greater than 92% average hole fill for every design variable in this experiment. Overall, the results indicated that the regular OSP chemistry in Pb-free wave soldering failed to meet the 50% hole fill required per IPC-A-610, for all the conditions studied. The 125mil thick PCB using Pb-free OSP chemistry also failed to meet the IPC requirements for all the conditions evaluated. However, the 93mil thick PCB using Pb-free OSP chemistry was able to meet this 50% hole fill requirement(although not meeting the general 75% minimum requirement), except when the hole diameter is 16mils larger than the pin.
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