Consistently achieving acceptable wave solder through-hole fill on thick boards is a well-known process challenge, but the introduction of lead free solders has created additional difficulties. There are many reasons why one might achieve lower fill with lead free solders and there is much room for improvement in flux materials and process development, but unnecessary scrap and rework may be avoided by allowing lower barrel fill in some cases. Most OEMs have a waiver process to allow lower barrel fill than required by IPC-A-610D Acceptability of Electronic Assemblies for individual holes, but it seemed critical to gather more information for lead free solders in order to support the possibility of lowering the fill requirements for more boards and components by class. This study updated the previous work that had been done on through-hole reliability by considering joints made with Sn-3.0Ag-0.5Cu (SAC305) solder and a range of fill percents, including lower fill percents than are required by IPC-A-610D. SAC305 through-hole joints (with components loaded) were soldered on 0.062", 0.097", and 0.130" thick boards, with fill percents between 10% and 100%. These boards were subjected to thermal cycling, shock or vibration. After the stress exposure, the pull strengths of the joints were measured. The data showed that pin wetted length correlates well with the pull strengths of through-hole joints for different PCB thicknesses. Shock and vibration were the most detrimental stressors in the range tested. Minimum fill requirements were determined, based on board thicknesses and load per pin., This work has shown that lower fill levels than are sometimes required by IPC-A-610D will produce reliable SAC solder joints.
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