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<style>.e_editor{font:14px/24px Roboto,Helvetica,Tahoma,Arial,'Microsoft YaHei','b8bf53';}.e_editor div,e_editor p,e_editor td,e_editor th,e_editor li{font-weight:inherit;font-size:inherit;font-style:inherit;font-family:inherit;}.e_editor ul{margin:-10px 0 20px;}.e_editor li{padding:5px 0;}.e_table{width:96%;border-collapse:collapse;empty-cells:show;}.e_table th,.e_table td{padding:5px;border:2px solid #eee;}.e_img{padding:10px 0;text-align:center;}.e_p{line-height:20px;padding:0 0 20px;text-indent:0em;}</style> <div class="e_editor"> <div class="e_p"> We are just starting to manufacture a PCB with a .039" fine-line PBGA. We are currently seeing voids, mainly in the center, that are as much as 45%. We also intermittently see the corner balls of the PBGA smaller than the center balls. We are using a 6-mil stencil with a 1:1 aperture size (.019" mil). We are using a convection oven and reflowing in air. The solder paste is an OA 62SN36PB02AG and the reflow profile is: Preheat - 0-150 degrees C in 90 sec Soak - 150-189 degrees C for 120 sec Reflow - 189-210 degrees C for 60 sec Thermocouples were attached to both the corner and center of the PBGA and they both had the exact same profile with a max temp of 210 Degrees C. Does anyone have any recommendations for minimizing the amount of voiding? Is 45% voiding acceptable? What would explain the corner balls being smaller than the center balls? </div> <div class="e_p"> Thank you for your input. </div> </div>