By intentionally varying the solder paste aperture size, BGA packagers can reduce coplanarity. The unique coplanarity/warpage topology for each package part number needs to be well understood prior to implementation. Thicker stencils amplify this effect. Fine powders are required for thin stencils. Type 5-6 for 25μ stencil, Type 4-5 for 50μ stencil, Type 3-4 for 75μ stencil Smaller starting ball diameters amplify this effect. Smaller UBM diameters with equal solder volume can increase ball height.
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