Why Mixed Signal Calls for Precise Stencils
Taking a middle ground is verboten to avoid assembly problems.
Stencil design calls for three main criteria. One, the stencil should be completely flat because it needs to evenly distribute the amount of paste on all sides of the board. Two, it should be able to control solder paste spillage. If solder paste is spilled on an adjacent pad (or ball, in the case of the BGA), it could cause a short. Three, the stencil must provide optimum stability, meaning it can be repeatedly used without any issue. This could be achieved by using framed stencils versus unframed ones.