1. A DOE was employed to optimize the paste hole fill for the printing process. The result was 100% hole fill for 63-mil thick boards and between 85% and 100% paste hole fill for the 93-mil thick board, depending on hole size. 2. Testing was performed on three stencil thickness, two board thickness, and three through Hole parts (Resistor, DIP, and Pin Header). Results show that a 6-mil stencil will provide good fillets without voiding or excess flux residue with proper design of the board barrel hole dimension to pin dimension, aperture size, and print process set-up. The 8-mil stencil and 15-mil stencil produces excess flux residue due to excess solder. The ability to provide acceptable Lead Free Intrusive Reflow results with a 6 mil stencil is significant because it eliminates step stencils altogether or at least makes a step stencil much more workable in the process environment by reducing the depth of step (6-mil down to 5-mil for example).
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