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+ | ====== Stencil notes ====== | ||
+ | Stencil thickness makes a difference! Thicker stencils allow more paste to be deposited which is good for large parts and connectors but can cause shorts with finer pitch parts. | ||
+ | |||
+ | To calculate the optimal stencil thickness for fine pitch placement, IPC standard #7525 states: | ||
+ | |||
+ | > Stencil Thickness = 2.64 + 0.0831 * Pitch of component (in mils) | ||
+ | |||
+ | So, say for an FT232RL chip, which is a SSOP part with 0.65mm pitch. First figure out the pitch in thousands of an inch: | ||
+ | |||
+ | > 0.65 mm / 25.4 = 0.0256 inches = 25.6 mils | ||
+ | |||
+ | Then calculate according to the equation above | ||
+ | |||
+ | > 2.64 + 0.0831 * 25.6 = 2.13 + 2.64 = 4.77 mil | ||
+ | |||
+ | So for SSOP parts, 4 to 5 mil is the thickest you should go |