DirectFET®; MOSFET: Stencil PCB Design
Stencil Design
- DirectFET MOSFETs have been designed to work with stencil thickness from 6mils (150µm) to 10mils (250µm)
- Most customers are using 6mil stencils
- Stencil design plays a significant role in creating the ideal solder joint
- Volume of solder is the critical parameter
- With the stencil thickness set for the whole board, solder volume for each individual device type is
controlled by the amount of aperture reduction vs the board pad area
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- Stencil design may often be reduced. The reduction can depend on stencil thickness and solder paste type
- The stencil does not have to match the pad outlines symmetrically and in some cases advantages can be obtained
it does not
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Stencil Design - Aperture Reduction
- From experience we know that a 25% area reduction gives good results with a 6mils (150µm) thick stencil and most paste types.
- The reduction is calculated against the area of the PCB outline
- To translate this reduction for other stencil thicknesses it is necessary to calculate the volume printed
- Print area x stencil thickness = volume of paste
- For our standard 6mil stencil: 1.700 x 0.850 x 0.150 = 0.217mm3 (25% reduction by area)
- Equivalent volume for a 5mil stencil :1.750 x 1.000 x 0.125 = 0.219mm3 (10% reduction by area)
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IR’s proprietary DirectFET®; technology is covered by US Patent 6,624,522 and
other US and foreign pending patent applications.
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