Semiconductor Packaging & Flip-Chip SMT
Capillary Underfill Dispensing & Fillet KOZ Calculator
Determine Washburn dynamic capillary flow times beneath flip-chip dies, micro-dispensing fluid volumes, keep-out zone (KOZ) fillet spreads, and automated L-shape/I-shape dispenser vector paths.
Process Parameters & Inputs
Die edge length in mm along the primary capillary flow axis.
Clearance between die and substrate in micrometers (µm).
Viscosity at pre-heated dispensing temperature in Pa·s.
Liquid surface tension in mN/m (dynes/cm).
Contact angle between liquid underfill and substrate/die in degrees.
Calculated Engineering Metrics
Capillary Fill Duration
18.4sec
Required Dispense Volume
9.2µL
Fillet Keep-Out Zone (KOZ)
1.35mm
Voiding Risk Index
Low(0.24)
Toolpath & Geometry Simulation
Engineering Reference:
→ Read the Capillary Underfill Dispensing Prepress CAM Dispenser Vector Guide
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Capillary Underfill (CUF) redistributes thermo-mechanical CTE mismatch strain between silicon dies ($lpha pprox 2.8 ext{ ppm/K}$) and organic substrates ($lpha pprox 16 ext{ ppm/K}$), boosting BGA/WLCSP thermal cycle fatigue life by $> 10 imes$.
Washburn Capillary Flow & Dispense Volume:
t_{fill} = rac{3 \mu L_{die}^2}{\gamma \cdot h_{gap} \cdot \cos heta}V_{dispense} = \left(L_{die} \cdot W_{die} \cdot h_{gap} \cdot (1 - \Phi_{bumps})
ight) + V_{fillet\_edges}KOZ = h_{die} \cdot \cot( heta_{fillet}) + 0.65 ext{ mm}
Dispenser motion must follow optimized L-shape or I-shape vector paths with controlled nozzle velocity and standoff to eliminate air entrapment voids.