The ability of HAL (Hot Air Levelling) circuit board surfaces to fulfil future requirements (such as increased part densities, reduced spacing between pins, etc.) continues to decrease.
This is because the HAL process creates the surface of the circuit board with a tin bath. The fluid tin forms "drops" on the surface areas and runs along the edged of holes and pads. This causes the surface of the circuit board to be very thin right at the edges, and may lead to solder problems.
A uniform surface thickness cannot be achieved with HAL.
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