I have a 1206 component that need to have all of the flux removed under it to achieve low leakage.
The standard footprint with solder mask between the pads has shown a tendancy to hold flux even after a soak and swish in the solvent base flux washer.
Looking at Johnashon dielectrics application note that tested slots, solder mask removed under the part and combinations of both that found that only removing the solder mask was good enough to sustaing high voltage across the part without flashover underneith due to flux. While my issue is not HV flashover i liken that to leakage currents.
Slots are fairly expensive and I will need this on ~ 12 parts in close proximity to each other. My concern is to compromose the strength of the board. Also I fear it would concentrate the bendinf force between the component lags and stress the solder joint.
I'm thinking of instead of putting a large slot, just drilling a unplated hole under the part to all the flux cleaner to flush under part and clear out any flux. This hole would need to be blown out after flux cleaning to removed the capliary action held cleaner but it should clean better than just removing the solder mask.
What so you guys think about handling a situation like this?
1) low cost 2) repeatable perforance for low leakage current 3) minimal compromise to board strangth.