Hi Team,
i am working 2-layer pcb. customer want to meet the thermal fillet should be 100%. for achieve thermal spokes are added for all PTH components. but i have not clarity how much anti pad need to provide for 1.75 pad /1mm drill.
5mil anti pad provided between pad edge to shape.
10mil spacing provided pad edge to shape to connect, which is best to meet 100% fillet.
I do not think that anybody can answer this directly. There is the combination of thermal relief gap, number of spokes/width present, layer copper weight, and number of connecting layers. I think that I have seen that spoke width total connections should not exceed 60% of pad width (per an IPC spec). I generally recommend that the relief gap should be maybe about the same as a spoke width. Example 10 mil spoke, use 10 mil gap.
Then there is the lead diameter to hole size ratio. If the hole is too tight, it will make it more difficult to flow solder into the hole. I think that a good hole oversize of about 12-15mils over the maxmium lead diameter. Square pins and press fit pins likely need different requirements.
The problem is that I have never seen a formula that considers these items in order to suggest a completely soldered fillet result. Even IPC tends to skirt this subject by allowing solder fill of maybe ~50% of the board height (depending on assembly class).
Follow-up:
Review IPC-A-610J section 7.3.5.1 Support Holes - Solder - Vertical Fill
Typically class 2 assemblies should have a 50% minimum fill.
Typically class 3 assemblies should have a 75% minimum fill.
IPC-2221C section 9.1.3 talks about how to calculate minimum land size based on maximum hole size and uses that result to calculate minimum spoke widths.
Neither of these areas talk about how to achieve 100% sollder fill but this is likely as close as it will get to answer this thread.
