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If you use this graph bellow as guideline, results a value from about 400 mils, that is impracticable.
So, a mask solder coverage must be applyed over track in order to allow reduce width.
0.4" (10 mm) trace/copper pour width isn't necessarily impracticable. I'm not aware of solder coverage considered as a reliable way to increase current capacity (e.g. in standards). Please correct me, if I'm wrong in this point. By the about factor 10 higher resistivity, solder must be quite thick to achieve a considerable effect.
For compact PCB layout, higher copper weight or paralleling layers should be considered.
BTA26 has TO3P package with 5.5 mm pin distance, this doesn't basically change the problem. It will help you at least to provide the required clearance without conformal coating or milled PCB slots.
Imagine the track end segment as a triangle with a corner at the pin rather than a round pin of full track width.
If you have wide tracks or copper pours on a power PCB, the thermal calculation will end up in determining point-to-point resistances, acceptable voltage drops and overall power dissipation. The risk of local overheating must be still kept in mind, but considering the lateral thermal conductivity of the copper structures.
An additional comment on the said solder coverage. I know that it's used in some circuits, e.g. SMPS. In my understanding, it will be utilized to reduce the track overtemperature and total power dissipation below permitted maximum values. But it's no reliable method if the copper structures don't have sufficient current capacity, e.g. because you can't guarantee a certain solder layer thickness.
I agree with you that punctual overheating at thin track can be dissipated over the larger track body.
I already proceeded this approach in a circumstance when solder mask cost must be avoided, but if possible I myself prefer this option.
Depending on PCB size, or if have mainly more logic than power circuitry, could be cheaper to place a solder coverage than specify 2OZ thickness against 1OZ.
This procedure requires a human handled assemblyng step, which reduces an automation attribute of this design to equipment manufacture.
Other probem at a metalic bar is the susceptibility to bad contacts due to mechanical shock.
As I said this amount of current is not critical...
I don't know if this post should continue here. But I have another doubt.
I made a board really simple with this TRIAC and I wanted to add an current sensor for me to monitor and turn off the TRIAC if I get some overload.
The problem is I cant find any sensor that can be used with the board, I find only the ones witch have to pass the cable through.. Is there any sensor that can be added to the board?
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