It's very rare that I get to design applications in need of cooling so I haven't had the need to study in-depth about that, but now I face an occation where I need cooling for a TO220 and I'm unsure how to calculate what I need.
TRIAC BTA08-600, data sheet: https://www.tme.eu/en/Document/229a1f149ceabe983b1ecaf8c207519b/BTA08-600BRG-STMicroelectronics.pdf
Page 4 tells me the power dissipation relative amps. In my circuit 3A is worst case, but regarding cooling I will calculate for 4A just for the sake of margins. The table tells me 4A => 4W.
Page 3 then tells me Rth(j-a) for TO220 is 60 degrees C per Watt. If I understand this parameter correctly, it would mean that for 4A times 60 degrees, it would go up to 240 degrees C in total. Then, page 2, tells me under "Absolute maximum rating" that Tj is +125 degrees.
If I'm guessing correct here it would mean I would have to use a heatsink that can cool down 240-125 = 115 degrees C.
Question 1: Is this assumption correct?
Question 2: How do I find a TO220-based heatsink that's able to cool 115 degrees? What parameters should I peek on / search for?