Need for thermal relifing for TO247 diode in ground plane?

[Faringdon]

Hi,
How little thermal reliefing can you get away with with a to247 Diode?
The attached is a TO247 diode (three pics at different zoom in levels) connecting to a ground plane of 1oz copper as pointed out.
(PCB screen grid is 1mm)
Can we just use an 80W soldering iron and not even bother with the thermal relief?...this is only a single prototype board.

[Kleinstein]

The main reason for the thermal relief is to aid soldering. With a powerfull iron one can still solder even without thermal relief and even in more difficult conditions (e.g. 2 Oz or 4 Oz copper).

[Gyro]

You don't appear to have used thermal reliefs on any of the components, including the electrolytic and plastic film capacitors. Are you going to use a hot soldering iron on those too?

As for the TO247 diode, I don't know why not having a thermal relief matters - it is attached to a heatsink.

[ebastler]

There are thermal reliefs on all the components -- they are just very narrow, hence hard to spot in the pictures at lower magnification, especially on the square pads.

@Faringdon: You didn't mention why you want or need to make the thermal reliefs so narrow?!

Even the narrow gaps will be "better than nothing" for thermal relief, since the thermal conductivity of FR4 is so much lower than for copper: A factor of 1600 in the W/(m*K) thermal conductivity, and approx. a factor of 35 for a 1 oz copper layer vs. 1.6 mm FR4 layer. But why not use a wider gap, e.g. the Eagle default setting?

[Feynman]

The gap between pad an plane on your thermals looks really small. Is this still within the specification of your fabrication shop? But maybe it's just me not being used to looking a THT boards

Anyhow, if you have problems with heat transfer one solution is preheating the board. If you don't have a dedicated PCB heating plate a simple heat gun can help, too. Just carefully (!) heat up the hole board.  Gently heating up the board to about ~50-60 °C already does the trick often times.

But as a default solution I would always use thermal reliefs, if you don't need the small thermal resistance for heat transfer in your application.