Metal cased diode bridge has worse Rth(JC)?

[cupoftea]

Hi,
How is it that the GBJ series diode bridges have Rth(JC) =0.8degC/W but the GBPC series have Rth(JC) of just 1.5degC/W?
How is this the case when GBPC have a metal heatsink tab?

GBJ series:

https://www.mouser.co.uk/datasheet/2/258/GBJ50005_7eGBJ5010_GBJ_-2510579.pdf

GBPC series:

FAIRS45603-1.pdf

rocelec.widen.net

 

[crutschow]

How is it that the GBJ series diode bridges have Rth(JC) =0.8degC/W but the GBPC series have Rth(JC) of just 1.5degC/W?
How is this the case when GBPC have a metal heatsink tab?

Differences in internal construction.

But it's the GBJ series that has the metal tab for connection to a heat-sink.
I would expect the diode chips to be directly mounted to the tab, giving a low Rth(JC).

 

[cupoftea]

Thanks, though the GBJ doesnt actually have any metal tab...the GBPC does.