High temperature of components to joining & soldering
Very few, if any, conventional components can withstand 600°C. If you have a datasheet of such a component it will probably offer application information. 

For thermocouples we just weld the junction using inert gas (TIG). 600°C is above the range for reliable long-term use of unprotected metals such as iron and copper in an ordinary atmosphere, you need metals that form a highly protective oxide such as Alumel or tungsten. Above 1000°C, noble metals come into play.