Please help me to know the best components for the process of welding an electronic circuit to operate it in a very high temperature environment up to more than 600 degrees Celsius? Note: I do not know if I can use the Ultrasonic welding in my application, and add on it another component to soldering with tolerate the temperature for example 500 ? Is this possible?
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.