No network but my simcard fine with other's phone

After you have eliminated antennae or network locks as the possible culprit, searching issues on the iPhone 6 are usually related to the baseband IC. The baseband IC is very sensitive, just like the Touch IC's on the 6 Plus; it also suffers from poor quality traces and pads.

 Go to your phone’s dialing keypad and dial *#06#. You should see the IMEI displayed.

If the IMEI is not displayed, the Baseband IC has to be reballed and two small copper traces (U1/V1) have to be rebuilt and solidified. This is commonly referred to as the “long jumper” solution. You can check out this answer (Service is "Searching" indefinitely) (by @teetopp) as it summarizes the issue really well.