iPhone keep restarting after disassemble

Hi,

I had a question recently due to i need to change my side volume adjustment so i disassemble & after i assemble back my phone start up with apple logo. abt 3 to 5 mins it came out the running cycle behind the logo awhile it restart again.

i had restore with itune was sucess but after a while it repeat again of restarting.

i also did disassemble another iPhone due to changing of battery & assemble back & it same thing happen as above mention,

Is there something wrong with my assemble or is it hardware problem/some parts broken/some parts i did not install properly.

Please help.

Rgds