iPhone unable to connect to cellular network after mid frame repair.
I've recently repaired my iPhone 4. Basically switching the mid frame of the iPhone. And now the iPhone can't pick up cellular network. It can definitely recognize my sim card (shown in "about"). But it just can't pick up cellular network. It is stuck as "searching..." and a few seconds later it says "No service" and after a few more seconds it says "searching..." again and the loop continues. Some said the blue coil was damaged which I'm really doubtful about because I barely touched the blue coil. I've asked some phone repair engineers and they say it might be a contact problem.
So here are my questions in specific:
1) Does different screws affect the connectivity of the device. If yes. What's the length and width of the 2 screws that should be near the cellular /antenna module (speaker module).
2) How does cellular data goes through the device. Which components are responsible for receiving cellular data