Common issue of iPhone, no matter you have 5,5s,5c,6,6s,7,8,X , they all share one same common issue, no service.
I thought iPhone SE used iPhone 6s parts so same parts of baseband should be the same as 6s. However I was wrong.
It uses iPhone 6 baseband chip and not surprisingly, it has the same design flaw, even on a completely different logic board. Exactlly same pad is weak as iPhone 6 and it is lose which leads to no service under baseband chip.
Microjumper, put it back, and problem solved.
Basically, iPhone SE uses iPhone 6s A9 CPU and NAND, iPhone 6 baseband for cellular signals and iPhone 5s screen, in an iPhone 5 casing.
Well done to clear the old stock Apple.