What paste for cpu reballing?

Hi,

I picked up an iPhone 8 from local online marketplace. Phone turned out to have cpu connectivity issues. I decided to reball it. Already have some experience in micro soldering so managed to litf up the cpu without damaging anything. Cleaned both, board and cpu pads. And here comes the hard part for me…

I do really struggle with putting new solder balls on it… I use mechanic solder paste 63/37 and quanli a11 cpu stencil. I do preheat stencil to avoid bending. However I can't get perfect balls, some of them are bigger than other. Some are bridged… I watched few YouTube videos of people doing it and I think they use different solder paste.

Can you advice me what solder paste are you using for the job?

Cheers,

Marcin