so anyway this has been driving me insane for like two weeks now. im using a ts100 set to 380c with 63/37 rosin core solder and my joints look fine when i finish them, shiny and everything, but after a few flights they crack and i start getting weird throttle behavior or motors cutting out. pulled apart my stack last night and sure enough two of the motor phase wires had just barely cracked right at the pad.

the ESC is a Mamba F45, pads are not huge but not tiny either. ive been tinning both the wire and the pad first then joining them. the solder itself looks fine when i do it but clearly something is wrong. someone mentioned maybe my iron isnt holding temp well or im using too much flux but i cleaned everything with IPA after. could it be vibration cracking them? the frame is pretty stiff carbon so i wouldn't think so but maybe

380 might actually be a little low depending on how fast you're working and what gauge wire you're using. if the iron is sitting on the joint too long trying to get the wire hot it can cause a cold joint that looks fine visually but isnt actually bonded properly. try bumping to 400-420 and work faster, get in get out. also are you using silicone wire? regular stranded wire is way more prone to cracking from vibration because it's stiffer, silicone wire has way more flex which helps at the joint

also the ts100 tip matters a lot. if you're using a tiny conical tip you're not transferring heat efficiently. grab a chisel or bevel tip, makes a huge difference for ESC pads specifically

had almost exact same issue and it turned out my solder was old and had dried out flux in it basically. switched to a fresh roll of kester 63/37 and the difference was insane, joints looked totally different. i know you said yours looks shiny but sometimes old solder just doesnt flow right even if it looks like it does. that plus the silicone wire thing the other guy mentioned, those two things fixed it for me