Chosen Solution
What to do If pin U4500-C2 went missing on a tristar repair
Is this the same device where the D2 pad was lifted or another device (iPhone 6s tristar ground pad missing where to run a jumper)? Lifting pads is the bane of micro-soldering repairs. Sometimes they are unavoidable but there are techniques you can put into practice to eliminate these from happening especially on smaller and easier IC’s such as Tristar on the 6/6S. Lifted pads can be caused by pulling/prying on the IC too aggressively when insufficient heat has been applied . You have to let the IC flow on the molten solder before pulling it otherwise pads will lift. The other thing to avoid is using wicking braid on these delicate pads. A lot of videos show this technique, in order to “clean” the pads. However, wicking pads works well on large and thick PCB’s but doesn’t work nearly as well on the thin, 10-layer iPhone logic boards. The copper pads/traces are so thin and the heat transfers so quickly that wicking just sucks up pads that are only tenuously held in place. Now, for your D2 problem, it is connected to R4510, which is hidden underneath the shield “ribbing” just north of the NAND. This is not easily accessible.
