The introduction of the iPhone X and XS completely revolutionized mobile hardware with the implementation of a double-stacked "sandwich" logic board. To maximize space, Apple split the motherboard into an upper layer (containing the A11 or A12 Bionic CPU and NAND flash) and a lower layer (containing RF and baseband components), fused together by a perimeter of solder middle-board joints.
When liquid penetrates a double-stacked iPhone, moisture becomes permanently trapped between the two boards, resulting in immediate electrical shorts along the interposer pins. Forensic recovery requires a cleanroom technician to place the dual-layer board onto a specialized separation hot plate. The boards are carefully un-sandwiched at precisely 180°C–200°C. Technicians then use a microscopic probe to isolate the top board (the logic layer) and wire it directly to an external power supply, bypassing the shorted lower board entirely to pull a bit-stream forensic image.
