Fault is still explainable by external parts
Connector, dock/flex, display, battery, camera, antenna, SIM tray, cable or software/restore evidence has not been isolated.
IPHONE LOGIC BOARD / SANDWICH / INTERPOSER FORENSICS
Prove the cross-layer fault.
Prove the cross-layer fault.
Split only when the evidence demands it.
Separate top-logic, interposer and bottom/RF-board dependencies before heating or reballing the sandwich. Use pre-split measurements, cross-layer continuity and post-split comparison to identify the actual defective side.
CROSS-LAYER EVIDENCE CHAIN
SYMPTOM
PRE-SPLIT
NET
SPLIT?
LAYER
VERIFY
The decisive question is not “can the board be split?” but “what new evidence will splitting create that cannot be obtained safely while assembled?”
01 — CROSS-LAYER SIGNAL & POWER HIGHWAY
Top board ↔ interposer ↔ bottom RF board
Select a stage to inspect the dependency and the measurement that should exist before separation.
02 — CROSS-LAYER FAILURE PROFILER
Short, baseband, SIM and boot-hang cases
V2 keeps multiple hypotheses open until split-board or cross-layer measurements actually discriminate them.
SELECTED CASE
Observed evidence
Competing domains
Proof required
03 — SPLIT-BOARD DECISION ENGINE
When should the sandwich actually be separated?
Split only when the expected information gain exceeds the thermal/mechanical risk.
No cross-layer net has been identified
A generic “No Service”, “Error -1”, boot loop or high current is not enough. Identify the rail/bus/control family first.
Assembled-vs-layer measurement can answer the question
Example: a main-bus short remains assembled but disappears on one separated layer, or a specific interposer net is open on one side.
Known impact / prior rework + cross-layer evidence
Board warp, impact corner damage or previous sandwich work raises interposer probability when the measured net also supports it.
04 — GENERATION FORENSICS
Architecture changes; do not use one universal sandwich recipe
The uploaded V1 contains generation-specific heat and failure claims. V2 preserves them only as source notes and requires model-specific process data before rework.
Early dual-board architecture
Use exact model boardview and known-good layer behavior. Do not assume every top board can fully boot standalone.
RF/baseband layout changes
5G generations add new RF/baseband dependencies. “No Service” needs modem-power/firmware/clock/IPC evidence before sandwich work.
Denser interconnect
Restore and SIM symptoms can have software, storage, baseband, reader/flex or interposer causes; stage-specific proof is mandatory.
USB‑C and newer RF paths
USB‑C/SuperSpeed, eSIM and newer modem/RF architecture create additional non-interposer branches. Avoid extrapolating older repair recipes.
V1 lists fixed separation temperatures and specific solder choices by family. V2 does not treat those as universal process specifications because fixture, alloy, preheat, board condition and rework history materially change the safe thermal profile.
05 — INTERPOSER NET REPOSITORY
Cross-layer voltage + GR + signal type
Source-derived references are preserved as page references. A matched static GR does not prove active bus integrity or healthy silicon on both sides.
| Bus | Interposer Net | Source Voltage | Top GR | Bottom GR | Signal Type | What abnormal supports |
|---|
06 — INTERPOSER PAD EVALUATOR
Compare top and bottom without overclaiming the verdict
V2 reports the electrical observation and next proof step rather than declaring “healthy silicon” from static measurements.
07 — SOURCE RULES CORRECTED
Do not convert correlation into a guaranteed interposer diagnosis
These are the most important V1 assumptions that V2 deliberately downgrades.
Does not automatically prove bottom board alone is defective
It raises bottom/interposer probability, but the exact shared net and altered standalone topology must still be considered.
Not automatically PCIe interposer separation
Restore-stage errors can also involve baseband power/state, storage, software, USB transport or board-specific dependencies.
Not automatically RFFE/TCXO pad fracture
Baseband PMU, modem silicon, clock, reset, IPC, RF control and software state must be separated.
Not automatically a torn perimeter pad
An open reading can occur in the board trace, series/filter element, via, pad or IC-side connection. Locate the discontinuity.
Does not prove both silicon connections are healthy
Static diode mode can look normal while active PCIe/RFFE/clock timing or intermittent interposer joints fail.
No universal temperature recipe
Use board-specific process control, fixture, thermocouple feedback and rework history rather than a fixed number copied from another generation.
08 — SANDWICH FORENSIC DOSSIER
Preserve pre-split and post-split evidence
Record why the board was split, what changed after separation and which net ultimately confirmed the repair.