Micro-Soldering Basics for Mobile Phone Repair Technicians

Micro-soldering on modern multi-layer mobile PCBs demands a precise understanding of thermodynamics, alloy melting points, and surface tension.

Essential Thermodynamics & Thermal Profile - **Leaded Solder Alloys (63/37 Sn/Pb):** Liquidus temperature at 183°C. Recommended for jumper wire attachment and structural pad re-creation due to superior ductility. - **Lead-Free Alloys (SAC305 / Sn96.5Ag3.0Cu0.5):** Liquidus temperature between 217°C and 220°C. Requires controlled pre-heating to prevent PCB delamination.

Hot Air Rework Principles 1. **Pre-Heating:** Always maintain board ambient pre-heat (100°C–150°C) to prevent thermal shock to adjacent ground planes and underfilled ICs. 2. **Airflow Calibration:** Use low airflow settings (15–25 L/min) when working near small 0201/01005 SMD components to avoid displacing neighboring elements. 3. **Nozzle Positioning:** Maintain vertical 90-degree nozzle orientation at a distance of 1.0–1.5cm from the target component, allowing uniform heat dispersion.

Pad Reconstruction & Jumper Wire Techniques When motherboard pads are torn due to physical impact: - Clean the underlying copper trace under a stereo microscope. - Expose raw copper using a micro-chisel blade. - Bond 0.01mm insulated copper jumper wire using high-grade tacky flux and micro-tip soldering iron. - Cure with UV solder mask resin to isolate and structurally anchor the repair.

Precision micro-soldering is built on repeatable mechanical discipline.