Core Methods for Improving Reflow Soldering Quality

Reflow soldering quality directly impacts the reliability and performance of electronic products, necessitating comprehensive optimisation across multiple aspects including temperature control, equipment maintenance, material selection, and operational standards. The following is a detailed explanation of key measures:

‌1. Precise Control of Temperature Curves

‌Preheating Zone‌: Temperature rises to 150–190°C, with a heating rate ≤3°C/second, ensuring uniform solvent evaporation and preventing solder ball residue.

‌Insulation Zone‌: Maintained at 150–200°C for 60–120 seconds, activating the flux and removing oxides to prevent cold solder joints.

‌Reflow Zone‌: Peak temperature set to 235–255°C (240–250°C for lead-free processes), maintained for 30–90 seconds to fully melt the solder and form a reliable connection with the pads.

‌Cooling Zone‌: Cooling rate controlled at 1–4°C/second to prevent stress cracks or voids in the solder joints.

Regularly test the temperature curve (e.g., using a temperature data logger) and calibrate equipment parameters to reduce drift risks.

‌2. Optimise equipment configuration and maintenance‌

‌Temperature zone settings‌: Select equipment with ≥8 temperature zones (recommended for lead-free processes), heating length >2950 mm, and cross-sectional temperature difference ≤±2°C to ensure uniform heat distribution.

‌Conveyor Stability‌: Use a servo motor-driven chain track with near-zero vibration to prevent component displacement or cold soldering.

‌Daily Maintenance‌: Regularly clean residual materials (e.g., flux) from the furnace chamber, inspect heating tube performance, and maintain unobstructed channels.

‌3. Material and Process Management‌

‌Solder Selection‌: Use high-activity lead-free solder paste (e.g., tin-silver-copper alloy) compliant with RHS standards, and store strictly (refrigerate then return to room temperature) to prevent oxidation.

‌PCB Design‌: Ensure proper pad layout and stencil aperture alignment to reduce the risk of bridging or uneven solder paste printing.

‌4. Enhanced Operation and Quality Verification‌

‌Operational Standards‌:

Avoid vibration interference; ensure PCB is placed in the correct orientation;

Conduct first-piece inspection at the start of each shift to confirm solder joint wetting angle <60° and pad coverage >90%.

‌Inspection Mechanisms‌:

Post-soldering X-ray inspection with void rate <3%, shear test strength >50N;

Train operators to identify and address anomalies (e.g., tombstoning caused by excessive preheating).