Reflow Soldering Classification and Process Requirements

Reflow soldering classification is primarily based on heating methods, while process requirements focus on temperature control, equipment operation, and quality verification, as detailed below:

‌1. Reflow Soldering Classification‌

Classified by heating area scope into two major categories:

‌Overall Heating Type‌ (Mainstream Solution)

‌Hot Plate Reflow Soldering‌: Heats the PCB substrate via thermal conduction ‌

‌Infrared Hot Air Reflow Soldering‌: Forced convection hot air + infrared radiation, with high heating uniformity ‌

‌Vapour phase reflow soldering: Utilises the heat released by the condensation of inert liquid vapour, suitable for high-reliability applications ‌

‌Localised heating type (special applications)

‌Laser reflow soldering: Precisely heats micro-solder joints using a focused laser beam ‌

‌Focused infrared/beam reflow soldering: Directs radiation to specific areas ‌

Hot air reflow soldering: Achieves local soldering by spraying high-temperature airflow

II. Core process requirements

1. Equipment operating specifications

Conveyor stability: Vibration is strictly prohibited; servo motors are used to drive the chain track to prevent component displacement

Nitrogen protection (optional): Nitrogen is used to reduce oxidation and improve the solder joint quality of high-end products such as automotive electronics

‌Temperature Zone Configuration: Lead-free processes require ≥8 temperature zones, with a heating length >2950mm to ensure temperature uniformity ‌

‌2. Quality Verification Standards

‌First-piece Inspection: Confirm that solder joints are fully melted, with a smooth, semi-circular surface, and no bridging/cold solder joints/solder balls ‌

‌Solder joint appearance: ‌Wetting angle <60°, solder coverage of the pad >90%, strength >50N. ‌

‌Defect prevention: ‌

Porosity rate <3% (X-ray inspection). ‌

Standing/bridging (control preheating slope ≤20°C/second). ‌

Regular calibration of equipment parameters (mandatory testing per shift).