SMT Reflow Oven Temperature Setting and Measurement Method

The following is the standardised process and key points for SMT reflow oven temperature setting and measurement, integrating equipment operation, parameter optimisation, and quality verification:

‌1. Core Steps for Oven Temperature Setting‌

‌Curve Analysis and Parameter Presetting‌

Refer to the recommended curve from the solder paste supplier or the customer's required curve diagram to define the target values for the heating zone, constant temperature zone, welding zone, and cooling zone.

‌Using an 8-zone equipment example:

Zone 1 (Heating): 155°C (base value + temperature difference compensation)

Zones 2-5 (Constant Temperature): 165°C → 180°C (stepwise increase)

Zones 6-7 (Welding): 230°C → 255°C (peak zone)

Zone 8 (Cooling): 225°C (initiate forced cooling).

Transportation parameter calculation:

Chain speed = furnace internal temperature measurement segment length / target total time (typically 45–90 seconds), variable frequency adjustment range 0–2000 mm/min.

Calibrate via actual measurement: if the temperature is too high, reduce the set value; if too low, increase the set value, gradually approaching the target curve.

‌Special process adjustments‌

‌Cooling control‌:

When rapid cooling is required, set the final zone to the highest temperature (directly activate forced cooling);

When controlled-speed cooling is required, set the second-to-last zone to the highest temperature (delay cooling).

Lead-free process: Peak temperature 245-252°C (maintain above 240°C for 30-40 seconds), cooling rate >4°C/second.

II. Standardised furnace temperature measurement process

Test preparation

Equipment: Furnace temperature tester + protective iron box, thermocouple probe wire, high-temperature resistant gloves, test PCB board.

Probe point arrangement: Attach the thermocouple to the actual solder joint on the PCB (secured with red glue) to avoid data distortion caused by loose connections.

‌Measurement execution‌

Connect the probe wire → Power on the device → Seal the box → Place in the furnace for testing → Remove after 5 minutes → Shut down the device → Export data

Operate throughout the process while wearing high-temperature resistant gloves, and monitor the exit temperature (must be <50°C).

Data analysis

Verify actual curve vs target curve:

Temperature rise rate: 1–2°C/second (too fast causes solder paste degradation);

Constant temperature time: 60–120 seconds (150–200°C to activate flux);

Peak duration: 30–40 seconds (critical window for lead-free process).