The wave soldering temperature is not a fixed value but a dynamic range. In our factory, the Sn63/Pb37 Eutectic Solder bar we use runs most stably when set at 252℃±2℃, but after switching to Sn96.5/Ag3.0/Cu0.5 lead-free Solder Bar, the temperature must be raised to 258℃～262℃ to ensure stable wave height. This is because lead-free solder bars have a high melting point and high surface tension; if the temperature is below 257℃, wave collapse, dull solder joints and solder dragging will occur.

The temperature probe is installed at the lower-middle part of the side wall of the solder pot. During the morning shift every day, a calibrated infrared temperature gun must be used to recheck the temperature three times. If the deviation exceeds ±1.5℃, the machine must be shut down to check the contact state of the thermocouple or whether the temperature control module has drifted. Last Wednesday, Line B had a loose thermocouple, which caused the measured temperature to be 3.2℃ lower than the displayed value. For two consecutive hours, boards with insufficient solder joint wetting were produced, and the rework rate jumped from 0.8% to 4.3%. Normal operation was not restored until the aging terminal block was replaced.

Solder bars must be added when the wave is stopped. Before being put into the pot, new solder bars must be preheated to above 120℃ and then slowly immersed. Otherwise, cold material sinking directly to the bottom will cause a sudden local temperature drop, leading to a sharp increase in solder dross and wave jitter. We once tried feeding material without preheating, and as a result, the amount of dross removed doubled within half an hour, and dense pinholes appeared on the solder joints. Later, we switched to batch preheating + feeding at 5-minute intervals, and the dross volume fell back to within 110% of the daily level.

The temperatures of Reflow Soldering and wave soldering cannot be confused. The former is designed with a four-stage profile for Solder Paste melting, while the latter maintains the overall thermal balance of the solder liquid. Therefore, the temperature fluctuation of wave soldering must be controlled within ±1℃, which relies on fine tuning of PID parameters rather than simply increasing the heating power. After we shortened the integral time from 120 seconds to 85 seconds and increased the derivative gain by 0.3, the temperature overshoot was reduced from 2.1℃ to 0.6℃, and the consistency of solder joints was significantly improved.

When switching solder bar batches, the temperature must transition in steps. For example, when switching from Sn63/Pb37 to SAC305, first raise the temperature to 255℃ and run for 30 minutes to drain residual lead, then raise it to 259℃ to run the first article. Mass production can be started only after confirming that there are no shrinkage cavities or copper corrosion on the solder joints. Skipping the lead draining step and directly raising the temperature will increase the risk of brittle fracture of solder joints, and the AOI false alarm rate will increase by more than 17%.

Changes in ambient temperature have a great impact on the temperature stability of wave soldering. When the winter temperature is below 10℃, the solder pot dissipates heat faster, so the machine must be turned on for preheating 30 minutes in advance and the insulation cover must be kept tightly closed. When the summer humidity exceeds 75%RH, the Flux volatilizes slowly, and it is easy to form a film on the surface of the solder liquid. At this time, the upper temperature limit should be relaxed by 0.5℃ to enhance disturbance; otherwise, the wave height will continue to decay.