During debugging of the JJY reflow oven, we found that 0.8mm-thick double-sided boards frequently exhibited cold solder joints under the original temperature zone settings, while 2.0mm-thick power boards suffered from frequent tombstoning of components. The root cause was that the dwell time in each temperature zone and ramp rate had not been adjusted according to PCB thickness differences. Thin boards have low thermal mass and heat up quickly; if the preheating zone is too long, the Solder Paste solvent will volatilize violently and cause splattering. Thick boards, on the other hand, have multiple copper layers and slow heat conduction, so the soak segment between 150°C and 183°C must be extended to allow the inner copper layers to fully accumulate heat; otherwise, during the reflow stage, the top layer will already be molten while the bottom layer remains below the liquidus temperature.

The impact of differences in component thermal mass is even more direct. For example, the thermal mass of a QFN48-packaged MCU is approximately 17 times that of a 0603 resistor. When both coexist on the same PCB, if the peak temperature is set solely based on average thermal mass, small components are prone to overheating and oxidation, while large components may experience insufficient reflow. In an automotive controller project, we tightened the temperature difference between Zone5 and Zone6 of the JJY reflow oven from 12°C to 5°C, while reducing the conveyor speed from 90cm/min to 72cm/min, which brought the void rate at the bottom of BGA packages down from 18% to 4.3%. This adjustment was not derived from theoretical calculations, but was obtained through repeated fine-tuning after measuring 12 key points with thermocouples.

In actual production lines, we do not create a full profile for each individual board; instead, we establish three tiers of basic templates. The first tier corresponds to 0.6–1.0mm board thickness plus small-to-medium thermal mass components. The second tier covers 1.2–1.6mm board thickness plus medium thermal mass components such as LCC or SOIC-28 packages. The third tier is dedicated to combinations of board thickness above 2.0mm plus components such as TO-263 packages or large heat sinks. Each tier fixes the conveyor speed, the temperature gradient between Zone3 and Zone6, and the soak time in Zone7. This way, when switching models, we only need to confirm whether a tier crossing is required, preventing engineers from arbitrarily changing parameters based on gut feeling.

The temperature zone division of the JJY reflow oven also affects the configuration logic. It adopts an 8-zone structure, where Zone1–Zone2 are responsible for rapid heating without overshoot, Zone3–Zone4 handle the main soak function, Zone5–Zone6 form a narrow reflow window, and Zone7–Zone8 are used for cooling rate control. This layout means we cannot simply apply empirical values from other brands' 6-zone ovens. For example, setting Zone3 to 150°C will inevitably leave Zone4 unable to compensate for heat in time; a stepped setting such as Zone3 at 142°C and Zone4 at 158°C must be used, followed by reverse-calculated corrections based on the board surface temperature rise curve measured with an infrared thermometer.

During on-site verification, the biggest mistake is relying solely on oven profile test board data. It is necessary to simultaneously collect three sets of thermocouple signals: the center point on the back of the PCB after placement, the edge point of the BGA solder ball array, and the area near the 0402 resistor pads. Because the hot air circulation method of the JJY reflow oven causes the board edge temperature to be 3°C–5°C higher than the center. If only single-point testing is relied upon, minor issues lead to redundant temperature zones and wasted energy, while severe issues mask the risk of local cold solder joints. We once had to rework a batch of medical device motherboards due to this problem, and later mandated that all new profiles must run continuously for 10 boards and undergo full X-ray inspection of the first article before mass production is allowed.