Thick copper board soldering has never been a problem that can be solved simply by raising the temperature in actual production lines, because the heat capacity of thick copper PCB boards above 4oz is more than four times that of conventional 1oz boards, which means each temperature zone of the reflow oven must be recalibrated during SMT placement. In particular, the heating ramp-up slope must be controlled within 1.2℃/s; otherwise, NTC thermistors and aluminum electrolytic capacitors will fail prematurely due to local overheating. If the time above the liquidus is less than 90 seconds, the intermetallic compound (IMC) layer at the interface between the copper substrate and the solder cannot grow sufficiently, and the solder joint shear force will drop directly below 8.5N.

Our actual tests with the JJY JL-8500 reflow oven found that when the thick copper PCB board enters the oven, the measured ramp-up curve of the first three temperature zones is 12℃ lower than the set value. This requires the operator to manually supplement hot air at the entrance of the second temperature zone, while forcing the peak temperature of the seventh zone from the conventional 250℃ up to 265℃±3℃. However, the holding time must never be simply extended; otherwise, the copper pads with OSP surface treatment will be excessively oxidized at high temperatures. Therefore, the nitrogen protection module must be activated synchronously to reduce the oxygen concentration to below 100ppm; otherwise, the silver element in the Solder Paste will react with copper oxide to form brittle Cu2O inclusions.

The wave soldering process is even more tricky. When soldering thick copper boards, the time the PCB passes through the wave crest is at least 1.8 seconds longer than that of ordinary boards. If conventional rosin-based Flux is still used, a large amount of carbonized residue will remain on the solder joint surface and cannot be completely removed by the cleaning machine. Therefore, it is necessary to switch to JJY's FP-718 highly active no-clean flux, with a solid content controlled at 28.5% and a specific gravity of 0.81g/cm3, paired with a preheating temperature stabilized at 150℃±2℃. This value is a critical point verified through 23 batches: below 148℃, the flux activation is insufficient, and above 152℃, the FR4 on the bottom layer of the PCB will blister and delaminate. The wave height must be strictly locked at 10mm: an extra 0.3mm may cause the solder to overflow the component body, while a 0.5mm deficit will lead to insufficient solder wetting in the thick copper area.

The clamping and conveying angle set at 5° is not empiricism, but is derived inversely from the warpage of thick copper PCB boards. When the board thickness is ≥2.0mm and the copper thickness is ≥4oz, the average warpage of the board after preheating at 150℃ reaches 0.87mm. If the clamping angle is greater than 6°, the board edge will hit the wave nozzle and cause solder splash; if it is less than 4°, the copper surface will be unevenly tinned, especially in the thick copper area at the bottom of the BGA, where incomplete penetration gaps of more than 0.15mm are likely to form, accounting for as high as 37% of such defects during X-ray inspection. After all parameters are adjusted, the same test board must be passed through the oven 12 times consecutively. The fluctuation of the solder joint IMC thickness at the 12th pass must not exceed ±0.3μm; otherwise, it indicates that the thermal field stability is substandard, and the thermocouple distribution inside the oven must be recalibrated.