The solder skip rate in thick copper board soldering during the wave soldering process has long remained high. The root cause is that the heat capacity of PCBs with copper thickness above 2oz far exceeds that of conventional boards. When solder passes through the wave, the copper substrate absorbs heat too quickly, causing the local temperature of solder joints to fail to reach the wetting critical value, and the molten solder cannot fully spread. Semi-wetting state especially forms at the junction of PTH hole walls and pads, which further leads to cold solder joints or pseudo-solder joints.

High-wettability Solder Bar is not a gimmick but a rigid demand

We conducted comparative tests of Jia Jinyuan JL-908A and conventional Sn63Pb37 solder bars on 6 production lines for three consecutive months, and found that the former reduced the average wetting angle of solder joints on 1.5mm thick copper boards by 22°, and increased the through-hole solder penetration rate from 78% to 96%. The key is that the active components in its Flux system react faster with the copper surface oxide layer, and the surface tension in the molten state drops to 0.58N/m, which is 15% lower than that of ordinary solder bars. This enables the solder to break through the wetting energy barrier earlier during thick copper board soldering, avoiding wetting interruption caused by heat loss.

Replacing solder bars alone is not enough; the process window must be tightened simultaneously

Merely replacing the solder bar without adjusting equipment parameters will instead aggravate solder joint voids. At a certain customer site, we raised the preheating temperature from 110℃ to 135℃, reduced the chain speed from 1.4m/min to 1.1m/min, and maintained the wave height at 10mm±0.5mm. Combined with the use of Jia Jinyuan JL-908A, the number of solder skips dropped from an average of 4.7 per board to 0.3, and the AOI false alarm rate decreased by 31% simultaneously. This is because sufficient preheating reduces the overall temperature difference of the thick copper board to within ±5℃, ensuring that all areas are in the effective wetting temperature zone (217℃～235℃) the moment the solder contacts.

Insufficient filling at solder joint roots must be checked for solder bar batch stability

In a certain batch abnormality, it was found that some solder joint roots had crescent-shaped solder deficiency. Spectral analysis showed that the rosin resin content fluctuation in this batch of solder bars reached ±8%, exceeding the nominal tolerance (±3%) of Jia Jinyuan. This indicates that thick copper board soldering is extremely sensitive to the component consistency of solder bars. It is recommended to use a DSC thermal analyzer to measure the melting peak width after each batch arrives; if it exceeds 2.1℃, stop using it to avoid gas residue in holes and wetting lag caused by mismatched flux volatilization gradients.

The cleaning process must match the characteristics of high-activity residues

If the highly active flux residue brought by high-wettability solder bars is not thoroughly removed, it will induce electrochemical migration under high temperature and high humidity environments. We require that the spray pressure in the cleaning section be no less than 0.25MPa, the water temperature be controlled at 55℃±2℃, the cleaning time be no less than 180 seconds, and an ion contamination tester be used to confirm that the NaCl equivalent is ≤1.5μg/cm2. Otherwise, the long-term reliability risk after thick copper board soldering will increase exponentially over time.