Selective Wave Soldering Solder Bars cannot be randomly taken from any roll and put into production. Our production line switched three batches of Solder Bars last year, and under identical parameters on the same equipment, the dross output fluctuated by 35%. The root cause was excessive residual copper and iron in the solder bars, which caused uneven rupture of the oxide film, further intensifying molten solder disturbance and dross particle agglomeration.

Melting Point and Thermal Stability Must Be Verified Simultaneously

JJY Sn99.3Cu0.7 Solder Bars have a measured solidus temperature of 227°C and liquidus temperature of 228.5°C. This narrow melting range ensures gentle changes in molten solder viscosity at the nozzle outlet, preventing both solder joint spikes in low-temperature zones and excessive wetting of pads in high-temperature zones. After mistakenly using a bismuth-containing solder bar once, a temperature difference exceeding 1.8°C in the reflow section caused nozzle clogging frequency to increase fourfold, indicating that Selective Wave Soldering requires far higher consistency in solder bar thermal response than traditional wave soldering.

Impurity Content Determines Dross Generation Rate

If copper content in solder bars exceeds 0.08%, Cu6Sn5 intermetallic compound particles will accelerate formation above 260°C. These particles not only become the core of dross but also adhere to the inner wall of titanium alloy nozzles. We tested a batch of incoming materials with XRF; the nominal copper content was 0.05%, but the measured value reached 0.11%. After three days of production, the scraper cleaning frequency increased from once every 4 hours to once every 1.5 hours. Iron impurities catalyze the SnO oxidation reaction, increasing the daily dross output per unit volume of molten solder from 0.8 kg to 1.9 kg.

Flux and Solder Bars Must Be Verified as a Set

Do not only look at the flux activity value; more importantly, check whether the rosin resin decomposition temperature overlaps with the solder bar wetting peak window. JJY's matching no-clean flux has an acid value attenuation rate of 72% at 235°C, which exactly matches the wetting inflection point of SN99.3CU0.7. If other brands of flux are mixed separately, even if the solid content meets the standard, carbonized residues will aggravate dross entrainment. We conducted comparative tests, and after mixing, the number of solder balls on the back of the PCB increased 2.3 times, and the AOI missed detection rate rose by 11%.

Daily Control Must Focus on Three Physical Indicators

Before each solder change, use a portable melting point meter to measure the liquidus deviation between old and new solder bars, observe the uniformity of the oil film on the molten solder surface using the filter paper adsorption method, and record the net weight change of the solder pot per shift combined with weighing. If these three data exceed ±0.3% for two consecutive days, stop the machine to investigate abnormal solder bar batches. Last month, a sudden increase in dross was caused by moisture absorption of solder bars during logistics and storage, which led to premature hydrolysis of the flux. Grayish-white floating dross had appeared on the surface but was not identified in time.