When soldering 10AWG copper terminals with 0.8mm ordinary rosin-core Solder Wire, the solder joints appear dull and have insufficient thrust. While the surface looks bright, cutting open the joints reveals a large number of internal pores and unfused interfaces. This is because the activity level of the solder wire is too low to effectively remove the oxide film on the large cross-section copper material, and the wire diameter is too small, causing a single solder feed to fail to fill the solder cup, ultimately forming cold solder joints. The correct approach is to switch to 2.0mm no-clean high-activity solder wire, and pre-tin the inner wall of the terminal.
After soldering aluminum shell terminals with the soldering iron temperature fixed at 380℃, obvious thermal cracks appear. The reason is that the aluminum substrate has fast heat conduction and a large thermal expansion coefficient. If the temperature is not adjusted in real time according to the thickness of the terminal body, thick-walled parts require higher instantaneous heat input to melt through the solder layer, while thin-walled parts will suffer from base material lattice distortion due to overheating. Therefore, an infrared temperature gun must be used to actually measure the temperature of the terminal body, ensuring that the soldering area is stable at 260℃±5℃ instead of only looking at the soldering iron set value.
It is common practice on site to use the same soldering iron to continuously solder copper terminals and nickel-plated terminals, resulting in gray solder joints on nickel-plated terminals with wetting height less than one-third. The root cause is that the wettability of nickel metal to solder is much lower than that of copper, requiring stronger reducing Flux combined with a higher starting temperature. However, blindly increasing the temperature will accelerate the dissolution of the nickel layer. Therefore, it is necessary to switch to special solder wire containing zinc chloride, and control the soldering iron temperature in stages: rise to 400℃ at the moment of contact to break the passivation film, and drop back to 320℃ within 3 seconds to complete wetting and spreading.
Some people use Leaded Solder Wire instead of lead-free solder wire to solder automotive-grade terminals. Although the thrust meets the standard in the short term, severe electrochemical corrosion occurs after high-temperature and high-humidity aging tests. This is because lead ions form a galvanic cell with copper terminals in a humid environment, accelerating copper corrosion. Automotive electronics standards mandate lead-free processes, so SAC305 or SAC405 series solder wires compliant with J-STD-006C must be selected, and their silver content must be confirmed to be no less than 3.0% to ensure thermal cycle reliability.
Applying solder directly to terminals without baking them at 120℃ before soldering leads to micro-cracking sounds inside the solder joints accompanied by pinhole-like defects. This is caused by the instantaneous vaporization of moisture adsorbed by the terminal injection molded body or plating layer at high temperatures, which is particularly typical in PA66 material terminals. Therefore, all batches of terminals must be dried in a constant temperature oven for 4 hours before being put into production. If the humidity indicator card shows a blue-to-pink color change, the batch is judged as failed.
Mistakenly leaving the soldering iron tip in the terminal solder cup for a long time waiting for the solder wire to melt causes local overheating, which anneals and softens the copper material. In subsequent plugging and unplugging tests, the terminal deformation rate reaches 73%. The fundamental reason is that the solder cup wall thickness of high-current terminals usually exceeds 1.2mm, with a heat capacity far greater than that of PCB pads. The rhythm of "touch, withdraw, touch again" must be adopted, with each contact time not exceeding 2.5 seconds, and the total soldering time strictly controlled within 8 seconds. At the same time, use tweezers to gently press the solder wire to assist heat conduction.
Simple inspection checklist: confirm that the solder wire diameter ≥ 1/3 of the terminal wire cross-sectional area, verify whether the solder wire activity level is marked as ROL0 or ROL1, measure whether the deviation between the actual soldering iron tip temperature and the set value is ＜±5℃, check whether the terminal body has a baking mark, verify whether the flux residue passes the ionic contamination test (≤1.56μg/cm2 NaCl), and observe whether the solder joint contour completely covers the edge of the solder cup and presents a rounded concave surface instead of a spherical protrusion.
