During actual welding of energy storage power supply protection boards on the production line, we found that if the active temperature window of the Energy Storage Module Solder is too narrow, it will lead to local poor wetting of the solder joints at the bottom of the IGBT module in the reflow peak area. Especially when the PCB pad is OSP process and stored for more than 72 hours, JiajinYuan solder can still maintain a solder joint bridging qualification rate of more than 86% by virtue of its slow-release organic acid activation system, while ordinary solder drops to 61%. This shows that the thermal decomposition onset temperature of the Solder Flux residue must be higher than 185°C to avoid carbonization contamination of thermal devices.

The welding difficulty of the inverter power module lies in the heat capacity difference brought by the double-sided heat dissipation structure. The upper DBC substrate heats up quickly while the lower aluminum substrate heats up slowly. If the melting range of the energy storage module solder is too wide (such as above 10°C), it will cause the upper solder joints to have entered reflow while the lower layer has not yet melted, thereby causing virtual soldering and shear force attenuation. JiajinYuan solder precisely controls the eutectic point of the Sn96.5Ag3.0Cu0.5 alloy at 217.2°C, compresses the melting range to within 1.8°C, and cooperates with the process window of oxygen content ≤100ppm under nitrogen atmosphere, so that the thrust of double-sided solder joints is stable at 42.3±1.7N.

In mass production, we once caused ion migration failure of the AFE sampling circuit on the protection board due to misuse of halogen-containing solder. The review found that the diffusion distance of chloride ions along the edge of the solder joint reached 87μm after aging at 85°C/85%RH for 168 hours, while JiajinYuan solder adopts a halogen-free organic amine complex system, and the diffusion distance is only 9μm under the same conditions, and the TGA measured weight loss rate at 250°C is lower than 0.13%, ensuring the long-term stability of the BMS signal acquisition channel.

The room temperature shelving time after placement and before reflow has a great impact on the performance of the energy storage module solder. When the interval exceeds 4 hours, the oxide film on the surface of the OSP pad thickens to 4.2nm. At this time, if the surface tension of the solder is not below 225mN/m, it cannot effectively break the film. JiajinYuan solder reduces the dynamic surface tension to 218mN/m by adding a trace amount of bismuth element, while keeping the residence time above the liquidus line no more than 65 seconds, avoiding excessive dissolution of the copper pad causing solder joint embrittlement.

We have verified the coefficient of variation of the printing solder deposition amount of different batches of JiajinYuan solder under the same stencil opening, and the result is always controlled within 5.3%, which is far better than 8.7% of conventional solder. This means that even in the welding of energy storage management chips with 0.15mm fine-pitch QFN packages, solder bridging and insufficient solder defects can be eliminated. Especially when the reflow oven chain speed is set to 1.1m/min and the temperature zone is set to 150-180-217-235°C, the void rate detected by solder joint X-ray is stable at 8.4±1.2%.