When we actually used SAC305 Energy Storage Module Solder on the production line, we found that the Solder Paste could still maintain good rollability after being left at a constant temperature of 30°C for 2 hours under the conditions of a stencil opening thickness of 0.12mm and an opening ratio of 75%. However, if the ambient humidity exceeds 60%RH and nitrogen protection is not enabled, the void rate of BGA solder joints after reflow will surge from 8% to 22%. This indicates that the solder paste is extremely sensitive to temperature, humidity and atmosphere control, rather than simply relying on the alloy composition itself.

The thixotropic index of JJY SAC305 Solder Paste is controlled within the range of 0.72±0.03. This value not only ensures that the solder paste can quickly fill the stencil apertures under the squeegee, but also avoids bridging caused by collapse after demolding. Especially for the dual-row QFN-48 packaged devices commonly used in energy storage modules, we once mistakenly adjusted the squeegee pressure from 4.5kg to 6.2kg, which led to excessive solder paste extrusion, ultimately causing micro-shorts at the 0.15mm spacing between adjacent pads, and the rework time was 3 times longer than normal.

For the wire solder application of energy storage module solder, we insist on using the specification with a diameter of 0.6mm and a rosin core proportion of 2.8%. When manually reworking the BMS sampling terminal block, if the preheating temperature is lower than 280°C or the soldering iron dwell time exceeds 3 seconds, it is extremely easy to cause the PCB pad copper foil to lift. Moreover, the Flux residue of the Solder Wire begins to corrode the FR4 substrate after 48 hours in a 75°C high temperature and high humidity aging test. Therefore, after each soldering, the residue must be completely removed using 99.8% absolute ethanol with an ultrasonic cleaning machine.

JJY SAC305 Solder Bars need to be used with a special flux with a specific gravity of 1.023 in the wave soldering process. When the solder pot temperature is set to 255°C and the chain speed is 1.1m/min, the wetting angle of the solder joints on the large-area copper foil heat sink of the energy storage module can be stably kept within 28°. However, if the silver content deviation of the Solder Bar exceeds ±0.03%, obvious slag accumulation at the nozzle will be observed after 8 hours of continuous operation, which will further affect the consistency of the solder joint climb height.

We once stored the same batch of JJY SAC305 solder paste in a 22°C air-conditioned room and a temporary shelf in a 38°C workshop respectively. After 72 hours, the viscosity change rate of the former was only 4.1%, while that of the latter reached 19.7%. This directly led to insufficient solder volume defects on 3 consecutive boards during printing with the latter. Therefore, the solder paste for energy storage module solder must implement the three principles of "use immediately upon receipt, constant temperature temporary storage, and mandatory scrapping 24 hours after opening", and must not be extended according to conventional material management logic.