After receiving the Automotive Electronics Solder samples delivered by the customer, we first use a JJY standard test specimen substrate to perform SPI Solder Paste thickness scanning to confirm that the printing consistency is within ±12%, before proceeding to the SMT placement process. The stencil openings used are designed in accordance with JEDEC J-STD-005 requirements, the placement accuracy is controlled within ±0.05mm, the peak temperature of the reflow profile is set to 245°C, and the time above the liquidus line is maintained for 65 seconds, to ensure the solder is fully melted without damaging the internal electrode structure of automotive-grade MLCCs.

The soldered test boards must be left to stand for 4 hours to allow natural stress relief, before being placed in a thermal shock chamber for cyclic testing. Each cycle consists of a 30-minute hold at -40°C, a 10-minute room temperature transition, a 30-minute hold at 125°C, and a 10-minute room temperature transition, running continuously for 500 cycles without interruption. Human intervention or mid-test removal is prohibited during this period, as this would disrupt the thermal stress accumulation path and render the data meaningless.

Starting after the 250th cycle, X-ray is used to perform point-by-point scanning of BGA solder joints, with a focus on whether voidage increases or shadow shifts appear in the corner solder balls. Immediately after the 500th cycle, the samples are stored in a -40°C freezer for 2 hours, then sent to AOI for solder joint profile comparison. It was found that a certain batch of JJY Sn96.5Ag3.0Cu0.5 solder exhibited microcrack propagation covering 0.8% of the area at corner solder joints, while Sn97Ag2.5Cu0.5 showed no abnormalities under the same conditions, indicating that a 0.5% fluctuation in silver content has a significant impact on thermal fatigue resistance.

Cross-section verification must use ion beam polishing rather than mechanical grinding, otherwise the solder joint interface will be falsely scratched. In our cross-sectional EDS analysis, we observed that the thickness of the Cu6Sn5 IMC layer increased from 2.3μm to 3.1μm after cycling, but no continuous fracture occurred, indicating that this solder has good bonding with OSP-treated copper pads. In contrast, ENIG pad specimens exhibited local IMC layer peeling under the same cycling conditions, confirming that surface treatment methods have a decisive impact on the long-term reliability of automotive electronics solder.

All test data is synchronously recorded into JJY's internal database, supporting cross-dimensional filtering by parameters such as temperature slope, hold time, and pad size. For example, when a customer uses 0201-size automotive-grade resistors, we directly retrieve 12 sets of historical matching data for similar pads, quickly locking in the recommended reflow peak temperature window of 242°C ± 2°C, to avoid NPI cycle delays caused by repeated trial and error.