In actual operation after the energy storage system is installed in a vehicle, the vibration experienced by the PCBA is far beyond what conventional laboratory sinusoidal sweep testing can cover. JiajinYuan has found in multiple projects that insufficient rigidity of the battery pack tray causes resonance amplification in the 15Hz~45Hz frequency band. Combined with the transient shock generated during motor start-stop (peak value up to 35g) and the broadband random vibration excited by road bumps (PSD up to 0.04g²/Hz), the traditional PCBA reliability test scheme becomes invalid. We directly imported the vehicle-measured acceleration spectrum into the vibration table controller, replaced single-axis testing with three-axis synchronous excitation, and extended the test duration from 2 hours to 8 hours, before reproducing pad peeling and 0201 resistor solder joint cracking on a certain BMS board.

JiajinYuan's SMT production line always adheres to the principle of performing X-ray scanning first before disassembly analysis for failure localization of post-vibration PCBA, because many bottom-side BGA cold solder joints or solder ball microcracks are completely invisible during visual inspection, and relying solely on AOI or ICT cannot capture such hidden defects caused by mechanical stress. We once encountered a batch of boards that functioned normally after vibration testing but failed in bulk three months after delivery. Sectioning revealed periodic micro-voids under the QFN thermal pad, which is exactly the fatigue damage caused by repeated pulling of high-frequency components above 200Hz in the random vibration spectrum. If the test does not cover this frequency band, misjudgment is inevitable.

Fixture design is not an auxiliary step but a key variable that determines the success or failure of testing. All vehicle-mounted PCBA vibration tests conducted by JiajinYuan use rigid clamping consistent with the vehicle installation posture, and silicone pads are installed under key components at the PCBA edge to simulate body damping characteristics. Otherwise, an overly rigid fixture will cause excessive stress concentration on Connector Solder joints, while an overly weak fixture will lead to abnormal board sway, masking the true failure mode. We once misjudged a batch of DC-DC control boards as having inductor pad desoldering during Z-axis vibration due to a 0.3mm deviation in the fixture base plate thickness, which was actually a false open circuit caused by fixture resonance.

Electrical retesting after testing must be performed after 4 hours of standing at room temperature, because some solder joint microcracks exhibit time-varying conduction characteristics under thermal expansion and contraction. JiajinYuan stipulates that all post-vibration boards must undergo three thermal cycles (-40℃/85℃ for 30 minutes each) before functional testing. Otherwise, defects such as microcracks in TVS tube pins will temporarily conduct at room temperature and escape detection. We had two customer complaints caused by skipping this step, which led to a sharp increase in early failure rate, and this step was subsequently incorporated into mandatory process control nodes.

Vibration testing is not a procedural formality but a process of finding boundaries. JiajinYuan engineers record the test spectrum shape, fixture status, board fixing method, and ambient temperature and humidity in handwritten logs every time. Because when the Tg value of the substrate material of the same model PCBA fluctuates by ±5℃ across different batches, or the copper thickness tolerance exceeds ±12μm, its anti-vibration performance varies significantly. If these details are not clearly recorded, it is impossible to reverse-locate the root cause of the problem, let alone optimize DFM design.