In failure analysis of electric vehicle (EV) PCB batches, delamination and plated-through-hole (PTH) cracking collectively account for over 60% of all reliability failures, with particularly severe issues observed in BMS acquisition boards, motor controller multilayer boards, and 800V high-voltage boards. Most manufacturers merely adjust parameters reactively after defects occur, failing to identify the root causes involving material compatibility, equipment settings, and process interactions. Consequently, repeated design revisions still fail to pass thousands of cycles of high-low temperature testing.

The lamination process is the core node for preventing PCB delamination. Delamination essentially results from insufficient adhesion at the resin-glass fiber interface or the copper foil-substrate interface, leading to interfacial peeling under thermal stress and moisture penetration. The root causes fall into two categories: material incompatibility and process control deviation. Standard FR-4 laminates exhibit excessive Z-axis CTE, creating a large thermal expansion mismatch with copper foil, which generates internal stress during thermal cycling. Additionally, moisture absorption in prepreg (PP), abnormal resin flow, or improper lamination profiles—such as overly rapid heating causing uneven resin bleed and inner-layer shift—result in entrapped voids and wrinkles.

The automotive-grade control scheme prioritizes material matching: selecting High-Tg (≥170°C) / Low-CTE substrates and compatible prepregs for engine compartment and high-voltage applications, while strictly controlling laminate moisture absorption. Incoming materials undergo mandatory baking at 125°C for desiccation. Lamination is performed under a sustained high-vacuum environment using a segmented heating and pressure profile: low pressure for outgassing in the initial stage, medium pressure for full resin infiltration in the middle stage, and constant temperature curing in the final stage. 100% SAM (Scanning Acoustic Microscopy) inspection is implemented to detect internal voids and delamination; lots exceeding bubble limits are reworked directly. Furthermore, symmetric stack-up designs are enforced for multilayer boards to prevent warpage-induced delamination caused by uneven thermal deformation.

The drilling process determines the fundamental quality of the hole wall. Burrs, resin smears, glass fiber pull-out, and micro-cracks significantly weaken the subsequent metallization bond strength, allowing minor flaws to propagate into hole wall fractures during long-term thermal cycling. Common erroneous practices include single-speed drilling, overuse of drill bits beyond their service life, and excessive aspect ratios.

Automotive-grade drilling controls specify segmented spindle speed and feed rates based on board thickness (thin vs. thick) and hole size; thick boards require low-speed, stable drilling to minimize hole wall roughness. A strict drill bit lifecycle management system is established—bits are forcibly replaced upon reaching their rated hit count to prevent glass fiber damage from dull tools. Post-microvia drilling, high-pressure water washing combined with ultrasonic cleaning is added to thoroughly remove debris. Design rules strictly limit the aspect ratio for automotive through-holes to ≤ 8:1, and adequate spacing is required in dense via areas to prevent vibration-induced micro-cracks. Shift-wise sampling and cross-section analysis verify hole wall roughness ($R_a$value); high-voltage PCBs must maintain roughness within a lower threshold to mitigate creepage and stress concentration risks.

Hole metallization is the most critical step in resisting PTH cracking, encompassing desmear, electroless copper deposition, and panel plating.

Resin smear left after drilling compromises adhesion if not completely removed, leading to plating peel-off. Conversely, over-desmearing excessively attacks glass fibers, also weakening the interface. For automotive-grade production, a potassium permanganate (${\text{KMnO}}_4$) desmear system is employed with precise control over concentration, temperature, and immersion time. High-reliability products receive supplementary plasma desmear treatment to enhance interfacial anchoring. Electroless copper parameters (copper ion concentration, catalyst activity) are tightly controlled to ensure a continuous, dense copper seed layer. Plating specifications mandate a minimum average hole wall copper thickness of 25 μm, with uniformity deviation controlled within 10% to eliminate local thin spots that act as stress concentrators. For dense vias in BMS and high-voltage boards, resin plugging technology is promoted to fill internal cavities, blocking moisture ingress while reinforcing structural integrity, thereby significantly improving resistance to CAF (Conductive Anodic Filament) formation and thermal cycling fatigue.

Regarding process implementation, a cross-process linkage sampling mechanism is vital: lamination first-articles undergo thermal stress pre-testing; drilling first-articles are cross-sectioned to confirm hole wall integrity; and metallization batches are sampled every 200 panels for hole copper verification. Engineers must conduct DFM (Design for Manufacturability) reviews concurrently, constraining stack-up symmetry, hole pitch, and aspect ratios to achieve synergy between design and fabrication. This holistic approach fundamentally reduces the probability of batch failures due to delamination and PTH cracking, meeting the stringent 15-year service life reliability requirements for electric vehicles.