In Power PCB (Printed Circuit Board) manufacturing, when the dielectric layer thickness of a power board is less than 0.4mm, using three prepreg (PP) sheets instead of a single or double layer is often necessary due to several critical factors related to reliability, manufacturability, and electrical performance. Here are the detailed reasons:
1. Process Reliability & Uniformity
Thinner PP Sheets = Better Control: A single thick PP layer (e.g., 0.4mm) may have inconsistent resin flow during lamination, leading to voids or weak spots. Using three thinner PP sheets (e.g., 3 × 0.13mm ≈ 0.39mm) improves resin distribution and minimizes thickness variation.
Avoids Resin-Starved Areas: Multiple layers help ensure uniform resin filling between copper layers, preventing dry spots that could cause delamination or reduced dielectric strength.
2. Electrical Insulation & High-Voltage Requirements
Breakdown Voltage Safety: Power boards handle high voltages, and dielectric thickness directly impacts insulation. Three PP layers reduce the risk of micro-voids or defects that could create weak insulation paths.
Electric Field Distribution: Multiple layers distribute the electric field more evenly, reducing the chance of partial discharge or arcing in high-voltage applications.
3. Mechanical Strength & Delamination Resistance
Stress Distribution: Thin dielectric layers are prone to cracking under thermal or mechanical stress. Three PP layers provide better stress absorption and reduce the risk of micro-cracks.
Improved Bonding: More PP layers enhance interlayer adhesion, preventing delamination during thermal cycling (e.g., reflow soldering or power cycling).
4. Manufacturing Process Optimization
Controlled Resin Flow: During lamination, thinner PP sheets allow more precise control over resin flow, preventing excessive bleeding or insufficient bonding.
Compatibility with Core Thickness: Ultra-thin cores (e.g., 0.1mm) require multiple PP layers to ensure proper filling and avoid resin starvation near copper features.
5. Signal Integrity & Thermal Management
Consistent Dielectric Properties: Multiple PP layers help maintain uniform dielectric constant (Dk) and loss tangent (Df), crucial for high-frequency power integrity.
Thermal Conductivity: Stacking PP layers can improve heat dissipation by creating a more homogeneous thermal path.
How to identify the PPs quantity?
Actually, we can do microsction for PCB board, it can be identify the quantity of PPs, we can check if the stackup meets our requirement.
Conclusion
Using three PP sheets for sub-0.4mm dielectric layers in power PCBs ensures:
✔ Better process yield (fewer voids/delamination)
✔ Higher voltage reliability (reduced insulation risks)
✔ Stronger mechanical structure (resists cracking)
✔ Controlled manufacturing (resin flow, bonding quality)
This approach is common in high-reliability applications like server power supplies, automotive electronics, and industrial PCBs. The exact number of PP layers may vary based on material specs (e.g., resin content, glass weave) and lamination parameters.
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