Selecting Appropriate HDI PCB Materials: A Guide
**Optimising High-Density Interconnect (HDI) PCB Material Selection for Optimal Performance**
When designing high-density interconnect (HDI) printed circuit boards (PCBs), selecting the right materials is crucial for ensuring optimal performance and reliability. Here are some key properties to consider.
**Common Properties to Consider**
1. **Dielectric Constant (Dk):** Affecting signal speed and impedance control, materials with a low and stable Dk are preferred for faster signal propagation and easier impedance tolerance management.
2. **Dissipation Factor (Df):** Represents signal energy loss as heat, and low-Df materials are chosen to minimise signal attenuation in high-frequency applications.
3. **Thermal Conductivity:** Helps dissipate heat from components, and high thermal conductivity materials aid in maintaining thermal stability by efficiently dissipating heat away from active components.
4. **CAF Resistance:** Prevents Conductive Anodic Filament (CAF) formation, which can cause shorts. Materials with proven CAF resistance are crucial for reliability in dense layouts.
5. **Material Stability and Durability:** Ensures the PCB can withstand manufacturing processes and operating conditions. Materials must be stable across various operating conditions and able to endure multi-stage lamination processes without compromising performance.
**Material Selection**
Commonly used materials for HDI PCBs include series from Rogers, Isola, and Panasonic, with the choice depending on the specific application requirements. For high-performance applications, materials like ceramic and polyimide are also considered due to their excellent thermal conductivity and electrical performance.
- Medium-speed materials exhibit a flatter D versus frequency response curve and are suitable for applications operating at 0 to 10 GHz. - Very high-speed and very low-loss materials are suitable for applications operating at 20-60GHz. - The operating frequency and acceptable signal loss are the first considerations when choosing dielectric materials for high-density boards.
**Construction Techniques**
To reduce conductor loss, PCBs should be constructed with wider traces and use rolled copper foils rather than traditional electrodeposited (ED) copper foils. Additionally, employing low-profile copper helps minimise conductor loss. For laser drilling, choose materials such as flat glass cloth with high resin content like 1035, 1067, and 1086.
**High-Density Boards and Applications**
High-density boards are suitable for small consumer applications, featuring fine lines and spaces (4 mil), microvias, small capture pads (16 mil), and high pad density (>20 pads/cm). When selecting materials for these boards, prioritise materials with low D to maximise signal integrity.
**Temperature Considerations**
Use higher Tg laminates to prevent thermal issues. For instance, if the operating temperature is 2000°C, choose a laminate with T ≥ 200°C. Prefer RoHS-compliant substrates such as lead-free and halogen-free substrates.
**Case Study: Panasonic's Megtron6**
Panasonic's Megtron6 is a high-performance laminate with a Dof 3.4 and D of 0.004 at 18GHz. This laminate offers excellent electrical properties and thermal conductivity, making it an ideal choice for high-speed and high-frequency applications.
In conclusion, when designing HDI PCBs, it is essential to consider key properties such as dielectric constant, dissipation factor, thermal conductivity, CAF resistance, material stability, and durability. By selecting the right materials and construction techniques, designers can ensure optimal performance and reliability for their high-density interconnect PCBs.
[1] "High-Density Interconnect (HDI) PCB Design: A Comprehensive Guide." I-Connect007, 2021. [Online]. Available: https://www.i-connect007.com/Guest-Editorial/High-Density-Interconnect-HDI-PCB-Design-A-Comprehensive-Guide/51648
[2] "Dielectric Constant (Dk) and Dissipation Factor (Df) in High-Frequency PCB Design." Altium, 2021. [Online]. Available: https://www.altium.com/learn/pcb-design/dielectric-constant-dk-and-dissipation-factor-df-in-high-frequency-pcb-design
[3] "Understanding the Importance of Thermal Conductivity in PCB Design." Altium, 2021. [Online]. Available: https://www.altium.com/learn/pcb-design/understanding-the-importance-of-thermal-conductivity-in-pcb-design
[4] "High-Performance PCB Materials: A Comparative Study." I-Connect007, 2021. [Online]. Available: https://www.i-connect007.com/Content/Articles/High-Performance-PCB-Materials-A-Comparative-Study/51670
A stackup designer should consider the controlled impedance technology when designing high-density interconnect (HDI) printed circuit boards, as it affects signal speed and impedance control, and is crucial for faster signal propagation and easier impedance tolerance management.
To construct high-performance HDI PCBs, various materials from manufacturers like Rogers, Isola, and Panasonic are used, with controlled impedance technology materials being preferred for high-speed and high-frequency applications due to their excellent electrical properties and thermal conductivity.
