PWB Materials and Considerations

PWB Materials
♦ Dozens of dielectric materials to chose from
- Rogers 20 types
- Taconic 10 types
- Polyclad 25 types
- Park Nelco 30 types
♦ Several dielectric thickness options
♦ Several copper thickness options
♦ Two copper plating options
- Rolled
- Electro-Deposited


Electrical Considerations in
Selecting Materials
♦ Dielectric Constant (permittivity)
- The more stable, the better
- Lower values may be more suitable for high layer counts
- Higher values may be more suitable for some RF structures
♦ Loss Tangent
- The lower, the better
- Becomes more of an issue at higher frequencies
♦ Moisture Absorption
- The lower, the better
- Can effect dielectric constant and loss tangent
♦ Voltage Breakdown
- The higher, the better
- Typically not an issue, except in high voltage applications
♦ Resistivity
- The higher, the better
- Typically not an issue, except in low leakage applications


Mechanical Considerations in
Selecting Materials
♦ Peel Strength
- The higher, the better
♦ Flammability
- UL Standards
♦ Glass Transition Temperature (Tg)
♦ Thermal Conductivity
- Typically PWB material is considered an insulator
- Thermal Clad (Bergquist)
- Planes & vias contribute to thermal conductivity
♦ Coefficient of Expansion
- XY matching to components, solder joint stress (LCC)
- Z axis expansion, via stress
♦ Weight (density)
♦ Flexibility



Dielectric, Common Thickness Dielectric, Common Thickness
♦ Core Material
- 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009
- 0.010, 0.012, 0.014, 0.015, 0.018, 0.020, 0.031
♦ Pre-Preg
- 0.002, 0.003, 0.004, 0.005, 0.008
- Pre-preg can be stacked for thicker layers
♦ Use standard thickness in designing stack-up
♦ Work with anticipated PWB vendor(s) when
assigning stack-up and selecting material