What are Mid Loss PCBs?

A mid loss PCB (printed circuit board) is a type of PCB material that has moderate dielectric loss characteristics. It falls between low loss and high loss PCB materials in terms of its dielectric loss tangent (dissipation factor). Mid loss materials typically have a loss tangent in the range of 0.02 to 0.05.

Some common mid loss PCB materials include:

• FR-4 glass epoxy
• Polyimide
• BT Resin

Mid loss PCBs provide a balance of performance and cost effectiveness. They have higher frequency performance than standard FR-4 boards but are less expensive than exotic low loss materials.

Key Properties of Mid Loss PCBs

Some key properties of mid loss PCB materials:

Property	Typical Values
Dielectric Constant	4.0 to 4.8
Loss Tangent	0.02 to 0.05
Dielectric Strength	400 to 1000 V/mil
Moisture Absorption	0.2 to 0.6%

Applications of Mid Loss PCBs

Mid loss PCBs are suitable for a variety of applications including:

• Wireless communications
• Automotive electronics
• Industrial controls
• Consumer electronics
• Medical devices

They provide good signal integrity up to several GHz while maintaining reasonable cost levels. Mid loss boards are a versatile choice for many RF designs.

Advantages of Mid Loss PCBs

Some notable advantages of using mid loss PCB materials:

• Cost effective compared to low loss PCBs
• Higher frequency support than standard FR-4
• Good thermal stability and dimensional stability
• Can support data rates in the Gbps range
• Superior signal integrity compared to high loss materials
• Widely available from most PCB manufacturers

Considerations When Using Mid Loss PCBs

There are some design considerations to keep in mind when using mid loss PCBs:

• May require impedance matching at higher frequencies
• Sensitive to board thickness variations
• Traces should be kept short, use ground planes
• Controlled impedance traces are recommended
• Vias can cause discontinuities and reflections
• May need to use lower dielectric constant for high speed designs

Careful layout and termination is important for optimal performance.

Frequently Asked Questions

What is the typical frequency range for mid loss PCBs?

Mid loss PCBs typically support frequency ranges up to 5-10 GHz depending on materials and construction. Many mid loss boards can handle frequencies in the 1-5 GHz range.

How do mid loss PCBs compare to FR-4?

Mid loss PCBs have lower loss, improved signal integrity, and higher frequency support compared to standard FR-4 boards. The improved electrical performance comes at a small cost premium over FR-4.

What fabrication processes are used for mid loss PCBs?

Mid loss PCBs can be fabricated using standard processes including photolithography, etching, drilling, plating, and lamination. Many mid loss materials are compatible with FR-4 processes.

When should low loss PCBs be used instead of mid loss?

For very high frequency applications above 10 GHz or circuits requiring exceptional signal integrity, low loss PCBs may be needed instead of mid loss. Mid loss provides a good balance for many applications.

Can microstrip lines be used on mid loss PCBs?

Yes, microstrip transmission lines can be implemented on mid loss PCBs. Careful impedance control and layout is needed to account for losses.