Some Printed Circuit Boards (PCBs) begin to underperform, mostly because of the signal issues. When a circuit board losses considerable signal, it is said to have suffered a “loss.”

There are different kinds of losses in a circuit board and in this article, we will talk about the mid loss in a PCB.

What is Loss and How Does It Affect a PCB?

A “loss” in a PCB is best described as the “loss of signal strength” especially when it passes through the system-level cabling/components and the circuit boards’ level traces.

The Role of Materials in “PCB Loss”

The types of materials and or substrates used in a circuit board’s construction could greatly impact the performance. In extension, these could increase the chances of the board suffering a loss when signals are being transmitted.

It is therefore, essential to choose the right substrate, especially by considering the appropriate mid loss PCB material to use.

In this section, we aim to introduce you to some of the reasons why the materials chosen for a circuit board might be the reason why the board wouldn’t be able to transmit signals.

The Need for High-Speed Materials

There is a growing demand to reduce the signal transmission issues on PCBs by leveraging on the appropriate materials, especially those designed for high-speed applications.

This is also based on the fact that the type of signal used or required in most high-speed applications is the square-wave signal. Due to the different compositions, it is essential for the materials used for the PCB match the requirements of this signal.

To this end, the circuit material’s dissipation factor is an important metric for choosing the best high-speed materials.

It is on the basis that the insertion loss of the material is considered. The major considerations are the mid-loss and the low-loss.

On the one hand, the mid-loss insertion loss refers to the substrates of PCB materials that have a dissipation factor of 0.010. Although these types of substrates might be less, the point is that they tend to cause higher insertion losses in the materials.

On the other hand, there is the low-loss PCB material, which has less than 50% of what the mid-loss substrates have. The low-loss substrates have a dissipation factor of 0.005 or lower.

How to Tackle Loss in PCB Substrates

The loss of signals in circuit board materials can be tackled, especially for the high-speed applications. If this must be tackled, then the right dissipation factor must be chosen, as well.

When placed side-by-side, the mid-low and low-loss insertion loss can be used, but the low-loss substrates, based on the dissipation factor, can be favored over the mid-loss. These are some of the reasons supporting the claim:

• The low-loss substrates with the dissipation factor of 0.005 or less may be preferred over the mid-loss materials due to the fact that it might cause higher insertion loss.
• To the low-loss materials or substrates will also be preferred, for the high-speed digital designs ranging up to 28 Gbps. In this case, the expected dissipation factor of the substrates should be 0.003 or less.

Can Mid-Loss Substrates be Used?

Yes, you can still use the mid-loss PCB materials, but on the condition that they are used with high-speed digital designs/signals of less than 10 Gigabytes Per Second (Gbps). If the signals are above 10 Gbps, then the low-loss substrates are preferred.

Any Other Option?

Besides the mid-loss and low-loss substrates, one other substrate worth checking out is the ultra-low loss material/substrate. With the dissipation factor of 0.0015 or less, this type of substrate is ideal for the extremely high-speed applications, of up to 56 Gbps.

Key Considerations of Mid-Loss PCB

The rule of thumb is that not all substrates are worth being used for high-speed applications. If you are choosing one for that purpose, then making in-depth research is a must.

a.    Understand the Relevance of Dissipation Factor

The first consideration is to understand the need for using the dissipation factor as a form of “measurement” in the first place.

To put it simply, the dissipation factor refers to the circuit board material/substrate’s support for the high-speed digital applications.

This consideration is most important when there is a need to correlate the material’s substrate to the need for insertion loss considerations in the target applications.

b.    High-Speed Signal Integrity

It is also important to consider the integrity of the high-speed digital signal. The core consideration here is the possibility of the PCB substrate/material to handle analog signals with the millimeter wavelengths ranging between 25 and 100 GHz.

c.    FR-4 or Not?

The Flame Retardant-4 or FR4 material is one of the most-used substrates in the Printed Circuit Board (PCB) industry.

However, you may be unable to achieve considerable success with using it, especially for the applications requiring high-speed signal transmission.

The FR-4 material is not recommended for these applications because of the introduction of distortion and insertion loss for millimeter-wave signals and analog microwave.

How to Choose the Right Loss Tangent for PCB Materials

Seeing how incompatible some of the mid-loss PCB materials can be, it is important to follow a specific procedure to choose one.

Most importantly, the dissipation factor, also called the loss tangent, can be a vital metric for determining the right type of PCB substrates to use.

a.    Choose a Low Df PCB Substrate

The best step is to choose a PCB material or substrate, which has a lower Dissipation Factor or Df. For example, the dissipation factor of 0.005 is the reason why the low-loss substrates are chosen over the mid-loss PCB materials.

A lower Df value helps to reduce or minimize the losses that the high-speed circuits will exhibit after being fabricated on the PCB substrate.

b.    Choose between Performance and Cost

Sometimes, you have to sit down and think of what you really want – are you opting for performance of the applications or looking to save the costs.

The fact is that the circuit board materials that have a lower Dissipation Factor (Df) are often expensive, while the ones that dissipate the most cost more.

To this end, you are torn between choosing the substrates based on the performances they offer and how much they cost.

Conclusion

The mid-loss or middle loss PCB substrates are not always considered, due to the high Df of up 0.010. This Df value might cause insertion-loss for the high-speed digital signals operating at up to Gbps.

However, you can get considerable advantage if you use the mid-loss PCB substrates/materials for the digital signals operating at less than 10 Gbps.