Fr4 is the best material for multilayer pcb？

 

One of the greatest hand-me-downs that can be passed on or embraced is a good tradition. For example, getting together with family for traditional holiday meals provides some of my most cherished memories year after year. And it is my hope that these will continue to be passed down forever. Not all traditions should be perpetual, however. There are those that should never have begun, and then there are the ones that have run their course and need to be changed. But alas, change is sometimes hard to institute and we often continue doing the same thing, simply because it is the tradition.

Believe it or not, becoming locked into a routine despite the possibility of a better option can occur in PCB design. A good example of this is simply using the default materials for your boards, irrespective of the type of board being designed. For example, high-speed boards have different requirements from high-density ones. Most PCBs are made using FR4 as the base material. Although this choice may not result in catastrophe, it may render your design much less than optimized for its intended function. Let’s take a look at standard FR4, along with alternatives, and see when it is and is not the best material for your board design.

What is FR4?

FR4 is the most common material grade that comprises fabricated circuit boards. ‘FR’ indicates the material is flame retardant and the ‘4’ indicates woven glass reinforced epoxy resin. Single or double-sided PCB structures consist of an FR4 core and top and bottom copper layers. Multilayer boards have additional prepreg layers between the center core and top and bottom copper layers. Now, the core consists of a substrate with copper covering, also referred to as a copper clad laminate. The core, laminate, and prepreg may all be FR4 with the copper sheets between the signal and ground layers.

The properties of FR4 may vary slightly depending on the manufacturer; however, it generally has favorable strength and water resistance attributes that support its widespread usage as an insulator for many electrical applications. It serves the same purpose in PCBs, namely to isolate adjacent copper planes and provide overall bending and flexural strength for the structure. FR4 is a good general purpose material for PCB fabrication; however, alternative materials are available.

Alternative PCB Materials

Prior to the explosion of multilayer PCBs, there were many alternative board materials to FR4. These included FR2, CEM 1, and CEM 3, which were paper-based. However, the strength of FR4, especially for multilayer boards, was a major factor in separating it from alternatives to become the industry standard. Today, there are other materials that are used for single-sided, double-sided, non-plated through-hole (NPTH), and multilayer PCBs, in addition to FR4. These are compared in the table below:

Important Guidelines for Selecting FR4 Material in PCB Fabrication

“Material thickness plays a key role in FR4 circuit board manufacturing. Some common units used to measure material thickness include inches, millimeters, and thousands. Apart from material thickness, there are several important pointers that need to be considered while choosing FR4 material for a circuit board assembly.

A.It is always a good practice to select a high-performance FR4 laminate when the operating temperature exceeds 150°C. As discussed earlier, these materials offer better thermal resistance and low expansion rates while retaining manufacturability.

B.Consider thin FR4 material with space constraints to make the PCBs reliable in terms of functionality. These lightweight materials support delicate components to make devices such as USB connectors, Bluetooth accessories, and much more. Thin FR4 material is widely preferred for applications where space is always a constraint. These materials are known for offering better flexibility, and hence they are used for building complex yet thin PCBs used in the medical and automotive sectors.

C.Choose a material having a uniform dielectric constant over varied frequencies, and FR4 fits into this aspect.

D.Avoid using other thin PCB materials that feature grooves as there may be a high risk of board fracture or damage.

Summary

FR4 is made and is available in various specifications and configurations because of the demand for the same. Their conducive physical and chemical properties have contributed to their popularity. If you are planning to consider FR4 for your upcoming electronic applications, then it is always a good practice to consult an industry player who may offer technical assistance including material selection. This post introduces Creative Hi-Tech, which is one of the reliable, trustworthy manufacturers of FR4 PCBs. With a vast market presence and highly skilled employees, the company has been helping its clients in making the right material selection and offering end-to-end solutions.