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Most PCBs are made of FR4. While this choice may not lead to disaster, it can make your design far less optimized for its intended functionality. FR4 is the most common material grade, including prefabricated circuit boards. “Fr” indicates that the material is flame retardant, and “4” indicates glass fiber reinforced epoxy resin. Single or double-sided PCB structure is composed of FR4 core and top and bottom copper layers. The multilayer board has other prepreg layers between the center core and the top and bottom copper layers. The core now consists of a substrate with a copper cladding, also known as a copper clad laminate. The core, laminate and prepreg can be FR4, and the copper sheet is between the signal layer and the ground plane.

fr4 circuit board material
fr4 circuit board material

The properties of FR4 may vary slightly, depending on the manufacturer. However, it usually has favorable strength and water resistance properties, which can support its wide use as an insulator in many electrical applications. It has the same purpose in PCB, that is to isolate adjacent copper planes and provide overall bending and bending strength for the structure. FR4 is a good general material for PCB manufacturing. However, other materials can be used.

Alternative PCB materials

Before the explosion of Multilayer PCB, there were many board materials to replace FR4. These include paper-based FR2, CEM 1 and CEM 3. However, the strength of FR4, especially the strength of multilayer board, is the main factor that separates FR4 from its substitutes and becomes the industry standard. Today, in addition to FR4, there are other materials available for single-sided, double-sided, non electroplated through holes (npth) and multilayer PCBs.

It has a copper adhesion of 2.0 n / mm, excels in structural integrity and is comparable to other alternatives in terms of flexural strength. However, compared with the substitute, the Tg of FR4 is lower. This means that the material may deform or break when exposed to excessive temperatures, especially over time.

When is FR4 not the most suitable material for your circuit board?

As mentioned above, FR4 is indeed the ideal standard or default choice for plate materials in most cases. However, in some cases, FR4 is not the best material for your circuit board, as shown below.

If lead-free soldering is required

If your circuit board will be sold in Europe and you have to comply with the RoHS or your customers need to use lead-free soldering, you may want to explore other material options. This is due to the fact that the reflow temperature of lead-free PCBA can be as high as 250 ° C, which is much higher than the Tg of many FR4 versions.

If a high frequency signal is used

At high frequency, FR4 board can not maintain constant impedance, and reflection may occur, which has a negative impact on signal integrity. This is the result of higher DK value.

If the circuit board is exposed to extremely high temperatures during operation

FR4 is also not recommended if PCBs are required to operate in extremely high temperatures. One example is near the engine compartment of an aerospace vehicle.



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