What are the disadvantages of FR4?

FR4 epoxy sheet, as a high-performance flame-resistant material, is widely used in circuit board manufacturing and multiple electronic industry fields. However, like all materials, FR4 epoxy sheet also has some inherent disadvantages and limitations.

1. High signal loss

In high-speed signal transmission scenarios, FR-4 has a high dielectric constant and high signal loss, which is not conducive to the construction of high-frequency and high-speed circuits, limiting its application in high-end communications, servers and other fields that require stringent signal quality.

2. Dimensional stability is limited

During the manufacturing process of FR4 epoxy sheet, due to the limitations of the material itself and the manufacturing process, its dimensional stability may be affected to a certain extent. Specifically, FR4 epoxy sheet may expand or shrink to a certain extent when it is damp or heated, resulting in dimensional changes. This dimensional change may affect the accuracy and performance of the circuit board, especially in electronic equipment with high precision requirements, this effect may be more significant. Therefore, when using FR4 epoxy sheet, user should pay attention to the control of its dimensional stability.

3. High hygroscopicity

The glass fiber component in the FR4 epoxy sheet has a certain hygroscopicity, which can absorb and retain moisture and solvents. This hygroscopicity may cause the performance of the circuit board to deteriorate in a humid environment, or even cause faults such as short circuits. Especially in electronic equipment working in high humidity or humid environments, the hygroscopicity of the FR4 epoxy sheet may become a potential risk factor. In order to reduce this risk, it is usually necessary to perform moisture-proof treatment on the circuit board, such as coating moisture-proof paint or using moisture-proof materials.

4. Brittleness problem during processing

Although the FR4 epoxy sheet has high mechanical properties, brittleness problems may still occur during processing. Especially during mechanical processing such as drilling and cutting, improper operation or defects in the material itself may cause cracks or fractures in the FR4 epoxy sheet. This brittleness problem not only affects the appearance quality of the circuit board, but may also have an adverse effect on its electrical performance and reliability. Therefore, it is necessary to strictly control the process parameters and operating specifications during the processing to ensure the processing quality of the FR4 epoxy sheet.

5. Insufficient adhesion of the copper layer

During the manufacturing process of the circuit board, the adhesion between the copper layer and the FR4 epoxy sheet is a key performance indicator. However, due to factors such as the surface characteristics of the FR4 epoxy sheet and the difference in the thermal expansion coefficient of the copper layer, the adhesion between the copper layer and the FR4 epoxy sheet may be insufficient. This insufficient adhesion may cause the copper layer to peel off or break during welding or use, thereby affecting the electrical performance and reliability of the circuit board. In order to improve the adhesion between the copper layer and the FR4 epoxy sheet, the FR4 epoxy sheet is usually required to undergo surface treatment, such as roughening, chemical copper plating and other processes.

6. The thermal expansion coefficient does not match other materials

The thermal expansion coefficient of the FR4 epoxy sheet may be significantly different from that of some other high-performance materials (such as ceramics, metals, etc.). This mismatch in thermal expansion coefficient may cause problems such as stress concentration and deformation between the circuit board and other components during temperature changes. These problems may have an adverse effect on the performance and reliability of the circuit board, especially in high-precision and high-reliability electronic equipment. Therefore, when designing the circuit board, it is necessary to fully consider the matching of the thermal expansion coefficient of the FR4 epoxy sheet with other materials.

7. ‌Higher cost‌

Although FR4 epoxy sheet has excellent performance in many aspects, its relatively high cost is also a factor that needs to be considered. Especially in large-scale production and high-end electronic devices, the use of FR4 epoxy sheet may increase the manufacturing cost of the product.