High frequency circuit substrate requirements

Abstract: This article introduces high-frequency circuits’ composition and characteristics, development status and performance of copper-clad polyimide fiberglass cloth laminates .

With the rapid development of electronic information technology and the high speed of information processing and dissemination, new requirements for PCB high frequency circuit substrates continue to be required.In addition to the performance of conventional PCB substrates, PCB substrates are required to be exposed to high temperatures and high frequencies (300MHz) with small and stable dielectric constant and dielectric loss factor . The conventional FR-4 foil-clad board has many defects. Therefore, it cannot be used to make high-frequency circuits.

a. FR-4 foil-clad board has low glass transition temperature and poor high temperature resistance.Therefore, when assembling high-power devices with high density, it is easy to cause copper wires to fall off and reduce the reliability of the PCB.When PCB drilling, the high-speed rotation of the drill bit causes heat and resin softened to produce greasy pore walls.

b. The dielectric constant of FR-4 foil-clad board is large.It can be known from the relationship between the signal propagation rate (V) and the dielectric constant of the dielectric layer at high frequencies that V-k1 C / e. The larger the dielectric constant, the slower the signal propagation speed, so it cannot be used in high-frequency circuits;

c. Conventional FR-4 board has a large z-axis thermal expansion coefficient. When multilayer circuit boards are welded and subjected to high and low temperature cyclic impact, thermal stress will reduce the reliability of metallized holes, so it cannot be used to make high-reliability and high-frequency circuits. The high-frequency circuit substrate introduced in this article, copper-clad polyimide fiberglass cloth laminate, is a substrate developed to meet high-temperature and  high-frequency circuits.

2. Characteristics of foil-coated polyimide fiberglass cloth laminate: Copper-clad polyimide fiberglass cloth laminate is a composite material composed of polyimide resin, E-glass cloth, and copper foil. The substrate has high temperature resistance (Tg> 250 ℃), radiation resistance and excellent mechanical properties at high temperatures; excellent high-frequency dielectric properties at 300MHz to 1GHz, dielectric constant 4.1, dielectric loss factor 0.007, and excellent dimensional stability and mechanical processing performance.

3. Development status of copper-clad polyimide fiberglass cloth laminates. Our copper-clad polyimide fiberglass cloth laminates for high-frequency circuits meet the strict requirements of the military industry. This product can meet the requirements of China's communication electronic equipment and other high-reliability electronic equipment, and is widely used. In recent years, with the application of such high temperature and high frequency PCB substrates gradually expanding from military industry to high reliability civilian electronic equipment, the application area is increasing year by year.

4, The main properties of copper-clad polyimide fiberglass cloth laminates. At present, FASTPCBA can produce military high-frequency circuit boards in large batches.

5.Military high-frequency circuit boards have high temperature resistance (Tg> 250 ℃), radiation resistance, excellent high-frequency dielectric properties, machining performance and dimensional stability, and are widely used in aerospace and other fields and high reliability electronic equipment Applications, which are the preferred substrates for today's high temperature and high frequency circuits.