PCB Blog - FR-4 VS aluminum plate

The material of FR4 circuit board is a composite material of glass fiber and epoxy resin,also known as glass fiber cloth-mpregnated epoxy resin.Normally,the ratio of glass fiber to epoxy resin is 1:2.Its advantages include good heat resistance, stable electrical insulation performance, and high mechanical strength, making it widely used in various electronic devices.CTE (Coefficient of Thermal Expansion) is the degree to which a material expands in response to a change in temperature and is usually expressed in ppm/°C (parts per thousand per degree Celsius.) FR-4 has a CTE value of approximately 15 to 19 ppm/°C, which is suitable for the majority of organic encapsulation needs. As industry demand for low CTE packages has increased, the CTE of FR-4 has come under higher scrutiny.

CTE is critical to the performance of PCBs, especially when subjected to thermal cycling, as CTE mismatches between different materials can initiate stresses that can lead to mechanical failure. Specifically, when FR-4 is combined with other materials (e.g., copper), temperature changes may cause cracking or peeling at the interface because of the different expansion rates of each material.The horizontal and vertical CTEs (CTEx, CTEy, CTEz) of FR-4 materials need to be accurately considered in order to ensure the reliability of the design.

The manufacturing process of FR4 circuit boards can be summarized as the following steps

1.Preparation of glass fiber cloth: glass fiber is connected by Loom to form glass fiber cloth.

2.Rough processing: Place the prepared glass fiber cloth into a large mold and add epoxy resin, and cure it with hot pressing technology to form it.

3.Precision processing:The pre-processed fiberglass cloth is processed through drilling,copper deposition,and inspection to produce various specifications and models of FR4 circuit boards.

FR-4 is a commonly used substrate for printed circuit boards (PCBs), and its coefficient of thermal expansion (CTE) is important in several applications in the electronics industry.

1.Thermal management and dimensional stability

The CTE of FR-4 material is usually in the range of 50-70 x 10^-6/°C, representing its dimensional stability during temperature changes. When an electronic device is in operation, the generation of heat causes the material to expand or contract, and an excessively high CTE may cause the board to deform, affecting reliability. Designers need to consider the impact of CTE to ensure the smooth operation of the board under various operating conditions.

2.Soldering Reliability

In the soldering process, the circuit board undergoes rapid thermal cycling, the sudden rise and fall in temperature may cause poor solder contact and subsequent connection failure. Choosing the right material for CTE can reduce thermal stress and ensure the strength and reliability of the solder joints. This is particularly important for high-density assembly and miniaturization of electronic equipment.

3.The importance of application in high frequency circuits

High-frequency circuits have strict requirements on the dielectric properties and thermal expansion characteristics of the material. FR-4 in high-frequency applications, if the material is not selected properly, may lead to signal delay and distortion . Proper CTE allows the board to maintain good signal integrity at operating frequencies and is one of the key factors in designing high frequency circuits.

4.Cost Effectiveness Considerations

FR-4 is a lower cost and relatively stable performance option compared to other materials (e.g. ceramics, PTFE, etc.). From a cost-benefit standpoint, FR-4 provides a high degree of economy in production while meeting basic CTE requirements. This cost/performance advantage has made FR-4 the dominant material in several areas, especially in consumer electronics.

An aluminum plate is a metal-based copper-clad plate with good heat dissipation function.Generally,a single panel consists of a three-layer structure,namely a circuit layer (copper foil), an insulation layer,and a metal substrate.Some designs for high-end use are also double-sided boards,with a structure of a circuit layer,insulation layer,aluminum base, insulation layer, and circuit layer.Very few applications are multilayer boards,which can be made by bonding ordinary multilayer boards with insulation layers and aluminum plates.

The difference between FR-4 and aluminum plate

1.Performance

The comparison of wire (copper wire) and fuse current on different substrate materials, from the comparison of aluminum plate and FR-4 plate,shows that due to the high heat dissipation of the metal substrate, the conductivity is significantly improved, indicating the high heat dissipation characteristics of the aluminum plate from another perspective.The heat dissipation of aluminum substrate is related to its insulation layer thickness and thermal conductivity.The thinner the insulation layer, the higher the thermal conductivity (but lower the pressure resistance) of the aluminum plate.

2.Processability

An aluminum plate has high mechanical strength and toughness, which is superior to an FR-4 plate.For this purpose,large-area printed boards can be made on aluminum plates,on which large components can be installed.

3.Electromagnetic shielding performance

To ensure the performance of circuits,certain components in electronic products need to prevent electromagnetic wave radiation and interference.Aluminum plates can serve as shielding plates to shield electromagnetic waves.

4.Thermal expansion coefficients

Due to the thermal expansion of general FR-4,especially the thickness of the plate, the quality of the metalized holes and wires is affected. The main reason is that the thermal expansion coefficient of copper in the raw material is 17 * 106cm/cm-C in thickness, and the thermal expansion coefficient of FR-4 plate is 110*106cm/cm-c,which has a significant difference and is prone to heating substrate expansion, changes in copper wires, and damage to product reliability caused by metal hole rupture.The thermal expansion coefficient of the aluminum plate is 50 ×106cm/cm-C, smaller than ordinary FR-4 board and close to the thermal expansion coefficient of copper foil. 

5.Application fields

The FR-4 board is suitable for general circuit design and ordinary electronic products.Aluminum plates are often used in electronic products with high heat dissipation requirements, such as LED light boards.

FR4 is a glass fiber-reinforced epoxy resin board, which is one of the most commonly used boards in PCB manufacturing. It has excellent mechanical strength, heat resistance,and electrical performance, and can work at high temperatures and frequencies. FR4 board has a small coefficient of thermal expansion and good stability,making it suitable for the manufacturing of high-precision electronic products.

An Aluminum plate is a metal substrate composed of an aluminum plate, insulation layer, and copper foil. It has excellent thermal conductivity and heat dissipation performance, suitable for the manufacturing of high-power electronic products. The heat dissipation performance of aluminum plate is better than that of FR4 plate, so it is suitable for the manufacturing of high-power LED lights, high-power frequency converters and other electronic products.

The diversity of PCB boards provides more choices for the manufacturing of electronic products. When selecting boards, it is necessary to comprehensively consider factors such as the performance requirements, working environment, and cost of electronic products.FR4 vs aluminum plate havs their advantages and disadvantages, which need to be selected according to the actual situation.