A PCB or Printed Circuit Board is a board on which electrical components are assembled using metal (mainly copper) connectors to create an electrical connection. Essentially, PCBs are the foundational building blocks of most electronic devices. From a small board in a smartwatch to a supercomputer, PCBs are vital while assembling the base of all devices. Their mechanical and electrical attributes are what make them suitable for such operations. Around 90% of the PCBs in the world are rigid PCBs. Some of them are flexible to the extent that they can be bent and folded into any shape and survive for a long time without any break. This credit goes to the use of the material in the PCBs. Considering this, let’s differentiate the two types of boards: 370hr PCB and Fr4 PCB.
We can take an example of a 370hr PCB by Isola to highlight its features, as it is one of the leading printed circuit boards in the industry. The designers employ Polycat to design it and laminate it with pre-peg sheets. Pre-peg sheets sandwich between copper and copper foils. They are then laminated to the board using heat and pressure. The 370hr PCB is used in many PWB designs and is extremely reliable.
Fr4 PCB is the backbone material upon which most rigid circuit boards are built. Fr stands for flame retardant, while 4 is the number given to differentiate between the numbers on a material sheet.
How to choose the material for your PCB?
While choosing a PCB material, many things need to be kept in mind. The first and foremost thought that should come to your mind is if the PCB is perfect according to your design. Match your needs to whichever PCB you think suits your system and choose accordingly. The differentiating qualities of the 370hr PCB and the Fr4 PCB are given below.
The weight, length, and thickness of each PCB and your project are significant to know before starting your project. A heavier project will require a denser and more stable board, while lighter projects will require a lightweight, handy board to keep the overall weight low. On average, the Fr4 PCB board weighs between 0.4 to 0.55lbs per 100 square inches of Fr4. The 370hr PCB, on the other hand, weighs 1oz per 35 micrometers, hence is more stable than the Fr4. In the wake of new technology, the size of any device must be reduced without compromising its performance in any way. Summing it, when it comes to size, the FR4 PCB board is preferred as it is thinner than the 370hr PCB board.
When choosing the size of a PCB board, it is necessary to keep in mind that any two-sided PCB board requires edge connectors, which greatly impacts the size of the PCB board. It is essential to understand that it requires enough space for the connectors to fit properly between the two sides of the PCB board. However, if that space is not provided, it can result in spills which can cause damage. When compared, the FR4 boards are thicker than the 370HR boards. It makes them a better choice for holding connections safely, given the size of the PCB itself is not significant. Since the 370HR PCB board is thinner, its ability to cater to multiple connections decreases the risk of spillage and, thus, damages increases with each added connection.
- Impedance matching and stability
PCB board requires good stability and the ability to match impedance for efficient functioning. Impedance is the effective resistance of the circuit/component to an AC power source. When making a PCB board and accounting for impedance matching, it is better to go for 370HR PCB. This is because, while FR4 is a good material, its DK value is not fixed. Therefore, it can get mixed when constructing the PCB board, while 370HR, on the other hand, has a constant DK value of 4.04.
- Dielectric constant value
The dielectric constant is a ratio of the ability of a material to carry alternating current against a vacuum. The dielectric constant for a Fr4 PCB can vary from 3.8 to 4.8. It depends upon the weaving style, thickness, and resin content of the PCB board. In contrast, the value for the dielectric constant for a 370HR board is fixed at 3.92. The Fr4 board can vary its dielectric constant, allowing better permeability, but this complicates the matter and results in errors if a board is constructed using boards of different DK values.
Over time and due to the competition in the market, different PCB manufacturers have started to manufacture FR4 boards with modified materials, which makes them increasingly flexible than their rigid counterparts. These types of boards can fit various spaces without compromising on the transmission. The 370HR boards offer a variant of rigid-flex boards, which are a little flexible but brittle compared to an FR4 board. Therefore, in situations, where you might require your PCB to be flexible, a Fr4 PCB board is a better choice than a 370HR PCB board.
- Component Compatibility
When choosing a PCB, it is crucial to check what components the manufacturers use on the board. This is because the size of the PCB board plays an important role when it comes to the compatibility of an element with the PCB board. For example, in the case of THT components, a 370HR PCB is better, as the thickness of a Fr4 PCB can cause unwanted consequences.
- Signal Loss
Losses in signals in PCB transmission lines happen due to differences in frequency, the value of the dielectric constant, and the loss factor of the material and are supposed to be considered at high frequencies. One way to tackle this problem is by managing the impedance of the circuit. Therefore, the preferable option is the 370HR board. With its dielectric constant value, it helps in controlling the impedance of the circuit.
- Temperature Management
For any electrical device, the circuits must remain insulated and their core temperature controlled. In the case of the FR4 board, the material used provides increased resistance to heat up and can perform well even at high temperatures. It is rated at an optimal performance of up to 130 Celsius. The 370HR boards, on the other hand, are graded at high performance of up to 180 Celsius. This rating makes them operational at a higher temperature than the FR4 boards.
- Operational Environment
The FR4 PCBs are rated at 130 Celsius. It implies that if we heat them beyond that value, they melt, losing their solid form. Therefore, the environment the PCB is required to work in has to be carefully examined. And in the cases where the PCB might be used in applications like oil, gas, or automotive, it is significant to note the temperature rating as it can get heated and thus destroyed. Other environmental conditions refer to the space available and the material of the casing. However, if the place is prone to moisture or chemical exposure, the better option would be to use the 370HR PCB, as it shows higher resistance to both.
When it comes to cost, the FR4 boards win due to a higher supply and a higher number of manufacturers. They are cost-effective, and they get the work done in most cases. In contrast, a 370HR board is a bit more expensive and can prove to be a nuisance when larger orders of PCB boards are concerned.
So, both the 370HR PCB and the FR4 PCB are reliable boards designed for different users and effective for tackling varying problems as per the need of the user. In situations where the size of the PCB is of no concern, it may be appropriate to go with the FR4 boards. Yet, in cases such as USB ports and other devices where the size needs to be kept closed, it is better to go with the 370HR boards as they are thinner.
If you need multiple connections on your PCB board, it is preferable to go with the FR4 PCB, as the increased thickness provides more room for the connections to fit snuggly. However, in cases where you might need to maintain and control the impedance of your system, it is better to go with the 370HR PCB board as its constant dielectric capabilities prove helpful. In the case of a circuit being designed for a system that takes in a lot of heat, such as a board near a car engine or for measuring the exhaust of a chimney, it is better to use a 370HR board. The rationale is it provides higher resistance to heat and moisture with various chemicals.
In the end, you, as a designer, must calculate all your variables and make sure you understand the limitations of each of the boards you are using. The user must understand the strengths of each of the different PCB boards and which would better cater to their need.