Components Of Printed Circuit Boards (PCBs) 2

What are Printed Circuit Boards Made Of?

PCBs can make use of a range of materials for component and substrates. The selection of the material is contingent on the needs of the particular application, since different materials can give the circuits different characteristics that allow for better performance in specific conditions.

Designers may select materials based on their electrical performance in high-speed applications or thermal or mechanical endurance such as automotive under-the-hood applications. Designers can choose to comply with the requirements of a regulatory agency. For instance EU's Restriction of Hazardous Substances (RoHS) directive prohibits the use of substances that contain all restricted chemicals and metals.

The most common factors to consider is whether the product are UL-certified, short to mean Underwriters Laboratories flame suppression characteristics. The score of UL is crucial for many electronic devices in order to ensure that in the case in the event of a fire the circuit board will not self-extinguish typically considered essential for consumer electronics and others.

Laminates are generally made of cloth fabrics and resins which have distinct insulative qualities. This includes dielectrics like FR4 epoxy Teflon Polyimide and others that make use of glass and resin coatings. A variety of distinct electrical and thermal aspects determine which one will work best for a particular PCB.

PCB designers must consider a variety of performance issues when they look at the material they choose to design their PCBs. Some of the most common aspects to consider include:

• Dielectric constant is a crucial indicator of electrical performance
• Flame retardance is a crucial aspect for UL certification (see above)
• The higher glass transition temperatures (Tg) for a better ability to endure higher temperatures for assembly processing
• Mitigated loss factors are essential for high speed applications where speed of signal is important.
• Mechanical strength that includes shear, tensile and various mechanical properties that could be required by the PCB when it is placed in service
• Performance of the thermal system is a crucial factor when operating in high-temperature service environments
• Dimensional stability, or, how much does the material shift and how frequently does it move in the course of manufacturing thermal cycles, and exposure to humidity

Here are some of the most well-known materials that are used in the production of circuit boards printed with electronic components:

1. Prereg and epoxy laminate FR4 The FR4 laminate is the most sought-after PCB substrate material around the world. The term 'FR4' refers to a group of materials that meets the requirements of NEMA LI 1-1998 specifications. The materials in FR4 exhibit excellent electrical, thermal, and mechanical properties in addition to the favorable strength-to-weight ratio, which allows them to be used in a wide range of electronic applications. Laminates and prepregs of FR4 are made of glass cloth and epoxy resin and they are typically the cheapest PCB materials available. It is particularly preferred for PCBs that have lower layers of double or single sided to multilayered structures generally smaller than fourteen layers. Furthermore this base resin may be mixed with additives that significantly enhance its electrical, thermal performance and UL flame safety/rating which greatly enhances its capability to be utilized for higher-layer count designs as well as higher temperature stress applications and higher electrical performance with a lower cost for high-speed circuit designs. Pregregs and laminates FR4 can be used in a variety of ways, and are able to adapt using widely-accepted manufacturing methods with reliable yields.
2. Polyimide laminates, and prepregs: Polyimide laminates have better temperatures than FR4 material and also an increase in electrical properties. Polyimides cost more than FR4, but they offer better durability in extreme and high temperatures. They also have a higher degree of stability when it comes to thermal cycling, and possess lower expansion capabilities, which makes them ideal for constructions with a higher number of layers.
3. Bonding and Teflon ply: Bonding and laminates made of Teflon materials have outstanding electrical properties, which makes them ideal for high-speed circuitry applications. Teflon materials are more expensive than polyimide, but give designers the speed and performance they require. Teflon materials are able to be coated onto glass fabric, however, they it is also possible to make unsupported films or by using specific additives and fillers to enhance mechanical properties. The production of Teflon PCBs usually requires a skilled and trained workforce, special equipment and processes, and the anticipation of lower production yields.
4. Flexible laminates These laminates, which are flexible and thin in thickness allow you to fold electronic designs without affecting electrical continuity. They do not use glass fabric to support them, but instead are built on a plastic sheet. They can be as a device folded in the one-time flex-to-install application, since they are in dynamic flex, which means that circuits will be continually folded throughout the life of the product. Flexible laminates can be constructed using higher temperatures of materials such as the polyimide or the LCP (liquid crystal polymer) or extremely inexpensive materials like polyethylene and pen. Because flexible laminates are extremely thin, making flexible circuits may also require a highly trained workforce, special equipment and processes, and also the anticipation of lower manufacturing yields.
5. Other: There are many different bonding and laminate materials available on the market, including BT and cyanate ester ceramics or blended materials that mix resins in order to achieve distinct mechanical or electrical features. Since the quantities are far smaller than FR4 and manufacturing is much more complicated to produce, they are often considered to be more expensive alternatives for PCB designs.

The selection of the right laminate is crucial to ensure that the PCB has the appropriate mechanical, dielectric, electrical and thermal properties to suit the final application.