Printed Circuit Boards Introduction and Types

Printed Circuit Board:

The Printed Circuit Board (PCB) is a physical base or platform upon which the electronic components can be soldered and the copper traces connect these components with each other so that the Printed Circuit Board (PCB) perform its function as it was designed.

 

Printed Circuit Boards are the heart of electronic devices and it can be of any shape and size depending on the application of electronic device. The most common base / substrate material of PCBs is FR-4. The FR-4 based PCBs are commonly found in many electronic equipment and its fabrication is common. Single sided and double sided PCBs are easy to fabricate as compared to multilayer PCBs.

PCBA

The FR-4 PCBs are made of fiber glass and epoxy resin in conjunction with laminated copper cladding. Some of the major examples of complex multilayer (up-to 12 layers) PCBs are in computer graphics card, mother boards, micro-processor boards, FPGA, CPLD, Hard Disk Drives, RF LNA, Satellite communication antenna feed, Switch Mode Power Supplies, android mobiles and many more. Also there are numerous examples where the simple single layer and double layer PCBs are used like CRT TV, Analog Oscilloscopes, hand held calculators, computer mouse, FM radio circuits.

 

Applications of PCB:

 

  • 1. Medical Equipment:

The today's advancement is medical science is solely because of rapid growth in electronic industry. Majority of medical devices like pH meter, heart beat sensor, temperature measuring, ECG/EEG machines,  MRI machines, X-Ray, CT-Scan, blood pressure machines , glucose level measurement devices, incubators, microbiological equipment and many other devices are solely based on electronic PCBs. These PCBs are usually dense and have small form factor. Dense means that more smaller SMT components are placed in smaller size PCBs. These medical devices are made smaller so as to make them portable, light weight and easy to handle.

 

  • 2. Industrial equipment.

The PCBs are also widely used in manufacturing industries, factories, looming mills. These industries have the high powered mechanical equipment that are driven by electrical circuits that operate on high power and needs high current. For this purpose, a thick layer of copper is laminated on PCB unlike sophisticated electronic PCBs, and these high power PCBs carry currents upto100s of Ampere. This is specifically important in applications like arc welding, Large servo motor drives, lead acid battery chargers, military industry, garments cotton looming machines, and similar.

 

  • 3. Lighting.

The world is moving towards energy efficient solution, in terms of lighting. Those halogen bulbs are now rarely found but now we see all around us LED lights and high intensity LEDs. These small LEDs give high luminosity light and are mounted on a PCB that is based on Aluminum substrate. The aluminum has the property to absorb heat and dissipated in air. Hence due to high power these Aluminum PCBs are commonly used in LED lights circuits medium and high power LED circuits.

LED PCB

 

  • 4. Automotive and aerospace industries.

Another application of PCB is automobile and aerospace industry. Here the common factor is the reverberations that occur when the aircraft or automobile is in motion. So in order to cater these high force vibrations, the PCBs are made flexible. So a type of PCB called Flex PCB is used. The flex PCB can withstand high vibrations and are also light weight which can reduce the overall weight of space craft. Also these flex PCB can be adjusted in tight spaces which is also a great advantage. These flex PCBs are used as connectors, interfaces, and can be assembled in the tight space like behind the panel, under the dashboard etc . A combination of rigid-flex PCBs are also used.

 

Types of PCBs:

Printed Circuit Boards (PCBs) are classified into 8 main categories. They are

 

Single Sided PCB:Single Sided PCB

The single sided PCBs have the components installed on only one side and other side is used for copper traces. The thin layer of copper foil is applied to one side RF-4 substrate and then the solder mask is applied to provide insulation. Lastly the silkscreen is applied to provide components marking info like C1, R1 on PCB. These single layer PCBs are very easy to design and manufacture on large scale and has high demand in market and also very cheap to buy. Very commonly used in house hold products like juicers/blender, charging fans, calculators, small battery chargers, toys, TV remote controls etc.

Single LAYER PCB

 

Double Layer PCBs:Double Layer PCB

The double sided PCB is the one in which the copper layer is applied on both sides of board. The holes are drilled and THT components with leads are fitted inside these holes. These holes connect the one side components to other side components by means of copper tracks. The components leads are passed through the hole and the excess lead is cut by cutter and the leads are soldered on the holes. This is all done manually. There can also be SMT components as well as THT components of 2-layer PCB. The SMT components do not need holes but the solder Pad is made on the PCB that will fix the SMT part on it by means of reflow soldering. SMT components use very less space on PCB resulting in more free space that will be used by board for more functions. Double sided PCBs are used in power supplies, amplifiers, DC motor drives, instrumentation circuits etc.

Double layer PCB

 

Multilayer PCB:Multilayer PCB

Multilayer PCBs are made from multiple 2 layer PCBs, which are sandwiched between dielectric insulation that ensures that the board and components are not damaged due to excessive heat. Multilayer PCBs are available in various form factors and different layers starting from 4 layer PCB to 12 layer PCB. The more the layers the more complex the circuit is and more complex the PCB layout design become.

The multilayer PCBs usually has separate ground plane, power plane, high speed signal layers, signal integrity consideration, thermal management. The common applications are military requirements, aerospace and aircraft aviation electronics, satellite communication, navigation electronics, GPS tracking, Radar, Digital signal processing and image processing.

4 LAYER PCB

 

Rigid PCBs:

All of the above types of PCBs discussed fall in the category of rigid PCBs. Rigid PCBs have the solid substrate material like FR-4, Rogers, phenolics and epoxies. These board do not flex and twist but the stay in their shape for many years up-to 10 or 20 years.  This is why the life of many electronic devices is very long because of stiffness, ruggedness and rigidity of rigid PCBs. The computers and laptops PCBs are rigid and TV , LCD , LED TVs common used in many homes are made of rigid PCBs. All of the above mentioned applications for single, double sided and multilayer PCBs are also valid for rigid PCBs.

Rigid PCB

Flex PCB:Flex PCB

The flexible PCB or Flex PCB is not rigid but it is flexible and can be bend easily. They are elastic and have high thermal resistance and excellent electrical characteristics. The substrate material of Flex PCB is dependent on performance and cost. The common substrate materials of Flex PCB are polyamide (PI) film, polyester (PET) film, PEN and PTFE.

The fabrication cost of Flex PCBs is more than rigid PCB. They can be folded or wrapped around corners. They take very less space as compared to their counterpart rigid PCBs. They are light weight but have very low tear strength.

Flex PCB stack up

 

Rigid-Flex PCB:Rigid-Flex PCB

The combination of rigid and flexible PCBs is very important in many applications where there is a constraint of space and weight. For example in a camera the circuitry is complex but the combination of rigid and flex PCBs will lower parts count and reduce PCB size. Also the wiring of both PCBs can be combined on single PCB. Common applications are digital camera, cell phones, automobiles, laptops and in those devices that have moving parts

 

High Speed PCBs:

The high speed or high frequency PCB is the one that is used in applications involving signal communication at frequencies above 1GHz. In this case, the signal integrity issues comes into play. The material for the high frequency PCB substrate should be carefully chosen so that the design requirements are fulfilled.

The common material is Polyphenylene (PPO) and Teflon. It has stable dielectric constant and small dielectric loss. They have low water absorption but cost is high.

Many other dielectric materials have variable dielectric constant which results in changing impedance thus distorting harmonics and loss of digital signal and loss of signal integrity

 

Aluminum PCB:Aluminum PCB

The aluminum based PCBs substrate material has the property to dissipate heat energy efficiently. Aluminum based PCBs cooling is more efficient than its counterpart copper based PCB due to low thermal resistance. It dissipates heat in air and as well as in thermal junction areas of PCB board.

Many LED light circuits, high luminosity LEDs are made from Aluminum backed PCBs.

The aluminum is a abundant metal and its mining is inexpensive hence PCBs cost is also low. Aluminum is recyclable and also not toxic so it is friendly to environment. Aluminum is sturdy and durable hence reduce damage during manufacturing, shipment and assembly

All these properties make Aluminum based PCB favorable for high current applications like motor controllers, heavy battery chargers and High luminosity LED lights.

 

Conclusion:

For recent years, PCB has grown from the simple single-layer version to more intricate systems, such as a high-frequency Teflon PCB.

PCBs are now commonly found in almost every sector of modern technology and evolving science. The fields like microbiology, microelectronics, nano science technology, aero space industry, military, avionics, robotics, artificial intelligence are based on the building blocks of Printed Circuit Boards (PCBs) in all of its forms.