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Different Types of PCBs

Printed Circuit Boards (PCBs) are classified into various types based on manufacturing processes, design specifications, and application requirements such as medical, automotive, defense, and space.  More complex designs based on consumers’ needs and requirements pave the way for manufacturing different types of PCBs. Before you pick a PCB, you must look for a few considerations like space required, stress handling, and mechanical and electrical stability.

The different types of PCBs available are

Single-Sided PCBs

A single-sided PCB is the most common type of printed circuit board. It has a single conductive copper layer above the substrate. The electrical components are soldered or placed on one side of the board, and the entire etched circuit is visible on the other. Since these boards only have one conducting layer, the conductive paths cannot intersect or overlap and hence take up a lot of space.

As a result, these PCBs are suitable for low-density design requirements. Single-sided printed circuit boards (PCBs) are used for basic and low-cost electrical/electronic instruments such as calculators, power supplies, LED lighting boards, FM radios, timing circuits, and so on.

Advantages of Single-Sided PCBs

Double-Sided PCBs

A thin layer of conducting material, such as copper, is added to both the top and bottom sides of the board in a double-sided PCB. Holes in the circuit board allow metal parts to be connected from one side to the other. These PCBs connect the circuits on either side using one of two mounting methods, through-hole technology or surface mount technology. Through-hole technology entails installing lead components into pre-drilled holes on the circuit board, which are then soldered to pads on opposite sides. Surface mount technology entails the precise placement of electrical components on the surface of circuit boards.

Double-sided PCBs are used in a variety of applications such as cell phone systems, power monitoring, test equipment, amplifiers, HVAC application, UPS system, and many more.

Advantages of Double-Sided PCBs

Multi-Layer PCBs

Multilayer PCBs have more than two copper layers. In general, any board featuring at least three conductive layers is included in this category. Multilayer PCBs are designed in a ‘sandwich’ fashion, with several double-sided conductive layers divided by an equal number of insulating material sheets. All of these must be bonded and laminated together under high pressures and temperatures to ensure that no air gaps exist and that the final PCB assembly is properly stable.

Multi-layer PCBs are used in computers, laptops, mobile phones, tablets, medical equipment, GPS trackers, and many other more complex circuits and devices.

Advantages of Multi-Layer PCBs

Rigid PCBs

As the name implies, a rigid PCB is a circuit board that cannot be twisted or folded. The board’s base material is a rigid substrate, which gives the board rigidity and strength. They are composed of multiple layers including a substrate layer, a copper layer, a solder mask layer, and a silk screen layer which are adhered together with adhesive and heat. Although some circuit boards are either single-sided, double-sided, or multi-layered, rigid PCBs may be any of these depending on the needs. However, once made, they cannot be modified or changed.

Rigid PCBs are used in GPS equipment, computer, laptops, tablets, mobile phones, X-rays, heart monitors, CAT scans, MRI systems, temperature sensors, control tower instrumentation, etc.

Advantages of Rigid PCBs

Flex PCBs

A flexible printed circuit board is made up of many printed circuits and components that are arranged on a flexible substrate. Flexible PCBs are commonly made from polyamide, PEEK (Polyether ether ketone), or a transparent conductive polyester film. Flex circuit boards, flex PCBs, flex circuits, and versatile printed circuits are other names for these circuit boards. These printed circuit boards are made using the same components as rigid printed circuit boards. The main distinction is that the board is designed to flex to the desired form throughout the application. These PCBs are available in single-sided, double-sided, and multilayer configurations. This contributes to a reduction in the complexity of the unit assembly.

Flex PCBs are used in organic light emitting diode (OLED) fabrication, LCD fabrication, flex solar cell, automotive industries, cellular telephones, cameras, and complex electronics products such as laptop computers.

Advantages of Flex PCBs

Rigid-Flex PCBs

A Rigid-Flex PCB is a hybrid circuit board that combines elements from both flexible and rigid circuit boards, resulting in a board that can be folded or continuously flexed and is typically shaped into a flexed shape or curve during the manufacturing process. The flexible portion of the board is typically used for interconnections between rigid boards, allowing for narrower conductor lines that take up less room, resulting in smaller boards. Using flexible PCBs for interconnections often removes the need for connectors, which are bulky and cumbersome, making rigid-flex printed circuit boards much lighter. Rigid-Flex PCB designs are a little more complicated since these boards are constructed in 3D, allowing the board to be folded or twisted to produce the desired shape for the product. Designing a board in 3D allows for greater spatial performance, which can then be used in special cases where space and weight reduction are needed, such as in medical devices.

Rigid-flex boards can be designed in a compact manner, and their lightweight nature makes them an excellent option for a wide range of applications in the aerospace, medical, and consumer electronics fields.

Advantages of Rigid-Flex PCBs


While choosing a PCB manufacturing partner think about cost optimization, adequate material usage, delivery time, and more. World electronics is your go to partner as we follow the latest IPC standards and tolerances and DFM and DFA rules to better suit your next upcoming PCB design.

For more on WORLD’s capabilities, visit our services page and follow us on LinkedIn.


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PCB Solder Paste Inspection Techniques

Printed Circuit Board (PCB) Solder Paste Inspection Techniques

Solder Paste Inspection, abbreviated as SPI, is a specialized process that evaluates/inspects solder paste deposit quality on PCBs. It ensures the correct deposition of solder paste on the board without faults. In most of the cases, the reason behind the improper functioning of the PCB is due to improper solder paste printing. Solder paste inspection is therefore an essential technique that ensures costs are kept as low as possible by detecting faults in the solder printing stage of the production line. Solder paste deposition during a printing process is an indispensable task to attach the components to a circuit board for maintaining a proper electrical connection.

WORLD’s Surface Mount Technology (SMT) inspection process utilizes both Automated Optical Inspection (AOI) and X-ray to visually scan the surface of the board using high-definition (HD) cameras and several light sources. These systems use the captured image and compare it with the ideal/conventional board image which is already saved in the system. A comparison is then made between the captured image and the ideal image to detect and highlight any defects or suspected areas.

World electronics uses AOI (Automated Optical Inspection) and X-ray for solder paste inspection and defects analysis on every PCB because we believe in quality.

Automated Optical Inspection (AOI)

AOI machine tests and evaluates PCBs for faults like presence or absence, component placement defects, dimensional defects, and surface defects. With the advancement of electronic contract manufacturing and circuit complexity, it has become unfeasible to manually perform SMT inspection. Thus, AOI plays an important role in boards after PCB assembly. The machine has the capability of detecting errors in the early stage of the manufacturing process to assure the PCB quality before moving to the next manufacturing step.

WORLD electronics has one AOI machine, made by Yestech. It uses a camera and light to scan the surface of the board for defects such as backward parts (polarity), shorts, opens, missing components, and incorrect parts, among others. The machine uses already installed SW and templates and compares them to the board it is scanning. If the scanned board doesn’t match with the template (sometimes by a certain percentage), the part and board will be flagged, and the defects will be highlighted.

This technique inspects the PCB by using captured images to check:

  1. Are components missing?
  2. Are components placed in the correct position?
  3. Are there defects?
  4. Are we able to validate the quality of the manufacturing process?

The AOI machine can inspect all size components such as 01005, 0201, and 0402s and packages like CSPs, BGAs, LGAs, PoPs, and QFNs. Initially, AOI machines were designed for 2D measurements/analysis (detection along X and Y coordinates only). With the addition of 3D systems, the measurement along Z coordinate has also become possible. At WORLD, we use a 3D AOI machine for measurement along all the axis. The ultimate aim of an AOI machine is to detect errors in the production line and immediately informing the same to AOI programmers (also known as feedback). Feedback to the AOI programmers is both helpful and necessary so that time could be saved during SMT inspection.

AOI Programmers

The Automated Optical Inspection machine runs on a dedicated program, developed by AOI programmers. The following are the situations under which feedback is generated:

SMT Inspection/Bare PCB Inspection via WORLD’s AOI Machine

WORLD’s 3D AOI machine tests PCB assembly for the following aspects:

X-Ray Inspection System/Automated X-ray Inspection (AXI)

A PCB X-ray inspection system, also known as Automated X-ray Inspection (AXI), uses X-ray radiation instead of visible light to identify hidden PCB defects such as:

The above-mentioned defects can’t be seen during the inspection by standard cameras or by the naked eye. X-ray inspection is a commonly used technique that can detect manufacturing defects.  The X-ray inspection machine can inspect the PCB from any angle.

WORLD electronics currently uses a 2D X-ray inspection system and are planning to upgrade it to a 3D AXI in the near future.

Structure/Principle of Operation for X-ray Machine

An inspection device based on X-rays consists of a chamber with a small gap where it is possible to insert and remove the PCB. The X-ray source is usually located at the bottom of the chamber. Within the chamber, a digital detector (phosphor screens) is positioned directly above the X-ray source. Using an edge conveyor belt, the PCB that needs to be examined enters the chamber and is located between the source and the detector. The backside of the PCB is exposed to the X-ray so that the X-ray can pass through the components.

While AOI produces full color images of the object surface, X-ray machine transmits X-rays through the objects and records grey scale images of the shadows. The image processing software then processes the image. It then detects the location and size/shape of expected features (for process optimization) along with the presence/absence of foreign objects or features (for anomaly detection).

Inside the component, the different molecular densities attenuate the X-rays by different amounts, resulting in the creation of light and dark areas in detective media. Consequently, we can easily identify cracks, i.e. the attenuation level of the dense part of the solder ball is heavy compared to the attenuation level of the crack or air.  The crack tends to be dark due to varying attenuation levels, and the dense portion of the solder ball appears as a light in the image.

Conclusion of AOI and X-ray SPI

Solder paste inspection is a vital part in a PCB production line. It is crucial to identify solder paste defects in the early production cycle, otherwise, it can cost you both time and money. WORLD electronics’ AOI and X-ray machines use advanced SMT inspection techniques to offer quality and defects-free PCBs to our customers.

For more on WORLD’s capabilities visit our services page and follow us on LinkedIn.


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