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Bare Board PCB Fabrication and Testing Guide

Bare Board PCB Fabrication and Testing Guide

A bare board PCB is a crucial product in electronics. For example, you can use it for R&D or as a prototype to correct design flaws before full-fledged production. Here’s more about it, including its fabrication process and testing methods. Let’s start with the meaning and types.

What is a Bare Board PCB?

A bare board PCB is a printed circuit board before populating it with parts. You can also call it a blank PCB or just bare board. It only features the substrate, the copper traces, and sometimes coatings like the solder mask and silk screen.

The substrate is commonly FR4 or other materials, such as ceramics, metals, Teflon, and polyimide. Its function is to provide structural support. It also offers electrical insulation, holds components, and helps dissipate heat.

The conductive layer is usually copper, with other possible options being silver and gold. This part forms the circuitry that transmits power and conveys signals between components.

The solder mask protects the copper layer against oxidation and short-circuiting. On the other hand, the silkscreen contains the board’s information, such as manufacturing date and component identities.


A thin conformal coating on the board surface repels moisture, dust, and other materials. The following section looks at the different types of unassembled printed circuit boards you can create.

A multilayer bare PCB
A multilayer bare PCB
Resource: https://www.researchgate.net

What are the Types of Bare Printed Circuit Boards?

Bare printed circuit boards can be in one of the following forms: single or double-sided and multi-layered or rigid and flexible. It can also be a rigid-flex type. These are the characteristics of each.

Single Sided PCB

A single-sided PCB only has one conductive layer backed by the insulating substrate. It’s simple, compact, and low-cost. These qualities make it suitable for simple projects.

Double Sided PCB

The double-sided type has a conductive layer on either side. Unlike the single-sided type, it provides a more complex circuitry and holds more components.

Multilayer PCB

A multilayer bare circuit board has more than three conductive layers. It offers more routing options, allowing you to use more intricate components like microprocessors and complex circuits that support high-density assemblies.

Rigid PCB

A rigid type remains stiff, providing better mechanical properties for demanding applications. However, unlike the flexible type, it cannot fold to follow a device’s shape or fit a small space.

Flexible PCB

Made from flexible materials like Teflon and polyimide, it bends and takes any shape. You can also use this bare board PCB type to test environmental resilience in high-vibration conditions.

Rigid Flex PCB

It combines rigid and flexing sections. As a result, you get the benefits of both circuit PCB types for thermal, mechanical, and electrical properties, among other characteristics.

Printed circuit board design
Printed circuit board design
Resource: https://www.youtube.com/watch?_eyby_rWn00

How are Bare Boards Made?

The PCB bare board manufacturing process starts with its design and material selection process. After that, the engineer can embark on the actual manufacturing steps that will produce the final product. The steps from the design to fabrication stages include the following:

  • The PCB is designed using a computer program. It involves drawing its circuit schematics and laying out the components in 3D.
  • The material is sourced and cut to size as required. It’s then laminated with a thin film of copper using either pressure or adhesive.
  • The circuit pattern is created using photolithography and chemical etching or directly created using lasers or mechanically with a cutting tool.
  • The panel is drilled with holes as required. They include installation holes, component assembly holes, and vias.
  • Soldermask and silkscreen may also be applied to the bare PCB or a layer of a protective film called conformal coating. These serve different functions.
  • Finally, the finished circuit board undergoes tests to detect (and correct) design and fabrication errors.
Testing and prototyping PCB
Testing and prototyping PCB
Resource: https://www.researchgate.net

What is a Bare PCB Used For?

This product serves as the foundation for electronic components and circuitry. There are various reasons why you would want a bare-board PCB. They include the following.

Testing and Prototyping

It allows you to test or prototype your project’s product before mass production or introduction to the market. You can identify errors during this time, saving yourself repair or product recall costs.

Product R&D

The bare PCB is helpful when carrying out product research and development. It allows engineers to experiment with different circuits and material options, promoting the discovery of new technologies.

Design Customization

If you’re creating a new product, existing boards may not work. In such cases, you want a unique type to suit your new application requirements. With a bare circuit board, you can customize various features, from size and o electrical to thermal performance.

Bare board inspection
Bare board inspection
Resource: https://www.researchgate.net

Bare Board Testing and Inspection Methods

After fabrication, the product passes through an inspection and testing process. Bare board testing verifies its correctness, identifying defects and allowing their rectification. The tests include manual, automated, and fixture or fixtureless testing.

Visual Inspection

It involves visually checking for defects using bare eyes or with the help of magnifying pieces and microscopes to improve accuracy. This testing method is inexpensive and doesn’t require custom fixtures. However, it’s slow and prone to errors.

AOI Inspection

AOI uses hi-tech cameras to capture images of the surface using filtered light sources. Error detection programs compare the images with stored data to identify discrepancies. Although more costly, AOI PCB testing is more accurate than manual inspection.

Flying Probe Test

This test uses “above-the-board” probes to check for flaws. The probes move above the panel’s surface, testing it at various parts as directed by the computer programs. The flying probe test is a slower process but automated and less laborious.

Fixture Testing

The fixture method involves placing the circuit board on a “Bed of Nails,” a testing jig with pins arranged on it. The pins contact the board at specific points, enabling the tester to check it for electrical continuity and isolation.

Conclusion

A bare board PCB is a crucial product in the electronics world. It allows research tests, prototyping, and other procedures that advance various technologies and create new products. You can produce it in many formats, from single to multilayer and rigid to flexible or rigid-flex printed circuit boards.

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