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PCB/PCBA knowledge

The basic component of a printed circuit board is the bare printed circuit board. It can be used to mount and connect other components. Since the board is relatively empty, technicians can run a range of tests according to the design of the PCB to ensure functionality. It allows the technicians to rectify the errors proactively.

Table of Contents

What is a bare PCB?

A printed circuit board, also known as blank PCB, bare PCB, and sometimes simply PCB, is a board that lacks all the components and has no holes drilled in it. While assembling a conventional PCB acts as a foundational piece upon which different electrical components are installed. Furthermore, the electrical connection between different components is also created by bare PCB via conductive pathways. Typically, a bare PCB has the following components;

  • Patterns
  • PCB substrate
  • Metallic coating
  • Essential conduction pathways

Besides these, some other features of bare board PCB include drilling, silkscreen printing, photo-resistance, and solder mask even in this empty state.

The fundamental purpose of the bare PCB is to support components on it by extending electrical and mechanical support. The bare PCB is better suited for mass production because of its versatility and flexibility.

Bare PCB is primarily used to assess the feasibility of circuitry prior to installing expensive components on it. These are essentially the fundamental part of PCB fabrication and consequently an important element for mass electronic production.

Advantages and disadvantages of bare PCB

Advantages-and-disadvantages-of-bare-PCB

  • Advantages

Bare PCB offers several benefits that go beyond just supporting the components mechanically. These include;

  1. Identification of defects
    Probably the biggest advantage of bare PCB is the identification of defects at the earliest. Testing and appraising bare PCB is much easier as the surface is free of components that can otherwise be obstacles. It allows the technicians to test the design and ensure there are no defects thoroughly. And if an issue is detected, it can be fixed before the completion of the circuit.
  2. Cost effective
    Fixing an error once a circuit is completed is not just tedious but expensive as well. The bare PCB prevents that additional cost and saves time by allowing the technicians to detect the errors early in production. Essentially, the risk of monetary loss is far lower with the bare PCB. Furthermore, early testing ensures error-free functionality for a specific design, reducing the time consumed if an error arises in an assembled PCB.
  • Disadvantages
    While the advantages of bare PCB sound appealing, one should be aware of potential drawbacks as well. The most important of them include the following;
  1. Handling damage
    Bare PCBs are delicate compared to complete PCBs, making them prone to damage. Hence, there can be false errors in the functionality of the design.
  2. Corrosion
    Once assembly is completed on a bare PCB, the tin remains exposed, which makes it vulnerable to corrosion.
  3. Not suitable for multiple reflows
    Bare PCB is not recommended for the multiple reflow and assembly processes because of certain limitations in the design.

What are bare PCBs used for?

What-are-bare-PCBs-used-for

The application of bare PCB includes electrical and mechanical support to the components on board. It also develops an electrical connection between different components by creating conducting pathways. Copper is etched to create these conductive pathways, and the copper sheets are laminated over the substrate, which is a non-conductive material. Bare PCBs are the basic components of most electronics, including LEDs, medical devices, maritime applications, and automotive components, among others.

What is bare board testing?

What-is-bare-board-testing

The testing of the board before components such as ICs are mounted on it is bare board testing. The Fixture and The Flying Probe are two commonly used methods to test bare PCP. Such tests are standard in the production of PCB and are mandatory for all types of bare boards except single layer type. These tests help identify problems in the circuit before the designs are cleared for mass production. Thus, thorough testing at the initial stages prevents the loss of time and capital that would be spent otherwise if the fault arises once mass production is complete.

Types of bare board testing

While some might believe looking at the bare PCB with the naked eye is adequate for assessment, it is not the case. Most times, shorts and disconnections cannot be observed without thorough testing. Plus, there is no way to check connectivity in multilayer with the naked eye. There are two tests to ensure there are no defects in the bare PCB, which include;

  • The fixture test
    In the fixture test, multiple pins are used to create a fixture, and the number of pins corresponds with the nets on the circuit. It essentially creates two nail beds to sandwich the bare PCB. Hundreds of connections between testing points and probes are created during the test, making it a very fast method. The downside of this test is that it is quite expensive. Furthermore, if you change the board after designing the nail bed, you will have to redesign it completely.
  • The flying probe test

The-Flying-Probe-Test
It is a relatively inexpensive test and typically uses only two probes to test the nets of bare PCB. Depending on the layout, the probes move along the x and y axis to detect defects in the board. Plus, there is no need to redesign the whole test if the board undergoes a change. However, it is significantly slower than the fixture test.

Why is bare PCB board testing important?

Testing bare PCB is important because it prevents errors and complications once it is fabricated. Despite technological advancements, the chances of mechanical errors exist, and occasionally some issues go unnoticed till the assembly. Testing the board helps prevent such nuisance.

Steps in fabricating bare PCB

The process of PCB fabrication includes the following steps in the same order;

  • Application of laser-directed imaging
  • Oxidation and lamination
  • Drilling of holes
  • Electroless copper deposition
  • Drying the outer layer of the film
  • Plating and stripping
  • Application of silkscreen and solder mask

Possible errors in bare PCB manufacturing

Common PCB manufacturing errors include;

  • Insufficient copper-to-edge clearance
  • Plating voids
  • Bad soldering
  • Silvers
  • Missing solder mask between pads
  • Acid traps
  • Starved thermals.
you asked we answer

The testing of the board before components such as ICs are mounted on it is bare board testing. These tests help identify problems in the circuit before the designs are cleared for mass production.

Advantages

1. Identification of Defects
2. Cost Effective

Disadvantages
1. Handling Damage
2. Corrosion
3. Not suitable for multiple reflows

Common PCB manufacturing errors include;

  • Insufficient copper-to-edge clearance
  • Plating voids
  • Bad soldering
  • Silvers
  • Missing solder mask between pads
  • Acid traps
  • Starved thermals.

Conclusion

A bare PCB is devoid of all components and holes and is used as the foundation of a PCB. It helps in the early detection and proactive fixation of errors. Manufacturers save time and a lot of capital by using bare PCB. However, it must be tested thoroughly to ensure no errors occur once the assembly is completed. And also, these boards must be handled with great care to prevent any damage. Lastly, if you are looking for a one-stop solution for PCB-related problems, IBE is where you should stop the search. We offer a range of services, from testing PCB to supply chain services.

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