Many people misunderstand the bare board and its role in electronics. This guide will define it, discuss its requirements, and explain its fabrication steps. We will also explore its application in prototyping and product R&D (research and development).
What is a Bare Board?
A bare board is a printed circuit board without components. Put another way, the board is a PCB that has not reached the assembly stage. You can call it a blank circuit board since it lacks electronic parts.
We use bare board PCBs in various product development stages, such as prototyping and testing. They also allow design optimization, especially when correcting or improving existing blueprints.
Bare Board Meaning in PCB Manufacturing
In PCB Manufacturing, a bare board means a circuit board that will not require populating with parts. In other words, the customer wants it unassembled. They cost less than assembled types and require fewer steps to produce.
Bare PCBs are often samples for customers before full-fledged production. Manufacturers also create them for in-house testing needs. Before understanding their fabrication, let’s discuss their parts and materials.
What is a Bare Board Made Of?
Various parts make a bare circuit board. They include the substrate, copper layer or traces, vias, and through holes. It also usually has coatings on its surface, as explained below.
Board Substrate
The substrate is the primary part. It has numerous material options, from simple, low-cost types to expensive, advanced, and better-quality variants. Possible substrates include those listed below.
- Flame retardant epoxy, FR4
- Composite epoxy material CEM
- Metal-backed substrates like aluminum
- Ceramics
- Teflon
- Polyimide
- Glass core substrates
Copper Layer
The copper layer is the conductive material laminated onto the substrate. Etching this layer produces the board’s conductive pathways (traces). The copper also makes other layers, including power and ground planes.
Vias and Through Holes
Multilayer boards have tiny holes drilled into them. The holes complete electrical connections that link the layers. Some go through the board (through vias), while some do not and are called blind vias.
Conversely, buried types exist inside the board, connecting the inner layers. Other holes include component assembly holes, test holes, and installation types.
Surface Coatings
Surface coatings protect the PCB from the elements. The films can differ depending on the required protection level, testing method, and other factors. They are typically polymer films and thin but effective.
How are Bare Circuit Boards Made?
Bare board fabrication follows normal PCB manufacturing stages. Key steps include design, fabrication, and testing. Here is a brief description of the phases, including what occurs in each step.
Design Phase
The customer or manufacturer uses a CAD program to design the board and produce Gerber files. These will help guide the fabrication steps and comprise the following:
- Bare board drawings
- Bill of materials files
- Netlist files
- Drilling files
- Coatings files
Fabrication Stage
The design goes to the fabrication stage when the manufacturer converts it into a physical product. The bare PCB manufacturing process takes these steps:
- Cutting the material to size
- Laminating it with copper foil
- Using lithography or other method to create the circuitry
- Drilling the laminate to produce various hole types
- Applying required coatings, including conformal film, solder mask, and the silkscreen
Bare Board Testing
The manufacturer uses electrical and non-electrical testing methods to check the PCB. Some offer more affordability and flexibility than others and include:
- Visual inspection
- Automated inspection, AOI
- Pinned fixture test/ bed of nails
- Flying probe test
- Continuity testing to detect opens and isolation testing for shorts
Types of Bare Board Circuit Boards
Bare PCBs are single-sided, double-sided, or multilayered. Their substrates are also usually either rigid or flexible. Sometimes, the board combines rigid and flexible sections to suit application needs.
Single vs. Multilayer Bare Boards
Single-layer PCBs use a single sheet of substrate material. They have a copper layer on one side but can be double-sided with the copper on each side. The number of layers varies widely, ranging from as few as two to as high as 32 or more.
Rigid vs. Flexible Bare Boards
Blank PCBs use stiff substrates, such as FR4, ceramics, and metal. They have good mechanical strength but are heavy and require more space. Flex PCBs bend to take various shapes, among other benefits, such as being compact and lightweight.
Bendable circuit board materials include Teflon, polyimide, and polyester. On the other hand, flex-rigid types use stiff and flexible substrates or blank FR4 stiffeners.
Bare Board Benefits
A bare board is essential when prototyping for an electronic device. You also use it for product R&D, such as when creating a new product. In these applications, the PCB serves these crucial functions.
Design Optimization
Some errors may not be apparent during the design process. The PCB designer and fabricator use blank board to identify and correct these errors. That way, they optimize the design before mass production or assembly.
Early Failure Detection
Passing the PCB through various tests enables the manufacturer to identify failure modes and their reasons. The test results help identify production mistakes, allowing early interventions to avoid costly recalls and failure.
Time and Cost Savings
Using the board to identify errors helps save time and cost. The manufacturer can quickly proceed to mass production, which reduces the overall turnaround time. It also helps them avoid expensive recalls that device failure could cause.
Bare Board vs. Assembly
We call a bare board a PCB and the assembled type a PCBA. The two products differ in various ways, as the following points highlight.
- One is a bare circuit board, while the other has required components mounted to it.
- A bare PCB is less costly to make. A PCBA contains expensive components and testing technologies.
- A bare board’s connections have no functional roles. On the other hand, a PCBA is ready for use.
- Blank PCBs take less time to make. PCBAs require lengthy testing procedures, such as environmental testing.
Conclusion
The bare circuit board is essential to the PCB design optimization and testing process. It has various benefits, such as validating unique creations and allowing early corrections. More importantly, it reduces time-to-market for electronic products and prevents field failures.
