Bare printed circuit boards play a crucial role in the manufacturing of electronic goods and products. With the introduction of new gadgets and life-changing electronic products, the world has become a better place. However, the types of electronics we use everyday has continued to change over the years. A bare PCB is the heart of these electronic products.
What is Bare PCB?
A bare printed circuit board has no through-holes or electronic components. This board comprises a substrate, conductive pathways and patterns, solder mask, and metal coating. These conductive pathways and patterns direct the flow of electricity in the circuit board.
The PCB serves a lot of functions which includes providing mechanical support to electronic components, the traces, and pads. An Etching process helps to form the conductive traces in these pathways.
A bare PCB is also known as etched wiring boards of printed wiring boards. Printed circuit boards mean bare boards or blank boards. Contract electronic manufacturers and OEMs attach electronic components on this bare boards to produce printed circuit assemblies (PCBAs). A printed circuit board assembly is different from a printed circuit board. PCBAs feature several electronic components and through holes while PCBs have none of these.
Bare PCBs are manufactured with the sole purpose of populating them with electronic components. A bare PCB is needed for the manufacturing of a PCBA. The presence of electronic components on a PCB makes it a functional PCBA. Also, the bare board is the foundation of a printed circuit board assembly.
The absence of electronic components on the bare board helps in conducting a wide range of tests. These tests ensure suitability of the desired PCB design, and as well evaluate the bare board to correct any preference problem.
Materials Used For Bare PCB Manufacturing
Bare PCB manufacturing involves the integration of different types of materials. The primary materials used in bare PCB manufacturing include metal, PTFE, and FR-4. These materials are very crucial in the manufacturing process of a bare PCB. Also, the performance of a bare PCB board depends on the types of materials it comprises. Also, materials such as silicon are used in bare PCB manufacturing.
PTFE
PTFE is a common material used for manufacturing bare boards. Also, this material features excellent mechanical and thermal properties. Teflon, as it is popularly known is a weather-resistant material with no adhesion.
FR-4
FR-4 is a flame-retardant material used in bare PCB manufacturing. This material comprises a glass reinforced epoxy laminate sheet. Also, the “FR” on FR-4 means flame retardant while the 4 refers to a glass-reinforced epoxy resin.
Metal
Another commonly used material for manufacturing a bare PCB is metal. The type of metal used can be copper, aluminum or iron. Copper is the most commonly used metal among these three metals. Also, the conductivity of this metal makes it durable and mechanically stable.
Steps involved in Bare PCB Manufacturing Process
The fabrication process of a blank PCB involves several steps. PCB manufacturers need to carry out these steps with enough carefulness and precision.
Drilling
This is the first step in bare PCB manufacturing. It involves creating holes for the connection of vias. In this step, the manufacturer creates the foundation for vias. Drilling of holes is crucial for the fabrication of a bare PCB. This process requires precision and accuracy as any error can result in losses.
Hole Metallization
The drilled bare printed circuit board passes through a conveyorized line. After which a thin layer of carbon lines the holes. Also, the thin layer of carbon acts as the cathode.
Photo Mech
In this step, the already drilled bare circuit board is laminated with photosensitive film plating resist. After this, a direct imaging machine images the circuit board.
Plating
This involves copper plating the bare printed circuit board. A periodic pulsed plating is the method used here. The bare PCB manufacturer plates the copper evenly. It is crucial to use the right amount of copper in each panel.
Etching
Etching helps to get rid of unwanted copper from a bare circuit board. This step involves dipping the circuit board in an etching chemical solution to get rod of the unwanted copper. Also, ferric chloride is the constituent of the chemical solution. Manufacturers need to be ensure enough precision and accuracy when Etching so as to prevent the under etching or over etching.
Solder mask application
This is a crucial step that involves the application of solder mask to both sides of the bare printed circuit board. Therefore, the mask serves as protection to the copper surface. Furthermore, solder mask prevents solder-shorting of components during PCB assembly and as well prevents traces from disconnecting.
Screen printing
The screen printing stage involves pressing some amount of ink on a mesh screen. Manufacturers are at the final stages of bare PCB manufacturing when Screen printing. Screen printing specifies crucial details on the bare printed circuit board. It helps in identifying marks, parts, and logos on the board.
Surface finishing
Surface finishing is an important aspect of bare PCB production. In this step, the manufacturer applies some finishes on the exposed copper pads. There are different types of surface finishes. These include immersion gold, HASL, silver finishes, and more. Manufacturers should use an X-ray fluorescence instrument to verify the thickness of the coating.
Inspection
This is the last step in bare PCB production process. It is an integral part of the process as it involves evaluating the panels and checking for any defects in the bare PCB. Also, it involves the correction of these defects.
Defects in Bare PCB Manufacturing
During bare PCB manufacturing, some errors are likely to occur. However, these errors can be prevented or corrected. It is important to understand the causes and prevention of these errors.
Missing copper or excessive copper
Copper is the essential material used for making traces on a bare circuit due to its highly conductive nature. This means it is capable of transmitting signals without any loss of electricity. However, if the copper is in excess or not enough, it can cause some defects on a bare PCB. Furthermore, excessive copper in a circuit board can result in corrosion while lack of enough copper can result in short-circuits to the board.
Short circuit is a common defect that occurs when wires that aren’t meant to be in contact touch each other. Also, a short circuit also occurs when there is a bypass of some electrical current.
Many designers face this issue when producing a bare board. However, this problem can be fixed by replacing the wire. If this isn’t done, your bare boards won’t function as required.
Extra holes
Blank PCBs usually have holes in them. These holes that pass through the board are what we refer to as through-holes. Holes carry conductive vias to create interconnection between the PCB layers. However, extra holes in a bare circuit board could cause another problem during production. This is because extra holes may limit the available space as well as the routing area required for signal tracing.
What does Bare PCB Testing Entail?
Testing a bare board is crucial before approving the board for final production. Some boards can be defective and early detention of any defects helps in reducing cost and time spent on manufacturing. Manufacturers need to test this bare board to verify its functionality. The best way to guarantee the functionality of your bare is board through testing.
Bare PCB testing is carried out to verify the isolation and continuity of a bare board’s electrical connection. The manufacturer verifies resistance between two separate electrical connections during isolation testing. On the other hand, continuity testing ensures there are no open points on a circuit.
Types of Bare Board Testing
Pinned Fixture Test
Also known as In-circuit testing and Bed of Nails, it is ideal for large scale manufacturing. The Pin fixture test evaluates every connective surface on the board.
The pinned fixture test is highly efficient. It is very easy to carry out and only takes a few seconds to perform. However, there are some downsides like lack of flexibility and high expenses since each PCB design needs the creation of a new fixture and as well as a custom array of pins.
Flying Probe Test
The flying probe test is a common way of testing bare circuits. This test makes use of two or more robotic arms. These robotic arms have poles which glide across the PCB surface to test each net and verify the connections of the circuit board. Also, the flying probe testers take instructions from software application to travel across the connections. These testers check for capacitance, diode, and inductance issues. They also check for any open circuit or short circuit.
Conclusion
Bare PCBs are manufactured with the sole purpose of populating them with electronic components. A bare PCB is needed for the manufacturing of a PCBA. There is a higher risk of producing dead boards if a manufacturer fails to test a board. A bare PCB must go through stringent tests before components can be assembled on it.
