PCB Fabrication

PCB Fabrication and Assembly: Key Components and Technologies

PCB fab and assembly

In the PCB fabrication and assembly, a bare board is created that will serve as the base of the PCB when all the stages are performed successfully. All manufacturers must remember that throughout the PCB fabrication and assembly process, extreme caution must be exercised because even small mistakes will later lead to disastrous results. To avoid loss of money and time, interaction among the engineering team and producers is crucial during the entire process.

Printed circuit boards can have one, two, or more layers, but the procedures for making them are always the same after the first layer is perfected. The complexity of printed circuit boards is directly correlated with the number of layers involved in their production, and any skipped step during the fabrication process might have a direct bearing on the functionality of the circuit board.

Difference between PCB Fabrication and Assembly

It is easy to get confused about these two processes and many might think that they are the same process with two names. That is false and there is a big difference between these two procedures. Putting a PCB together is a method of manually adding parts to the panel to allow operation and after that stage is completed, the procedure of putting a printed circuit layout into the real board begins.

The construction of a printed circuit board is a matter of maintaining details, and sometimes, a single element change might lead to a malfunctioning system. Therefore, an exhaustive engineering evaluation of the circuits is necessary before the process begins. The checking of full circuit simulation, examination of power integrity, reliability of signals, synchronization of schematic and layout databases, and verification of PCB design guidelines and restrictions must all be performed.

Steps of PCB Fabrication Process

PCB Fabrication

  • Step 1: Circuitry Image Creation

Transferring the layout of the PCB schematic data from the assembly documentation to the panel that will be constructed later is the first step of the PCB manufacturing process. Although many formats and databases are available, the data typically arrives in a specific format and can be sent to the board in two ways. The initial operation is called “Phototooling”, and it’s a traditional scanning technique employed in PCB production that goes way back to the time when boards for electronics are manufactured in bulk. Utilizing an accurate photoplotter, the electronic components’ images will be created on microfilm in this technique, which will operate as a blueprint for the production procedure of graphic imprinting on the printed circuit board. In the next method, known as “Direct Imaging”, no extra machinery is required; instead, a beam of laser imprints the electronic images directly on the printed circuit boards. Compared to film, this method has the benefit of being more accurate, not requiring frequent reconstruction to replace worn-out films, and not having alignment problems, but it costs more to laser print each layer separately.

  • Step 2: Circuit Board Layers

Layer combinations comprise a multilayer circuitry in the surface, which is composed of several conductive metal layers and insulating layers. Above the dielectric core made of glass filaments and epoxy resin, also known as FR-4, are two additional layers of foil made of copper. Although there are alternative insulating substances, FR-4 is the most widely used primary component in PCB manufacturing. Multi-layer boards will fuse a thinner variant of the exact same base framework, which is used to build a double-sided PCB that has extra base constructions, in order to construct the surface layers. Tight monitoring of each layer’s width, metallic material size, and layer-to-layer synchronization is necessary throughout production to produce an item of outstanding quality.

  • Step 3: Creation of the Inner Layer Circuitry

Printing circuitry pictures onto the inner layer cores is the initial stage in the PCB fab and assembly, and the core foil gets covered with a film of photoresist material during this stage. The photoresist is exposed to UV light by photo tooling or direct laser imaging. Nevertheless, photoresist solidifies or polymerizes over the component layouts and only the uncovered metal circuitry’s panels and connections are left visible. After the copper-based plates that comprise the fundamental structure are erased, just the electronics protected by the polymerizing photoresist remains. The copper electrical wiring remains after the reflective material has been eliminated during this operation and a fully automated optical inspection device has to examine the base levels for defects following this process. After this process, all of the board’s innermost layers will be ready for the lamination process, creating one, completed electronic board that is ready for the next step.

  • Step 4: Oxide and Lamination

Once all the layers of the design have been imprinted on the board, it is time to reinforce the connectors. For that process, certain types of oxides are applied to some of the layers that make up the entire PCB. Next, temperature and a press operated by hydraulics are used to fuse the prepreg and metal foil plates. Prepreg is a type of substance that has been infused with the material called epoxy resin. These two elements can get fused under high temperatures and pressure, which is done during the multi-layer lamination process.

  • Step 5: Drilling

When information needs to be successfully sent between a particular layer to a different one on a layered printed circuit board, apertures must be drilled to form vias that connect the layers together. Drilling frequently occurs on an array of two to three sections at a time, nevertheless this might change according to the kind of via being employed for that PCB. Through a process called electroless copper depositing, these openings will be coated with copper to help in the passage of electricity and the finished result is usually larger than the source. Incorporating a few extra steps such as fabricating hidden vias during the lamination might increase the price of the PCB fabrication assembly. However, going with these steps will ensure that the board is functional and will help you avoid issues in the long run.

  • Step 6: Electroless Copper Deposition & Dry Film Outer Layer

After apertures have been punched into the outermost layer, leftover adhesives and particles get eliminated mechanically and chemically. After the removal procedure, the exposed areas of the outermost layer are lightly treated with metallic copper. The outside portions of the metallic screen are coated with a material, which is subsequently subjected to laser mapping to produce an electrically conductive structure.

  • Step 7: Electroplating, Stripping, and Etching

After the apertures are finished being drilled and the electric conductivity layouts are identifiable, the entire assembly is submerged in an electroplating solution. A one-millimeter-thick coating of copper emerges on the board’s surfaces after an electric charge is applied to it and the plate is then taken out. Subsequently, the plate is removed and immersed in an aluminum coating fluid to serve as an etching buffer. Following the procedure, all of the copper that hasn’t been covered in tin is scraped off, leaving the plate’s surface adorned only with imprints along with designs.

  • Step 8: Solder Mask, Silkscreen, and Surface Finish

Using the same UV light sources, a soldering overlay will be applied on the printed circuit board to safeguard it throughout the PCB fabrication assembly. A thin coating of polymeric material is affixed to a board to prevent the etched lines from deteriorating. Additionally, it gets rid of soldered connections which are accidental contacts among two wires that make a PCB less reliable. Manufacturers may now choose the hue of solder mask, and bright colors are typically used because of its superior visibility and ease of tracing which help identify flaws throughout the PCB prototype phase. Darker colors aren’t as good for tasks that call for extreme conditions as they absorb more heat and hinder the system. Lastly, the exposed metal components that are not protected by the soldering barrier must receive an external coating for extra protection.

  • Step 9: Assembly Preparation, Inspection, and Testing

After PCB fabrication, the completed boards are put through a series of testing and assessments to ensure they perform as planned. The circuit boards are scanned by automated testing instruments for defects that might impair their operation and the faulty boards are promptly disposed of.

Also read: Common Mistakes to Avoid in PCB Assembly and Manufacturing

Steps of PCB Assembly Process

PCB Assembly

All the companies that offer PCB fabrication and assembly China remain careful about the assembly process because a PCB is not functional until its component pieces are correctly set on the surface. These component pieces include many elements that are all necessary to enable the final PCB board to work successfully.

  • Step 1: Pre-Production

The layout document is often reviewed prior to PCB assembly in order to correct any possible shortcomings. Before manufacturing, a review of the design or manufacturing capability monitoring is conducted to make sure issues are resolved thoroughly in advance. The purpose of this stage is to identify the design elements that may give rise to problems throughout the entire manufacturing phase. For instance, the desire for downsizing usually leaves too little space among elements, which may lead to sections that are malfunctioning and fragile. Through proactive problem-solving and early detection, a review may minimize wastage and preserve costs for the manufacturers.

  • Step 2: Solder Paste Printing

The first step in the board building procedure is the application of solder paste jet etching. Soldering paste is a material that, if subjected to heat, mixes tiny metallic balls with a specific compound to help the particles stick to the outside of circuit boards. A soldering paste jet printer dispenses the solution at a speed of three hundred dots a sec and because of the remarkable precision and minimal component loss of this technology, panel modifications can be done fast and the time required for manual application can be avoided. Just the regions where parts will be linked following treatment will retain the soldering paste. After that, a machine check will verify the PCB to ensure the solder paste was put uniformly, and that the printed circuit board is prepared for the next step.

  • Step 3: Pick and Place

A pick-and-place device supplies the assembled PCB with soldering while adhering to predefined sections. A mechanical arm could precisely place surface-mount components on the laminated circuit board and the surface-mount components may be promptly attached to precise locations using these robotic tools. At this stage, the soldering paste and electronics are connected yet not melted and joined together.

  • Step 4: Reflow Soldering

In order to connect the outermost mounted electronics to the PCB surface, the solder paste must now be preheated. Conveyor belts are used to transfer the printed circuit board into a “reflow oven”, which melts the solder paste by providing just the right amount of heat for just the right length of time.

  • Step 5: Inspection

Since most of the setup process has already been completed at this juncture, this is the final phase of the PCB fabrication and assembly. Since reflow during the PCB fab and assembly may occasionally trigger displacement on the printed circuit board, that can lead to faulty loops or poor connections, quality assurance and examination are essential. Although the testing procedure is primarily automated, small quantities of PCB may still be individually scrutinized. Solder links may show in a variety of ways based on the condition of the bond because systems are made to detect weak connections rapidly. X-ray imaging may also be used to analyze multi-layer PCBs and the final operational assessment simulates regular tasks that a printed circuit board can encounter all throughout the course of its service life. If any voltage or information flow is beyond the allowed limitations, the circuit board will be refurbished or destroyed. Regular inspection is necessary for every step of the PCB assembly procedure to ensure that the board’s performance remains constant throughout their production phases.

Also read: PCB Assembly Process: Methods, Processes, and Defects Explained

Conclusion

In general, we should take a holistic approach to PCB fabrication and assembly. Factors like components, technologies, and steps should be considered ahead of time. Many components and technologies are employed in the PCB fabrication and assembly. More importantly, we should also put more emphasis on the PCB fab and assembly process.

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