The process of manufacturing bare boards that will serve as the basis for printed circuit board assembly is known as PCB fabrication.
You should exercise caution when selecting a PCB manufacturing provider since even little mistakes might destroy the whole board, leaving the ultimate product unusable. Communication between the design team and the manufacturer is crucial, particularly now that production has migrated offshore.
In this article, we will go over everything you need to know about the PCB manufacturing process, including the pre-process, PCB fabrication in general, and factors to consider when selecting a PCB fabrication business.
What is the difference between PCB fabrication and PCB assembly?
PCB fabrication and PCB assembly are two separate steps in the PCB manufacturing process.
The process of translating a circuit board design into the actual structure of the board is known as PCB manufacturing. PCB assembly, on the other hand, is the process of actually inserting components into the board to make it functional. PCB manufacturing is analogous to a city’s roads, streets, and zoning, but PCB assembly is the physical structure that enables a printed circuit board to function. More information on PCB assembly may be found here.
Before Beginning the PCB Fabrication Process
It’s all about the details when it comes to making a printed circuit board. The initial design must be finished since even a single component change that is not synchronized might result in a faulty board assembly. This includes the following:
- A thorough engineering evaluation of the circuits
- Schematic and layout databases that are synchronized
- Analysis of whole circuit simulation, signal integrity, and power integrity
- PCB design guidelines and restrictions were double-checked.
- The bill of materials and design for manufacturing regulations are examined.
- Read our Design-for-Manufacturing (DFM) Principles Guide.
The Process of PCB Fabrication
Laser Direct Imaging and the Develop/Etch/Strip Method
Before work on a multi-layer printed circuit board starts, laser direct imaging (LDI) is used to apply regions that will become traces, pads, and metal ground.
A copper laminate is coated with a dry film.
In the form of the PCB layout, laser direct imaging exposes certain sections of the board to light.
Any exposed board portions will develop away, leaving the remaining film as an etch barrier.
The residual film acts as an etch barrier, which will be removed from the exposed copper in order to construct the copper circuitry.
The layers are then inspected for flaws using an automated optical inspection before being laminated together. At this point, any problems, such as possible shorts or openings, may be remedied.
Lamination and Oxide
After all of the layers have been etched, a chemical treatment known as oxide is applied to the inner layers of a printed circuit board to strengthen the connection. Then, using heat and a hydraulic press, alternating layers of prepreg and copper foil are bonded together. Prepreg is a fiberglass material that contains an epoxy resin that melts during lamination due to the heat and pressure, connecting the layers into a “PCB sandwich.”
It is critical to pay close attention to the alignment of the circuitry between each layer.
Drilling
To transfer signals from one layer to another on a multi-layer printed circuit board, holes must be drilled or laser-cut to generate vias. Drilling varies based on the kind of via utilised, however it is typically done on a stack of 2-3 panels at a time. Because these holes will be plated with copper to aid convey electrical impulses using a technique known as electroless copper deposition, the final result will typically be 5 mil bigger than the finished product.
Before the lamination process can begin, blind and buried vias must be created. Incorporating them into your PCB design may raise the cost owing to the additional processes that must be completed.
Deposition of Electroless Copper and Dry Film Outer Layer
Excess glue and debris are removed using chemical and mechanical techniques after holes are drilled into the surface. Following removal, a thin layer of copper is deposited on all exposed regions of a panel, forming a metallic foundation for the electroplating process. Dry film is put to the outer layers of the copper panel and subjected to laser direct imaging, leaving a conductive pattern, similar to the previous develop/etch/strip processes.
Stripping, electroplating, and etching
The panel is immersed in a copper plating solution comprising sulfuric acid and copper sulphate with a conductive pattern and drilled holes exposed. When an electrical current is applied to this, copper with a thickness of roughly 1 mil is deposited into the conductive surface of the board. After that, the plate is removed and deposited in a tin plating bath to act as an etch barrier.
When the plating is finished, the dry film is removed, and the exposed copper that has not been covered by tin is etched away, leaving just the traces, pads, and other patterns on the plate. The residual tin is then chemically scraped away, leaving just copper in certain locations.
The printed circuit board is now assembled, but it is not yet ready for assembly.
Surface Finish, Silkscreen, and Solder Mask
The printed circuit board will be covered with a solder mask before proceeding to the PCB assembly step, utilizing a similar UV exposure as in the photoresist stage. Although various colors are available, this is what gives printed circuit boards their unique green color.
A solder mask is a thin coating of polymer that shields the printed copper traces on the board from oxidation. It also avoids solder bridges, which occur when unintended connections develop between two wires, leaving a printed circuit board inoperable.
The color of the solder mask may be selected at this point, but most manufacturers prefer green since it aids in defect checking due to its high contrast and trace visibility, which is crucial during the PCB prototype stage. The color of a solder mask has little effect on the operation of a board in general, while darker colors are more heat-absorbent, making them unsuitable for high-temperature applications.
Following the application of the solder mask, component reference designators and extra board marks are silkscreened onto the printed circuit board. By baking the circuit board in an oven, the solder mask and silkscreened ink are hardened.
Finally, exposed metal surfaces that are not covered by the solder mask are given a surface finish. During the PCB construction process, this shields the metal and aids in soldering.
Preparation of the assembly, inspection, and testing
After the PCB manufacturing process is completed, the final boards are inspected and tested to guarantee operation before assembly or shipment. Automated test equipment looks for any shorts that might jeopardize a board’s operation, and any PCBs that fail the test are eliminated.
Thoughts For The PCB Fabrication Process
PCB creation is a detailed process, and even little errors may cost organizations money due to defective construction. Consider hiring PCB fabricators with a track record of success when selecting your PCB fabrication firm. Imagineering Inc manufactures aerospace-quality PCBs and is capable of handling both the manufacturing and assembly procedures. Our credentials include the following:
- Turnaround time may be as small as 24 hours.
- Low-to-mid loudness with a high mix
- Class II and III inspections
- ITAR compliance and AS9100D certification
- RoHS assembly with lead and without lead
- 100% on-time delivery guarantee
- Outsourced design services
- Complete box construction
Look no further than Imagineering Inc. for the top-quality PCB manufacturing business. Our prices are low, and our turnaround time is unrivaled. Request a PCB manufacturing quotation right now.
