The process of making the bare boards that will be the basis for printed circuit board assembly is known as PCB manufacturing.
To assure the performance of the end product, a complicated process is needed during the printed circuit board (PCB) manufacturing process. Despite the fact that circuit boards might be single, double, or multilayered, the fabrication methods are the same up until the creation of the first layer. Some PCBs may take 20 or more steps throughout the manufacturing process due to changes in the PCB’s construction. Their complexity is inversely correlated with the number of steps needed to produce them. Any step that is skipped or the process is shortened could have a detrimental effect on the circuit board’s performance.
We cover all you need to know about the PCB manufacturing process in this article, including the pre-process, complete PCB fabrication, and factors to take into account when selecting a PCB manufacturing business.
THE pre-PROCESS
Step 1 – The Design and Design review
Of course, design comes first in any PCB manufacturing process. PCB manufacture and design always begin with a plan: the designer draws up a layout for the PCB that complies with all of the specifications.
Extended Gerber is a great piece of software for PCB design because it also functions as an output format. Extended Gerber encrypts all the information required by the designer, including the quantity of copper layers, required solder masks, and additional component nomenclature. All the various components and features of the design are verified thoroughly to ensure there are no problems after the Gerber Extended program has encoded a design blueprint for the PCB.
After the designer has done reviewing it, the finished PCB design is forwarded to a PCB fabrication firm so that the PCB may be constructed. The PCB design plan is subjected to a second inspection upon arrival by the fabricator, known as a Design for Manufacture (DFM) inspection.
Step 2-Pcb Design Review And Engineering Questions
Examining the PCB design for any flaws or faults is a crucial phase in the printed circuit board manufacturing process. Our engineers thoroughly review the PCB design to ensure that there are no omitted parts or improper construction, and to ensure that it complies with our process criteria. If it doesn’t satisfy the specifications, we’ll raise engineering concerns, and the PCB design won’t move on to the proofing stage until we have the customer’s approval. assuming you deliver a comprehensive PCB schematic, Gerber files, and all other supporting documents.
Step 3-Printing the Design
Designers output PCB schematic files, and manufacturers perform a DFM check before PCB printing starts. Circuit boards are printed by manufacturers using specialized plotters, which create photo films of the PCBs. The films will be used by the manufacturers to image the PCBs. It isn’t a typical laser jet printer, despite the fact that it uses laser technology. Plotters produce a highly detailed film of the PCB design using incredibly fine printing technology.
The finished item is a plastic sheet printed in black ink with a picture negative of the PCB. Black ink is used to depict the conductive copper components of the PCB for the inner layers of the PCB. used for the PCB’s copper circuitry and traces. The sections of non-conductive material, such as the fiberglass base, are indicated by the remaining clear area of the image. This pattern is inverted on the outer layers of the PCB design, where black ink also denotes regions where copper will be removed and clear ink designates the line of copper routes. The film is automatically developed by the plotter and then safely kept to avoid any unauthorized touch.
A separate transparent and black film sheet is applied to each layer of the PCB and solder mask. A two-layer PCB requires four sheets in total: two for the solder mask and two for the layers. Importantly, every movie has to match every other movie exactly. Together, they lay out the alignment of the PCB.
They are lined up once the film has been printed, and a registration hole is then punched through them. Later on in the procedure, the films are aligned using the registration hole as a guide.
Registration holes should be punched through each film to ensure exact alignment. By changing the table that the film is set on, the hole becomes more precise. The hole is punched when the table’s minute adjustments result in the best possible match. In the following step of the imaging process, the holes will fit into the registration pins.
The manufacturing process
The design and verification phases of the PCB design process are followed by the production of the circuit boards. In order to guarantee accuracy and avoid short circuits or incomplete circuits, several stages require computer guidance and machine-driven equipment. Before being packed and sent to clients, the finished boards must pass rigorous testing.
Step 1 – Printing the copper for the Inner Layers
The manufacturer begins the process of making the PCB by printing the copper for the Inner Layers.
Epoxy resin and glass fiber, often known as substrate material, make up the laminate board that is the foundation of the PCB. An suitable body for holding the copper that supports the PCB is laminate. The PCB’s foundation is made of robust, dust-resistant substrate material. Each side of the copper is already bonded.
The clean laminate panel is then covered with a resist, a kind of photosensitive film. A coating of photo-reactive compounds that become rigid after being subjected to UV light makes up the resist. The photoresist enables experts to achieve a flawless match between the blueprint’s pictures and what is printed on it.
The exposure machine will pass UV light through the translucent area of the film after the resist masking and lamination have been positioned using the holes from before. This will harden the photoresist. This suggests that specific copper trace sections must to be set aside for via circuits. Black ink, on the other hand, blocks all light from entering regions that should not solidify so that it can be removed afterwards.
The board is cleaned with an alkaline solution after preparation to get rid of any remaining photoresists. After pressure-washing the board to remove any remaining debris, it is allowed to dry.
The copper traces at the top of the PCB, which are kept when it is finally removed as part of the PCB, should be the only resist that is kept on the PCB after drying. The employees check the PCB for errors before moving on to the next stage if there are any.
One consideration is that cleanliness is important when building PCBs. The copper-sided laminate is cleaned before being placed in a clean area. It’s crucial that no dust settles on the laminate throughout this process. A stray piece of dirt could otherwise short a circuit or keep it open.
Step 2-Removing Unwanted Copper
Before the PCB fabrication process can continue, surplus copper must be removed from the printed circuit board’s core or inner layers. The necessary copper on the board is covered during etching, and the remaining board is subjected to a chemical. The PCB’s unprotected copper is completely removed during the chemical etching/dissolving process, leaving only the minimal amount required for the board.
Copper boards vary greatly from one another. Some heavier boards call for longer exposure times and higher concentrations of copper solvent. As a side point, track spacing needs to be carefully considered when using heavier copper boards. Standard PCBs often use the same specifications.
Step 3-Layer Alignment
The layers need alignment punches once they are all clean and prepared to guarantee that they line up. The inner layers are aligned with the outer layers by the registration holes. The technician inserts the layers into the optical punch machine. To align the PCB layers, optical punchers force the pins through the holes.
Of course, the layer alignment also heavily depends on the layer direction.
Step 4-Automated Optical Inspection
A different machine performs an optical examination to keep any faults after optical punching. The importance of this automatic optical inspection stems from the fact that once the layers are assembled, any mistakes that may exist cannot be remedied. We must compare the PCB and the Gerber Working files using the AOI machine to verify that there are no errors.
The PCB moves on to the last stage of PCB fabrication and production if it has passed the inspection (i.e., the technician and AOI machine have found no flaws).
The AOI stage is crucial to the PCB printed board’s functionality. Without it, boards that could have shorts, wouldn’t comply with PCB design requirements, or wouldn’t have had extra copper traces removed during the etching process would be able to proceed on to the next step. Midway through the manufacturing process, AOI acts as a quality checkpoint to stop defective boards from operating. After engineers have done imaging and etching the outer layers, this procedure is repeated.
Step 5 – Laminating the Layers
At step four of the procedure, all of the PCB layers are assembled and ready for lamination. The layers are prepared to be fused once it has been determined that they are defect-free. The lay-up phase and the laminating step are the two steps in the PCB lamination process.
Fiber glass sheets that have already been pre-impregnated with epoxy resin make up the outer layer material. The abbreviation for this is prepreg. The copper trace etchings on the original substrate are also covered with a thin copper foil on the top and bottom. Put them in a sandwich right now.
On specialized press tables, metal jigs are used to interlayer these layers. Specialized pins are used to secure each layer to the table. Pre-impregnation, also known as prepreg, is a coating of pre-applied epoxy that lamination technicians first apply to the bench’s aligned basins. On the substrate, a layer of the pre-impregnated glue is applied, followed by a layer of copper traces foil. The copper foil is covered with further sheets of pre-impregnated resin one after the other, and is then completed with the final piece of copper traces, known as the pressing substrate.
As soon as the copper pressing laminates are in place, the stack can be pressed. It is brought to a mechanical press where technicians press the layers together. To make sure the pins are properly seated, the stack is then pushed through.
The PCB stack will be transported to the lamination press, the following press, if the layers are securely fastened. The laminator presses and heats the lamination using two heating plates. The circuit board’s heat and the press’s pressure combine to melt the layers of circuit boards together as the epoxy glue inside the fibrous material is fused together.
As soon as the PCB layers are pushed together, some separation work is necessary. Before removing the actual PCB, the technician must remove the top platen and pins.
Step 6 – Drilling
Finally, the stack board is drilled with holes. Precision drill holes must be accurate in order for later-added components like leaded elements and copper-linking through holes to function properly. The holes are drilled to a hair’s width; a human hair is typically 150 microns wide, whereas the drill only reaches a diameter of 100 microns.
An x-ray finder detects the appropriate drill target sites in order to locate the drill points. The stack is then secured for the subsequent series of more precise holes by drilling the appropriate registration holes.
To guarantee a clean bore is executed, the technician installs a board of buffer material beneath the drill target prior to drilling. When the drill exits, the exit-material prevents any needless tearing.
Every tiny movement of the drill is managed by a computer; it makes sense that a product that controls how machines behave would rely on computers. The drilling file from the original design is used by the computer-driven device to determine the appropriate places to hole.
Air-driven spindles that rotate at 150,000 rpm are used in the drills. Drilling may seem to occur quickly at this speed, but there are actually a lot of holes that need to be made. There are typically far over 100 bore intact places on a PCB. Drilling takes time since each person needs their own unique moment with the drill. The vias and mechanical mounting holes for the PCB are later housed in the holes. These components are finally fastened after plating.
After the drilling is finished, a profile tool is used to remove the extra copper that lines the manufacturing panel’s edges.
Step 7 –PCB Plating
The panel is prepared for plating once it has been drilled. The many layers of the PCB are joined together chemically during the plating process. The PCB is properly cleaned before being given a chemical treatment. A micron-thick layer of copper is applied to the panel as part of this bathing procedure, covering the topmost layer and going into the just drilled holes.
The perforations only serve to reveal the fiberglass substrate that makes up the panel’s interior before they are filled with copper. The walls of the previously drilled holes are covered when those holes are bathed in copper.
Step 8 – Outer Layer Imaging
Photoresist is put to the PCB during step 1 of the procedure. It’s time to add yet another layer of photoresist in step 8. This time, photosensitive resist is only used on the outer layer because imaging is still required. They are plated in the same manner as the inner layer of PCB in the stage prior to photolithography and imaging of the outer layer. The outer tin plating aids to safeguard the copper traces on the outer layer despite the fact that the technique is the same.
Step 9 – Plating
We head back to the plating area. We electroplate the panel with a small layer of copper, just as we did in Step 7. The copper electro-plating is applied to the panel’s exposed areas from the outer layer photo resist stage. The panel often receives tin plating after the initial copper plating baths, allowing all of the copper that was left on the board to be removed to be removed. The copper-covered area of the panel is protected by the tin during the subsequent etching process. Copper foil that is not wanted is removed from the panel by etching.
Step 10 – Outer Layer Etching
The tin guard is utilized to help safeguard the copper during the etching process when it’s time to etch the outer layer for the final time. The same copper solvent from previously is used to remove any extra copper, and the tin shields the valuable copper in the etching area.
The areas that need to be removed are one of the key distinctions between the inner and outer layer etching. The inks used for conductive areas and non-conductive surfaces in the inner layers are black for the inner layers and transparent for the outer layers, respectively. As a result, copper is covered in bright ink while the non-conductive layers are covered in dark ink. The tin coating can cover the copper and shield it thanks to this transparent ink. Engineers prepare the outer layer for AOI and solder masking by removing any unnecessary copper and any lingering resist coating during etching.
Step 11-Outer Layer AOI
The outside layer must also go through automated optical inspection, much like the inner layer. This optical examination makes that the layer satisfies all of the design specifications. Additionally, it confirms that the preceding procedure successfully removed all excess copper from the layer to produce a printed circuit board that will operate correctly and prevent faulty electrical connections.
Step 12 – Solder Mask Application
The panel must be meticulously cleaned before the solder masking is applied. Each panel’s surface finish features solder masking and ink epoxy after cleaning. The board is then exposed to UV light (ultraviolet light) to show where the solder masking has to be removed.
The PCB board is placed in the oven to cure the solder masking after the technical staff has removed it. This masking offers further defense against corrosion and oxidation damage to the copper traces on the PCB circuit board.
Step 13 – Silkscreen Application
Fabricators must print critical information on the board’s surface using a method known as silkscreen application or legend printing because PCBs must have information directly on the board. This data contains the following:
- Company ID numbers
- Warning labels
- Manufacturers marks or logos
- Part numbers
- Pin locators and similar marks
- Information requested by customers, such as component instructions, model, customer LOGO, etc.
The printed circuit boards (PCBs) have their surface finish added after the aforementioned data has been printed onto them, frequently using an inkjet printer. They then move on to the processes of testing, cutting, and inspection.
Step 14 – Surface Finish
Finishing the PCB requires plating with conductive materials, such as the following:
Silver immersion: Low signal loss, lead-free, RoHS compliant, although the finish is tarnish- and oxidation-prone. A hypallage response, or almost a sub-micron covering of pure silver, is immersion silver. However, the immersion silver process also uses some organic material, mostly to prevent silver degradation and solve the silver migration issue. This small layer of organic stuff is never easy to determine. According to the survey, the organism weight was less than 1%.
Hard gold is pricey, long-lasting, RoHS compliant, lead-free, and durable. The earliest method of treating the surface of PCBs is electroplated nickel gold. Since the invention of PCB boards, it has been accessible, and additional procedures have gradually emerged. The surface conducting body of the PCB is electroplated with nickel electrocladding as the first layer and gold electrocladding as the second layer. The main purpose of nickel cladding is to prevent spreading between copper and gold. Electroplated nickel gold comes in two varieties: soft gold plating and hard gold plating. Gold wire used in chip packaging is primarily affected by electroplated nickel soft gold; electrical connections in non-soldered locations are primarily affected by electroplated nickel hard gold.
One of the most popular finishes, long shelf life, RoHS compatible, but more expensive than other choices is electroless nickel immersion gold (ENIG). The process of electroless nickel/immersion gold plating, often referred to as nickel-gold, immersion nickel-gold, or electroless nickel-gold plating, involves chemically coating a layer of nickel-phosphorus alloy on the palladium core before replacing the palladium on the copper surface. The gold layer formed by the reaction covers the nickel. The semi-reduction mixed plating and the substitution semi-replacement are the two methods for the immersion gold of nickel and gold.
Hot air solder leveling (HASL) is affordable, durable, and reworkable but includes lead and is not RoHS compliant.
Lead-free HASL stands for high-quality, low-cost, lead-free, and reworkable.
Hot air leveling, often referred to as hot air solder leveling, is a process where molten tin-lead solder is applied to a PCB’s surface and leveled with heated compressed air to provide a layer that prevents copper oxidation and improves solderability. A copper-tin metal combination that is produced by joining copper and solder in hot air and leveling to a thickness of between one and two mils.
To create a coating that is resistant to copper oxidation and has good solderability, coat the surface of the PCB with molten tin-lead (lead and lead-free) solder and heat compressed air to level it out (blow). Immersion tin (ISn): Frequently used in press-fit applications, precise hole tolerances, RoHS compliant, touching the PCB can cause soldering issues, tin whiskers. smooth surface, high cost performance, and RoHS compliant, lead-free;
The term “immersion tin” describes the plating of an immersion tin layer over copper circuits. Hot air leveling (HAL) and other immersion tin processes can produce flattened copper-tin chemical compounds with high solderability, but there is no flatness issue. Additionally, there is no electroless nickel plating/dipping diffusion between the gold and the metal; the immersion tin plate can only be kept for a short period of time.
RoHS compatible, inexpensive, and with a limited shelf life is the organic solderability preservative (OSP). OSP is distinct from conventional surface treatment methods because it serves as a barrier between copper and air. More specifically, OSP is the chemical-free development of a thin coating on bare copper. In a typical environment, this layer of film resists thermal shock, antioxidants, and moisture to prevent the copper surface from rusting; nonetheless, it must be easily removed in the succeeding high-temperature welding step with the scaling powder to make soldering easier.
High solder strength, less corrosion, requires careful processing for appropriate performance, more expensive than alternatives that don’t employ gold or palladium. Electroless nickel electroless palladium immersion gold (ENEPIG).
The right material should be chosen based on the customer’s budget and the design requirements. However, using such finishes gives the PCB a crucial characteristic. An assembler can mount electronic components thanks to the finishing. The copper is additionally covered in metals to prevent oxidation from happening when it is exposed to air.
Step 15 – Electrical Reliability Test
A technician conducts electrical tests on the PCB as a final precaution. The automated process verifies the PCB’s usability and conformance to the original design. In order to verify the electrical performance of each net on a bare circuit board, PCB Cart offers Flying Probe Testing, an advanced method of electrical testing that uses moving probes.
Step 16-Profiling and Route Out
We are now at the final phase, cutting. The original panel is cut into many boards. Either a router or a v-groove are used as the main components of the technique. A v-groove cuts diagonal channels along both sides of the board, whereas a router leaves little tabs along the edges. The boards can simply come out of the panel in either direction.
Step 17-Quality Check and Visual Inspection
After the boards are scored and split, the PCB must undergo a final inspection before packaging and shipping. The final inspection verifies several aspects of the board construction:
Hole sizes in all layers must match and meet pcb design requirements.
Board dimensions must match those in the pcb design specification.
The manufacturer must ensure the cleanliness of the board free of dust.
Finished boards must not have burrs or sharp edges.
All boards that fail electrical reliability testing must be repaired and retested
Step 18: Packaging and Delivery
Packaging and delivery are the final steps in the manufacture of PCBs. Printed circuit boards are generally packaged with materials that seal around them to keep out dust and other extraneous objects. The encapsulated boards are then placed in shipping containers that guard against damage. Lastly, they go out for delivery to the customers.
PCB fabrication is a meticulous procedure, and even little errors can result in incorrect design that costs organizations money. Consider hiring PCB fabricators with a track record of success when selecting your PCB fabrication business. PCBs of aircraft quality are produced by Imagineering Inc, which also has the capacity to handle PCB manufacture and assembly. Our credentials include:
- Turnaround in as little as 24 hours
- High mix low-to-mid volume
- Class II and Class III inspection
- AS9100D certified and ITAR compliant
- Leaded and lead-free RoHS assembly
- 100% on-time guarantee
- Design services (Outsourced)
- Full box build
PCB Manufacturing Process FAQs
Typically, copper circuitry is layered between non-substrate materials to create PCBs. However, the architecture of various PCB types varies. For instance, more sophisticated printed circuit boards may have multiple layers of copper circuitry instead of just one.
Common Types of Printed Circuit Boards
Single Layer PCB. Single layer printed circuit boards are among some of the simplest to design and manufacture. ...
Double Layer PCB. ...
Multi-Layer PCB. ...
High Density Interconnect (HDI) PCB. ...
High Frequency PCB.
Electrical components are put directly onto the surface of a printed circuit board using surface-mount technology (SMT) (PCB). A surface-mount device is an electrical component installed in this way (SMD).
The different types of PCBs available are
Single-Sided PCBs.
Double-Sided PCBs.
Multilayer PCBs.
Rigid PCBs.
Flex PCBs.
Rigid-Flex PCBs.
In order to create a multi-layer PCB, prepreg, an epoxy-infused fiberglass sheet, and conductive core materials are alternately bonded together using a hydraulic press at a high temperature and pressure. The prepreg melts under the pressure and heat, connecting the layers together.
The first step in the PCB design process is schematic capture.
The schematic, which uses industry-standard symbols and notations to represent various components and their values, is the logical representation of the electronic circuitry of the circuit board that needs to be constructed.