What is The PCB Manufacturing Process?

Material Preparation

Material Preparation is the foundational step in the PCB manufacturing process. It involves the precise cutting of the base material, which will form the substrate of the PCB. This material is typically a type of fiberglass like FR4, or a more advanced composite if the application requires it. The dimensions must be accurate to ensure that the subsequent layers, which include copper, solder mask, and silkscreen, align correctly. This step sets the stage for the entire manufacturing process, and any errors here can propagate through later stages, leading to defects in the final product.

Board Material Baking

Once the base material is cut to size, it undergoes a baking process. This step is crucial as it removes any moisture that may have been absorbed by the material. Moisture in the PCB can cause a variety of issues, such as delamination or blistering when the board is subjected to the high temperatures of soldering during assembly. The baking process stabilizes the material, ensuring it can withstand the thermal stresses of subsequent manufacturing processes and the final operating environment.

LDI Drilling

LDI Drilling, or Laser Direct Imaging Drilling, is a precision process where lasers are used to drill very fine holes, known as vias, into the substrate. These vias are crucial for creating electrical connections between the different layers of a multilayer PCB. The accuracy of LDI drilling is paramount, as the vias must align perfectly with the circuit pattern to ensure functionality. This process also sets the stage for plating, which will later coat these vias with copper to create conductive pathways.

Inner Layer Dry Film

The Inner Layer Dry Film process involves applying a light-sensitive film to the surface of the copper-clad substrate. This film is then exposed to UV light through a patterned mask, which hardens the film in the shape of the circuitry. The unexposed film is then developed away, leaving behind a protective layer over the copper circuits that need to remain after etching. This step is critical for defining the precise electrical pathways that will carry signals through the PCB.

Inner Layer Etching

Inner Layer Etching is the process of removing the unwanted copper from the substrate, leaving behind only the circuit patterns protected by the dry film. This is typically done using a chemical etching solution that dissolves the unprotected copper. The precision of this process is critical, as it defines the electrical functionality of the PCB. Any errors in etching can lead to short circuits or open circuits, which can render the PCB non-functional.

Inner Layer AOI

Automated Optical Inspection (AOI) for the Inner Layer is a quality control step where an automated system scans the etched circuit patterns for any defects such as shorts, opens, or thinning of the copper. This inspection is crucial for ensuring that the inner layers of the PCB are defect-free before proceeding to the lamination process, where these layers will be permanently bonded together.

Oxidation

The PCB brown oxide process, also known as PCB brownization or black oxide process, serves the purpose of enhancing the adhesion and solderability of copper surfaces on the circuit board. This process involves the controlled chemical oxidation of the exposed copper, forming a thin layer of brown or black oxide on the copper surface. This oxide layer improves the bonding between the copper and the substrate materials, as well as promotes better wetting during the soldering process. Additionally, the brown oxide layer acts as a protective barrier, safeguarding the copper traces from oxidation and ensuring prolonged shelf life and reliable performance of the PCB.

Lamination

Lamination is the process of bonding the various layers of the PCB together under heat and pressure. This includes the copper-clad substrates, prepreg layers, and any additional copper foil for outer layers. The lamination process must be precisely controlled to ensure that the layers are perfectly aligned and that the heat and pressure are sufficient to fully cure the epoxy resin, creating a solid, unified board structure.

Drilling

After lamination, the PCB is drilled to create mounting holes for components and vias for interlayer connections. This drilling must be done with precision to ensure that the holes are placed correctly and do not damage the circuitry. The size of the holes is also critical, as it must be large enough to allow for plating and the insertion of component leads, but not so large as to weaken the structure of the PCB.

Deburring

Deburring is the process of removing any rough edges or burrs left from the drilling process. These imperfections can cause problems during component insertion and can lead to electrical shorts if conductive debris is left on the board. The deburring process ensures that the holes are clean and smooth, which is essential for the reliability of the PCB.

Electroless copper deposition

Electroless copper deposition forms a delicate copper layer on the interior walls of drilled holes, establishing electrical continuity between layers. This precise chemical process requires careful control to ensure a reliable deposit even on non-metallic surfaces. The subsequent through-hole plating envelops the hole walls and board surface with this thin copper coating.

At Highleap, we expertly balance the copper plating thickness between 5-8 microns during panel plating. This follows the initial PTH layer and optimizes the copper for subsequent etching according to exacting track and gap specifications. Our meticulous plating orchestration fulfills the most demanding PCB requirements.

Negative Image Plating

Negative Image Plating is a critical step in defining the outer layer circuitry of the PCB. A photoresist material is applied to the entire board, and then the board is exposed to light through a negative image of the desired circuit pattern. The exposed photoresist is then developed away, leaving behind a protective layer on the areas where copper should remain after the plating process.

Negative Electroplating

Here are a few key points about negative electroplating in PCB manufacturing:

• Negative electroplating is used to plate copper into through-holes and vias on a PCB. It helps to interconnect the front and back side of a board.
• The board acts as a cathode in the plating tank. It is submerged along with a copper anode. An electrical current is passed between them.
• Areas that were previously etched or drilled (holes) will now accumulate a deposit of copper from the solution onto their surfaces. This metallic coating bridges across the opening.
• The plating solution contains copper sulfate and sulfuric acid. Copper ions are attracted to and adhere to the cathode (board), building up a smooth, even layer of copper.
• Thickness and quality of the deposit is carefully controlled. Sufficient plating ensures holes are fully lined to allow soldering of components from both sides.
• Negative plating is a key step that converts an insulated board into a conductive circuit by metallizing interlayer connections like vias. It enables multilayer board fabrication and improves electrical performance.

Negative Image Dry Film

Negative image dry film is a dry film photoresist used in the PCB manufacturing process. Here are some key points about it:

• Dry film photoresist is applied as thin film laminate sheets rather than a liquid photoresist. It is convenient to use.
• For negative image dry film, the film is laminated onto the copper clad board with a thermoplastic adhesive backing.
• It is then exposed to UV light through a photomask, just like liquid resists. But the unexposed areas are soluble.
• After UV exposure, the soluble/unexposed areas are removed by developing chemicals like sodium carbonate, leaving the circuit image in relief.
• This is the “negative image” as the resist remains only where copper will be etched away later.
• The board then undergoes etching to remove copper from the areas not protected by the dry film resist.
• This results in the final circuit pattern of etched trenches in the copper foil.
• After etching, the remaining dry film resist is stripped off, completing the imaging process using a convenient film-based resist.
• Negative image dry film provides an efficient alternative to liquid resists for circuit definition on PCBs.

Dry Film Inspection

The applied dry film is carefully inspected to ensure that it has been applied correctly and without defects. Any imperfections in the dry film can lead to defects in the final etching process, so this inspection is critical for ensuring the quality of the final PCB.

Negative Image Etching

The final etching process removes the unwanted copper that is not protected by the dry film, leaving the final circuit pattern on the outer layers of the PCB. This step must be precisely controlled to ensure that the final traces are the correct width and that there is no unwanted copper left on the board.

Outer Layer AOI

The outer layers of the PCB undergo Automated Optical Inspection to check for any defects in the final circuit pattern. This inspection is crucial for ensuring that the PCB will function correctly and meets the design specifications.

Soldermask

A solder mask is applied to the PCB to protect the copper traces and to prevent solder bridges from forming during the component soldering process. The solder mask also provides a level of protection against environmental factors and helps to insulate the copper traces.

Soldermask inspection

After the solder mask is applied, it is inspected to ensure that it has been applied correctly and is free of defects. This inspection is important for ensuring the reliability of the PCB during assembly and in the final application.

Iegend

The PCB character printing process provides clear visual identification by precisely applying labels, symbols, and alphanumeric markings. These legible and permanent markings impart crucial information like component designators, reference numbers, logos, and manufacturing details. Character printing aids assembly, debugging, and maintenance by facilitating efficient and error-free PCB handling. This enhances overall organization, traceability, and professionalism of the final product. Effective board printing and labeling enables seamless communication and operation within intricate electronic systems.

PCB Finish Options

Applying a finish to the fabricated PCB is essential to enable component assembly and protect the copper from oxidation. Common finishes include:

• Immersion silver – Low loss, lead-free, can oxidize over time
• Hard gold – Durable with long shelf life but expensive
• ENIG – Electroless nickel + immersion gold, a popular finish with good shelf life
• HASL – Traditional hot air solder finish, contains lead
• Lead-free HASL – RoHS compliant version of HASL
• Immersion tin – Suitable for press-fit applications but can cause soldering issues
• OSP – Organic solderability preservative, low cost but short shelf life
• ENEPIG – Electroless nickel-palladium-gold, provides high solder strength

The optimal finish depends on budget, design needs, and RoHS compliance requirements. But application of a suitable finish is critical for solderability, oxidation resistance, and reliable PCB performance.

Electrical Testing

Impedance testing and electronic testing are pivotal for ensuring PCB functionality and quality. Impedance testing validates signal trace impedance, which is crucial for high-speed circuits. Precision measurements verify adherence to design specs, enhancing signal integrity.

Electronic testing assesses circuit integrity by identifying opens, shorts, and proper connectivity. Methods like flying probe and fixture testing scrutinize the board against original data to assure quality and functionality. Together, these testing phases underpin the reliability, performance, and precision of the final PCB product.

Milling

Once all PCB fabrication steps are completed on the panel, it undergoes precise milling to cut out the individual PCBs. Before milling, a final verification of the dimensions and tolerances is performed to ensure each PCB matches the design specification. The milling must be extremely accurate to obtain boards of correct size and shape per the design. During milling, the panel edge quality is also critical, as any roughness or irregularities will reduce strength. Post-milling inspection validates that each singulated PCB has smooth, clean edges free of defects, with no copper smearing or fraying.

Functional Inspection

A Functional Inspection is performed to ensure that the PCBs operate as intended. For simple designs, this may involve basic power-up and in-circuit tests using automated test equipment. In-circuit tests quickly check continuity of power and ground planes as well as input/output signal paths. Any issues are immediately flagged for troubleshooting.

Final Inspection

The final inspection process at the manufacturing facility is comprehensive to ensure PCB quality. It involves meticulous visual and electrical checks conducted by experienced technicians. During visual inspection, each PCB is carefully examined under a microscope. Technicians will inspect for any defects such as incorrect component placement, missing or broken traces, impurities on the board surface. Any issues found are recorded for correction.

Electrical performance is validated through automated testing. Tests such as trace continuity and pin connectivity checks are carried out using dedicated automatic test equipment. For boards intended for high reliability applications, additional functional validation may be required, like simulation testing and environmental stress testing. Only after passing all inspection criteria will boards be released for packaging and shipping. The thorough final inspection helps confirm all quality specifications are met before the customer receives the finished PCBs.

Packaging

The finished PCBs are carefully packaged to protect them during storage and transit. The packaging commonly uses anti-static foam, plastic bags and boxes. The anti-static foam cradles the PCBs and fully encapsulates them to prevent any movement and physical shocks. The foam also provides moisture protection. PCBs are then placed in static shielding bags to guard against electrostatic discharge. Multiple PCBs may be packaged in plastic storage boxes for bulk orders. The packaging must be designed to prevent physical damage while allowing efficient storage and transportation. It aims to fully protect the delicate PCBs from moisture, impact and static electricity throughout the entire logistic process.

Finished PCB Storage

The packaged PCBs are typically stored in a controlled environment, such as a Finished Goods Warehouse, to ensure their quality and prevent damage. These storage conditions include maintaining appropriate temperature and humidity levels, as well as protecting the PCBs from dust, moisture, and physical impacts. The PCBs are carefully organized and labeled for easy identification and retrieval when needed for shipment to customers. In cases where customers require further assembly, such as PCBA (Printed Circuit Board Assembly), the PCBs may be transferred to the PCBA process as per the customer’s requirements.