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How to make a PCB – PCB production process in 33 steps
NCAB Group
Overview
This video details the intricate 33-step process of manufacturing a Printed Circuit Board (PCB), emphasizing the complexity and precision required. It breaks down the production into 12 main stages, starting from receiving customer design data (Gerber files) and progressing through material preparation, inner and outer layer imaging, etching, plating, lamination, drilling, surface finishing, electrical testing, and final inspection and packaging. The process highlights the critical importance of quality control, material selection, and adherence to strict specifications to ensure the reliability and functionality of each unique PCB design.
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Chapters
- Customer Gerber files are received and meticulously checked for completeness and alignment with drawings.
- Manufacturing instructions are defined, including process steps and necessary tooling.
- Working Gerber files are generated for production, defining circuitry, solder mask, and drilling locations.
- Internal specifications and agreed routines ensure data integrity and prevent unauthorized changes.
Accurate interpretation and preparation of design data are foundational; errors at this stage propagate through the entire manufacturing process, leading to incorrect PCBs.
Over 30% of received data has an issue that needs addressing, underscoring the importance of this initial check.
- Appropriate materials, such as inner layer cores and prepreg, are identified based on customer requirements.
- Materials are sourced from approved suppliers and inspected upon arrival.
- Strict storage conditions and a first-in, first-out (FIFO) approach are maintained to preserve material integrity.
- Traceability is ensured through batch numbers and certificates of compliance.
The quality and proper handling of raw materials directly impact the electrical, thermal, and mechanical performance of the final PCB.
Prepreg must be stored in controlled temperature and humidity conditions with a maximum shelf life of 6 months due to its uncured state.
- Circuitry patterns are transferred from Gerber data to the copper layers of inner layer cores using photosensitive film and UV light or laser direct imaging.
- Unwanted copper is chemically removed (etched) to leave only the desired circuitry.
- The remaining photosensitive film is stripped, revealing the final inner layer copper design.
- Tight control over chemical processes (pH, temperature, concentration) and physical parameters (speed, pressure) is crucial for precise etching.
This stage defines the fundamental conductive pathways of the PCB, and any inaccuracies will lead to functional failures.
The etching process uses solutions like ammonia or cuprous chloride, requiring precise control to avoid etching too much or too little.
- Automated Optical Inspection (AOI) scans inner layer cores, comparing them against Gerber data to detect defects like shorts or opens.
- Operators verify AOI findings, ensuring conductor width and spacing meet specifications.
- Inner layer cores are cleaned and roughened, then treated with an oxide layer to promote adhesion during lamination.
- The oxide layer is delicate and requires careful handling to prevent damage.
Ensuring the integrity of inner layers before lamination prevents costly rework and guarantees reliable connections within the multilayer board.
Open circuits are not allowed to be repaired to maintain reliability, while short circuits can be fixed.
- Inner layer cores and prepreg sheets are stacked in the correct order and orientation, precisely aligned using tooling pins.
- The stack is heated under pressure in a lamination press, melting the prepreg resin to bond the layers together.
- Controlled cooling prevents warping (bow and twist) of the panel.
- The lamination process creates a solid, stable multilayer structure capable of withstanding environmental stresses.
This is the critical step where individual layers are fused into a single, robust multilayer PCB, forming the foundation for subsequent processes.
The lamination press uses specific pressures and temperatures tailored to the materials and desired build, followed by a slow, controlled cold press.
- X-rays are used to locate internal reference markings, enabling precise drilling of new tooling holes for alignment.
- Drill files dictate the location and size of holes, which can be vias (connecting layers) or component holes.
- Drilling parameters (feeds, speeds) are controlled to ensure hole accuracy and prevent issues like resin smear.
- Holes are cleaned and activated to prepare for copper plating.
Accurate drilling and preparation are essential for creating functional electrical connections between layers and for component mounting.
Aluminum entry sheets are used during drilling to prevent drill deflection and avoid burrs on the panel's bottom side.
- Electroless copper plating deposits a thin conductive layer on non-metallic surfaces, including the walls of drilled holes.
- Electrolytic plating adds a thicker layer of copper to the entire panel surface and within the holes, building up the required conductivity.
- Process controls, including chemistry, time, and current, are critical for uniform copper deposition.
- Backlight tests and microsections verify the quality and thickness of the copper deposit.
Plating makes the non-conductive hole walls conductive, establishing the electrical pathways that connect different layers of the PCB.
A thin layer of electroless copper (around 1 micron) is applied first, followed by a thicker electrolytic copper deposit (5-8 microns).
- A photosensitive dry film is applied to the outer copper layers, and the circuit pattern is imaged using UV light or laser direct imaging.
- Unwanted photoresist is removed, exposing copper areas where additional plating is needed.
- Electrolytic plating adds copper to the exposed areas, building up the final circuit trace thickness.
- A protective tin layer is applied over the plated copper before etching.
This process defines the external circuitry of the PCB, enabling component placement and final device functionality.
During outer layer imaging, the dry film is removed in areas where tracks are desired, allowing for subsequent copper plating.
- The remaining dry film is stripped, and unwanted copper is etched away, leaving only the desired circuitry.
- The protective tin layer is removed, revealing the final copper traces.
- Automated Optical Inspection (AOI) verifies the outer layer pattern against Gerber data, checking for shorts, opens, and correct dimensions.
- Repairs are limited, particularly for open circuits, to maintain reliability.
This stage finalizes the conductive patterns on the outer layers, and rigorous inspection ensures the integrity of these critical connections.
AOI checks for issues like missing copper or damage to the copper pattern, ensuring conductor width and spacing meet requirements.
- Via holes are filled with ink to enhance reliability and prevent contamination during assembly.
- The PCB surface is prepared (roughened) for solder mask adhesion.
- Liquid solder mask is applied, then precured to make it handleable.
- The solder mask is imaged using UV light and artworks to define areas for component soldering and protect circuitry.
Solder mask protects the copper circuitry from oxidation and environmental damage, while via filling improves reliability and assembly.
Via filling uses a screen printing process with solder mask ink or special via plugging ink, aiming for at least 70% fill.
- Unexposed solder mask is chemically removed in a development process, leaving the polymerized mask in place.
- The solder mask undergoes a final cure in an oven to fully harden and adhere it to the PCB surface.
- Quality control checks ensure proper thickness, adhesion, and registration of the solder mask.
- Statistical Process Control (SPC) is vital for managing the chemistry involved.
Properly cured solder mask is essential for the long-term reliability and functionality of the PCB, protecting it during assembly and operation.
The final cure involves passing the panels through conveyorized ovens with different temperature zones to complete polymerization and evaporate solvents.
- Various surface finishes (ENIG, Immersion Tin, HASL) are applied to protect copper from oxidation and facilitate soldering.
- Each finish has specific application processes and suitability for different component types (e.g., fine pitch SMD, press-fit pins).
- Strict process controls and quality checks are implemented for each surface finish type.
- Traceability is maintained through markings like date codes and batch references.
The surface finish is crucial for solderability and long-term reliability, ensuring components can be securely attached and remain functional.
Electroless Nickel Immersion Gold (ENIG) is a high-reliability finish involving nickel plating followed by a thin gold layer.
- Controlled depth score lines (V-scoring) or routing are used to create individual PCBs from the production panel.
- Electrical testing (bed of nails, flying probe) verifies connectivity, checking for shorts and opens.
- Visual inspection (manual and automated) checks for cosmetic defects and adherence to specifications.
- Microsections and other tests verify build integrity, copper thickness, and plating quality.
These final steps ensure that each individual PCB is correctly formed, electrically sound, and meets all specified quality and functional requirements.
Electrical testing includes methods like the four-wire Kelvin test to assess hidden defects like hole integrity, crucial for HDI structures.
- PCBs are counted and marked for traceability (part numbers, date codes).
- They are packed using protective materials like desiccant and moisture barrier bags to prevent humidity damage.
- Packaging must comply with specific instructions to maintain solderability and protect against transit damage.
- Final labeled packages are prepared for shipment to the customer.
Proper packaging is essential to protect the finished PCBs from environmental damage and physical stress during storage and transit, ensuring they arrive in optimal condition.
Desiccant is added to absorb humidity within the shrink-wrapped package to preserve solderability.
Key takeaways
- PCB manufacturing is a highly complex, multi-step process requiring meticulous control at every stage.
- Accurate interpretation of customer design data (Gerber files) is paramount to avoid errors in production.
- Material quality, proper storage, and handling are fundamental to the performance and reliability of the final PCB.
- Precision in imaging, etching, and plating is critical for creating functional conductive pathways.
- Lamination is the core process that fuses multiple layers into a single, robust board.
- Rigorous inspection and testing, including AOI and electrical tests, are essential for quality assurance.
- Surface finishes play a vital role in protecting the PCB and enabling component soldering.
- Effective packaging is crucial to maintain PCB integrity and solderability until they reach the customer.
Key terms
Printed Circuit Board (PCB)Gerber DataInner Layer CorePrepregPhotosensitive FilmLaser Direct Imaging (LDI)EtchingAutomated Optical Inspection (AOI)LaminationVia HoleElectroless PlatingElectrolytic PlatingSolder MaskENIG (Electroless Nickel Immersion Gold)HASL (Hot Air Solder Leveling)Flying Probe TestBed of Nails TestMicrosection
Test your understanding
- What are the primary challenges in the initial data preparation stage of PCB manufacturing, and why is it critical?
- How does the lamination process combine multiple layers into a single PCB, and what factors ensure its structural integrity?
- Explain the purpose of both electroless and electrolytic plating in PCB production.
- Why is solder mask applied to a PCB, and what are the key steps involved in its application and curing?
- What are the different types of surface finishes mentioned, and how do they impact the PCB's functionality and assembly?