Introduction
A printed circuit board (PCB) forms the backbone of an electronic product, providing the foundation to mount and interconnect components. Designing and manufacturing high-quality PCBs is a complex, multi-step process requiring expertise across electrical engineering, industrial processes, and quality control.
This guide will walk through the end-to-end PCB production process spanning design, fabrication, assembly, and testing phases. Understanding the big picture helps streamline executing each step smoothly. We’ll cover key concepts like schematic capture, layout considerations, generating manufacturing files, selecting materials and finishes, assembly methods, and inspection processes.
Let’s get started on a step-by-step journey following a PCB from initial concept through volume production!
PCB Design Phase
Before manufacturing, a PCB design must be created and optimized. This frontend design process involves:
Schematic Capture
A schematic in CAD software connects symbolic representations of components logically using wires showing connectivity and net names. This turns an electrical concept into a virtual circuit diagram.
Simulation and Verification
The schematic gets simulated using SPICE models to verify proper component behaviour prior to physical layout.
PCB Layout
The schematic nets then get assigned physical connections and routed on board layers respecting electrical and physical design constraints.
Layout Optimizaton
The layout gets iteratively improved to enhance manufacturability, testability, and performance using guidelines like:
- Component placement for efficient routing and assembly
- Thermal management of heat-generating parts
- Matching trace lengths and widths to signals
- Minimizing loop inductance and maximizing decoupling
- High-speed topologies like controlled impedance traces
- Partitioning for panelization and board sections
Design Rule Checking
The finished layout gets programmatically checked against a myriad of fabrication and assembly rules to avoid both physical and functional issues.
3D Modeling
An optional 3D model of the board and components provides a realistic visualization of the final product.
With the design optimized, manufacturing output files are generated.
Manufacturing Data Processing
To fabricate and assemble PCBs, the design data gets processed into specialized formats like:
- Gerber files – Standard files describing copper layers, solder masks, silkscreens, drilling info, etc.
- Drill files – NC drill files with tools for all required hole sizes
- Assembly drawings – Documentation for fabrication, test, inspection, etc.
- BOM files – Bills of materials with part numbers, values, quantities
- Netlists – Connectivity listings for assembly testing
Additional outputs like centroid data, testpoint reports, and IPC-2581 manufacturing archives help enable production. The data then gets transferred to the PCB fabrication facility and assembly house.
PCB Fabrication Process
The PCB fabrication process transforms the design files into physical boards ready for part mounting. Key fabrication steps include:
Substrate Preparation
The laminate substrate material gets conditioned through processes like cleaning, graining, desmearing, and via hole metallization.
Photolithography
A photosensitive dry film gets laminated onto the substrate then exposed to UV through the Gerber masks and developed to form the conductive pattern.
Copper Plating
The boards get electroplated to build up etched copper on exposed tracks to the target thickness defined in the design.
Etching
Chemical etching removes unwanted copper leaving only the desired conductive traces on the laminate.
Stripping and Etchback
The remaining photoresist gets stripped away and roughened copper gets etched back.
Soldermask
The soldermask layer gets laminated using the solder mask Gerber file exposing only solderable pads.
Silkscreen
Ink or epoxy graphics are applied for the silkscreen layer according to the silkscreen Gerber outline.
Surface Finish
The conductive traces get plated with solder, gold, or other finishes per specification to protect copper and facilitate soldering.
Routing
Mechanical routing cuts board outlines from the panel based on the fabrication drawing.
Testing
Bare boards get electrically tested against the netlist prior to component assembly.
The completed boards are now ready for part population by the contract manufacturer.
PCB Assembly Process
Once fabricated boards are received, the assembly process populates components onto the boards. This involves:
Printing Solder Paste
Solder paste gets printed onto pads through a stencil aligned to the PCB.
Pick-and-Place Assembly
Robotic pick-and-place machines populate components onto pads according to the bill of materials and centoid data.
Reflow Soldering
The boards pass through a reflow oven melting the paste to form solder joints securing components.
Inspection and Testing
PCBs get inspected for defects using automated optical inspection and other techniques, then tested for proper function pre-enclosure.
Conformal Coating
A protective coating gets applied to shield components from environmental factors.
Backplane/Daughter Card Assembly
For larger systems, boards and modules get mechanically assembled into card cages and rack infrastructure.
Enclosure Assembly
PCBs get integrated into plastic or metal product enclosures through alignment pins, clips, and fasteners.
This completes the board-level assembly process, with fully populated boards installed into final products.
PCB Manufacturing Quality
Throughout fabrication and assembly, quality standards are upheld through:
- Statistical process control tracking defect and scrap rates
- Extensive inspection checking operation output
- Regular calibration and maintenance of machines
- Conformance to stringent industry standards like IPC and ISO
- Strict supplier quality management systems
- Quality assurance oversight of manufacturing floor environment
- Comprehensive testing of raw materials, in-process, and finished boards
- Continuous improvement initiatives to drive down defects
Attention to quality ensures reliable, consistent PCB production.
PCB Design Key Factors
To summarize, when architecting your PCB design, keep in mind these vital elements for manufacturing success:
Electrical
- Component placement minimizing wire length
- Trace widths matched to current
- Controlled impedance on high-speed nets
- Decoupling capacitance placed near ICs
- Minimal antenna risks and crosstalk
Mechanical
- Adequate clearance between traces and pads
- Thermal relief to dissipate heat
- Large pads and traces for higher current
- Connectors placed with clearance for cables
- Stress relief on components susceptible to vibration/shock
Manufacturing
- Standard PCB dimensions for panel utilization efficiency
- Test points designed for probing process validation
- Component spacing within pick-and-place tolerances
- Thermal profiles optimized for soldering
- Assembly fixtures designed upfront
Getting the design right from the start smooths the entire downstream production process resulting in a functional, reliable, manufacturable PCB.
Conclusion
This comprehensive guide walked through the journey of a PCB from initial schematic design through factory fabrication, assembly, inspection, and testing based on real-world manufacturing processes. Understanding the sequence of steps provides helpful context for electrical engineers designing boards destined for volume production.
Key takeaways include laying out PCBs with manufacturing in mind, generating quality design data, communicating effectively with fabrication and assembly partners, and upholding rigorous quality assurance to ensure robust boards ready for installation in products. By following this PCB production roadmap, electrical engineers can transform ideas into fielded products reliably and efficiently.
Frequently Asked Questions
What design practices help make PCBs easy to manufacture?
Some best practices include providing clearance between traces, avoiding tiny cutouts in planes, using standard component sizes and pitches, labeling layers clearly, and designing with the assembly process in mind through strategies like maximizing access to connectors and minimizing component height variations.
How long does PCB fabrication and assembly normally take?
For prototype volumes, fabrication can typically be completed in 5-10 days, with assembly requiring another 1-2 days. In production, fabrication lead times are usually 3-4 weeks, with assembly adding another 1-2 weeks. More complex designs may require even longer.
What are some key tests performed during PCB production?
Bare boards get electrically tested. After assembly, boards are visually inspected, undergo in-circuit testing, get programmed, experience functional validation testing, and undergo environmental stress screening through thermal cycling, vibration, and other techniques before shipping.
What tolerances should PCB layout accommodate?
Critical tolerances include solder mask registration (±0.075mm), hole position accuracy (±0.1mm), hole size variation (±0.075mm), conductor width and spacing (±0.075mm), and conductor thickness variation (10%).
How can I get quotations for PCB fabrication and assembly?
Reach out to manufacturing partners with your board files, BOM, target quantities, and any specialty requirements. Most will provide free assessments and quotations analyzing your design for manufacturability and providing estimated pricing.
Conclusion
Designing a board is only the first step – seamlessly navigating manufacturing processes transforms the ideas into reality. By understanding the progression from design to high-volume production, engineers can make decisions ensuring smooth fabrication and assembly resulting in functional, cost-effective boards. This PCB production primer provides helpful guidance for getting robust products to market.
Electronics rely heavily on printed circuit boards, as it helps in the transmission of electric signals to satisfy the device’s mechanical and electrical circuit requirements. As such, printed circuit boards become indispensable to the proper functioning of electronic devices. Every economic sphere has increasingly relied on digitization, increasing the demand for computational electronics and thus PCBs.
PCB Design Manufacturing
As a circuit designer, the aspect of visiting and communicating your PCB designing and fabrication needs to a fabricator proves critical. However, physical visits have increasingly become impractical as major clients outsource their inquiries regarding PCB manufacturing needs to overseas manufacturers and suppliers. Therefore if you need a company to manufacture your design, you only have to contact them virtually. What’s more, online PCB design and manufacture instructions exist today, something that can become valuable if you want to design and produce one by yourself at home. In this section, I intend to demonstrate the relevant processes of PCB manufacturing to help you design and produce printed circuit boards.
Process Steps
- Designing and output. All circuit boards must demonstrate compatibility with the designed PCB layout developed through a printed circuit board design software. Some of the standard software for designing PCBs include OrCAD, KiCad, Eagle, Pads, etc. However, it becomes crucial to inform the manufacturer of your PCB design tool to smoothen and ensure no discrepancies exist.
Once completed and approved, the PCB design can now go into production. As the designer, you have to export your design in a suitable format that the manufacturer can support. One renowned and agreeable output format is the Gerber. Additionally, please note that diverse PCB design and manufacturing tools require distinctive generation steps of the Gerber file. It encodes all-inclusive and important information that includes drill drawing, copper tracking, component notations, apertures, etc. All the design aspects undergo checks at this stage, where the program executes oversight algorithms to make sure that no errors pass undetected. At this point, you can also study the plan, especially aspects like the spacing of the board edge, track width, hole, and track spacing, besides hole size. After that, the PCB design can then get forwarded to manufacturers like RayMing PCB & Assembly. Here, the DFM gets carried out to ascertain that the PCB design meets the minimum tolerance requirements under production.
- Conversion from the file into film
- Once you have developed the schematic files and the manufacturer also completes the DFM check successfully, printing can start. Most manufacturers use a plotter to develop photo films, instrumental in the printing of the circuit boards. The films get used for imaging the PCBs by the laser printer, proving incredibly precise in providing a detailed film.
What results from the process includes a unique plastic sheet complete with a black-inked photo negative. The black ink denotes the PCB’s conductive copper segments, while the clear part represents the non-conductive material. A similar pattern happens for the outer layer though this happens in reverse: clear denoting copper and black denoting the segment to get etched away.
Every solder mask and PCB layer gets its black and clear film sheet, and this implies that a double-layer PCB will require four sheets. Remember, all the sheets have to get used with one corresponding to the other. Additionally, you have to punch registration holes through every film to realize a perfect alignment.
- The inner layer’s printing process
- Here, the intention entails printing the mapped-out copper path created on the film on a foil of copper. It acts as a preparatory step in the PCB’s manufacturing process. The laminate, composed of fiberglass or epoxy resin substrate, acts as an ideal platform to receive the copper, which provides structure to the PCB. It not only provides a platform but a dust-resistant and sturdy material to support the PCB fabrication. Since copper proves pre-bonded on either side of the substrate, this process entails whittling it away to divulge the design.
Cleanliness becomes a crucial part of the PCB construction process, and thus, the copper-sided laminate has to get cleaned and passed through a decontaminated. During the decontamination process, avoid any dust particles from settling on the PCB laminate. Otherwise, it can end up making the circuit short or open.
In the next stage, the panel gets a photo-sensitive film layer called the photoresist. It comprises elements that end up toughening upon exposure to UV. It ensures a perfect match in the photoresist as it had proved on the photo film.
After preparation, the board must get washed with an alkaline liquid to eliminate all the unhardened photoresist. Subsequently, the pressure wash that follows will leave the surface spotless and free from anything remnants. It then undergoes drying before another round of examination by a technician to eliminate errors. Remember the step applies to multi-layer boards only.
- Removal of unwanted copper. The next stage entails the elimination of the unwanted copper using a copper solvent liquid. Remember the weight of the board determines the quantity of solvent used. Another round of washing happens after the removal of the unwanted copper. Here, the hardened resists safeguarding the desired copper gets washed off. You will end up with the glistening copper substrate needed for the printed circuit board.
- Optical inspection and layer alignment
- Now the layers prove clean and ready to punch the alignment holes to ensure a proper alignment. The next step in this stage entails aligning the registration holes of both inner and outer layers. The layers get optically punched to allow exact correspondence. Remember, once placed together; the layers cannot get corrected for any inner layer errors. Because of this, another round of automatic optical scrutiny to ensure the panels are free from defects. Here, the Gerber acts as the standard and digitally compares the image with the original. Any inconsistency gets displayed for immediate attention, and once it passes the test, it moves to the final phases of the printed circuit board production.
- Layer up before bonding. All the different layers get fused, with the outer layers joined with the FR4/substrate. The process has a two-step process of fusing the substrate with copper. The next step entails bonding where the layers get fit on the table-attached pins. It becomes crucial to secure it snuggly and avert shifting when aligning. Once every layer gets fit and layered properly over each other, you can now go ahead with pressing. The process gets carried out by a bonding-press computer that determines and organizes the automatic heating besides determining the pressure points to act on. It then follows an unpacking process after every layer gets molded together to form a PCB sandwich. Here, the pins used to restrain the board gets removed, and the upper pressure plate is discarded.
- Drill. It entails boring holes into the board stack. The minuscule nature of the holes demands precision, as every other component that comes later depends on this precision. The drill target location gets determined by an x-ray finder before drilling and subsequent hole registration. Additionally, the micro-movement of this drill gets controlled by a computer, which controls the movement by using prior design details. The extra copper lining the edges gets removed using a profiling device.
- Copper deposition and plating. It is the next step after the drilling process. Here, you get a fusion of diverse layers using chemical deposition. After that, the panel has to go through subsequent chemical baths, with each bath depositing a thin copper layer on the panel’s surface, covering the new holes.
- Imaging of the outer layer. It involves applying the photoresist again, though it concentrates on the PCB panel‘s outer layer. It has to go through a similar process explained earlier to gain the toughness. Further, black ink film gets held by pins in preventing any misalignment until after exposure to high UV rays. After that, any unhardened resist material gets removed.
- Plating. The plating process proves similar to the one illustrated in the eighth step. It entails electroplating with copper before a subsequent plating with tin. It will allow the elimination of extra copper left. Further, the tin safeguards the panel section that remains encased in copper in the subsequent etching stage. Etching always removes any undesirable copper foil on the panel.
- Final etching. The tin layer safeguards the copper during this phase, where the undesired copper (including from beneath any resist layer) gets removed. Chemical solutions get applied to eliminate the extra copper. At this point, all the connections and conducting areas prove properly established.
- Application of the solder mask. Clean and cover the panel with epoxy solder ink before applying the solder mask. After that, it receives another UV light blast that toughens the uncovered segments while the covered and soft segments await removal. It then has to get heated to cure the applied solder mask.
- Surface finish. In this stage, the application of silver and gold coats happens, which incorporates additional solder-ability. Additionally, hot-air leveling ensures uniform pads and leads to surface finish generation.
- Silkscreen. The almost complete board has to receive an ink-jet surface writing to indicate crucial details concerning the printed circuit board. It then passes through the coating and subsequent curing phases.
- Electrical test. It then becomes crucial for the PCB to undergo an electrical test as the ultimate precaution.
- V-scoring and profiling represent the last process where the board gets cut using a v-groove or router.
