List of printed circuit board (PCB) manufacturers and an explanation of how they are made
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A printed circuit board is a non-conductive board that has conductive circuitry materials mounted on it. Each of the components of a PCB is connected by conductive tracks, referred to as traces, to form a working circuit or assembly. PCBs are made of plastic or glass fiber and have traces made of copper. The inner copper layers of a printed circuit board are etched to leave traces of copper that connect electrical components.
The development of modern PCBs is due to the bulky and cumbersome characteristics of the original circuit boards, which had components connected using wires. As technological advancements decreased the size of electronic devices, engineers needed to find a method for producing circuit boards that were smaller and less bulky. The result of their efforts was the introduction of the printed circuit board that has become an essential part of modern electronics.
From their introduction over one hundred years ago, printed circuit boards have been continually improving to meet the requirements of modern electronics. Over the years, wires have been replaced with traces as boards have become more complex, a factor that has forced changes in design and engineering practices. Regardless of the technical changes, the basic structure of PCBs has remained the same.
The three main forms of printed circuit boards are single sided, double sided, and multilayered. Single sided printed circuit boards have all of their components on one side of the substrate. When the space on single sided printed circuit boards is not sufficient, a double-sided circuit board is used to accommodate the additional components with holes provided to connect both sides. Multilayer printed circuit boards are more complex and have sandwiched layers that are separated by insulation. Like double sided printed circuit boards, the multiple layers of a multilayer printed circuit board are connected by holes drilled in the different layers of the boards.
The substrate or core of a printed circuit board is made of a dielectric material consisting of fiberglass reinforced epoxy resin copper foil due to its strength, endurance, and durability. In some cases and for custom PCBs, ceramic filled polytetrafluoroethylene (PTFE) composites are used to enhance the dielectric characteristics of printed circuit boards. For custom printed circuit boards that require thermal performance and for high frequency applications, ceramic based materials are used. In high temperature environments, PCB manufacturers use cyanate ester or polyamide. When affordability is a concern, paper reinforced phenolic resin with bonded copper foil is used, a material commonly found in domestic electronics. The selection of the substrate material determines the mechanical, thermal, and chemical properties of a circuit board.
Dielectric materials provide insulation between conducting layers and dictate the performance of a PCB assembly. The properties of PCB substrates are electrical, thermal, chemical, and mechanical.
The prepreg, or pre-impregnation, is an insulation layer made of dielectric material that is sandwiched between cores or a core and copper foil. It binds cores or copper foil and cores together. Prepreg is made of glass fiber cloth that has been soaked in partially cured epoxy. Under heat and pressure, it glues the layers of a PCB. The prepreg is positioned beneath the substrate layer. With the addition of additives and catalysts, the prepreg can be modified and specialized to meet the specific needs of custom PCBs, such as the addition of selective conductivity. The basic function of the prepreg is to protect a PCB assembly from short circuits.
The metal foil in a printed circuit board forms the circuits of the board and normally consists of thin copper sheets that are formed into traces and pads. The thickness of the copper material can vary and is used for its electromagnetic shielding and antistatic properties. It is the conductive material used to form circuits and facilitates the flow of electrical charges in a PCB assembly.
The choice of copper metal foil is due to its high conductivity, affordability, and availability. It is applied to the base layer of a PCB assembly and custom circuit boards to create conductivity. Circuit patterns are formed by printing protective layers and etching of the substrate. Metal foils can be single or double sided and self-adhesive.
Since copper foil has a low rate of surface oxygen, it can easily be bonded to the insulating layer. The foil has exceptional continuity and provides electromagnetic shielding when combined with the substrate. The copper metal foil used has a purity of 99.7%, which is copper alloy C99700.
Coatings, referred to as conformal coatings, are a thin film that is applied as a lightweight protective layer to shield circuit boards and their components. They add to the durability of a printed circuit board assembly by protecting it against heat, humidity, moisture, ultraviolet light, chemicals, and abrasion. In addition, they have thermal and electrical insulation properties. The application of coatings helps extend the useful life of a printed circuit board assembly and is widely used by printed circuit board assembly manufacturers.
The different types of coatings include acrylic based, silicone based, polyurethane based, epoxy based, and parylene based. The factors that determine which coating printed circuit board manufacturers choose are their thermal properties, the operating environment of a PCB, and the application for which a board is made.
The application of coatings to printed circuit boards is a necessity for protecting them from their operating environment, potential failure, and assists in prolonging their useful life. PCB board manufacturers choose coatings in accordance with the function and purpose of the circuit boards they manufacture.
Bonding film or bonding sheets are used on single and multilayer PCBs. They protect wiring, fragile elements, thermal insulation, and provide static protection. Bonding film is used as a laminate for the substrate or a method for binding multilayer PCBs. The adhesives used for bonding film are polyester (PET), polyimides (PI), acrylics, and epoxies. The type of bonding film chosen for a circuit board is dependent on the application for which the board will be used.
In addition to the types of adhesives used to make bonding film, the thickness of the film varies between 12μm (0.5mil) and 100μm (4mil), which is adjusted in accordance with trace thickness and other copper on a circuit board. Bonding film consists of an adhesive coat applied to release paper. It provides a strong reliable bond between layers of a circuit board and lasting durability.
The types of bonding films include:
The choice of bonding film depends on the types of materials to be bonded, surface prep, the requirements of an application, and cost. For bonding film to be successful, it has to be compatible with the materials to be bonded.
Vias are small drilled holes that allow exist between layers of circuit boards. They provide a path for signals to move between layers and offer inter-layer connectivity. The three types of vias are blind, buried, and through hole. Vias are differentiated by the number of layers they connect and their positioning.
Blind Vias originate on the surface of the top or bottom of a circuit board and connect at least one inner layer. They appear on one side of the board and do not go through a circuit board. Blind vias free up space and are used in BGA assemblies and HDI PCBs.
Buried Vias connect inner layers of a multilayer PCB and are not visible on the outside layer of a PCB. They connect inner layers to avoid signal interference and are used with HDI PCBs, which are compact, small, and complex.
Through Hole Vias connect the inner and outer layers of a circuit board and penetrate the entire circuit board. They are used for internal connectivity and as mounting holes for components.
The covering process for vias takes three forms, which are tenting, uncovered, and plugged. Tenting covers the annular ring of a via with a solder mask for insulation. Uncovered vias have their annular ring exposed and do not have a solder mask. Vias that are plugged with a solder mask prevent solder balls from popping out.
The initial process for manufacturing a printed circuit board requires very careful planning due to the significance of PCBs in electronic devices. During the design phase, PCB assembly manufacturers work to ensure the quality and performance of a PCB. Engineers, designers, and PCB assembly services work with clients to create a circuit board that meets the requirements of an application. Once the final rendering has been completed, the multistep process of manufacturing a printed circuit board begins.
During the design phase, PCB assembly manufacturer engineers use software, such as Extended Gerber or Siemens Computer Assisted Design (CAD), to create a computer rendering and blueprint of a printed circuit board’s layout. The wide variety of PCBs and custom PCBs necessitates the creation of the form, shape, and structure of a PCB with a layout of the components so that they perfectly match the requirements of the device for which the board is being manufactured.
A key part of the design phase is thorough research of the components to ensure that they meet design requirements. Aside from aiding in the design of custom PCBs, the computer software provides data regarding PCB layers, solder masks, and notations regarding component placement. The provided data guides workers during the production phase of PCB assembly manufacturing.
As with all aspects of manufacturing, once the design has been finalized and saved, PCB assembly services examines the prototype circuit board assembly for minute errors that may lead to system failures. Although the overall structure of a PCB may be acceptable, there is the possibility of missing components and difficulties with manufacturing a PCB design. The final check of the computer rendering is a detailed examination. Due to the significance of the design phase and its impact on a PCB assembly, it is essential that errors be corrected in the early stages prior to printing.
A specialized plotter printer that prints PCB board designs are film printers that provide an image of the PCB. The printed image is a photo negative of a PCB. During the printing process, each aspect of a PCB is printed in layers that are represented by different colors. Black is used to represent the traces. Clear ink represents the non-conductive areas of a PCB. Each of a PCB’s layers and solder masks has their own film. The simplest PCB is represented by four sheets of film with one sheet for each layer and one each for the solder masks.
Although the process for creating the film involves several steps, the next part of the printing process is the punching of holes in the film. In order to properly align the films for the PCB manufacturing process, registration holes are punched in the film. The holes guide technicians in the alignment of the film during PCB assembly.
Regardless of the advancements in computer software and design, the printed film representing a PCB ensures proper proportions, wiring, and component placement. It serves as a practical and viable tool as well as another step for ensuring PCB quality.
After the planning, designing, and printing of the initial phases of PCB manufacturing comes the construction of a printed circuit board assembly. The first step in this part of the process is the etching of the substrate that is a laminated panel that has been covered with a photosensitive film referred to as resist. The key to this aspect of PCB construction is the photo reactive chemicals that are the composition of the resist.
Resist is a light sensitive material that hardens when exposed to ultraviolet light. It allows technicians to create a match between the blueprint for a PCB assembly and what is printed on the resist. The registration holes that were drilled in the film make it possible to perfectly align the substrate with the hardened resist to the film. UV light is placed in a position over the film such that it passes through the film and hardens the exposed photoresist.
The areas of the resist that have not been hardened by exposure to the UV light are the pathways for the traces. The black ink of the film prevented the paths of the traces to be hardened. The developed substrate has copper foil or coating applied and bonded to the substrate.
The inner layers of the substrate are treated with an etch resist to protect the copper during the etching process. In addition, the substrate is washed with an alkaline solution to remove excess photoresist. A final pressure wash removes particles, debris, and other fragments of various materials. The PCB is dried leaving the resist covering the copper portions.
Chemical etching removes any excess copper prior to the manufacturing process. Necessary copper is protected from the chemicals while the rest of the substrate and unnecessary copper are left exposed. Unprotected copper is removed leaving conductive copper traces needed for functions of the PCB. The amount of time devoted to this process is dependent on the size of the PCB. Larger PCBs and heavy multilayer PCB assemblies necessitate more time in the etching process.
For the traces to match the dimensions of the blueprint, any excess copper has to be removed such that the traces have the proper width. Although the removal is necessary, it has to be administered carefully in a controlled environment to prevent damage to necessary parts of a PCB assembly. The treatment is very intense and requires perfect timing. The delicate nature of the process requires a trained technician to complete it.
There are three basic types of printed circuit boards, which are single layer, double sided, and multilayer. Single layer and double-sided PCB assemblies do not require any layer processing since they have a simple single layer construction. Multilayer PCBs have at least three conductive layers that are double sided and sandwiched together divided by insulated sheets. During the manufacturing process, the layers of multilayered PCBs have to be aligned properly in order to function.
There is intricate interplay between the layers of multilayer PCBs that requires that each of the layers be aligned. As with other aspects of PCB construction, the correct alignment of the layers is dependent on the registration holes that were added during the development stage of the printed film. The slightest misalignment hinders the performance of a PCB assembly and diminishes its durability and causes malfunctions.
As part of the layer inspection process, each layer is subjected to an optical inspection. This aspect of the layering process is essential because once the layers are placed together, errors are nearly impossible to correct.
The layers of a multilayer PCB are bonded together using epoxy resin-soaked fiberglass sheets and copper foil, referred to as pre-impregnated or prepreg. Using heat and pressure, the laminated layers are pressed together using a specially designed machine with metal clamps. The two common lamination presses are tank pressure and hydraulic press, each of which has their advantages and disadvantages. The process enhances the rigidity of a PCB and tightly bonds the layers creating a layer of insulation between them. It is a key factor in multilayer PCB construction.
Using the data from blueprints and PCB assembly design, technicians place the layers together in a special order that includes copper foil, dielectric, core, dielectric, and copper foil. Once each of these factors are assembled, they are pressed. To ensure proper alignment, pins are forced through the layers. The heat applied to the layers melts the prepreg and combines the layers. At the end of the process, the pins are removed and the PCB is pulled free.
After the removal of the PCB layers from the press, they are carefully handled to avoid deformation and warping. A controlled specially designed cooling process is used such that the raw PCB will be ready for further processing.
An essential aspect of the construction of PCBs is accuracy, which is apparent in every step of the manufacturing process. As would be imagined, the drilling process requires the greatest amount of accuracy and requires the use of special equipment to guide the drill. The registration holes, again, play a key role in this part of construction. The drilling of holes in a PCB is important for all types of PCBs but especially important for multilayer PCBs and double-sided PCBs.
Before drilling begins, an X-ray machine is used to position the drill where holes are required. The registration holes are used to secure the layers. Once the holes are located, a computer guided drill, such as a computer numerical control (CNC) machine, drills the holes in the layers. The holes are drilled in such a way that each layer of a PCB is electronically connected. In order to ensure conductivity, the holes are lined with a layer of copper, and leftover copper at the edges of the holes is removed.
The plating process provides protection for PCBs from oxidation and deterioration as well as a clear clean substrate surface for soldering components. The four common methods for plating are through the hole, brush for selective plating, finger plating, and reel linkage. Clients who depend on PCB assemblies for their products need to understand the different plating methods in order to make an informed decision regarding the type of board for their project.
Prior to beginning the plating process, drilled holes are cleaned of residue and any contaminants. A thin layer of copper is deposited on the surface substrate and the board’s holes that have received micro etching to enhance copper binding. Photoresist, that has been added to the board, is exposed to UV light to mask specific areas of the board. A cathode with electrical current is attached to the board, which is immersed in a chemical bath. After which, tin is plated on the copper circuitry for protection. The final step is the removal of the tin leaving the circuitry.
The process for etching and imaging the outer layer is the same as that used to etch and image the other layers. As with the other layers, photoresist is applied to the outer layers that need to be imaged. Once the outer layers are imaged, they are plated. Tin is used to protect the copper on the layers. During the etching process, a copper solvent is used to remove any unwanted copper and resist coating. At the end of the process, AOI is performed to ensure the layers meet the requirements of the original design.
The solder mask or resist is a protective layer that insulates the traces from external contaminants such as dust, dirt, debris, and moisture. As anyone who has seen a PCB can attest, the solder mask is normally green but does come in other colors such as red, blue, and white. The significance of solder masks has become more important in the modern era due to the rapid development of complex and miniaturized electronics.
Common solder masks are composed of thermosetting polymers that have exceptional heat and chemical resistance. Types of solder masks include epoxy, acrylic, and urethane. The properties of solder masks include:
Of the various types of solder masks, epoxy-based masks are of the highest quality with exceptional chemical resistance and adhesion. Acrylic based solder masks have the highest flexibility while urethane solder masks are average in all areas.
To ensure the quality of a PCB, the board is cleaned several times before having the solder mask applied. The mask prevents oxidation, erosion, and conductivity between solder pads. After the application of the mask, the PCB is oven cured. Once cured and solidified, important informational data is printed on a PCB assembly, such as its serial number, part number, place of origin, manufacturer, and other pertinent data. The printing processes used for applying necessary information include silkscreen and legend printing.
Every step of the construction process for PCB assemblies involves careful handling and inspection due to the critical nature of PCBs. Although there have been verifications and certifications at each juncture, PCB assembly manufacturers complete a final inspection to ensure the quality of their products. The main concerns, aside from cleanliness, are dimensional compliance and electrical reliability, which are examined and checked prior to shipment.
Once approved, PCBs are ready for box board assembly used in the manufacture of electrical components. The importance of PCBs in the production of electronics necessitates that they be of the highest quality for flawless performance. Once encapsulated in a device, PCBs become a critical part of product quality.
The many types of PCBs are classified based on how they were manufactured, design specifications, and the application for which they are used, such as medical, automotive, defense, and aerospace. In addition, there are physical parameters that determine the type of PCB that include required space, level of stress, mechanical ability, and electrical ability. From their origins as wired boards, PCBs have progressed due to the development of complex consumer products and advancements in manufacturing techniques.
Single sided PCBs are the most common form of PCB. They have a conductive copper layer that rests on the substrate. Components are configured on one side of the board with etched circuits on the other side. With one conducting layer, single sided circuit boards avoid having conductive paths intersecting, which is why single sided circuit boards take up so much space. The low-density design of single sided PCBs makes them ideal for basic low-cost electronics such as power supplies, LED lighting boards, radios, and timing circuits.
As a cost effective and easy to manufacture PCB, single sided PCBs are commonly used for low density designs. They are easy to repair, practical, and are easy to design. They have a back surface composed of copper and are coated with a solder mask.
Double sided PCBs allow for components to be placed on either side of the board. Interaction between the sides is through drilled holes. They have two layers of conductive material for the conduction of current. Double sided PCBs have higher circuit density and are more flexible than single sided PCBs. They can handle complex and intricate designs.
The mounting methods for double sided PCBs are through hole or surface mount. Through hole mounting requires the installation of lead components into pre-drilled holes soldered to pads on both sides. Surface mounting involves precision placement of components on the surface of the board.
The reduced size of double sided PCBs makes them compact and condensed. They have increased flexibility and increased circuit density making them suitable for advanced electronic systems. Double sided PCBs are used for phone systems, power monitoring, testing equipment, amplifiers, HVAC systems, and UPS systems.
Multi-layer PCBs have three or more conductive layers with the appearance of a sandwich design. They include several double sided conductive layers that are divided by insulating material. They are bonded and laminated together under high pressure and temperature to remove air gaps and to ensure stability. The designs of multi-layer PCBs increase the complexity of PCBs with interlayer connections provided by vias. Circuits can be more complex and intricate while being in close proximity. Multi-layer PCBs are one of the most technologically advanced forms of electronic components and can be single or double sided.
The number of layers of a multi-layer PCB usually includes 4, 6, 8, or more layers. Although the PCB manufacture of PCBs involves several steps, the process for manufacturing multi-layer PCBs requires high precision and complex processes. The high circuit density of multi-layer PCBs allows them to be more compact and space saving. This aspect of multi-layer printed circuit board assemblies makes them ideal for high-speed applications.
The substrate of rigid PCBs cannot be twisted or folded. They have multiple layers that include the substrate, copper layer, solder mask, and silkscreen layer. Rigid PCBs can be single, double, or multi-layer and are defined by the material from which they are made. After a rigid PCB is made, it cannot be changed or modified. They are made for applications that require PCBs to be unchangeable and capable of maintaining their position.
The key factor that differentiates rigid PCBs from other forms of PCBs is their durability. They are a hard-wearing custom circuit board with increased circuit density. They are popular when it is necessary for components to remain fixed. In addition, the inflexible nature of rigid PCBs enables them to endure hostile and hazardous environments where there is a high level of stress and heat.
Rigid PCBs can be found in GPS equipment, computers, laptops, tablets, mobile phones, X-ray machines, CAT scans, airplane instrumentation, and many many more high stress industries.
Flex PCBs are on the other end of the spectrum from rigid PCBs. They have a flexible substrate made of polyamide, polyether ether ketone (PEEK), or transparent conductive polyester film. These materials dissipate heat which makes it possible to install flex PCBs where heat will impact the performance of a PCB assembly. The endurance temperature range for flex PCBs is between -200°C and 400°C (-328°F and 752°F). Flex PCBs are designed to adapt to the form of the application for which they are used. As with rigid PCBs, flex PCBs are available as single, double, or multi-layer PCBs.
Regardless of the flexibility of the materials from which flex PCBs are made, they are capable of containing the same components as rigid PCBs. Their flexibility makes it possible to fit them into complex and complicated geometric shapes and forms. Flex PCBs are used in organic light emitting diodes (OLED), LCDs, solar cells, the automotive industry, cell phones, cameras, and complex electronics.
A special form of printed circuit board assembly is one that is a combination of the features of a rigid PCB and a flex PCB. The structure of a rigid and flex PCB is a set of rigid PCBs that are connected by a flexible polyimide ribbon. This combination design is used when a rigid PCB requires movable elements.
Metal core PCBs, also known as thermal PCBs or metal backed PCBs, have metal as their base. The metal, aluminum or copper, covers one side of the PCB. The purpose of the metal is to redirect heat from critical board components. The most common form of metal core is aluminum with brass and stainless steel considered but not the best choices. The thickness of the metals varies between 30 mm up to 125 mm (1.18 in up to 4.92 in).
As would be expected, the manufacture of metal core PCBs is different from the processes used for non-metal PCBs. Metal core PCBs can be one or two sided depending on the complexity of an application or the dictates of the original design. They are used for high power applications and provide better energy efficiency than typical PCBs. Common applications for metal core PCBs are LED lighting, power supplies, and automotive electronics.
The factor that differentiates HDI PCBs from other forms of circuit boards is their high wiring density. They have micro-vias, blind and buried vias, extra laminations, and high signal performance. HDI PCBs are in response to the need for smaller and more compact PCBs to meet the requirements of modern electronics. Their higher density wiring makes HDI PCBs lighter and more compact with lower layer counts.
The defining factor that makes HDI PCBs popular is their ability to do more with less due to the refined precision of modern copper etching. This factor has made it possible to combine the functionalities of several PCBs into one HDI PCB. By shortening the distance between devices and trace spaces, HDI PCBs make it possible to have several transistors for better electronics performance with lower power consumption.
An additional benefit to shortening the distance between connections and lower power requirements is an enhancement of signal integrity. Also included are stable voltage rail, minimal stubs, lower EMI, and closer ground planes and distributed capacitance. HDI PCBs are a cost-effective solution due to their fewer layers and smaller size. Their micro-vias are highly reliable and have a smaller aspect ratio, which makes them more dependable.
The unique properties of HDI PCBs are due to the specialized methods printed circuit board assembly manufacturers use to produce them. The components of HDI PCBs have a high pin count that require specialized manufacturing practices and special materials. Each of these factors make it possible for a HDI PCB to have high density copper connections.
The box build assembly process is a later stage of printed circuit board assembly manufacturing and is completed after PCB fabrication and component assembly. The process for box build assembly combines mechanical, electrical, and aesthetic designs to produce a completed product. It necessitates careful management, supply chain coordination, and mechanical integration. Companies that use the box build method are contract manufacturers and electronic manufacturing services (EMS).
The key steps to box build assembly are:
The factors that make box build assembly popular are its ability to get electronic products to market faster, allowing designers to focus on designs, cost savings, quality of final products, the ability to scale up or down, and having products produced at one location.
Each of the steps of the box build assembly process has to be carefully followed to ensure its success. It requires close attention to details and precision planning.
Kitting is materials planning and is the procurement of the supplies and components necessary for the assembly process. Items to be collected include:
In essence, the kitting process is the foundation of successful box build assembly since every aspect of the process depends on the units supplied from kitting.
There are those who shutter at the words “supply chain” due to its critical nature in any manufacturing process. The supply chain process requires a team of specialists that work with vendors, oversee inventory, and provide logistical control. Proper management of the supply chain supports kitting and avoids shortages. The key to the process is exceptionally careful inventory management, which has been improved with present day technological advancements.
If kitting and supply chain functions have been handled properly, the next step in the assembly process is the creation of small modules and components that are pre-manufactured for inclusion in the final product. Hard drive cages, power supplies, wire harnesses, and input/output panels are all produced during sub assembly.
Enclosures designed for PCBs have pre-threaded holes, pillars, or standoffs for mounting a PCB. Thermal design and heat dissipation are determining factors regarding the positioning of the PCB in the enclosure as well as sufficient clearance. Planned layouts guide PCB assembly services as to positioning, clearances, and cabling and wiring. This aspect of the process is crucial for the performance, safety, quality, and longevity of the completed PCB assembly.
The many features that are part of this phase of the assembly include:
Electronics have to pass through a set of tests before being released for packaging. Each of the tests are designed to measure equipment functionality and performance. Tests that are normally performed on electronics include:
With all electronics, there are a set of standards and certifications that are required by governmental agencies for the safety of the population and industrial operations. The factors that require oversight include safety and electromagnetic compatibility (EMC) and electromagnetic interference (EMI) to ensure adherence to the established stringent governmental standards. Additionally, as with all modern industrial operations and products, PCB electronics are checked for compliance with environmental standards for environmental protection.
The box build assembly process is an excellent example of the steps that are taken for the shipment of electronics that contain PCB assemblies. The process is fast, efficient, and well-coordinated to ensure the safety of electronics. Although it is not generally practiced, box build assembly provides a general overview of how PCB assemblies are combined with other elements to produce a viable product.
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