Basics of Flexible PCB Fabrication

Flexible PCB fabrication is widely used in various industries and its application is still increasing. Allied Market Research Report showed that the value of flexible PCB industry could reach $27 billion by 2022. Flexible PCB allows manufacturers to change the physical properties from rigid to flexible and use conductive materials.

So how to fabricate flexible PCB? The steps involved are not the only way but are typical processes.

The first step in fabricating PCBs is to plan the design and output according to PCB requirements. Usually, Extended Gerber, an industry standard design software, is used to create the layout. The designer then informs the output to the manufacturer.

You can now print the design on a special printer called Plotter. The finished product will be a plastic sheet containing a photo negative of the design in black ink which will be the conductive copper parts of the PCB.

The next step is to make the substrate. Holes are then drilled and plated according to the design. Printed circuit patterns will be created by addictive or subtractive process. In the subtractive process, the entire surface is electroplated first. Discard or subtract areas that do not belong to the original design. In the addictive process, copper is plated on the surface following the desired pattern.

With epoxy, the panel will be sealed, the components attached, and any markings or indications printed on it. The components are then installed in place, and finally, the finished product is packaged.

Flexible PCB boards have many advantages, such as reliable, adaptable, fair temperature-resistant, effective for fast movement and high-stress conditions, flexibility in design to match up with the electronic device, efficient interconnection solution, educed system maintenance, designed to save space, etc.

PCB Schematics

PCB schematics are representations of electronic circuits along with its components and connections using specific and standard symbols. The two symbols used in the PCB schematic are resistors.

These two symbols represent the same component and are allowed to be used anywhere. The symbols shown below represent two different types of capacitors, the symbols on the left represent non-polar capacitors and the symbols on the right represent polar capacitors.

Different types of diodes are indicated by different symbols, and the right diode indicates a light-emitting diode (LED).

Voltage and current sources are represented with the subsequent symbols:

The IC is shown as a rectangle, with the corresponding pins as shown below:

The BJT transistors below are of NPN and PNP type.

The following symbols represent the op amp, inductor, ground, VCC source, and a 2-pin connector.

The schematic that uses these symbols and their connection designed and placed on paper is used to create the layout for PCB to be printed during manufacturing. Circuit components must be realigned to best fit the printed circuit board and meet all the standards for a professional PCB. Components may have different sizes, and the board size may be limited, so the design of PCB layout contains artwork in addition to the engineering design. 

Understanding of Heavy Copper PCB

Heavy copper PCB is a growing trend in power supply system and power electronics industry. The main reason for high demand about these products is that the finished copper weight of printed circuit board is between 4 oz and 20 oz. They are much better than standard copper circuit board units with relatively less weight between 1 oz and 3 oz.

Today, most available PCBs in the market are designed for low power applications. However, the trend has shifted to heavy copper PCB products thanks to the following benefits:

a.With heavy copper, the current carrying capacity and heat-resistant capacity are increased.

b.Minimize the risk of circuit failure at high temperatures. Therefore, exotic materials can give full play to their potential.

c.PTH holes and connectors improve the mechanical strength due to heavy copper PCBs.

d.Product size can be reduced because there can be multiple copper weights in the same circuit layer.

e.With heavy copper circuit boards, manufacturers can increase copper thickness.

f.Heavy copper circuit boards can be connected to standard copper circuits.

The demand for heavy copper PCB has been increasing day by day, it’s high time you should start using it. Choose an experience and professional supplier at your back, you'll have endless opportunities of success.

PCB Layout Software Functions

PCB layout can be simplified and optimized by using the design software that best suits designer's needs. Some functions can be used in many software products, while others are further improved, all greatly enhance the layout process.

Different PCB layout software have different features, because not all of them are created equal. When selecting the right layout tool, you should consider the following points.

Functions that match the designer's work style- many designers begin with a schematic and move the results into the PCB layout design. If the software you choose is not support this process, it is best to choose another system.

Flexibility- creating a great layout is one thing, but if it's the end of the program's functionality, it does not provide great value. It is important to provide the flexibility to examine the layout for potential manufacturability errors before proceeding the PCB design.

Update- how often does the software supplier update the program? With the continuously technology development, PCB layout is required to evolve constantly. Software that does not change over time will definitely be useless in a relatively short period of time.

Using layout software in the PCB design process will increase the efficiency of component placement and reduce the number of problems encountered when it comes to prototyping and final manufacturing stages. The earlier the problems in the process are found, the lower the costs of handling and correcting.

This becomes even more important as engineers design more complex, multilayer, thinner PCBs for advanced electronics and miniaturized devices. Smartphones and smart flat-screen TVs are just some examples of applications for increasingly complex PCB layouts.

Making layout software work in your PCB design process will improve quality, produce designs ready for manufacturing, reduce costs and time-to-market.

Solution to PCB Layout Problems

Advanced computer-aided design (CAD) and computer-aided manufacturing (CAM) software systems are now available for most PCB designers and manufacturers. These sophisticated and specialized tools have many advantages over traditional engineering methods listed as follows.

Cost savings- efficiency equates to savings in redesign or manufacturing errors.

Documentation- designed to generate detailed documentation about component use, error reports, design status, version control, and more.

Drag and drop design- place components easily and accurately, then have the software produce the connected traces. Easily move or add components.

Efficiency- using such specialized programs can reduce errors and shorten the time to market.

Error detection- check basic errors in real time to avoid errors detected by manufacturer which will cause delays.

Generate manufacturing files- quickly create Gerber files or other formats for manufacturers to ensure accurate manufacturing specifications including component placement, via specifications, traces, silkscreen, solder mask and drilling hole files.

Reuse- once the layout is approved and saved, it can be reused as a template for new PCB projects and used by other engineers.

Custom rules- many programs support creating custom rule sets that are specific to designers’ purposes. Creating these rules and storing them allow designers to share and enhance the functionality of the software.

Layout verification- tolerances, compatibility, component layout, etc., need to be verified during the design phase, as well as before making a PCB, or even a prototype.

Always take design for manufacture into account during PCB layout and design process. If it can’t be manufactured within the project budget or beyond the fabrication capability of your designated manufacturer, then even the most creative and most innovative PCB layout is of little value.

PCB Solder Mask Color

The solder mask is a layer made of polymer material used on the PCB board to protect the copper from corrosion or to prevent shorts between traces or component pins.

PCB solder mask can be in various colors, of which green is the most common and classic one. In addition to the green, solder mask colors can be red, blue, black, white and yellow.

Other colors like purple and grey can be used in smaller ranges. Mat colors are also available, but very few suppliers offer this mask as it is more expensive compared to standard colors mentioned above. The selection of solder mask color is based on a variety of reasons, such as the ability to easily see the track, the visibility of white markings used for orientation line, as well as the manufacturer's name, the source and type of the PCB, the look and style of the product, thermal properties and harmony with other components. We will briefly describe the common solder mask colors in this article.

Red solder mask- track less obvious than the green and yellow PCB, but still used very  common.

Black solder Mask- tracks are very difficult to notice in black color without auxiliary tools. Poor thermal performance but suitable for LCD displays when they are exposed to the user.

Green solder mask- the most commonly used, classic and practical color allow people to see the trajectory and markers by naked eyes.

White solder mask- unless otherwise specified, it is not recommended. Tracks almost invisible and hard to clean, thus it is rarely used.

Blue solder mask- it is often used. Tracks are a little more difficult to see compared with green solder mask.

SMT Assembly Work Process

During SMT assembly manufacturing process, fabrication typically contains several highly automated processes, here we briefly discuss some of them for your reference.

Printed circuit board material contains solder pads without holes where solder paste is applied to the pads by a screen-printing-like process. You can control the solder placement by using the exact stencil template for single PCB being fabricated to apply the material only where needed.

Automated component pick-and-place machine then accurately positions the desired SMDs and other components on the board, typically on reels or tapes, or on static-free media with components like integrated circuits.

The circuit board then continues the soldering operation, heating pads to the point where the applied solder paste melts and bonds the components to the circuit board.

When board’s both sides are used for the component, the placement/soldering process is repeated for the reverse side.

When heat-sensitive components are mounted on the PCB, they can be installed manually or by a process that does not damage the components after they have been soldered automatically.

Then clean the board to remove excess flux or solder residue that may cause short circuits of the components due to the extremely tight placement tolerances.

Finished, clean, and dry products can then undergo final quality check, including missing components, alignment problems, or soldering problems that may produce potential problems.

SMT board inspection can also be automatically implemented. The device preserves the correct visual image of the circuit board structure and compares the produced circuit board with the reference image. The machine operator can then be alerted to take action or to conduct a more detailed manual inspection.

Finally, check the board, then test any required circuit and function inspection.

PCB Background

Printed circuit boards are independent modules of interconnected electronic components, always found in devices ranging from common buzzers, pagers, radios to complex radar and computer systems. The circuit is formed by depositing or printing a thin layer of conductive material on the surface of an insulating board known as the substrate. 

Individual electronic components are placed on the substrate surface and soldered to the interconnected circuitry. The contact fingers along one or more edges of the substrate serve as connectors to other PCBs or external electrical devices like on-off switches. The printed circuit board may have circuitry that performs multiple functions or a single function like a signal amplifier.

Printed circuit board structure has three main types: single-sided, double-sided and multilayer. Single-sided panels have components on one side of the substrate. When components number on a single-sided board is excessive, a double-sided board can be used. Electrical connections between the circuits on each side are made by drilling holes through the substrate at appropriate locations and plating the interior of the holes with a conductive material. The third type, multilayer board, has a substrate composed of a printed circuits separated by insulated layers. The surface components connect to the appropriate circuit layer through plated holes. This greatly simplifies the circuit mode.

Components on a printed circuit board are electrically connected to the circuit in two different ways: through hole technology and surface mount technology. With through-hole technology, each component has thin wires or leads that pass through the holes in the substrate and are soldered to the connection pads on the opposite side. Gravity and friction between leads and hole sides keep the assembly components in place until they are soldered. 

Using surface mount technology, stubby J-shaped or L-shaped legs on each component make direct contact with the printed circuits. A solder paste consisting of glue, flux and solder is applied at the contact points to hold the assembly components in place until the solder melts or reflows in the oven for the final connection. Although surface mount technology requires more attention to component placement, it eliminates the time-consuming drilling process and space-consuming connection pads inherent with through hole technology. Both technologies are in use today. Therefore, it is used more widely than through-hole technology currently.

The other two types of circuit assemblies are related to the printed circuit board. Integrated circuits, also known as ICs or microchips, perform similar functions to printed circuit boards except that integrated circuits have more circuits and components. The hybrid circuit, as its name implies, looks like a printed circuit board but contains some components that grow on the surface of the substrate instead of being placed and soldered on the surface.

The Process of Handmade PCBs

Since PCBs produced by manufacturers are expensive, if you are not in urgent need of your boards, hand-made is a good choice. Below, we conclude the process of hand-made PCB in four simple steps:

1.A hand-made PCB started with the circuit design in a PCB design software, but this time it is saved in PDF format so that it could be printed on laminated paper using a random laser printer. PDF does not change the size of the circuit, so it is the recommended format. The printed circuit board will be placed on a copper plate, after all the paper is etched away, the black paint on the paper will stick to the plate.

2.The first thing to do after placing the paper on a copper plate is to iron over the laminated paper when the PCB board is put on the plate for at least five minutes, so we can make sure that all the paint is adhered on the plate. Remember that improper ironing can cause short circuits.

3.In this step, you must prepare a solution of warm water, hydrogen peroxide and acid. The ratio between water and peroxide is about 2:1, add a small amount of hydrochloric acid, and then immerse copper plate into the solution. Within about 10 minutes, all copper in the board will be etched away except for the area where the paint is applied4.The final step is to remove the paint from the board with acetone, exposing the connection. 

However, hand-made PCB boards have many shortcomings. The most serious is the poor connection quality which may lead to short circuit; the lack of solder mask makes it susceptible to the impact of external force and shorten its service life. Another obvious disadvantage is that the maximum layer of a hand-made PCB made in this way can’t exceed two layers. This means multilayer printed circuit boards are hard to make at home or in the workshop. 

How to Etch a Printed Circuit Board

Have you ever thought of making a printed circuit board at home? You can now use it for all types of home-made electronics.

1.Wear goggles and gloves (not optional). Always remember safety first. You can blind yourself easily!

2.Make sure the area is well ventilated before mixing. Chemicals will produce harmful fumes that may do harm to your health.

3.Use non-metallic basin. Check if it can tolerate the acid using a few drops.

4.Gently pour one part hydrochloric acid into every two parts hydrogen peroxide (add acid to water). When mixed together, they can generate severe skin irritants and can produce toxic chlorine gas.

5.Enough solution to completely submerge the circuit board.

6.Gently place on the circuit board and stir for 10 to 15 minutes. The solution will be warmer and smoky. 

7.Continue stirring until all copper is dissolved and the solution appears slight green tinge.

8.Do wear gloves when cleaning. Clean circuit board with cold water to remove any etching solution. Then completely dry it with a towel or rag. Put it aside. Make sure there are no solutions in the work area or in the container and then take off gloves and goggles.

9.Mix acetone and rubbing alcohol at 1:1 ratio. Pick up the paper towel, immerse it in the solution and gently wipe the board surface. Permanent markings will begin to fall off. Continue rubbing until all markers disappear. You should see your circuit is now carved in copper.

10.Etching solutions are toxic to fish and other water organisms. Do not pour it into the sink when you finished. This is illegal and can damage your pipelines.

Useful PCB Layout Software

With the introduction of high-density circuit boards, printed circuit board design becomes more and more challenging as more functionality are required in a smaller space. Electronics and PCB boards are integrated into almost all devices in our daily life, such as smart phones, tablets, home appliances, home automation, even children's toys, etc.

Designing smaller boards with tighter routing and a larger number of components can make circuit board layout more complex. Thus, PCB layout software is almost a mandatory tool for designing effective layout that can be successfully converted to a working product whether for prototypes or production-ready boards.

PCB layout software can contribute to design and production efficiency in a number of ways:

PCB Board Quality

Layout software can analyze complex designs which may cause conflicts between components or circuit paths where problems may be produced from track widths, physical components, board size, or even electromagnetic interference from other circuit board components.

Design for Manufacturing or DFM

PCB layout software designed for this purpose can prevent the creation of PCB layouts that look good on paper or screen, but can not be made in the current world of manufacturing. Many software tools will warn you to avoid such situation.

Design Rule Check or DRC

Verification features like DRC can detect problems before they are designed into the PCB. Based on component types, these features ensure that the spacing is within tolerance, there are no size limit issues, and other layout rules related to object type, layer, etc.

Documentation

Software tools save layout designs in a standard format for future reference and reuse. Illustrations and layout documents can also be printed for working with manufacturers or for submitting designs for quotes by potential suppliers.

Ease of Placement

Drag and drop simple board layout can improve layout design efficiency.

Process Flow

Layout software enforces best practices for PCB design. By using tools in the software, designers can make schematics and layouts in accordance with standard methods and techniques.

Save Templates for Reuse

When you create a template with similar capabilities in the past, you do not need to recreate the new template. Starting with a working template, make sure the process starts with a time-proven design and add or remove components from that point. And this will shorten the development cycle and improve the quality.

PCB Manufacturing Machine

Expensive PCB manufacturing machines are used to make PCB boards. The better the quality, the higher the precision, the higher the machine cost, so a relatively high investment is required for PCB manufacturing equipment. PCB manufacturing machines range from laser plotters for printing PCB circuits to films to pick-and-place machines for assembling components for PCBA (PCB assembly) fabrication. We will describe 3 most common PCB manufacturing machines used in the PCB manufacturing process in this article.

Automatic Optical Inspection Machine 
It is used to detect PCB board automatically for errors by using a special algorithm. The machine also has a screen projection of the PCB board in the computer monitor. The zoomed view can be used for clear eye inspection. Optical inspection can also be used to precisely punch holes in the exact place with the aim of aligning holes with other planes of multilayer PCBs.


Laser Plotter
It is a plotter with laser technology for printing negatives films on computer-designed PCB circuits. The difference between this plotter and random plotter lies in its high precision and high accuracy. An important thing to consider is to ensure that no dust or other unwanted pieces are present on the laminated sheet during the printing process. This is because the presence of such particles can cause the connection in the PCB to be cut off or short-circuited.


Pick-and-Place Machine 
It used to place components on a PCB assembly board. The component is extracted from stripes by a magnetic nail and then pressed them on a solder paste board at the exact coordinates. The paste is put onto the board by using a PCB mask, while the coordinates are read from the computer, in most cases from an excel file. Complex pick-and-place machines place the paste in an automated way by using the same principles as placing components. This precision machine can also cure PCBs at the temperature of about 90 degrees after assembly.

PCB Layout Considerations

Printed circuit board layout may be considered by the circuit designer as an art form. Creating the most reliable, functional and cost-effective finished PCBs is really a challenging task, especially in today's increasingly demanding requirements for compact, light-weight, and even flexible boards.

One of the primary considerations for PCB layout is its size and shape. The end result must adapt to the environment where circuit board will be installed and used to promote the design process. Space considerations may require the use of multilayer or high density interconnect (HDI) designs. Some projects require specialized board shape and weight limitations, making the layout particularly challenging.

Though this may not be a major consideration when designing a initial but functional circuit, it will become a higher priority when laying out PCBs for product manufacturing.

Consider your manufacturer in PCB layout phase. Not all manufacturers can fabricate high volume of multilayer boards or HDI PCBs. Most PCB layout designs require a review of technologies such as flexible or rigid-flex structures and the proposed vendor needs to be reviewed to ensure layout design and material requirements are met.

Most PCB layout designs require a review of technologies like flexible or rigid-flex structures with your manufacturer to ensure layout design and material are met the requirements and within their capability. 

Special requirements such as the need to incorporate lead-free construction or avoid potentially hazardous materials can be key points when making layout and construction decisions.

Lack of effective and accurate layout can lead to almost limitless issues, including: electromagnetic interference from conflicting components or trace placement, conflicts between components on opposite sides of the board, redesigned and delays in manufacturing, limited board functionality, etc.

Processes for Manufacturing Multilayer PCBs

Due to the considerable demand for multilayer PCBs used in technical equipment, medical equipment, military, and even consumer products such as TVs and home surveillance equipment, most competitive manufacturers have positioned themselves in response to the needs of these boards. The capacity of a manufacturer associated with mass-production capability and the amount of PCB layers that can be produced are still mixed.

The fabrication of multilayer PCBs involves the process of combining alternating layers of prepreg and core material into a single unit, utilizing heat and high pressure to ensure uniform encapsulation of the conductors, eliminating air between layers and correctly curing the adhesive that bonds the layers together.

Due to multilayer material, it is necessary to carefully observe and record the performance of drilling holes between layers. For successful multilayer PCB manufacturing, it is important for engineers to use symmetrical layout across layers to avoid twisting or bending of the material when heat and pressure are applied.

When sourcing manufacturers for multilayer printed circuit boards, it is critical to check their manufacturing capabilities, standard tolerances and manufacturing design (DFM) techniques.

Top 10 Design Tips for a Working PCB Prototype

We all want our PCB prototypes to get done fast and cheap, but sometimes this will not happen. After all, when you start a new design and focus all your time on the circuit design or component selection, little time is left for your PCB layout. But during PCB manufacturing, the layout process is the most important. So what’s the key to design a PCB that gets you a working prototype back right the first time? We have concluded 10 design tips below for your reference, and the last 3 of them are discussed in this article.

h.Leave gap between copper plane and board edge
Whenever designing a PCB board, it is always recommended to leave a small amount of clearance between the board edge and any copper plane or trace. The last thing you will do is to have your PCB cut off from the panel during the manufacturing process and your copper should be trimmed as well. If this happens, the exposed copper will short your circuit board.
Before designing, set some design rules in your DRC to define copper-to-edge or plane-to-edge clearance. It is better to keep a clearance of at least 50 mils, besides, you should always check with your manufacturers ahead of time to see what clearance requirements they suggest.

i.Avoid heat issues
If you had a circuit whose performance decreased over time, then you know how important the thermal is in a manufactured product. To help check your heating problem, always know which components on your board will pump out the most heat. You can find this information in any datasheet by looking for the thermal resistance ratings and their accompanying guidelines.

j.Double check acute angles for traces 
Most designers try best to avoid making acute angles in traces, but they can still slip through the cracks, especially when two traces combine. During PCB etching, the existence of acute angles can cause the accumulation of acid material which will consume copper and damage the circuit.
When your routing process is complete, always check all traces, especially the segments where two traces nay connect, to see if there are any acute angles. Besides, it is better to choose 45 degree trace angles instead of 90 during your routing process.

Take time to incorporate these 10 design tips into your own PCB design workflow, then you can get your prototypes fast and cheap without wasting any money in the process. 

SMT Assembly Consideration

Surface mount technology or SMT is a widely-used alternative to older through hole during printed circuit board design and PCB manufacturing process. Though through hole manufacturing still has a place, SMT has largely replaced them where size, weight and automated manufacturing processes are considered.

SMT uses surface mount devices (also abbreviated as SMDs) to replace larger, heavier, and more cumbersome counterparts used in through-hole PCB construction. Today, more and more PCB devices are available as SMDs or packages, making SMT board design and manufacture more practical and cost-effective.

Surface mount technology has promoted the use of electronic devices that are impossible or not practical with the older through-hole fabrication techniques.

Due to the nature of SMT board structure and smaller and lighter components, automation of the PCB construction is facilitated and has become very effective for manufacturing, especially for mass production. To get the maximum manufacturing advantage, SMT construction must be mechanized as much as possible.

SMT assembly manufacturing has following advantages:

a.Drilling holes are nearly or completely eliminated with SMDs connecting the board surface directly.

b.Reliability is enhanced because it is not necessary to mount the component leads through holes for subsequent soldering. Soldering SMDs to surface pads is quicker and easier with assembly time reduced and quality improved.

c.SMT assembly is highly automated, speeding up production and reducing customer turnaround time.

d.Through-hole manufacturing needs to be carefully aligned with the drilling hole, and leads are typically pre-formed to accommodate a particular PCB layout and component placement. SMT assembly eliminates most SMD placement interference, allowing for more automation, thereby reducing costs. SMD leads are small or even none at all.

Best Practices of PCB Design

Though the demand for highly-featured boards is increasing, custom PCBs still performs an important role in electronic industry. In this article, we outline several best practices of PCB design, which are very useful and can generally be applied to any PCB design project.

Decoupling capacitors are not optional. Do not try and optimize your design by avoiding decoupling power lines. Capacitors are inexpensive and robust, you should take the time to fit them in wherever possible.

Design rule check as often as possible. The design rule check function on PCB software takes a little time, but it can save hours on more complex designs. Though every layout decision is important, the design rule check is absolutely the most important one.

Double check your PCB manufacturing data before fabricating PCBs as per your data. You may catch an error unintentionally before it's set forever in fiberglass, resin, and copper, etc.

Get a right grid. Find a grid spacing that suits as many of your components as possible and use it throughout. A little additional thought at the early stages of the layout can avoid spacing difficulties and will maximize board use. 

Keep trace length as short and direct as possible. This applies particularly in analog and high-speed digital circuitry where impedance and parasitic effects will always play a part in limiting your system performance.

Use silkscreen wisely. The silkscreen can show the board builder, device operator, etc. Full use of silk screening on both sides of the board streamlines can reduce re-work.

Manage the distribution of power lines and ground. Using a power plane is a quick and easy option in most PCB design software. It helps ensure power flows as effectively as possible with minimal impedance or voltage drop. If possible, run multiple supply lines in the same area of the board and remember that if the ground plane is run over a large section of one layer, it can have a positive impact on cross-talk between lines running above it on an adjacent layer. 

Hope the above 7 basic rules can help you in printed circuit board design. 

Benefits and Drawbacks of Multilayer PCBs

Most PCB manufacturers are finding the demand for multilayer boards growing rapidly due to the need for smaller, lighter circuit boards used in electrical devices, military equipment, healthcare miniaturization, etc.

Multilayer printed circuit boards are perfectly used in application like smart phones and computers thanks to their compact, light weight and sophisticated functions.

Besides space-saving and weight-saving, there are numerous advantages to use a multilayer from a technical point of view.

a.By combining multiple layers into a single PCB, boards can add functionality.b.Multilayer PCB manufacturing process can produce high quality, reliable end products.c.Multilayer board provide high capacity and speed with a small footprint through its inherent electrical features.d.Higher density of assemblye.Reduce or eliminate the number of connectors required for multiple separate PCBs, thus can simplify construction and reduce weight.f.Multilayer PCBs can be made of rigid and flexible structures. In spite of this, the more layers included in the flexible printed circuit board, the poorer the flexibility.

Each technique has its advantages and disadvantages, and multilayer printed circuit boards do have the negative attributes:

a.One of the major negative aspects of designing multilayer PCBs is its high cost. Specialized process is required to make these boards, so manufacturers need to invest significant capital to provide these services. This makes multilayer boards cost more than traditional single-sided or double-sided boards.b.The compactness of multilayer boards causes design issues such as crosstalk and impedance problems.c.As functions increase, a single PCB needs to be tested more extensively. Due to the complexity of the manufacturing process, the manufacturing cycle may also be longer.d.Repairing a multilayer PCB can be very difficult and may not even be possible. This makes unqualified multilayer boards costly as it may need to be completely replaced.

PCB Color

Traditionally, printed circuit boards always use green epoxy as the base material because of its low cost and ease of manufacture. In the early stages of epoxy development, green adhesives are the only economic choice. There is no standard or protocol to determine the color of printed circuit board. Manufacturers use different PCB color codes instead of green to distinguish between prototype boards and finished printed circuit boards.

There are various colors to choose when making a PCB. Among them, black, white, blue, yellow and red are the most commonly used PCB color. Although some modern PCB types have already described the purpose of specific color, most boards are still manufactured using green epoxy.

Black PCB color is made by mixing carbon and cobalt. Due to the presence of carbon, this type can form a conductive layer on the PCB traces, and used as a protective shield to isolate sensitive signals from external noise. However, black PCB color is relatively expensive because of expensive cobalt mixture.

White PCB color is generally used for LED applications. Since the dielectric material which is used to isolate the aluminum substrate, the heat sink and copper traces is white in nature. The white back area can help to reflect the light generated by the LED.

Blue PCB color is used to avoid distractions caused by LCD display and bright areas. It makes the screen look isolated and illustrate a focused light source. 

Red PCB color makes the board stand out. Often it is used to identify specific components in an assembly. Most measurement and precision equipment such as bench multi meter, oscilloscope, analog reference, etc. use red PCB color.

Benefits and Drawbacks of HDI

High density interconnect (HDI) is a technology that is rapidly becoming popular in PCB design and various electronic product integrations. It offers a more denser construction on the board by placing smaller components in a closer position, which also leads to shorter paths between components. However, every coin has two sides, so in this article, let’s discuss its benefits and drawbacks.

Benefits of HDI

HDI board has micro vias of incredibly diameter, buried or blind vias or a combination to facilitate the incorporation of more technology into less space with fewer layers. Multilayer HDI boards are commonly used, many of which are accommodated by various building methods that use blind, buried, stacked, and staggered vias.

With smaller components, blind via and via in pad technology, components can be placed closer together, and this can increase signal transmission rates, and reduce crossing delays and signal loss. These are all key considerations for improving HDI PCB performance.
HDI board is the top choice for applications where space, performance, reliability and weight are concerns. This makes them suitable for almost every applications related to electronics, consumer products, computers and aerospace.
Multilayer HDI boards provide a powerful interconnection with stacked vias, so they are of high-level reliability even in more extreme environments.

HDI Drawbacks
While the benefits of HDI are considerable, HDI has its drawbacks as well.
Machine used to manufacture HDI boards are expensive. Such equipment includes laser drilling machine, laser direct imaging processes, and other specialized manufacturing equipment and materials. 
Attention to detail is crucial in the design and manufacture of HDI printed circuit boards, and this requires professional knowledge and experience. Thus, the high cost of HDI board also includes operator training expense.

11 Rules for PCB Components Placement

PCB components placement is a major part during the board design. In this article, we concluded 11 rules for your reference, but please note that we will not take any responsibility for anything that results from this article.

1.Start by placing big/ major /critical components (such as MCU, DSP, FPGA, DDR, clocking devices), and then placing support components like resistors, capacitors, etc., around them.  

2.Use 50 or 100mil as a component grid to place these large components (like QFP, BGA, SOP, SOIC or through-hole connectors). Use 25mil as component gird for these SMT resistors/ capacitors or other small passive components.

3.Isolate analog, digital and power sections.

4.The clock driver/ synchronizer should be placed as close as possible to the clock oscillator.

5.Arrange components in rows and columns with the same orientation for easy installation, inspection and rework. If possible, all polarization components like tantrum capacitors and diodes are placed in the same direction. The polarity of these components should be marked on the silkscreen.

6.Keep at least 40mil space between components, and 100mil space from component to board edge is at least. Locate connectors on one edge or one corner of the board.

7.Try to place all components on the top side only. If not possible, small size and low thermal dissipation components (such as SMD passive components) can be on the bottom side.

8.Placing the decoupling capacitor as close as possible to the VCC pin on the active component.

9.Maintain a gap of at least 200 mils from transformer to electrolytic capacitor.

10.Placement for indication LEDs, test points, switcher, jumpers and adjustable components should be easy access.

11.Carefully check signals about analog, high frequency, RF, high voltage, high profile, high heat signals or heavy components before starting to trace routing.   

A Method for Creating PCBs

Your choice for creating PCBs is usually based on the availability of the materials needed for the method, the technical difficulty level of the method, or the PCB quality you want to achieve. Here's a brief description of different methods and their main features for your reference.

Acid Etching: This method requires extreme safety precautions, the availability of many materials like etchant, and it is somewhat slow. The quality of the PCB obtained depends on the material you use, but in general this is a good way to get simple or medium complexity circuit boards. Circuits involving more close wiring or tiny wires often use other methods.

Laser Etching: This is usually used by large manufacturing companies, but still can be found at some universities. This concept is similar to mechanical etching, but the laser beam is used to etch the circuit board. It is often hard to get such a machine, but if your local college has such a machine, you can use their facilities if they allow.

Mechanical Etching/Routing: This method requires special machine which can mechanically remove unwanted copper from the circuit board or route empty separators between wires. It can be expensive to buy such a machine, however, this method is useful if you need to create multiple circuit copies and fabricate qualified PCB boards.

UV Etching: This method is used to convert PCB layouts to PCB boards and requires more expensive materials that might not be available everywhere. However, these steps are relatively simple and can produce finer and more complex circuit layouts.