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What is High TG In PC Board Fabrication?

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The making of PCB involves different steps, technologies, and terms, and TG is one such term that refers to the Glass Transition Temperature. High TG PCB is the board made at a high temperature. We will discuss this topic in detail, including the TG value, features, applications, materials, parameters, and much more.

What is High TG PCB?

If a PCB’s temperature goes beyond a set TG value, its condition will change. Like, the solid board will turn rubbery, affecting a PCB’s function. Depending on where you use a PCB, the temperature of the application should be at least 10 to 20C less than the PCB temperature.

Understanding TG Value

TG means Glass Transition Temperature like there is a certain limit of this temperature for PCB and that specific temperature is the TG value. TG value helps in understanding the PCB material, and you can find which temperature is required for its service.

Secondly, it helps you to find the condition of the PCB material, like if it’s solid, flexible, or solid-flex.

High TG PCB and Its Features

You have to choose a high TG Printed Circuit Board for your application carefully, because it involves multiple features, including thermal, electrical, mechanical, and chemical features.

Thermal Features: they include the TG or Glass Transition Temperature, thermal conductivity, thermal temperature’s coefficient, and decomposition temperature. TG is the temperature at which the state of the PCB material changes. But, when the board cools down, it gets back to its initial condition.

Electrical Features: they include the surface resistance, electrical power, volume relativity, and the dielectric constant and loss tangent.

Chemical Features: the chemical properties of a high TG PCB include the moisture absorption and the methylene chloride resistance of the PCB material. The TG PCB should be able to resist moisture if it’s near water.
Mechanical Features: the mechanical features are also important to know regarding the TG PCB. They include the flexural and peel strength, and the young’s module.

Suitable Materials for High TG PCB

A PCB has two materials, including laminate and substrate. The substrate includes epoxy resin, glass, or paper weave. The substrate should be compatible with the TG. Some common substrates that we use for a high TG PCB are;

  • CEM-1, 2, 3,4, and CEM-5
  • G-10 and 11, FR-1 to FR-6
  • Aluminum
  • Knapton
  • Pyralux

The last three materials are flexible.

The laminates should also be compatible with your TG PCB in terms of strength and temperature. Some common laminates are:

  • FR-1, and FR-4
  • CEM-1, CCEM-3
  • Teflon

Criteria for High TG PCBs

Printed circuit boards with a high TG value are based on certain criteria as described below:

  • The selection of a PCB, depending on the components like it can be single or double-sided PCB or embedded.
  • The stack-up PCB with a single layer or several layers
  • The design of such boards can be based on a module or it can be custom
  • The strength of the board also matters, like it should be robust either electrically or mechanically
  • PCB’s bendability also helps to classify the TG PCB, like if it’s hard, flexible, or hard-flexible
  • The electrical strength also helps classify the TG PC Board

Generally, manufacturers use bendability and strength to classify a TG PCB‘s physical properties.

Where Can You Use The High TG PCBs?

You can use the high TG circuit boards in intense conditions, as the environments with high-vibration devices. They are also suitable for applications with shocks, chemical components, and high temperatures. Like, missiles and car parts often come up with chemicals. So, the suitable industries for high TG PCBs include aerospace, telecommunications, military and defense force, automobile, and down-hole drilling.

What to Consider While Designing a Rigid PCB?

You must hire a professional PCB manufacturer for the right design, manufacturing, and assembly of these boards. The engineer must know the kind of environment that suits a TG PCB to function precisely. Below are a few examples to help you understand it.

Commercial Use

Many telecommunication companies use the best materials for mobile devices to enable them to bear high shocks. Like, the phone should not get damaged easily when you drop it.

Auto Industry

PCB has to be safe under a car’s hood as it’s mostly vibrating, so a shock or crash might happen. Hence, a rigid PCB is the best solution in this case.

Aerospace Industry

The flying machinery always needs the high TG PCB because there is intense vibration, like in the jet engine, as there are thousands and millions of micro-vibrations in one minute. So, equipment related to aerospace should be able to tolerate extreme temperatures, like from -45°C to 85°C.

Other Applications

These boards are also ideal for solar power equipment, such as power inverters and cogeneration equipment. As these boards resist temperature, they work well in many industries. Like, one of its applications involves Lead technology, like the medical, computer, and telecommunication industries.

The TG PCB is also used in broadcasting, like booster stations. Besides, the fire detectors and burglar alarms also need such boards.

Use of High TG Flex PCB

It is clear from the name that a flex PCB can adapt any design or shape to get compatible with certain products. Like, they can tolerate intense environments better than rigid PCBs. You can use the high TG flex PCB in defense and military, aerospace, medical equipment, consumer electronics, auto, wireless networks, as well as industrial equipment.

What To Consider While Designing a Flex PCB?

You must hire a professional PCB manufacturer for the right design, manufacturing, and assembly of flex PCB. The engineer must know the kind of environment that suits a TG PCB to function precisely. You should see if:

  • You need a flex PCB for an ordinary environment or an extreme environment like an explosion. Whereas the cell phone has a normal environment.
  • The environment should be free from any moisture before installing a high TG circuit board.
The Design Process

The design of a high TG PCB involves different steps, such as

  • Using the right software, like CAD, Eagle, Altium Designer, etc.
  • You must know the power requirements to suit different components on the PCB. You should also consider a specific plan for noise reduction caused by a TG PCB.
  • Preparation of the stack-up plans documents as it is essential for making the best TG PCB.
  • The floor layout for a PCB with proper sections, including components. Like you can place them together or separately.
  • TG PCB should be complete in terms of a power plane and ground details. These details ensure proper routing for signals.
  • The board should be compatible with patterns in terms of sizes. All components should be well-placed to help a PCB function the right way.
  • It is important to design routs for high-frequency signals, as the route should be clear for a flawless signal transfer. This step involves vias, as they help in proper signals. You need the reverse via and signal via in this case.
  • You must follow the 3W-rule to increase the traces’ distance which helps to reduce the coupling effect.
  • Another rule to reduce the coupling effect is the 20 H rule.
  • In the end, check the routing guidelines to see if you are doing everything the right way.
Specs and Design Parameters

The fabrication of a high TG PC Board Fabrication involves certain parameters and specs, depending on the application. Some standard parameters are described below.

How Many Layers Do You Need

Designers prefer the even number of layers while developing the high TG PCBs. But, the odd numbers of layers are also suitable in certain applications.

Dimensions of PCB

The PCB dimensions depend on its application. Like, you need a large circuit board for a broader application. Besides, there should be enough space on the board to place the electrical components.

Well-Finished

The high TG PCB should be well-finished, and the material depends on where you want to use this board. Like, some common materials are;
HASL, or hot air leveling – It is ideal as it is cheap and can be stored for longer.
OSP, or organic protective surface
Immersion silver – It gives a smooth surface, and it is cost-effective. It has many storage limitations
Immersion tin – It suits the SMT

Immersion gold – It can be stored for longer with a few limitations.

ENEPIG, nickel palladium – It can be stored longer, but it involves a complex process.

Solder mask – It protects the PCB from environmental elements.

Weight of copper – You must also consider the weight of copper like it includes both initial and finishing copper. Generally, the weight is 1 oz. to 1.5 oz. or 5 oz. It also depends on the layer and board thickness.

Assembled PCB thickness – The TG PCB thickness depends on its material and type. Like, if it’s flexible, hard, or a hard-flex board.

Distance between layers – The distance or spacing of electrical components and layers should be equal for high-frequency signals. As it reduces the coupling effect.

Via sizes – The drill aspect ratio and the hole size should also be appropriate. Generally, the PG PCB can have either plated-through or non-plated through holes, depending on the placement and layout design.

Board quality – The board should have a high-grade material to ensure an effective function during application. Besides, you must check the quality of the TG PCB to evaluate its performance in terms of specs. Like, you should test its lamination, vias, copper plating, solderability, finishing, components, and cleanliness.

Interested to know more about PCB TG or PCB Assembly? Email us at sales@pnconline.com

What is Back Drilling in PC Board Manufacturing

What is Back Drilling in PC Board Manufacturing?

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Back Drilling is a way to remove the copper barrel’s stub from the through-hole. A stub is an unused part of the plated-through holes as it does not perform any function on the circuit, so it’s not needed.

For example, while producing a 12-layer PCB you have to make a hole to connect the first to 10th layers. In general, via holes are drilled and then copper plating happens which connects the first layer to the 12 layers, whereas you only have to connect the first layer to the tenth layer.

The part from the 11 to 12 layer is useless as there is no electrical connection, so it is only a pillar. This extra length of via affects the signal passage, making the communication weak. So, that extra pillar or stub has to be removed from the back through another drilling.

Moreover, back drilling is also known as CDD, controlled depth drilling and you can use it in any Printed Circuit Board having weak signals.

Why Do You Need To Remove the Stub

The stub is not just a waste, but it affects high-speed signals by distorting them. When these signals pass through a copper barrel having a long stub, it results in a high distortion. Thick or multi-layered PCBs and back panels are more vulnerable to weak signals due to stubs.

Printed circuit boards of high-frequency should have blind and buried vias, as well as back drilling. Besides, you don’t have to consider the layout design in the back drilling. On the other hand, you have to consider the aspect ratio in blind vias.

When the Circuit board fabrication is over, the fabricators redrill the holes to remove the stubs. This process involves a large drill compared to other holes. In other words, you have to back drill the holes to a controlled or limited depth, like it should not reach the last layer including via.

However, the back drilling is not a clean process like other drilling methods, as the copper gets electrolyzed in this case. Besides, the drill point is sharp in this case, so the fabricator leaves a small point. Moreover, the b-value or the remaining stub length should be from 50 um to 150 um.

What Are The Benefits Of Back Drilling Or CDD?

Back drilling has many benefits as described below;
• It involves fewer bit errors
• It reduces the deterministic jitter
• It provides more data rates
• You get more channel bandwidth through back drilling
• The enhanced independence matching helps reduce the signal attenuation
• It helps reduce the resonance mode’s excitation or noise
• It does not involve the consideration of any aspect ratio
• It reduces a stub’s EMI radiation
• Back drilling reduces the thickness of local plates
• It enhances the signals, making them powerful
• It eliminates the need for blind holes
• It enhances a PCB’s production process

Back Drilling Principles

During the drill bit drilling, the tip of the drill connects with the substrate board’s copper layer. This process produces a low-level current to evaluate the PCB’s surface height, drilling with an appropriate depth. So, drilling stops after the set depth.

Applications of Back Drilling

You can use the PCBs with back drilling for different industries, including aerospace, computers with large servers, medical equipment, communication, and military.
In the case of military or aerospace, only the manufacturers having a background with these industries are eligible to provide the back drilling in PCBs. This means the ordinary PC Board companies can’t get such projects.

How to Proceed With Back Drilling

The back drilling or CDD process involves a few steps, such as:
• It involves the PCB with tooling holes through drilling
• Copper plating of holes before sealing of the dry film
• Developing graphics on the external surface when the plating process is over
• After graphics, making plating with patterns and providing the sealing of the dry film of positioning holes. However, the sealing is done before the pattern process.
• The tooling hole’s s drilling and vias’ back drill
• Cleaning of vias from the residual that occurs during a back drilling of holes.
• The back drilling of the left via is done from the top surface, whereas the back drilling of the right via occurs from both sides.

PCB Features for Back Drill

The PCB with back drilling consists of certain features, such as:
• Only a rigid PCB can go through back drilling
• PCBs with 8 to 50 layers can have a back drill
• Its thickness is 2.5 mm or more than that
• The aspect ratio of the PCB is also large
• There is less trace in the external surface, like in a square array with press-fit holes.
• PCB dimensions are larger than the boards without back drilling
• The depth clearance for a back drill has to be +/- 0.05mm
• The thickness of the insulation should be at least 0.17mm
• Generally, the back drill hole is larger than other vias, like more than 0.2 mm
So, the PCB drilling involves various stages and back drilling is the second stage that removes the unused plating of vias. It involves a specific depth and the side of copper.
The secondary drilling has to be precise, and that depends on the expansion and contraction of the board, drilling technique, tool accuracy, and certain other factors.

Precautions to Follow While PCB Drilling

Whether it’s back drilling or some other, you need high-quality tools to bring the best results.
• Drills often wear while making holes in the thick boards, especially, small drills and they can affect the surface finishing, as well as the size of the hole. It also increases the drilling force, so your tool must have no wear.
• A worn-out drill needs more force to operate, besides, its temperature also increases, and eventually, the chemical and physical reaction of the drill wear also increases, causing a poor drill.
• You can reduce the drill wear by keeping the aspect ratios low, however, this is not in the case of back drilling.
• Also, take care of the chip load that depends on the drill diameter. Often drills with a small diameter break faster than the drill have a large diameter.
• You should hire professional services for your PCB design, execution, and assembly.

A Technique to Calculate the Drill Diameter

You can do it through the below formula,
Size of the back drill = size of the via or pad hole + 2 x design rule of an oversize back drill

Frequently Asked Questions

What Is The Main Purpose Of Back Drilling?

The basic function of the PCB back drilling is to remove a part of the through-hole that does not transmit the current. If you don’t remove a long hole, it will affect the high-frequency signal transition, causing reflection or distortion.

What Is A Stub In PCB Fabrication?

The stub is an unused part of plated-through holes, as it does not perform any function on the circuit, so it’s a waste. It will affect the signals if you don’t remove the stub.

What Are Plated-Through Holes?

The PTH or plated-through holes connect multiple layers of copper in a PCB to provide an electrical connection to the components.

What Is CDD In PCB?

CDD stands for controlled drilling depth or back drilling that removes stubs or wasted copper parts from the PCB holes.

What Are Other Factors Affecting The Integrity Of The Signals?

Not only stubs, but some other factors also affect the transmission of the electric signals in PCB components. Like, PCB material, connector type, chip package, vias, transmission lines, etc.

Why PCB Should Have Drilling?

The printed circuit boards have become more advanced and their demand has also increased that needs high quality. PCB involves through-hole drilling to create a transition path for the electric signals in various circuits.

Final Thoughts on Back Drilling In PCB

PCB drilling process has different stages and back drilling is the second stage that removes the unused copper plating. It involves a specific depth and the side of copper. It has to be precise, and that depends on the expansion and contraction of the board, drilling technique, tool accuracy, and certain other factors. Printed circuit boards of a high-frequency should have blind and buried vias, as well as back drilling.

The stud or extra length of via affects the signal passage, making the communication weak. So, that stub has to be removed from the back through another drilling. The back drilling is not a clean process like other drilling methods, as the copper gets electrolyzed in this case.

PCBs with back drilling is used in different industries, including communication, computers, military, aerospace, etc. you may have to go through some challenges while back drilling, but by following some precautions you can overcome them.

Interested to know more about Back Drilling or Printed Circuit Board assembly? Just email us at sales@pnconline.com

PC Board Fabrication, V-Scoring-Purpose and Benefits

PC Board Fabrication, V-Scoring-Purpose and Benefits

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PCB or a printed circuit board has different holes, cuts, and elements, and V-scoring is one of them. V-scoring pre separates the PCB and designers also call it V-groove because a groove resembling V is cut on the circuit board’s top and bottom. Generally, the depth of the groove is 1/3 of the board depth and there is a thin layer between two Vs for the board processing.

The boards with V-grooves are either end to end or side by side with adjacent edges. The groove helps break boards with a little force, and you can divide a single panel into several parts with the help of V cuts.

Purpose of V-Scoring

Manufacturers use V-scoring while combining an array’s circuit boards for an effective assembly. It makes the assembly process less hectic, and you can easily set apart the assembled PCBs.

V-scoring helps to reduce pressure during the placement of SMD components on the circuit board by an SMT machine, and while separating the assembled PCBs.

The PCB panel helps manufacturers to insert the components at a high speed, using one panel at a time, rather than one circuit board.

The panel boards are loaded with their parts through an automated machine that performs the pick-and-place function.

These uses motivate PCB engineers, manufacturers, and buyers to use the V-grooves.

Specifying V-Scoring

Engineers specify V-scoring according to the groove depth, or a distance between the two grooves or Vees through a cross-section. The residual material in this case is known as Web. Each measurement has to be equal, including 1/3rd on the top, bottom, as well as a 1/3 web in the center.

The practice of the 90 degrees or the 30 degrees scoring is also there in some cases. However, the 90 degrees scoring is easy to break compared to the 30 degrees scoring.
You can alter these measurements according to your needs, depending on the array size and the ease of separating the boards later on.

You have to use a 30-degree cutter for a score-line cutting with a certain depth. You can calculate the rest of the web based on the material thickness. However, the tolerance of +/- .002″ is essential in this case.

When to Use a Jump Score

Jump score is used in some conditions though it is not that common. In jump score, the score does not go from one end to another, instead, it ends before the circuit boards end. Like, the cutting blade stops before another end comes. The jump scoring provides a firm array while assembly.

Some V-Scoring Terms

There are certain terms to consider while making PCBs with V grooves, and we will discuss them one by one.
• PCB board has some borders or extra material that helps in making a panel, and they are called Rails or Waste Tabs. They enhance a panel’s mechanical strength, allowing an extra material or borders that help to clamp a panel while assembling.
• Another term used in V-scoring is Fiducials which are marks being etched on the borders or a PCB’s inner surface, like on upper and lower layers of copper. Fiducials help the SMT assembly to identify the position of the PCB and SMD components.
• The other important elements are tooling holes located on a PCB’s four corners. The manufacturers use these holes to align a PCB during drilling and routing. Like, the alignment that involves the SMT carriers, solder plate printing, and PCBs’ final assembly.

Process of V-Scoring

It involves two blades being beveled at 30o, or 45o, or 60o, and the blade resembles a wheel with several gears or knives that make V-grooves. Both top and bottom blades rotate while cutting. When the PCB assembly is over, an individual assembly of the board occurs by dividing the sub panels.

Rules To Follow In V-Scoring

Some fabricators think that the perfect size of the board is compatible with an 18”×24” sheet of CCL, but this is not so. Because the fabricator has to use some part of the sheet while processing. Both customer and manufacturer should discuss the kind of a PCB they require, besides, it should be the best.

Some Rules for Exceptional Circumstances

1. There should be zero space between two circuit boards
2. If you opt for V-scoring, your PCB’s size should be at least 75×75 mm, and it can go up to 450 x1250 mm. So, the scoring won’t be successful if the board size is not as per the rule.
3. Make sure the V-scoring path or line is straight, whether it’s continuous like end to end, or discontinuous like jump scoring.
4. For a perfect V-groove, the minimum thickness of the board should be 0.6mm.
5. You can choose the groove angles from 30o, 45o, or 60o.
6. The space between the PCB edges and parts should be a minimum of 6.35 mm
7. The minimum distance between the PC Board Fabrication outline and V-grooves’ line has to be 0.35mm.

Benefits of V-Scoring

• V-scoring helps to use a PCB surface effectively
• It helps reduce the manufacturing cost by fabricating many boards on one PCB.
• It helps to place more than one circuit through one assembly, helping in precise sub-assembly.
• V-scoring tools are cost-effective, portable, and require minimum maintenance.
• It helps save time as it allows you to separate different parts from a final assembly.

Drawbacks of V-Scoring

There are some restrictions of V-scoring like it is not suitable for PCBs with components placed near edges.
V-scoring can affect the PCB structure, reducing its strength due to the mishandling of a solder machine. However, fabricators apply jump scoring to maintain a PCB’s strength. You can read the above section to understand the jump scoring.
In the case of V grooves, you have to allow a 0.05 inches clearance between the grooves and components. The blade should not come between the components, especially for taller parts. Likewise, you should keep enough clearance for components located on the wide connection surface.

Difference Between PCB Scoring and PCB Panels With Tab-Routing

The PCB design determines if you should choose V-scoring or tab-routing. However we have a guideline for better selection, but you have to follow it.
1. The circuit board shape helps to select the right scoring. Like, V-scoring is suitable for rectangular or square PCBs, whereas the tab-routing goes well with an irregular shape.
2. You should choose a tab-routing if the components are hanging on the PCB edges. Besides, the tab-routing does not affect the edge quality. Whereas V-scoring makes edges rough.
3. V-scoring works faster than tab routing, besides, it is cost-effective than tab-routing in terms of labor.
4. At the same time, there is less wastage of material in V-Scoring compared to the tab-routing, which also reduces the total cost.
5. It also depends on the number of boards in an array and the number of PCBs in both directions, including the X and Y planes.

Frequently Asked Questions

What Is The Difference Between The PCB And PCBA?

The process is the same, but it involves two stages. Like, PCB is just a circuit board with components, whereas PCBA is an assembled board with necessary components, and it is ready for application.

What is Jump-Scoring and Its Use?

Jump scoring involves a cut that starts from one end of PCB but it stops before the other end, unlike V-scoring. Jump scoring strengthens a board for multiple processes.

What Is Tab-Routing In PCBs?

Tab routing helps you to process different circuit boards on one panel. It also helps you to isolate boards by breaking the tabs that exist between various boards.

What Is The PCB Penalization?

A process of connected small boards in a single array is called the PCB penalization. It helps fabricators to move the circuit boards while assembly.

What SMT Stands For In PCB?

SMT stands for Surface Mount Technology, and it’s a process of installing the electrical components on the PCB directly. Whereas the component installed through SMT is known as SMD or Surface Mount Device.

Final Thoughts on V-Scoring

PCB fabrication becomes economical by adopting cost-effective processes, including V-scoring. The boards with V-grooves are either end to end or side by side with adjacent edges. The groove helps break boards with a little force, and you can divide a single panel into several parts with the help of V cuts.

It involves less routing space, so you can add several rows in the PCB panel to be fabricated. It eliminates the wastage of the laminate, besides, V-grooves also save money and time by streamlining the PCB processing and manufacturing.

V-scoring helps to reduce pressure during the placement of SMD components on the circuit board by an SMT machine, and while separating the assembled PCBs.

V-scoring tools are cost-effective, portable, and require minimum maintenance. Moreover, it helps save time as it allows you to separate different parts from a final assembly.
But, V-scoring can affect the PCB structure, reducing its strength due to the mishandling of a solder machine.

Interested to know more about V-scoring or PCB assembly services, email us at sales@pnconline.com

Castellated Circuit board fabrication (Uses, and Design Guide)

Castellated Circuit board fabrication (Uses, and Design Guide)

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Electronic goods are increasing with a time that demands smart, high density, and multifunctional PCBs. You will see smarter PCBs than in the past as their geometric index is continuously increasing. Advanced PCBs with reduced sizes need to have updated soldering with a better electrical connection. Large holes result in poor connections, affecting a product, hence, the hole size has reduced to half.

PCB’s need different holes for connections and one of them is plated half hole and designers also call it a castellated hole. It is a drilled hole finished in copper and it exists on the board boundaries.

As holes are semi-plated, so we call them plated half holes. These holes help mount one PCB to another and simplify the assembly of PCBs. The hole looks like a broken circle and enhances the PCB’s soldering. In other words, plated half holes help in board-to-board soldering.

You can enhance various Printed Circuit Board modules through castellation, including Bluetooth or a Wi-Fi module. You can install these modules together during soldering. The castellated holes can directly connect two circuit boards, creating connections between the board and its module.

You can apply these holes in different displays, high frequency, as well as ceramic modules that need soldering to a standard board. Remember that this technology is not compatible with single-layered PCBs.

The boards with semi-plated holes can benefit different industries, including power, computers, consumer electronics, automobiles, and telecommunications.

PCB fabrication of PCB Castellations

PCB has to go through a certain process for plated half holes, and it involves a certain order. So, let’s look at all the manufacturing steps.

• Holes drilling process
• Castellated hole making
• Making of panel plating
• Image transfer
• Pattern plating process
• Stripping is done
• Etching process
• Solder masking process
• Surface finishing
• Implementation of castellated holes

Stacking Of PCBs through Plated Half Holes

The use of plated half holes for stacking of two PCBs involves two criteria, such as

• First, the circuit boards must have an electrical contact, as just a physical connection won’t work. So, both PCBs should have electrical connections.
• The boards should be tightly placed without any space between them. Even a little space between the boards will result in incomplete or wrong soldering.
The semi-plated holes technology is cost-effective and effectively changes a PCB into a surface-mounted assembly. As PCBs are plated and concave, so they offer an excellent soldering base. Mounting of one PCB over another involves a zero distance between them, so plated had holes are best because they lie on the board edges. Besides, dust won’t stay between two PCBs, providing flawless connections.

Uses of Plated Half Holes in PCB

Half holes or castellated holes are located on the circuit board’s edges and resemble several PCB parts. There are different ways to use these holes, such as:
• PCB with plated half holes serves as a breakout board for bigger circuit boards.
• These holes help you to have a custom design of the component like you can alter the pin layout according to your needs.
• Castellated holes help manufacturers to install one PCB to another without any hassle.
• These holes join two circuit boards without leaving any void between them, helping in precise soldering.
• Plated half holes help you to develop a single PCB based on integrated modules. The board is ready for another assembly through its modules.
• The Wi-Fi modules and breakout PCBs also depend on semi-plated holes. Moreover, these holes help you to develop wireless connections between PCBs.
• These holes also help engineers to use complex components with a breadboard which is often a great challenge.

• Castellated holes allow you to reuse the IC without any fear of the damage that happens in direct usage.
• The holes help to work easily with leadless components, such as LGA, QFN, BGA, etc. during SMT assembly
• Small PCB with castellated holes act as subcircuits for large boards containing inverters or filters etc. They are compatible with multiple modules, including GOS, GPRS, GMS, and several other smart modules.

Guidelines for Making Plated Half Holes

You have to consider some design parameters for PCB soldering with castellated holes. There are some guidelines to follow in this case, including diameter, distance, size padding, surface finishing, etc. You can successfully use these holes by following the below parameters.

Holes Diameter
PCB is either advanced or standard and castellated holes are compatible with both. In the case of a standard PCB, the diameter of a hole should be at least 0.6 mm. whereas, you can keep it lower than 0.6 mm in advanced PCBs.

Holes Distance
On the other hand, the distance between two half-plated holes should be at least 0.55 mm. Make sure it is not less than this figure, as it would hinder the soldering.

Surface Size
The surface for making castellated holes for a PCB mount should be large enough. Small size won’t let you keep enough distance between the holes.

Surface Finishing
You must well prepare a surface for PCB mounting like you can do it through an ENIG finish as it is more practical. But, the purpose of PCB also helps to determine the right finishing material.

Suitable Pads
You must use heavy pads as they help join two castellated PCBs without any flaw. There should be a minimum number of holes while using them for soldering, as it can enhance PCB assembly and alignment. Whereas the circuit board’s design also determines the number of holes it should have. But, you can reduce or increase this quantity according to your requirements.

After following the above guidelines, the mounting and assembly of boards would be simple and flawless.

The Design of Plated Half Holes

In terms of design, castellated holes are developed in different styles, such as
• Half holes
• Half holes with small cuts
• Holes with small leads for connectors
The design process involves drilling and copper plating, but via is not like normal PCBs, instead, it is smaller than a standard hole. The micro vias diameter is less than 150 microns, and you can make them using laser technology or a mechanical technique. The laser technology is more convenient in developing a PCB and a small via ensures more output.
You can select any process that suits your PCB, and once the holes are ready, they are cut into half, resembling a semi-circle that’s why we call it a half hole. The holes opening is always on the PCBs edges.

Indicating Plated Half Holes In PCB Design

Different software brings different designs for holes, however, the Gerber files include specific results. You can add a hole directly on the edge of the board, then can cut it across. So, make sure the half portion of the hole is on the PCB, and half is on another side of the outline.
It should include;
• The GTL copper layer and a GBL copper layer, which are copper pads for both upper and lower layers for every half hole.
• Solder mask layers, including the GBS and GTS, and openings for a solder mask on both sides.
• Each plated hole requires drilling that involves a drill layer, including DRL and TXT.
• Likewise, the mechanical layer should cut the drill hole. This layer includes the GKO and GML.
But, you should consider what your design software offers in terms of documentation.

Cost of Plated Half Holes
The manufacturing of plated half holes involves more work and time, and you need to do every step with care. So, a PCB with these holes becomes expensive than standard boards. However, the cost also depends on the design, your requirements, and a circuit board’s size.

Certification
Plated half holes should be certified, depending on the country of manufacturing. Like, it should be RoHS-certified in the United States. A certified board ensures a high-quality product that you can trust in terms of application.

Frequently asked questions

What Is The Difference Between Plated And Non-Plated Holes In PCB?

Plated holes are finished or plated in copper, whereas non-plated holes are without copper finishing.

Why Do PCB Vias Require Plating?

PCB connects different layers on the PCB, providing a path for electrical signals. Your product won’t work without connectors, so vias are essential.

Can You Use Plated Half Holes For A Single-Sided PCB?

No, a single-sided PCB has a single layer, whereas half holes are suitable for more than one layer as they help join two PCBs.

Can The Number Of Drills Affect The PCB Cost?

Fabrication of PCB requires holes through drilling, and more holes mean more drilling. If the number of drills is more, it requires more time to complete, hence, it will increase the manufacturing cost. So, the total cost of PCB will also increase. However, you will have to consider this factor for bigger PCBs as small boards are cost-effective.

Final Thoughts

PCB needs different holes for connections and one of them is plated half hole and designers also call it a castellated hole. It is a drilled hole plated or finished in copper and that exists on the board boundaries.

The boards with semi-plated holes can benefit different industries, including power, computers, consumer electronics, automobiles, and telecommunications.

Interested to know more about Circuit board fabrication of castellated holes. Email us at sales@pnconline.com

Blind and Buried Vias in PCB Board Technology

Blind and Buried Vias in PC Board Technology

PC Board, pc board assembly, pcb assembly, PCB Design, Printed Circuit Board, , ,

PCBs are used to enhance a circuit’s function and stability. There are different vias in a PCB, PC Board, including the blind and buried via. We need to connect different layers in the PCB through a specific via, depending on its design. In general, vias are holes finished in copper, and their position depends on if the PCB is double-sided, or multi-layered.

Here, we will explore the blind and buried via, their benefits, construction, and guidelines to implement them. Before we go into details, you must know the meaning of via, and its role in the PCB.

Understanding Vias

A copper-finished hole in the PCB is known as via, and it joins both layers of a two-sided PCB. The standard via is a hole that starts from one layer and goes up to the second layer in a double-layer board, and it is also known as a through-hole via. A through via is not ideal for a high-density PCB because it takes more space, affecting the board thickness or density.

So, PCB designers prefer a blind or buried via for the multi-layered or HDI boards.

What Is A Blind Via

In blind via, the hole connects the outer layer of the PCB to its inner layer. The outer layer, in this case, can be either top or the bottom layer. It is applied to the HDI or high-density interconnection boards. Blind via enhances the PCB density through the closed placement of its components.

What Is A Buried Via?

The buried via is a hole that connects two inner layers of a PCB board. The name buried is because the hole is buried in between both upper and lower layers. Besides, you can drill it in many layers of a multi-density PCB. A buried via is also used in the HDI PCBs. There are also other types of PCB vias that we will discuss in the end.

Manufacturing Of Via

There are two ways to make a PCB via like the hole is drilled either before adding various layers to the circuit board, or after making all layers. The manufacturer drills all vias and then finishes them in copper.

• You must take care of the drill depth while making the buried and blind vias, because an extra deep hole can distort signals, reducing their speed.
• On the other hand, a very shallow hole can break a connection, affecting the PCB performance. Even, the PCB can stop working due to poor drilling, so give it to expert hands.
• The manufacturer should also know all the dos and don’ts of pcb assembly. So, always hire a good designer and manufacturer for your custom PCB.

How To Fill Or Cover Vias

Via cover must prevent the entrapment of chemicals or other substances within the holes, which can eventually cause defects to the printed circuit board. Vias are filled with conductive or non-conductive paste. Blind vias and via-in-pads are filled with well-designed electroplating.
If you are looking to move heat from one side of the printed circuit board to the other, you will likely opt for a conductive fill.
Vias must be sealed or covered by copper plating. The combination of the sequential build-up of technology and the mechanical processes can disturb the buried via plating, resulting in problems with the board. To prevent this problem, the vias are filled with resin before being plated.
A via-in-pad must be plated because you are putting in a component connection, and you can’t have a recessed hole.
Now, we will discuss the advantages and disadvantages of blind and buried vias.

Advantages That You Get From Blind And Buried Vias

1. The blind and buried vias help design a PCB faster than other methods.
2. In the case of typical boards, these vias are compatible with the component density, and you don’t need to add more layers to your board.
3. Both blind and buried vias enhance the function of the HDI boards, providing high power. They are ideal for BGA components of precise pitch, as they provide a wide surface area, unlike the through-hole vias.
4. They are the best for a multilayered PCB, like a board with a minimum of 4 layers. These vias help where a through-plated via fails to meet the PCB performance requirements. These holes don’t have to face the density limitations of a typical PCB design.
5. They enhance the board density without a need to increase the PCB size. So, you can use the blind and buried vias for high-end PCB products. Such types of vias are ideal for consumer products or electronics.

Disadvantage

The blind and buried vias increase the overall cost of the PCB because of extra manufacturing work. So, they are costly than typical PCBs, because you need more time for hole drilling and other processes. Keep this factor in your mind before ordering your HDI circuit board with blind and buried holes.

Tips To Consider For Selecting The Right PCB Via

Both users and PCB designers should work together to bring the best product. The buyer should tell the designer about his requirements, like PCB components, size, type of via, number of connectors, etc.

Select A Suitable Type Of Via

You must choose the right type of via for a PCB. Like, if the board has several layers, go for blind and buried via. But, choose a through-hole via for a one-sided PCB. There are also other types of vias and the designer must know where to fit them.
Compatible Via Size And Tolerance

Generally, the PCB thickness determines the size of via it should have. A standard via has a 10 mil size that becomes 7 mils after copper plating. Whereas in micro via, you can have a 4 mil via, be it mechanically or laser drilled. Moreover, the hole or via should have enough size or tolerance to hold the connectors.

Compatible Technology

The blind and buried vias don’t go well on all boards. So, the PCB supplier must choose a stack up compatible with via technology, and the same goes to other via types.

Follow The IPC Guidelines

The designers should always consider the IPC guidelines in terms of technology. Like, they should focus on the right distance between vias in case of several layers. Every PCB supplier should have the IPC design guidelines to avoid any mistakes. The guidelines regarding Class 2, Class 3, Class 3DS are essential to consider as they are not similar.

Consider The Angular Ring Requirements

After drilling each layer’s pad, comes the stage of the annular ring and its requirements should be according to Class 2 and 3. The driller should know how to deal with tolerances while drilling through PCB.

The annular ring helps to have enough surface in the internal layers, maintaining the copper connection on a specific layer before a through-hole plating. Like, you should maintain the electrical connections keeping in mind the material and drill tolerances,

Micro Via Plating

When it comes to a micro via, you should give the right requirements to your PCB supplier. Like, how do fill via; through electrical or thermal epoxy and then copper plate it? This step helps to have a well-finished PCB, preventing vias from external elements.

The Drill File
Each connection has a via or hole that must be according to the drill file. In a blind via, the drill diameter and hole’s depth ratio should be 1:1; however, it can be more depending on the PCB thickness.
In the case of buried via, this ratio should be 1:12, but it can be more depending on the HDI PCB.

Other via Types

We have discussed the blind, buried, and through-hole vias, but there are also types of vias used for PCB design, so let’s study them.
Micro via: A micro via is smaller than all other vias. Even a naked eye can’t see it as it’s so small, so you need a microscope. They are used for a high-density PCB to provide more routing area.
A micro via reduces the issues, such as parasitic resistance that is common in the HDI boards. But, the micro via involves more time to drill and care, so the PCB designers prefer teardrops.
Stacked via: The stacked vias are also laminated and they are either buried or blind vias. A stacked via connects different layers on PCB. They appear to be on top of each other, so they are known as stacked vias.
Staggered via: the staggered vias are also used for multilayered PCBs, but they don’t overlap so we call them staggered. This via has a complex design but it involves less cost compared to the stacked via.
Skip via: The skip via is a hole that passes through different PCB layers but it does not have any electrical connection with specific layers. A skip via is either blind, buried, or overlapping.
Via-in-pad: It is common via used for large PCB pads, such as BGA or MOSFET. Such vias help to have components’ thermal dissipation. However, the designer knows if via in pad is suitable or not because it may affect soldering.
Whether it’s blind, buried, or some other via, you must hire an experienced PCB manufacturing company. The manufacturer should be professional and know the drilling techniques to make these vias.

PNC is providing top-notch PCB design and assembling services at affordable rates. Interested to know more about PCB Vias, write us at sales@pnconline.com