Hi readers! I hope you are having a great day and finding something new to learn. Today, the topic of our discourse is PCB Castellation and Castellated Holes.
Printed Circuit Boards (PCBs) are the core of nearly all electronic devices and are a structured platform on which components are mounted and interconnected. As electronics are moving toward more miniaturization, modularization, and mass production, PCB technologies must advance to be able to support these new requirements. Part of this advancement is the use of PCB castellations or castellated holes, a technology that supports small, modular board-to-board connections.
Castellated holes are tiny, plated half-holes on the border of a PCB. They allow one PCB, a module, or daughterboard, to be soldered onto another directly, much like a surface-mount device. This process eliminates connectors and enables easy integration of pre-tested, reusable modules within a system. Castellated PCBs find extensive use in Wi-Fi and Bluetooth modules, DC-DC power supplies, and sensor interfaces, where space is limited and utmost reliability is needed.
By having a simple yet robust technique of stacking or soldering PCBs along with each other, castellated holes enhance design flexibility without adding complexity to assembly, thus emerging as a highly desired solution for prototyping as well as volume production.
In this article, you will learn about PCB Castellation, its characteristics, manufacturing process, design guidelines, applications, and quality testing. Let’s dive into in-depth details.
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PCB castellation is the term used for producing half-plated holes along the periphery of a PCB. Holes are drilled and plated as regular vias, but subsequently partially routed off when milling the outer profile of the board. The consequence is a half-circular hole cutting through the edge of the PCB, with the copper plating exposed. These notched holes look like the battlements on a castle, hence the name "castellation".
As compared to conventional vias, castellated holes have both a mechanical and electrical purpose, allowing soldering of the PCB module onto a higher motherboard with consistent electrical connections.
Castellated holes, otherwise known as half-holes, are special features along the edge of some PCBs that allow for complete electrical and mechanical connections with other boards. They are made by plating through-holes (PTHs) along the edge of a board and then milling or routing them in half during the last profiling phase. This leaves a series of half-semi-circular notches that reveal the internal copper plating along the edge of a board.
These packages are often utilized in surface-mount modules like RF transceivers, sensor breakouts, and power management modules, in which a sub-board has to be mounted directly on a host PCB.
Every castellated hole contains a conductive lining of copper, electroplated for superior electrical continuity and solderability. The copper wall assures that when the module is reflow soldered onto the base PCB, there is a strong electrical bridge between the two boards. Proper plating is important—thin or uneven plating can lead to poor connections or increased resistance.
The half-hole shape provides self-centering on placement. The shape naturally seats onto the respective SMT pad on the base PCB, and reflow solder surface tension assists in centering the module. The design also provides maximum contact area, enhancing the integrity and stability of the solder joint.
The castellated edge serves as a functional terminal, similar to a standard surface-mount lead. Solder paste is placed on the pads of the receiving PCB, and during reflow, the solder flows up the copper surface of the castellation to form a secure connection.
Castellated holes enable a plug-and-play design philosophy, as pre-validated modules can be reused in various product lines. This speeds development and minimizes the risk of board-level design flaws.
Casting away the use of connectors or sockets, castellated PCBs conserve precious board space. This is extremely important for applications such as wearables, IoT nodes, drones, and handheld devices, where real estate is precious.
These PCBs are well-suited to standard SMT assembly methods, pick-and-place and reflow soldering, so they're great for automated manufacturing environments.
There is easy access for visual inspection along the exposed edges, and occasionally, electrical probing. Modules can be tested by engineers before soldering and retested afterwards without specialized test arrangements.
Production of high-quality castellated holes involves precise execution of a number of accurate manufacturing processes. Castellated holes are not simply edge embellishments; they are functional electrical and mechanical interfaces. Their manufacture, therefore, must be a controlled process to provide structural integrity and best solderability.
The operation is initiated in the same manner as conventional plated-through-hole (PTH) production. Drilling machines with precision drill holes through the PCB at specific locations close to the board edge. The holes are drilled into the required layers and chemically cleaned to make the walls of the holes ready for metal deposition. The second operation is electroplating, in which copper is deposited along the walls of every hole, forming a conductive cylinder electrically interconnecting the inner layers of the board.
After plating is finished, the PCB is milled or routed to establish the final shape of the board. In this process, the outer edge of the PCB is cut, specifically cutting through the holes that have already been drilled and plated. This routing is a very precise process that must be executed so as not to destroy the copper plating or distort the unbalanced hole exposure. This produces a series of half-holes or semi-anchored notches that create the castellation.
Accurate fixturing and CNC calibration are critical during this phase. A millimeter-sized misalignment will lead to non-uniform copper exposure, decreasing the efficiency of the solder joint or weakening the mechanical interlock between the host board and module.
To prepare the board for soldering, selective solder mask coating is applied, typically excluding the castellated edges. Exposing these edges facilitates improved wetting of solder in assembly. Surface finish is applied to shield exposed copper and enhance solderability. Typical finishes are:
ENIG (Electroless Nickel Immersion Gold) for excellent flatness and oxidation resistance
HASL (Hot Air Solder Leveling) for economy
OSP (Organic Solderability Preservatives) for use in lead-free applications
Castellated PCBs are inspected and tested thoroughly after fabrication. Automated Optical Inspection (AOI) verifies plating integrity and hole exposure. In high-reliability industries like medical, aerospace, and defense, the X-ray inspection can also be applied to identify internal plating or misalignment defects. The tests verify that the process of castellation is in compliance with both electrical and mechanical reliability requirements.
Castellated PCB design involves close attention to electrical and mechanical considerations to achieve long-term performance and manufacturability. These guidelines are used to optimize reliability and functionality:
Parameter |
Guidelines |
Hole size |
0.3–0.8 mm for proper plating and edge integrity |
Hole spacing |
≥ 0.5 mm to prevent solder bridging and milling issues |
Pad alignment |
Match base PCB pads with castellated holes for strong solder joints |
Thickness of copper |
1 oz standard; 2 oz for higher durability and current loads |
Mechanical reinforcement |
Add mounting holes or connectors for mechanical stability |
Castellated holes are usually between 0.3 mm and 0.8 mm in diameter. Holes under 0.3 mm can experience inferior plating quality, causing poor electrical connection. Larger holes above 0.8 mm will use up more board space and can weaken the module's edge strength. Selecting a suitable size is pivotal in trading off compactness against ruggedness.
Keeping a proper spacing between holes minimum of 0.5 mm is prevents solder bridging during the reflow and provides mechanical integrity of the board edge. Insufficient spacing is also making PCB milling challenging, with potential edge chipping or delamination.
The castellated holes on the module must be directly over the surface-mount pads on the base PCB. This assures strong, consistent solder joints during assembly. Misalignment results in cold joints, open circuits, or elevated resistance.
1 oz thickness of copper is generally standard enough, but employing 2 oz copper in high-current or mechanically stressful applications improves thermal performance and mechanical strength, particularly at the solder joint.
To provide mechanical reinforcement for heavier or larger modules, use mounting holes, board-edge connectors, or stiffeners. These elements reduce stress on the castellated joints, particularly under vibration or cycling.
The reliability of castellated PCBs requires the following quality assurance processes:
X-ray Inspection: To check for voids or defects in the plating.
Solderability Testing: To ensure that exposed copper interfaces are properly finished.
Functional Testing: As modules, castellated PCBs must be fully functionally tested before mounting onto a host PCB.
Also, the manufacturing companies utilize Design for Manufacturability (DFM) tools to check the location, alignment, and spacing of the castellated holes during the design process.
Castellated PCBs find widespread usage in a large number of areas of electronics due to their small size, solderability, and rigid interconnection. The major areas where these PCBs are applied are given below:
Castellated holes are typical in wireless communication modules such as Wi-Fi, Bluetooth, LoRa, and ZigBee transceivers. They are typically designed to be small and compact to be embedded within systems. Castellated build eliminates the use of big headers or connectors, which can be directly soldered on a main PCB, saving space and money.
Voltage regulator modules like buck and boost converters are typically available in castellated PCB configurations. These mini boards undertake tasks like voltage conversion and power filtering, and their castellated edges make them easily integrate into main designs without much space, making them appropriate for battery-operated and space-limited applications.
The majority of microcontroller breakout boards on ESP8266, ESP32, and STM32 use castellated PCBs to allow simple soldering onto a host board. Prototyping, IoT development, or permanent low-profile mounting in an application is all especially suitable for this.
Sensor modules with temperature, humidity, motion, light, or gas sensors typically use castellated edges to facilitate integration. Sensing capability can be easily incorporated into PCBs by designers without requiring a change in the base design.
Castellated boards are handy in test instrumentation where signals or transitory circuits should be connected. They give connections in a safe manner without the need to permanently attach, therefore ideally suited for debug, firmware flashing, or hardware validation stages.
PCB castellation is an extremely efficient design construct that helps meet increasing demands for compact, modular, and scalable electronic systems. By incorporating semi-circular plated-through holes at the edges of a PCB, designers can convert sub-circuits into surface-mount modules that are solderable with ease. Not only does this ease complex function integration, such as wireless communication, power regulation, and sensing, but it also helps ensure a cleaner, connector-free design with cost and space savings.
Castellated PCBs are now critical in high-speed industries with demanding needs for rapid prototyping, simple assembly, and miniaturization. They are used in RF modules and power converters, microcontroller development boards, and sensor platforms, to name a few applications.
Though precise design and accurate fabrication are needed to guarantee structural integrity and sound soldering, the advantages far outweigh the difficulties. With electronics progressing toward more modular architectures and compact footprints, PCB castellation will continue to be a useful tool in both prototype and production settings, enabling designers to create with flexibility and velocity.
Hi readers! Hopefully, you are having a great day and exploring to learn something new. Heat is the silent killer in power electronics, and thermal vias are the unsung heroes that keep your circuit cool under pressure.
As electronic devices are miniaturized and powered with higher power, the amount of heat generated by high-speed and high-power devices has increased significantly. Proper thermal management is now one of the greatest challenges of modern-day PCB (Printed Circuit Board) design. Whether it is power supplies and LED light systems, or processors and RF modules, all electronic circuits are heat-generating. Unless treated carefully, such heat can cause degradation of components, reduced performance, signal instability, and even irreparable system damage.
To prevent such issues, designers must incorporate efficient cooling systems. Thermal vias are the most economical and efficient method. They consist of small, vertically drilled holes in copper-plated PCBs designed for heat conduction but not for electrical connection. Thermal vias create an efficient thermal path by transferring heat from the board surface, where components that generate heat reside, to inner copper levels or external heat sinks.
It not only lowers the temperature of critical components but also improves the overall thermal equilibrium of the PCB. Thermal vias significantly improve the reliability, performance, and lifespan of high-power electronic components and thus form an indispensable part of thermal design guidelines in present times.
This this article, you will learn about thermal vias, their characteristics, why it is important in PCBs, how they work, their types, and applications. Let’s unlock.
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Thermal management is a vital aspect in high-power applications on today's PCBs to achieve a reliable and optimally performing device. Examples are LEDs, power transistors, and voltage regulators, which generate huge amounts of heat from load conditions. Thermal vias, small plated holes in the PCB, provide a direct thermal conduction path from components to internal copper layers or sinks. Contrarily, thermal vias are designed to conduct distributed heat away to prevent an over-temperature in the components rather than as a regular signal via. They facilitate the heat dissipation and thus lead to increased longevity and steadiness of electronic devices, which is now necessary concerning today's high-power and density PCB applications.
Thermal vias are crucial components in printed circuit boards (PCBs) employed for heat management generated by power-dissipating components. Unlike normal signal vias, they possess as their principal purpose thermal, not electrical, conductivity. It is important to know how they work and what they look like so that high-power electronic systems can be designed with reliability.
Thermal vias, as the name implies, are plated through holes (PTH) drilled right through the PCB. The plating is on the side walls of the holes, which is the path of conduction of heat from the board surface to the inside or back copper layers. The thickness and quality of the copper plating are directly responsible for how efficiently the via conducts heat as well. For example, a thicker layer will conduct the heat more efficiently.
Some thermal vias may be filled with conductive material to provide increased thermal flow or tented depending on whether solder paste is passing over them.
Unlike electrical vias, thermal vias do not route signals from one layer to another. They are typically situated beneath components that dissipate heat, such as power transistors, voltage regulators, or LEDs, where thermal vias will be used just to conduct the heat away from the device. Since there is no real concern about noise or maintaining signal integrity, designers are more flexible in using solid arrays of vias, which will give better thermal performance. That is the purpose of thermal vias. Thermal vias allow heat to flow from the hot surface to internal copper planes or heat sinks, which lowers the temperature at the source.
The thermal via is a bridge between a hot surface pad and the internal or bottom copper layers, which are heat spreaders. The copper layers spread and dissipate heat, thereby avoiding high temperature buildup in the component.
On a 2-layer PCB, thermal vias may be interfaced to a bottom-side copper pour. In multi-layer boards, they may be interfaced with several internal layers so heat can spread more effectively through the stack of the PCB. Thermal pads or heat sinks may also be affixed over the copper area interfaced to the vias on certain designs to provide for increased dissipation.
With the use of copper's high thermal conductivity (~400 W/m·K), thermal vias minimize thermal resistance between the component and heat-spreading layers. This keeps the operating temperatures stable, prevents thermal failure, and improves circuit reliability overall.
Thermal vias, in short, provide a simple, passive, and effective way to manage heat in high-power PCB designs without adding complexity to electrical routing, yet are essential to thermal performance.
Thermal vias are flexible and can be applied to anything from basic two-layer boards to intricate multilayer HDI PCBs. The size, number, and pattern of vias can be scaled based on the cooling and power needs of the device.
These vias can be produced using regular PCB manufacturing processes. They could be left open, tented with solder mask, or filled with epoxy or metal for enhanced performance. This makes it possible for designers to customize the vias to functional and manufacturing requirements.
Thermal vias are usually between 0.3 mm and 0.5 mm in diameter. They improve their thermal performance when they are densely populated, particularly under surface-mount component thermal pads. Increased via density enhances the effective thermal conductivity of the path.
Thermal vias present a passive cooling solution with no extra components needed, so they are economical. They're perfect for small designs where active cooling (such as fans or heavy heat sinks) is impossible. Simple as they are, they are crucial in the long-term performance and reliability of high-power electronics.
Power and performance, unfortunately, tend to come in concert with heat in today's electronics. With PCBs populated by quicker processors, energy-intensive LEDs, and densely packed voltage regulators, the outcome is straightforward: more heat in a smaller space. And when that heat isn't dissipated correctly, it begins to create serious issues.
Excessive heat is a quiet killer. It seeps in and begins to cause problems that will not necessarily be apparent at first, but eventually, they result in deterioration and breakdown. When parts run hotter than their design temperatures, the internal materials start to degrade more quickly. Integrated circuits, for instance, can incur permanent damage if their junction temperature rises beyond safe tolerances. Heat also raises electrical resistance in copper traces, lowering the efficiency of a circuit and distorting signal integrity in high-speed designs.
It's not only the components that are at stake. Solder joints, the same joints that keep components secure, are susceptible to heat, too. When a board is repeatedly heated and cooled (known as thermal cycling), the solder contracts and expands. This causes fatigue and cracking over time, particularly beneath components that produce a great deal of heat. Cracking joints equates to an unreliable connection, which can lead to everything from flickering LEDs to a dead board entirely.
PCBs consist of materials such as FR4 that have only so much ability to endure heat. Prolonged heat exposure weakens the core of the board, destroys insulation between layers, and even causes delamination (peeling away of the layers). High power usage is a serious reliability issue in these cases. If the base material deteriorates, the entire board can fail despite all the components remaining intact.
For power electronics, automotive control, and industrial system engineers, good thermal management is not a nice-to-have; it's a requirement. When the PCB is being designed, the heat needs to be thought through so it can be allowed to escape. Without thermal vias and other methods to spread the heat, you're left with the risk of premature failure of your component, increased maintenance, or a recall of the product altogether.
No matter what the event, the ultimate goal of a PCB design is reliability; the secret to reliability is in thermal management. This could be adding copper, component placement, or effectively utilizing thermal vias; the more ways that you can manage heat, the more you can increase your product's life cycle and performance.
Don't forget, you can't visualize heat, but if you don't pay attention to it, your design won't last long.
Thermal vias are an important aspect of high-power PCB design, and they form a low-resistance path for heat to travel away from the hot components. Below is how they work in detail:
Thermal vias are normally located underneath or near heat-dissipating components such as MOSFETs, power ICs, and LEDs. They conduct heat from the surface layer where these components are soldered or mounted down through the PCB to inner copper planes or a bottom-side heatsink. Vertical heat flow aids in keeping safe operating temperatures on the surface.
Each via is copper-plated, which is a good conductor of heat. When thermal energy builds up in the component pad, it migrates through the copper walls of the via and is distributed into larger copper areas beneath. These are heat sinks, which spread the energy across the board.
Thermal via effectiveness relies on:
Number and density of vias: The more vias, the quicker the heat transfer.
Thickness of copper plating: Thicker walls are better conductors.
Daisy chaining of copper pours or thermal pads: Proper contact is critical for effective heat spreading.
Thermal vias act as miniature heat channels, quietly doing their job of cooling high-power devices, making them efficient and long-lived.
Type |
Description |
Use Case |
Open Vias |
Simple through-hole via, left unfilled |
General purpose, easy fabrication |
Tented Vias |
Covered with solder mask |
Prevents solder wicking in the reflow process |
Filled Vias |
Filled with conductive/non-conductive epoxy |
Improves thermal and mechanical strength |
Via-in-Pad |
Placed directly under the component pad |
Best for high-density, high-power areas |
Thermal vias play a crucial role in power-dissipating circuits such as DC-DC converters, motor drivers, and power amplifiers. All these applications dissipate considerable heat, particularly near power MOSFETs and regulators. Vias facilitate this heat transfer to internal copper planes or bottom-side heat sinks to ensure stability.
High-brightness LEDs can quickly overheat unless well-cooled. Excess heat is directed into metal-core PCBs (MCPCBs) or external heat sinks through thermal vias located under the LED pads, slowing lumen degradation and extending LED lifespan.
Where there are severe environments and higher ambient temperatures, such as in automotive ECUs or aerospace control units, operational safety and prevention of thermal failure of essential systems are ensured by thermal vias.
Small devices like laptops, mobile phones, and game consoles employ thermal vias for silent, passive cooling. Thinner designs are enabled without large fans or external heat sinks.
The reliance on the proficiency of thermal management is increasing as electronic systems advance further. It is safe to estimate that as power densities increase and device sizes decrease, conventional cooling schemes become less and less effective. As such, thermal vias are a smaller, reliable, and effective way of dissipating heat from key components to retain a stable, well-functioning system over a long period.
From power electronics and LED lighting to space and consumer devices, thermal vias are integral to prolonging product life and ensuring reliability in extreme or thermally abusive environments. The fact that they can quietly and passively dissipate heat without contributing to size makes them a precious commodity in today's PCB design.
In the future, the smart placement and optimization of thermal vias will be a determining aspect in obtaining high-performance electronics. Engineers who can think intelligently about how to strategically integrate these features will have a clear edge in creating strong, thermally efficient, and long-lasting products for the future.