Castellated Circuit board fabrication (Uses, and Design Guide)

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

Written by Sam Sangani

Sam Sangani is the President & CEO of PNC Inc., a Nutley, NJ based Printed Circuit Board manufacturer. Sam graduated from L. D. Engineering College with a BS Degree in Mechanical Engineering. He also continued his education and graduated from Steven’s Institute of Technology where he acquired a Master’s degree in Computer Science.

After completion of his BS, Sam worked as a QC Manager, for Xerox, Romania and London. He was responsible for the Quality Control of Cable and Wire Harness imports from Romania. After completing his Master’s Degree, he worked as a Senior Programmer with IBM, Tucson, Arizona. Sam was responsible for leading the Mainframe System Programming Team.

In 1997, Sam acquired PNC INC., a Nutley, NJ based PC Board fabrication Shop. From 1997-2013, Sam has made tremendous improvements and changes within PNC INC., as he added many new Products and Technologies in PNC’s portfolio. With his proven track record and leadership, PNC has never had an unprofitable year and has continued its growth yearly since 1997.

His current responsibilities are Strategic Planning, Corporate Management, New Business Ventures, Sales & Marketing, Trade Shows, Professional Services and leading productive teams to achieve peak potential. He has also utilized Lean Management techniques which have built a foundation for PNC’s high-paced growth. Sam also enjoys real-estate investing, web design & SEO, trading stocks, options, futures and Forex markets.