Plating Learn to use Castellated Holes Reasonably in PCB Production

Castellated holes are becoming more and more common, especially with the rapid development of the high-tech industry. Designers in the PCB industry need to get a good understanding of everything to do with castellated holes. So, what’s the importance of castellated holes? How do you go about designing them?

This article introduces the importance of castellated holes. It highlights how to use them in PCB production. At the end of the article, you’ll get an in-depth understanding of castellated holes. You’ll understand how to go about these holes quickly and accurately. Read on for a better understanding of how to use castellated holes reasonably in PCB production.

1. What are castellated holes?

1.1 Introduction

Castellated holes are indentations whose creation is in the form of semi-plated spots. Mostly, you’ll find these plated holes on the edges of printed circuit boards. Based on the application, these holes may differ in appearance. As opposed to the standard half holes, some may appear like a large or small portion of a circle that’s broken.

The half holes do serve as pads with an obvious intention. The intention is to create good connections between the module board and another board; that’s the board where the soldering will occur. As mentioned earlier, castellated holes are increasingly becoming popular.

1.2 How are castellated holes formed?

Creating or instead of forming castellated holes is not a complicated process as such. It’s a straightforward process than you may imagine. The creation of these holes is through a normal via the method. It includes drilling and copper plating full holes in the PCB, which involves cutting the top spot in half. These will form partial or half holes on the edge of the PCB.

(A close pic of castellated holes on a PCB)

2. Why do We use Castellated Holes?

We use castellated holes for a whole lot of different reasons. Mostly, designers use them to create printed circuit board modules. Examples of these PCB modules include Bluetooth and Wi-Fi modules. We also use castellated holes in combining two boards. Castellated holes bring about excellent wireless PCB-to-PCB links.

Advantages of using castellated holes

Without a doubt, castellated holes come with their advantages worth noting. They are the new thing, especially in the world of PCBs. The following are some of the merits of using castellated holes:

Easily change the pin layout of components.

Castellated holes are advantageous when it comes to changing the pin layout. These holes give designers an easy time when they want to change the pin layout. Sometimes, users may have different pin layout requirements. With castellated holes, it’s relatively easy to change the pin layout.

Verify solder joint quality

Designers use castellated holes to combine two boards. When it comes to solder joint quality, castellated holes play an important role here. They are helpful as they help in validating the quality of the solder joint.

For small modules such as patch panels or Wi-Fi modules

Castellated holes are also helpful, especially for breakout boards and small modules such as Wi-Fi modules.

Create wireless PCB-to-PCB link

If there’s anything good about castellated holes, then it’s the fact that they foster wireless PCB-to-PCB links. Wireless links increase efficiency, flexibility, and bring about cost savings.

Further use in another component

Castellated holes are also advantageous as designers can use them in another component. PCBs that have castellated holes can easily mount to another PCB during production. The ease of mounting is another significant advantage that comes with castellated holes.

Easy installation

The ease of installation is an excellent reason to use castellated holes. Installing such holes on a PCB isn’t a complicated process as such. Unlike other types of holes, it’s easy to install castellated fixes.

2.2 PCB with teeth-the breakout board of the part.

Breakout boards take a single electrical component and then make it easy to use. Mostly, the electrical part here is an integrated circuit (IC). As you may know, IC does have pins on them. PCBs with teeth find heavy use as breakout boards. Better yet, they have their advantages as briefly highlighted below:

Make the IC reusable.

Printed circuit boards with teeth make the ICs reusable. The pins on the breakout are slightly heavy duty. Designers manufacture them with a design for re-use at the back of their minds.

Complex components that simplify assembly (such as high pin density) or leadless components

PCBs that contain castellated holes simplify matters to do with assembly. While they may seem or appear complex, the assembly process is relatively easy.

Force reorganization of component pin layout

The reorganization of the component pin layout is another advantage. Printed circuit boards with teeth have castellated holes in them. These holes make it easy when it comes to the reorganization of the component pin layout.

(A picture of PCB holes)

3. How to Design Castellated Holes

Designing castellated holes is not a complicated process, as you may imagine. However, when done wrong, you may end up affecting the functionality of your PCB. The following is what you need to know when designing castellated holes:

Half Holes

A half hole is a plated half hole with a half on the edge of the board. There are several steps to follow to design them.

Drilling PTH is the first step, followed by panel plating. After that, image transfer follows. Pattern plating is the fifth step, followed by striping then etching. The application of some solder mask then the surface coating follows. The final process involves plating the half holes.

Holes with Smaller cut-in Half Holes

Holes with Smaller cut-in Half Holes require modern small drills. The drills need to be slightly smaller than what those meant for half castellated holes. These holes sit on the periphery of the larger dilled castellated holes.

Holes with smaller lead-in holes for post-processing

Holes with smaller lead-in holes for post-processing find use in connector applications. Their design requires a post-processing cutting tool. The tool produces smaller castellated holes here needed.

The minimum diameter of the cast hole

The minimum diameter of the castellated hole should be 1.0 mm or 0.04 inches. When designing castellated holes, you need to be mindful of the minimum diameter. The recommended diameter is 1.0 mm.

Always use the top and bottom edge as the location of the hole.

Always use the top and bottom edge as the location of the hole. Make sure that you don’t use the vertical edges (right and left). The reason for this is that they mostly act as bridges—these bridges the PCB in place.

Place the center point of each toothed hole accurately on the edge/board outline of the PCB. Again, you need to ensure that the holes are PTH (plated-though holes). These holes have to be in the drills-layer for the best results.

(Inspector checking the design of castellated holes PCB)

4. PCB Manufacturing Process for Electroplating Half Holes

The manufacture of a conventional castellation hole is a simple step. Designers begin with drilling, followed by the application of chemical copper, and then panel plating. Later on, image transfer follows, followed by pattern plating, and then stripping the film. Etching, solder mask printing, and surface finishing soon follow. The final process is hole castellation and outline milling.

However, the above steps lead to a decrease in the performance and yield of the entire product. Today, the formation of castellated holes is somewhat different. While it doesn’t drift far away from the traditional method, it’s slightly different.

The formation of castellated holes begins with drilling the substrate plate edge. Here, specialized drilling equipment is a necessity. Without special drilling equipment, everything else that follows might go wrong. After preparing, plating through the hole then follows. Plating is of high importance; the scale ensures a copper layer on the hole wall. The copper layer brings about the excellent conductivity of a board’s components.

Panel plating is the third step.

Panel plating gives room for even copper distribution on the panel. After the completion of panel plating, image transfer follows. Image transfer is the transfer of the conductor pattern. The transfer of the way is from the film master to the copper-clad base material. After that, pattern plating follows. Pattern plating is masking off a majority of copper surfaces. It’s all about plating only the pads and traces of the circuit pattern.

Striping is the sixth step of PCB manufacturing for electroplating half holes. Etching soon follows stripping. Etching of the substrate to eliminate exposed copper is the seventh step; the solder-mask application comes after the etching process. The application of a solder-mask is to shield the PCB from oxidation.

Surface coating follows solder masking. The surface coating shields the exposed copper circuitry. It also provides a solderable surface during the assembly of PCB components. Plating half a hole in the last step. Plating the half holes allows for the desired electrical flow through the entire board.

(A close image of PCB holes)

5. Stacking Conditions of Castellated Holes

When it comes to PCBs, you may often hear of PCB stack-up. But what does it mean? PCB stack-up is the arrangement of insulating and copper layers that make up a PCB. The stack-up you choose plays a significant role in the performance of aboard.

Castellated holes play a significant role when it comes to stacking up PCBs. The easiest way to manufacture PCBs meant to stay on top of the other is easy. Such is achievable through the creation of castellated mounting holes. They ensure that printed circuit board stack-up is excellent.

Without castellated holes, PCB stack-up may not come out as intended. Of importance to note is that some methods should be feasible for PCB stack-up. If PCB stack-up should go as planned, some conditions are a requirement.

First, there should be no gaps or spacing between the two printed circuit boards. If there are spaces between the two PCBs, it would be hard to meet the stacking conditions. Secondly, electrical contacts are required. Electrical connections are necessary, not just physical attachment. Third and last, you have to assume something. You’ll have to think that the upper PCB is about a third of the bottom PCB size.

The above are some of the methods you have to meet if PCB stacking remains a strong possibility. Those are the stacking conditions of castellated holes.

(Stacked PCBs)

6. How to Display More Castellated Holes Information in the File

Half hole designs aren’t the same. If you happen to be keen enough, you’ll notice that they vary. They vary from software to software. However, the result in Gerber files needs to be as follows. You need to add plated or via hole directly on the outline of the PCB boards. It is where the plated half holes are a necessity. Still, you need to ensure that half of your via is on the board with the other half being on the outline.

To display more castellated holes information in the file, you need to include the following:

Copper layer (GTL and GBL):

It displays information on copper pads. The information here is the number of copper pads on both the bottom and top layers for every half hole. Manufacturers must ensure that this information is present in the file. Such information makes it easier for buyers to find what they want. Each half hole on a PCB contains copper pads. It should then be easy to find such information with ease. The easiest way to do so is by displaying or showing information on copper layers.

Solder mask (GTS and GBS):

Solder masks or solder resist is a skinny lacquer-like layer made of polymer. Manufacturers apply solder mask to copper traces of printed circuit boards. The primary function of the solder mask is to shield copper traces from oxidation. It also prevents the occurrence of solder bridges. Solder bridges typically occur between pads that sit close to each other. When it comes to solder masks, information on solder mask openings should be there.

Most importantly, you must include the information on solder mask openings on both sides of a PCB. Solder mask openings are those places on a board that lack a solder mask. Again, such information is necessary, especially for those who’d need to use these PCBs. Manufacturers must provide such information during the manufacture of their boards.

Drilling layer (TXT / DRL):

It is the drill hole information/data for every half-hole. The data of the half-hole must come with drill hole information of the holes. What’s the diameter of the half holes? Such information must be there. The diameter and size of the half-hole should be there, both in inches and in millimeters. If your standard minimum diameter of the half hole is 0.55 mm, then you should indicate that information in the file. It makes it easy for users to find PCBs with half-holes consisting of the diameter they need.

Mechanical/contour layer (GML/GKO)

The contour needs to pass through the drilled hole and nothing less than that. When displaying castellated holes information, don’t forget to include the information on the contour layer. The contour must pass through the drill holes. Before releasing PCBs to the market, the provision of such information is necessary.

It appears as is half-holes in the manufacture of PCBs is a simple process. Many people think that it only involves drilling, followed by plating and routing. However, it calls for attention to detail coupled with careful production planning. For this reason, it’s imperative to work with a professional PCB maker for the best results.

(A well-drilled castellated hole)

7. Specification of Castellated Holes

When designing castellated holes, there are some design attributes to follow. Failure to comply with design attributes may end up being futile. It could affect the functionality of the board in totality. The following are what manufacturers need to follow.

Compliance with design attributes

When designing a castellated hole, compliance is necessary. Manufacturers need to comply with all the design attributes. That way, they’ll be able to manufacture boards that meet market expectations. If they happen to skip some steps, then the problem awaits them. Compliance is imperative. If there are steps, you need to follow them. Is there any necessary equipment to use? Don’t ignore them. Compliance is a significant specification when designing castellated holes. It’s as simple as that.

Size

Besides compliance with design attributes, size also matters. According to industry standards, it’s advisable to use the largest sizes. Do you have a chance to use the largest possible size? If so, then use it. But why does size matter? The size of the feature allows the use of any surface finish.

Surface finish

A surface finish is necessary for the design of a castellated hole. When designing castellated holes, surface finishing is essential. Manufacturers use surface finishes for two fundamental reasons: to ensure perfect solderability and protect the exposed copper. Of importance to note is that the surface finish that you use varies. Mostly, it depends on the intended use of your boards. The most recommended finis is ENIG. There are several types of finishes besides ENIG. Others include HASL and OSP, to mention but a few.

Pad Design

Pad design is another design attribute that you need to follow. It is advisable to use the most massive possible pad. It should be both on top and on the bottom of the place. By going for the largest possible residence, rest assured the best-castellated holes. Large pads give you room to drill holes with a lot of ease and precision. For the best results, consider using the most considerable places.

Number of Holes

Mostly, the number of holes depends on the design. Again, it’s advisable to go for the maximum number of spots. Many holes make things relatively easy for assembly. The optimum number of holes ensures easy alignment. Many holes provide that the assembly process isn’t complicated. It will be easy to see where each component will fit. Therefore, for an easy assembly process, many holes matter. The lesser the number of holes, the more difficult the PCBA assembly process will be.

ISO9001, UL, RoHS certification

Certifications matter during the design of castellated holes. Do they follow ISO9001, UL, and RoHS certification standards? Certificates are necessary here. Failure to follow certifications may see you producing faulty boards. For instance, RoHS certification calls for the best disposal methods of waste products. The castellated hole must follow UL and ISO9001 standards. They must meet criteria such as outer layer copper thickness and the minimum diameter of plated half holes.

(Castellated holes on a green PCB)

8. Application of Castellated Hole

Castellated holes on printed circuit boards find use in a wide range of industries.

They find use in computer application, telecommunication, power, and high-end consumer electronics, just to mention but a few.

Castellated holes find use as breakout boards in PCBs.

Castellated hole also combine two PCBs to validate the quality of the solder joint. Better yet, it’s easy to mount PCBs with castellated holes to another PCB in the final production. Castellated holes also help in the creation of wireless PCB-to-PCB links.

As you can see, castellated holes find use in many industries such as computer applications, telecommunications, and high-end consumer electronics. They also find use in automobiles, industrial control, and power, to mention but a few.

(A batch of ready-to-use PCBs)

Summary

Castellated holes are essential. They find heavy use in computer applications, automobiles, industrial control, and telecommunications. Do you have any castellated holes projects? Do you want to learn how to use castellated hole technology better in PCB production?

We understand the stacking conditions and the manufacturing process of half holes. Our products meet ISO9001, RoHS, and UL standards. Are you in need of a high-quality castellated hole in your design? Let us assist you. With us, you’ll find nothing but the best-castellated holes in your system. At a suitable time, feel free to contact us to discuss more in regards to PCB technology.