Designing a printed circuit board is a complicated process, especially if you need a multilayer PCB. Via plays an integral role when it comes to boards with multiple layers.
If you would like to know more about via filling, and the differences between conductive and non-conductive via fill PCB, you’ve come to the right place! Check out this article, and discover everything you need to know about via fill and its role in PCB design.
- What Is Via Filling?
- What Are the Benefits of a Via Fill PCB?
- What Is the Difference Between Via Plugging, Tenting, and Active Pad?
- Why Is Copper a Better Choice than Gold for a Via Fill PCB?
- Conductive Via Fill – Overview
- Non-Conductive Via Fill – Overview
- How to Choose Between Conductive VS. Non-Conductive Via Fill PCB
1、What Is Via Filling?
Vias are usually an integral part of PCB design, and there is a good reason for that. Their task is to ensure that signal transferring between the board layers functions properly. It means we can consider vias to be conduits.
Via is nothing else than a copper filled hole. In some cases, the manufacturers may decide to use other materials, but copper is most frequently used for this purpose. Now, you can use a via fill to connect two layers, but there are also designs where you can connect more.
The manufacturer will first ensure to make a through the hole, and then fill it with copper. It is vital for the assembler to ensure that the copper is equally distributed in the via. It is imperative to avoid making the outside layer too thick.
If you add an unnecessary amount of copper, it will make the board heavier than expected. Additionally, it will increase the price of the PCB while increasing the chances of defects occurring.
Since the overall PCB design is getting more compact-sized than ever, via holes, have also become exceptionally small. The manufacturers may face a challenge to ensure everything is done right in a small space, but a reliable company will do the job flawlessly.
2、What Are the Benefits of a Via Fill PCB?
If you are going to choose a via fill PCB design, you should know why that is a smart decision. Here are some crucial reasons why you would want to fill a via:
- Your surface mounts will be more reliable
- The chance of trapping liquids or air is lower, which increases reliability
- The assembly yields will be increased
Now, if we compare copper-filled via design with the one that involves copper plating, we can make some interesting conclusions.
For starters, the filling will enhance the thermal conductivity of the via. That can be vital for the longevity of the board, especially if you are planning to use it in an application that needs to withstand high temperatures.
Copper will use its properties to attract the heat, which means the other vital areas of the board will remain cool. The heat will only move from one copper on the board to the other. That will decrease the chances of a potential
defect happening in PCB's areas vital for its functioning.
It is also vital to mention that filling a via with copper also secures improved electrical conductivity. Thanks to that, you can use this approach if the desired use involves high current levels. A filled via can play a vital role in conducting current to all layers while preventing PCB overloading.
3、What Is the Difference Between Via Plugging, Tenting, and Active Pad?
You have three different options for handling the vias in your PCB structure. These include tenting, filling, and plugging.
Via tenting is the most affordable option, and it is also straightforward to install for the manufacturer. It won't increase the cost of your board as all you need to do is to identify the vias for tenting and eliminate mask clearances from them.
The process of tenting involves using a solder mask to cover via hole and annular ring. You do not have to take any particular actions to be sure the opening will stay closed. That means there is no guarantee the hole will remain covered. However, if you use small vias that have a diameter of no more than 12mil, the odds of them staying closed are growing.
As you can assume, closing the hole or opening isn't the primary priority of tenting. It is covering the annular ring that is the main task as it should ensure there is no element exposure, and decrease the risk of circuit contact or accidental shorting.
This process has several different names – we call it a mask-plugged via, but it is nothing else than a non-conductive fill. If you choose this approach, you will secure covering of the annual ring and plugging and sealing the via with a mask. The most frequent case of using a mask-plugged is noticeable in a BGA design. There, we can find vias placed close to the SMD pads of a BGA.
The disadvantage of via plugging may be noticeable during the assembly process. I may happen that solder detaches from the pad and go down, which may cause non-existent or weak solder joints.
We also know this process as via in pad, and we can see it more applications every day. It is a useful option in the time when we can notice that everyone tries to make BGA packages as tight as possible.
The manufacturers usually use a land pattern called a “dog bone” to ensure that via receives the signal from the BGA. Via can then pass this signal throughout different layers.
A via in pad changes the “dog bone” approach and allows the manufacturer to drill the vias directly into the BGA pads. You can solder straightly over the via, which ensures easier routing.
4、Why Is Copper a Better Choice than Gold for a Via Fill PCB?
We already established that copper is the most common choice for a via fill PCB. However, you will find some designers and applications that use silver conductive epoxy resin. When you compare the two materials, it may seem like the latter is a better choice.
However, there are valid reasons why copper is a better choice. In short, it performs better than gold. But instead of only making a claim, we will support it with the following facts:
• Copper has improved thermal and electrical conductivity compared to gold
• It should also ensure that the PCB lasts longer
• Copper has an impressive ratio between cost and effectiveness, which makes it an excellent value for money
• The boards that use copper for via fills have increased reliability
• Copper is the logical choice for applications that require high power
As you can see, the decision should be quite simple. Not only copper is more affordable, but you will also get better performance compared to gold. Regardless of your desired application, you should always go with copper. In a majority of cases, it will meet and exceed your expectations.
5、Conductive Via Fill – Overview
If you are wondering when a conductive via would be a good choice, you should consider your particular board application. If you have a plan that involves a high level of current or heat, and you want to find a way to carry it throughout the board, you can consider a conductive via fill.
A conductive fill is a smart pick if you are worried about overheating the board. The fill has metallic characteristics whose working process reminds of a radiator. That means it will attract the heat and naturally distribute it to the other board sections.
You should also consider a disadvantage of using a conductive via fill. It lies in how its thermal expansion coefficient (CTE) is different between the metallic fill and the laminate around it. Metal tends to expand quickly when heated, and laminate is slower in expanding. That may result in fracture defects, which is why you need to ensure that a conductive fill is a right fit for your application.
6、Non-Conductive Via Fill – Overview
If you speak the term non-conductive out loud, it may not sound like it even deserves consideration. You may think that a non-conductive via fill doesn't have any capability of getting an electrical signal to pass through the via. It is essential to mention that it is a misconception.
Even in cases of non-conductive fills, copper is still used to plate via barrels. The primary distinction of this approach is that you use a fill material instead of leaving a barrel with empty air. The objective of this technique is to keep contaminants, such as solder, from penetrating the via.
We already mentioned that mask plugged vias and non-conductive fills are the same thing, so don’t let that confuse you.
7、How to Choose Between Conductive VS. Non-Conductive Via Fill PCB
Finally, we will offer some factors you may consider when choosing between the two via fill PCB approaches:
• Consider your application – the best board design is the one that perfectly suits your use and application.
• Keep in mind the price – you want to get the highest value for money and a high-performing PCB, but the idea is not to overpay for a board.
• Aim to make the design as straightforward as possible – while a complicated design may be suitable in some cases; simple boards tend to be exceptionally reliable.
If you need advice on choosing the right via fill, don’t hesitate to contact WellPCB. This company has an experienced team ready to help you choose the perfect board for your application. The skilled staff will also ensure to take care of the assembly process and manufacture your boards in the shortest possible timeframe.
We hope that you now have the necessary information about via fill PCB design, and know how to choose between a conductive and non-conductive approach. If you are still unsure, the best thing you can do is to rely on an experienced manufacturer. They can help you to choose the smartest option for your application and maximize the reliability of your board while optimizing the cost!