The through hole technology is crucial in printed circuit board designs. These holes offer connections between components and conductors on various board layers. The through hole technology gained popularity during the construction of the second-generation computers. Through hole can b e plated or non-plated. Both plated through hole and non plated through hole both refer to drilled hole on a board.
Plated through hole vs non-plated through hole seem like a straightforward and simple topic to discuss. However, there are some important details you need to know about these two different technologies. Therefore, some clarity would help you understand how these technologies operate, their similarities and differences.
Plated through holes have metal layer coating in their inside. These holes connect various layers on the circuit board. Basically, plated through holes are integrated for cases where components need a perfect electrical connection like connectors, switches, and ICs. Electroplating creates the plated through holes. The electroplating process involves the use of chemical to create plated through holes.
Non-plated through holes don’t feature any metal coating on their inside. These holes also connect various layers of the printed circuit board. However, they don’t offer a perfect electrical connection. Non-plated through holes are ideal for components that doesn’t need a high level of electrical reliability. They are ideal for passive components like capacitors and resistors. A mechanical drilling process is used in creating these holes in a board.
What is a Plated Through Hole?
A plated through hole is a hole drilled inside with conductive metal. The technician attaches a circular pad on the hole’s top and underside during a through hole assembly. The circular pad creates a connection between the hole and the circuit board’s traces. The inside of the hole which links the pads plated with a conductive metal links the two sides.
Plated through holes enable the flow of current through components on the side of the PCB, via the PCB’s non-conductive substrate, and to the other side of the board. Also, plated through holes ensure that circuit boards hold components firmly on the two sides. With this, designers can maximize the space they have more efficiently.
A circuit board will need to be bigger if it will be accommodating more components. Circuit boards used in large machine or device will need a bigger size circuit. However, smaller devices integrate smaller printed circuits. The integration of plated through hole requires you to vertically stack the circuit boards. Hence, thus helps to minimize the overall size of the circuit board. This allows the circuit to accommodate more components.
Plated through hole is designed in such a way that it goes through a circuit board entirely. Some PCB designs integrate heat sinks to suck heat from components and discharge to conductive layers. Designers have to make use of vias instead of PTH in order to access the inner layers without the need to go through. While PTH goes through the circuit entirely, vias only go through one surface. Vias create connection between the top layer and inner layer. When using vias, designers don’t need to breach the other side of the circuit board. A hole is considered through hole when it goes entirely through the board.
Importance of Plated Through Hole
PCB manufacturers plate through holes to enable components to connect with the conductive layers. Plated through holes offer exceptional electrical conductivity and desired functionality in a circuit board. There are several benefits of plated through holes. A few of these benefits includes faster prototyping. PTH makes it easy for manufacturers to solder components on the circuit board.
Furthermore, plated through holes, guarantees manufacturers high power tolerances and component durability. These holes help in achieving excellent connections. Plated through hole is highly preferred among PCB manufacturers because of the benefits it offers.
What are Non-plated Through Holes?
The major difference between these holes is that the inside of non-plated through holes doesn’t have conductive plating. This means that the inside of these holes don’t feature any conductive plating. A non-plated through hole (NPTH) can’t allow the flow of current through it. Therefore, this hole doesn’t offer the same function as a plated through hole. The design specification of a board will determine if a plated through hole or a non plated through hole is required.
A non plated hole may have pads on any side in some scenarios. However, this doesn’t mean there is a connection. Designers use pads for placing NPTH while some don’t use them at all. In fact, the majority of non-plated through holes don’t use pads. Regardless of the method of through hole assembly, it is crucial for designers to define n NPTH. Mistaking an NPTH for a PTH can result in problems. Issues can arise in the PCB’s pathing.
If a PTH is placed where an NPTH is required, this will make the charge to spread and as such, weakening the charge. This might as well cause bridging those results in short circuits. A non-plated through hole offers a channel where screws or bolts can secure the circuit board. In some scenarios, pins or wires go through this hole.
Plated Through Hole Process
Circuit boards have different sizes of holes for vias. Also, these boards feature different through-hole component pins. Here, we will be taking a look at the process of plating a through hole in a circuit board during fabrication.
- Plating commences after pressure and heat has composited the circuit board and all the through holes are drilled.
- The technician cleans the through holes in order to remove any residue. Debris can leave a residual resin in the holes or there might be other contaminants. Therefore, abrasive processes and chemical agents are used for cleaning.
- A copper layer is chemically coated on the surface of the circuit board and via the holes. The deposition of Electroless copper offers a strong base in the holes for the copper plating.
- The PCB fabricator can micro-etch the inside of the holes. This helps in improving the base for the copper to hold during plating.
- On the external layers, a circuitry is created. This is done through the exposure of an image on a photoresist. The inner layer also uses this same process, except that a reversed image is integrated.
- Chemical is used in removing the unexposed material and as such, this reveals the copper circuitry while a hardened resist protects the remaining part of the board.
- Copper is used in plating the exposed copper circuitry in order to increase the metal weight. After this, the plated through hole is achieved.
Challenges of Plated Through Holes
There are challenges associated with plated through holes. Let’s consider these challenges and possible solutions to them.
Lack of copper in PTH
Lack of enough copper in plated through holes is a big challenge. If the copper isn’t adequate in the PTH, there will be plating voids. These voids can affect the flow of current. This problem can be solved by ensuring there is adequate copper in the PTH. Also, ensure the copper isn’t too much as this may block the plated through holes.
Furthermore, too much acceleration may cause little copper in the plated hole. You need to reduce the accelerated treatment conditions.
Plughole
Plughole is crucial for functioning of a printed circuit board. It prevents a board from short circuits and flux residue from reaching the vias. When plugholes are not properly done, the whole PTH circuit board can damage. Copper may not liquidate well if copper particles remain in the plated through hole cylinder. Therefore, it is necessary to check the filtering system for any fault to prevent such.
Lamination and blistering on a board
Lamination and blistering on a printed circuit is a major concern for PCB manufacturers. Blistering happens due to a chemical reaction of copper and the copper base. You can avoid this problem by maintaining cleanliness in your work. Furthermore, select a conformal coating that is appropriate with your board. Match the conformal coating to the solder of the circuit board to achieve good bonding.
There are other reasons blistering and lamination on a circuit board will occur. The inability to get rid of oil stains and adhesive can result in lamination on the circuit board. You can solve this problem by pressing and drilling. This will assist you in getting rid of oil stains and adhesive.
Considerations for Through-hole Parts Design
In the past, through hole parts were the components available for PCB layout. Things have different presently with the presence of surface mount parts. The SMT parts are popularly integrated when in printed circuit board design. These parts have a lot of benefits. They are much better than their large through hole counterparts. SMT parts offer improved signal performance, take less space on a circuit board, and greater availability. Also, these parts are cost-efficient, they are cheaper than through hole parts.
However, all these benefits offered by SMT parts doesn’t mean through hole parts aren’t useful in some cases too. Through hole components are still being used in some cases. Below are considerations for through hole parts design
Power
It can be very complex to appropriately solder large SMT parts since a larger amount of metal needs to go through heat. Also, large through-hole connection ensures thermal and mechanical stability which is beneficial to power components.
Strength
The mounting of robust through hole pins is beneficial to interfacing parts like switches and connectors. Furthermore, you can rip off SMT connectors from their pads if their mating connector is unplugged with the use of force.
Heat
Plated through hole pin is better for high-temperature parts as it offers better conductor. The majority of these parts will be bolted to the PCB.
Design Guidelines for Through Hole
Regardless of the popularity of SMT components, through hole components will still be in use for a while, therefore, it is important to take note of some design guidelines.
A wave soldering system is often used to assemble through-hole components on the printed circuit board. Wave soldering involves passing the circuit board over a molten solder which is forced in the holes. Also, the molten wave of solder is force around the component leads to offer strong solder joint.
It isn’t ideal to place SMT parts on the back of the PCB during this process. The PCB assembler needs to block off SMT parts from the wave. Alternatively, you can solder the through hole parts manually. Manual soldering is another soldering option aside from wave soldering. It is crucial to ask the manufacturer about parts placement to prevent any assembly issues.
Footprints
Ensure you go with the footprint dimensions recommended by your part manufacturer. This helps in ensuring the circuit board is easily assembled. While some components such as through hole resistors can make use of differently spaded holes, most components can’t.
Spacing
Spacing is crucial when soldering the through hole parts. When you space components properly, this enhances automated soldering systems. Sometimes, larger through-hole parts can overshadow SMT parts and as such, preventing them form being soldered properly. Therefore, allowing enough space between parts is important for manual rework.
Hole size
Ensure you use the hole size recommended for the part’s lead diameter. Very large through holes won’t accommodate the molten solder. Therefore, this would eventually lead to poor solder joint. Also, too small holes won’t allow you to insert the lead of the part.
Plated Through Hole Vs Non Plated Through Hole – What is the difference?
A lot of issues arise during the PCB design process. One of such is the possible problem from PTH and NPTH. It is necessary to comprehend the differences found between these through hole technologies in order to achieve a functional circuit board. Knowing the difference between these two will help you know the function they serve and the right applications for each of the technologies.
The significant difference between NPTH and PTH is the plated copper in the base material of the PCB. A plated through holes features a conductive material known as copper inside. The presence of this conductive material has an effect on mechanical stability and electrical performance.
When the PCB manufacturer solders component leads via plated holes, there is improved mechanical stability and the electrical resistance becomes less. However, this is different for non plated through holes. Therefore, PTH offers more benefit than NPTH.
Another difference between PTH and NPTH is in terms of area and cost. It is more expensive to design plated through holes circuit boards. Plated through holes take less space compared to non-plated through holes.
In terms of applications, plated through holes are integrated for cases where components need a perfect electrical connection like connectors, switches, and ICs. Non-plated through holes are ideal for components that doesn’t need a high level of electrical reliability. They are ideal for passive components like capacitors and resistors. Also, these holes don’t offer a perfect electrical connection.
A plated through hole is designed in such a way that it goes through a circuit board entirely. A non-plated through hole offers a channel where screws or bolts can secure the circuit board.
How to Reduce the Cost of Through Hole PCB
The cost of a through hole circuit board will depend on factors like hole density, annular rings, and how the holes are designed. With careful consideration, you can easily reduce the cost of the through hole circuit. Below are some ways to reduce the cost of your through hole board.
Use larger holes
You can make use of larger holes and annular rings if possible. This is because small holes are more expensive to drill. The manufacturing of small holes requires the use of high precision machines. Since these machines are very expensive, some PCB manufacturers charge more for holes diameter that ranges between 0.15mm and 0.33mm. Therefore, you have to make enquiry from your manufacturer to know the additional charges for small holes.
Large annular rings
Annular rings refer to the border of the hole and the minimum distance of the pad. Minimum annual ring determines the cost of through hole boards. If your manufacturer’s standard requirements are more than the minimum annular ring, the board will cost more. Integrating larger annular rings is a way to save cost.
Benefits of Through Hole Technology
Before the advent of surface mount technology, the through hole technology was the popular method of mounting electronic components on boards. Regardless of some limitations of through hole technology, it offers its own benefits.
Through hole components offer better reliability in products that need stronger connections between layers. The leads of these components can tolerate environmental stress since these leads can run via the board while the solder of the PCB surface secure SMT components. Due to this advantage, through hole technology is a suitable option for printed circuit boards used in military and aerospace devices. These devices are usually exposed to extreme accelerations, collisions, and high temperatures and as such, their circuit boards need stronger connections.
Furthermore, through hole technology is widely integrated in applications that need prototyping and testing due to its adjustment capabilities and manual replacement. Through hole PCBs are more expensive due to their capability to offer stronger boards. This is why THT is now commonly reserved for bulkier or heavier components like electrolytic capacitors or semiconductors used in bigger packages.
Also, through hole technology is widely integrated for elements such as plug connectors that require reinforcement. THT is highly preferred among designers and manufacturers for prototyping. This is because through hole is ideal for use in breadboard sockets. However, THT isn’t ideal for high-speed or high-frequency boards that need low inductance and stray capacitance in wire leads. Also, through hole isn’t a good option for very compact designs.
Plated Through Hole Decomposition Process
Alkaline cleaning
Alkaline cleaning involves removing the board oil and fingerprinting. After this, you can dust the hole carefully. The negative charge will need adjustment for the entire wall. This helps the colloid palladium to absorb. During this period, be sure you maintain cleaning.
Micro etching
This involves removing the oxide on the circuit board and roughening it. Micro etching is crucial as it helps to ensure strong bonding between the PTH layer and the base copper. You need to understand that the new copper is active and performs well in the absorption of colloid palladium.
This step protects the palladium slot. Prepreg helps in extending a circuit’s shelf life. The main ingredients in this step is similar to the palladium slot. Prepreg is crucial for wetting the hole wall. The layers of the board won’t hold without, therefore, prepreg helps to fuse etched cores.
Activation
This is an essential step in the plated through hole. There is a positive charge on the hole wall which helps in the absorption of the colloidal palladium particle. Negative control helps in achieving this. With this, plated through hole becomes compact. Activation plays a significant role in ensuring the copper sinks’ quality.
Decontamination
The colloidal palladium particle comprises stannous ion. The decontamination process helps to get rid of the stannous ion. This helps to expose the palladium nucleus. Fluoroboric acid is the most suitable chemical to use for this process. Most manufacturers use this acid because of its debonding capability. Although there are other chemicals to use, the fluoroboric acid seems to perform better than others.
Conclusion
Plated through hole and non plated through hole have their benefits and limitations. While plated through hole is commonly integrated by most PCB manufacturers, some manufacturers still use non-plated through hole. When discussing plated through hole vs non plated through hole, we realized there are notable differences between these holes.
The path difference between these holes differentiates them. The vast applicability of plated through hole makes it relevant in today’s PCB manufacturing. Non plated hole is not as applicable as plated through hole as it is only suitable for single layer PCBs. The relevance of these holes is another factor that differentiates them.
