A PCB capacitor, a two-terminal electrical component, is responsible for storing electric charges and facilitating the flow of alternating current (AC). Alongside resistors and inductors, capacitors form the core group of fundamental passive components found in a wide array of circuits. In terms of sheer quantity, capacitors are the second most prevalent components on a circuit board, following resistors.
Considering the significance of capacitors and their impact on circuit board functionality, it becomes evident that selecting the appropriate capacitor components is crucial for the success of a circuit design. Capacitors are one of the primary elements that can make or break a project. Therefore, the careful and meticulous selection of the right capacitors is vital to ensure the triumph of a circuit design.
This article aims to outline the various types of capacitors commonly integrated into PCBs, offer a comprehensive guide on selecting the suitable capacitor for your project, and emphasize the imperative aspect of handling capacitors safely. If you are seeking detailed information about PCB capacitors for your electronics project, this article provides valuable insights.
What is a PCB capacitor?
A PCB capacitor is an electronic component specifically designed for use in printed circuit boards. These capacitors consist of two conductive plates separated by an insulating material called the dielectric. To connect to the power source, the plates are linked with wires.
The capacitance value of a PCB capacitor depends on the size of the plates and the type of dielectric material employed. The unit of measurement for capacitance is Farads (F).
While there are different types of PCB capacitors available today, they all share a common purpose: to store an electric charge and discharge it when necessary. This functionality allows them to be utilized as filters or regulators, ensuring the stability of electrical signals during power surges.
Materials Used in PCB Capacitors
In the construction of PCB capacitors, two foil plates are utilized, which are separated by a dielectric material. These foil plates are commonly referred to as “plates” or “electrodes,” while the dielectric material is known as the “dielectric.”
Typically, aluminium or copper foil is employed for manufacturing the plates in PCB capacitors, although alternative materials may be utilized to enhance performance. The thickness of the plates can vary based on the manufacturer and the intended application. Capacitors with thicker plates will exhibit higher capacitance values, whereas those with thinner plates will yield lower ones. This thickness variation plays a significant role in determining the overall characteristics and performance of the PCB capacitors.
How Does PCB Capacitor Work?
Capacitors are widely recognized as passive components commonly present in circuits, akin to resistors. Their primary function is to store electrical charge, allowing for various options depending on circuit design. Capacitance, measured in Farads, quantifies the energy or charge capacity of a capacitor.
At its fundamental form, a capacitor consists of two plates separated by an insulating dielectric. Different types of capacitors exist, distinguished by their composition of various dielectric materials, each serving specific purposes.
Given that the Farad unit is relatively large, capacitance is typically expressed in microfarads (µF) or picofarads (pF). Capacitors can be either non-electrolytic or electrolytic. Non-electrolytic capacitors can be connected in any direction within a circuit, while electrolytic capacitors must be installed with correct polarity—specifically, one lead being positive and the other negative. Incorrect placement of electrolytic capacitors can adversely affect circuit performance or even cause damage.
Capacitors find a multitude of applications, with a critical role in digital electronics being to safeguard microchips from noise interference. Additionally, capacitors are employed in lasers, flashes, capacitive sensing, and other circuit devices due to their ability to rapidly discharge stored charge. Circuits incorporating capacitors exhibit frequency-dependent behavior, making them suitable for frequency-dependent signal amplification.
Similar to resistors, capacitors can be connected in parallel or series configurations. However, the calculations involved differ. Series connection shares a common node, while parallel connection requires both nodes to be shared. To determine the total resistance in a series connection, the individual resistances are summed. For capacitors connected in parallel, their capacitance values are added to obtain the total capacitance.
Types of Capacitors
Capacitors can be categorized into two main types: fixed and variable capacitors, based on their capacitance values. Fixed capacitors have predetermined and unchangeable capacitance values, while variable capacitors offer the flexibility of adjusting their capacitance.
Fixed capacitors can be further divided into non-polarized and polarized capacitors. Non-polarized capacitors, such as ceramic capacitors, have the insulating material made of ceramic and typically possess low capacitance values ranging from 1 picofarad (pF) to 1 microfarad (μF). Ceramic capacitors exhibit minimal current leakage and a high dielectric constant, making them suitable for various applications, including RF (radio frequency) and audio circuits.
Film capacitors are another type of fixed capacitor, available in different variations such as polyester, metalized, polypropylene, PTE, and polystyrene. Film capacitors offer high insulation resistance, excellent temperature characteristics, negligible dielectric loss, low inductance, stability, and cost-effectiveness.
Electrolytic capacitors, visually resembling small tin cans, are commonly used in circuits requiring larger capacitance values due to their ability to store substantial electric charge. The dielectric material in electrolytic capacitors is a thin oxide layer situated within small cans. It is important to note that electrolytic capacitors are polarized, necessitating correct wiring to prevent the risk of explosion.
Mica capacitors, particularly silver mica capacitors, are highly regarded for their compactness, temperature stability, and precision in PCB designs. They consist of metal-coated mica sheets encased in epoxy for environmental protection. Mica capacitors exhibit low charge loss and are frequently employed at high frequencies. Additionally, they offer exceptional chemical, electrical, and physical stability due to their unique layered crystalline structure.
These diverse types of capacitors cater to various application requirements, providing engineers and designers with options to address specific circuit needs effectively.
The Importance of Capacitors in PCB Design
In today’s electronics industry, printed circuit boards (PCBs) are pervasive, and capacitors play a vital role in ensuring their optimal operation. In the context of PCBs, capacitors serve multiple essential functions beyond the mere storage of electrical energy. Here are some of the key benefits of capacitors in PCBs:
Energy charge and discharge: Capacitors excel at rapidly charging to the desired voltage and swiftly discharging the required energy when needed.
Voltage level stability: Capacitors play a crucial role in maintaining voltage stability by minimizing fluctuations and reducing voltage pulsations. Additionally, they mitigate ripples that may occur during current conversions.
Noise reduction: Decoupling capacitors are instrumental in creating independent circuits. By interrupting and blocking DC signals, they ensure smoother AC flow and effectively reduce unwanted noise.
Frequency filtering: Capacitors possess the ability to filter out undesirable frequencies, making them effective in noise reduction and signal conditioning. They maintain their functionality even under varying temperature conditions and are suitable for managing power loss. Certain capacitors are designed to handle high-voltage applications as well.
Considering the significance of capacitors on PCBs, their impact on the overall functionality of a product becomes apparent. Without capacitors, electronic components on the PCB would fail to function correctly, significantly limiting the capabilities of the PCB. Therefore, selecting the appropriate capacitor for a project is of utmost importance.
Choosing the Right Capacitor Components for PCB Design
During the design phase of a printed circuit board (PCB), selecting the appropriate electronic components, including capacitors, is a critical task. Inadequate component selection can lead to malfunctions, total failure, or undesired performance of the PCB.
When choosing capacitors for your PCB design, simply considering the capacitance value is often insufficient for most applications. Similar to resistor components, capacitors have tolerance factors that result in variations in their actual capacitance. These variations can be influenced by manufacturing processes, aging, DC biasing, and operating temperatures.
Therefore, it is crucial to consider the tolerances of the capacitance when selecting capacitor components. The price difference between high and low tolerance capacitors can vary significantly. However, if cost is not a constraint, it is advisable to opt for capacitors with tolerances below 10%. For most low-power circuits, tolerances of 10% or even 20% are generally sufficient.
Determining the appropriate capacitance value is also important. Capacitors can suffer damage if subjected to voltage stress or if the applied voltage exceeds their specified limit. When capacitors are connected in parallel to an output, a subcircuit, or a circuit, the anticipated voltage drop across the capacitor should be calculated or known. It is recommended to choose a capacitor with a rated voltage at least 50% higher than the expected voltage drop. For example, if the expected voltage drop across the PCB capacitor is 10 volts, selecting a capacitor with a rated voltage of 15 volts or higher is advisable.
Considering the lifetime expectancy of capacitors is critical, particularly for electrolytic capacitors. The lifetime of a capacitor refers to the duration during which it remains in a healthy state and provides the intended capacitance. Manufacturers usually provide the normal operating lifetime of capacitors in the product datasheet.
The temperature range for a capacitor’s operation should be taken into account, similar to resistors. Advanced designs, depending on the application type, ripple current, and equivalent series resistance (ECR) value, should consider the frequency of operation.
Taking these considerations into account when selecting capacitors for your PCB design will contribute to the overall functionality, performance, and reliability of the circuit.
Factors To Consider When Choosing Capacitor on Circuit Board
The lifespan of a capacitor refers to the duration in which it maintains normal functionality and retains its specified capacitance.
Voltage stress is a critical factor to consider as exceeding the rated voltage can lead to potential damage. To ensure sufficient voltage protection, it is recommended to choose a capacitor with a voltage buffer of at least 50% above the anticipated voltage drop.
The dielectric material used in a capacitor significantly influences its capacitance and thermal stability characteristics. Selecting a suitable dielectric type is essential based on the specific requirements of the application.
Considering the working temperature range of a capacitor is crucial to ensure its reliable operation. It is generally advisable to provide a temperature buffer of 50% of the maximum ambient temperature to account for potential temperature variations during operation.
Tolerance is an important parameter that indicates the allowable deviation from the nominal capacitance value of a capacitor in both positive and negative directions. Understanding the tolerance value helps in determining the acceptable variation of the capacitor’s actual capacitance from its intended value.
Taking these factors into consideration when selecting capacitors for a PCB design ensures proper functionality, optimal performance, and greater longevity of the circuit.
How to Measure PCB Capacitance?
The capacitance of a printed circuit board (PCB) is a measure of the amount of electrical energy that can be stored in a capacitor. Each capacitor has a specific capacitance value, typically measured in Farads (F). A Farad represents a substantial amount of energy storage, so capacitance values are commonly expressed in practical units such as microfarads (µF) or picofarads (pF).
To determine the amount of electric charge currently held by a capacitor, you can use the equation Q=CV, where Q represents the total charge stored, C represents the capacitor’s capacitance, and V represents the voltage across the capacitor. Thus, multiplying the capacitance by the voltage gives the total charge stored in the capacitor. It is important to note that the capacitance of a capacitor has a direct relationship with its voltage. Consequently, any change in the voltage source will affect the capacitor accordingly, either by increasing or decreasing its charge.
Capacitance is a measure of the ratio of electric energy stored in a capacitor to the voltage applied to it. Capacitance values typically range from 1 picofarad (10−12 F) to about 1 millifarad (10−3 F). A capacitor’s capacitance is higher when the surface area of its conductors is larger, as this allows for a greater charge storage capacity.
How Do I identify a PCB capacitor?
The most common method of identifying a capacitor on a printed circuit board (PCB) is by examining its value, which indicates the number of pico-farads (pF) or nano-farads (nF) the capacitor can hold. The value of a PCB capacitor is typically specified in pF or nF units.
Alternatively, if you have access to a multimeter, you can also use it to identify capacitors. While some capacitors may have markings indicating their values, many capacitors do not have these markings. In such cases, using a multimeter becomes necessary. By measuring the resistance of each capacitor with the multimeter, you can obtain information to calculate its capacitance value.
Tips on How to Place your PCB Bypass Capacitor
The proper placement of bypass capacitors is a critical step in the design process of a printed circuit board (PCB). Incorrect placement can negatively impact overall performance. Likewise, when there are limited capacitors available for certain components, it is essential to communicate this information to the engineer so that the schematic can be updated accordingly.
It is important to consider whether components should be placed on the top or bottom side of the PCB, depending on the specific requirements of the design.
When multiple capacitors of different values are assigned to a supply pin of an integrated circuit, it is recommended to place the capacitor with the lowest value in close proximity to the device pin.
For larger tantalum and non-polarized capacitors, it is advisable to position them as close as possible to the device or pin, arranged in ascending order of their values.
Devices with multiple power pins should have one or more bypass capacitors allocated per power pin to ensure sufficient decoupling.
Always validate the schematic when placing a bypass capacitor, as these capacitors are typically used to tie logic input pins high, and their correct placement is crucial for proper operation and signal integrity.
How To Replace a Capacitor on Circuit Board
Step 1: Determining when to replace a capacitor
If your system experiences failures or exhibits certain symptoms, it may be due to a blown-out capacitor. Common indicators of a blown capacitor include the device not switching on, intermittent power cycling, or flickering/distorted screen. To troubleshoot these issues, it is crucial to inspect the capacitors on your circuit board. Remember to power off and unplug the device before conducting any examinations.
Step 2: Gathering the necessary tools for capacitor replacement
To replace a capacitor, you will need the following tools:
●Screwdriver
●Soldering iron
●Replacement capacitors
●Soldering wick
Step 3: Accessing the damaged capacitor
Use a screwdriver to open the electronic casing, allowing access to the circuit board. Locate and remove the screws and tabs securing the casing. Blown-out or damaged capacitors often exhibit a convex shape with the top bulging outwards. Be sure to look out for these visual signs.
Step 4: Removing the damaged capacitor
After identifying the blown-out capacitor, apply a soldering braid to the base of its leads. Heat the braid with the soldering iron, allowing the solder to heat up and be drawn into the braid.
Carefully remove the capacitor from the circuit board by gently pulling until the leads are free of solder. Use a soldering wick to remove any residual solder from the contact points on the circuit board.
Step 5: Installing the new capacitor
Prepare the new capacitor by trimming its leads, making them even and at a similar height to the previous capacitor. Insert the leads of the new capacitor into the respective holes where the old capacitor was located.
Next, position the soldering iron’s tip directly onto the joint on the back of the circuit board. As the iron tip touches the hole, press the wire lead through the hole and then withdraw the iron. The old solder joint will solidify, securing the new capacitor in place.
Disposing Your PCB Capacitor
Disposing of non-PCB capacitors requires compliance with federal government regulations governing their disposal. Specific guidelines and procedures for proper disposal are outlined in an available document that scrap yards can refer to.
Crushing and shredding methods are no longer acceptable alternatives due to the contamination risk they present. To avoid violating requirements, it is recommended to remove and store non-PCB capacitors, minimizing the potential for environmental harm.
For proper disposal, one option is to engage a transporter specialized in handling PCB waste. It is essential to maintain accurate records during this process, including the quantity of drums, dates of pickup and haul, and the name of the transporter. Following these procedures helps ensure compliant and responsible disposal of non-PCB capacitors.
Conclusion
A PCB capacitor is a component used in circuits to store electrical energy, similar to a battery. However, capacitors have a lower energy density compared to batteries, meaning they can’t store as much energy in the same size. Despite this drawback, capacitors offer certain advantages over batteries. They typically have longer lifespans, making them a more environmentally friendly option. Additionally, capacitors are capable of delivering energy at a faster rate compared to batteries, which makes them suitable for applications requiring short and high bursts of power. For example, a camera flash often utilizes a capacitor for its quick power needs, often charged by a battery.
Decoupling capacitors serve the purpose of providing a nearby energy reservoir to smooth out voltage variations when there is a sudden demand for current. Power supplies typically have some delay in their voltage response due to inductance, and decoupling capacitors bridge this gap. It is crucial for the decoupling capacitor to be positioned close to the digital chip to minimize the impedance caused by inductance in the leads. This ensures that additional current can be rapidly delivered without hindrance.
