A circuit board capacitor is one of the most critical electronic components. Our article explores the role of this PCB component and the various types of capacitors.
What is a PCB Capacitor?
Fig 1: Parts of a Capacitor
A capacitor is a core electronic component in circuit boards responsible for energy storage in an electric field. A typical PCB capacitor features two conducting plates separated by an insulator. The insulator is a dielectric material; it varies from one capacitor to the other.
In addition to storing electric charge, capacitors are handy in protecting microchips from noise.
Lastly, actual capacitance is the amount of electric charge in the capacitor.
Types of Capacitors
Below are some of the common types of capacitors.
Fig 2: Capacitor Types
Fig 3: A decoupling capacitor
After a decoupling capacitor fully charges, it’ll repel any alteration of the input voltages. A bypass capacitor will do either of the following:
- In case of an input voltage dip, it’ll feed sufficient power supply to the IC for a stable voltage.
- Conversely, it’ll take the electronic circuit’s excess energy in case there’s a rise in voltage. Again, this keeps the voltage stable.
Lastly, decoupling capacitors are significant in minimizing circuit boards’ electric noise.
Fig 4: Capacitor Parts
Embedded capacitors feature a fragile dielectric material between two copper plates. In manufacturing, the manufacturer adds an epoxy laminate material coating.
Like decoupling capacitors, you’ll commonly find them near an IC, and relatively short electrical paths characterize them. The characteristic minimizes the parasitic inductance and parasitic capacitance. Further, it decreases electromagnetic interference (EMI) and keeps the power bus noise low.
In addition, these capacitors have a high capacitive density and hence can feature as decoupling capacitors. Also, their discrete size makes embedded capacitors valuable in telecommunications and miniature electronic components.
Fig 5: Many ceramic capacitors
They feature a coating on either side of a ceramic disc and store relatively lesser electric charge than others. Notably, the ceramic disc is a dielectric material. Also, these capacitors don’t leak significant electric current.
Most ceramic capacitors are immune to parasitic resistance, inductance, and capacitance. In addition, ceramic disc capacitors have a relatively high dielectric constant. Further, they have a 3-digit code, often with the capacitance value in picofarads.
There are two main classes, 1 and 2, each with exceptional stability and thermal characteristics. Class 1 capacitors are more stable and have more nominal value tolerance and thermal stability than Class 2.
Multilayer Ceramic Capacitors (MLCC)
They are among the commonest capacitors in surface mount PCBs. They feature nickel-plated silver or silver palladium electrodes in a tin enclosure. Further, a ceramic dielectric encapsulates the electrodes.
Notably, the ceramic dielectric determines its overall thermal stability. In turn, its impacts the capacitor’s DC voltage features and frequency.
They fundamentally operate like decoupling capacitors and often as ripple filters. Mica capacitors comprise mica dielectric material with metal deposits on either side. The upsides of SMT mica capacitors are as follows:
- They have excellent stability, reliability, and precision.
- Secondly, their nominal value tolerances include +-5%, +-2%, and +-1%.
Fig 6: Film capacitors
They are the commonest capacitors with polycarbonate, Teflon, and polystyrene as dielectrics. Primarily they are suited to their roles because they have no dielectric losses. Furthermore, they feature good temperature properties and high insulation resistance.
This feature is synonymous with polyester film capacitors. These capacitors have a stable temperature and frequency and feature a polyethylene naphthalate (PEN) film. Furthermore, they have low Equivalent series resistance (ESR) or internal resistance. Hence, this yields excellent high-frequency performance.
Consequently, the capacitors are helpful in the following applications.
FCP Polyphenylene Sulfide (PPS) Stacked Metalized Film Capacitors
They offer a high-frequency response and high capacitance over an extensive temperature range. Also, they have exceptional DC power bus noise attenuation.
Fig 7: A Tantalum capacitor
Tantalum capacitors have an oxide film (dielectric) encompassing a tantalum layer. Their current capacity doesn’t match that of electrolytic capacitors. Nonetheless, they have high capacitances, endurance, and stability.
Further, they operate over a wide temperature range and have a relatively small footprint.
Aluminum electrolytic Capacitors
Fig 8: An electrolytic capacitor
The high capacitances facilitate the smoothing of ripples as they operate as decoupling capacitors and in power supply systems. They have the highest capacitance of all the circuit board capacitors. Nonetheless, their nominal tolerance values are relatively broader.
Also, electrolytic capacitors have extensive tolerance values, and equivalent series resistance rises with frequency. Hence, they’re incapable of handling high frequencies.
How do Capacitors Work?
Fig 9: Illustrating charging a Capacitor
A capacitor will store as much voltage as what’s in the battery when fully charged. After connecting a capacitor to the battery, the following happens:
The capacitor plate on the battery’s negative terminal will draw electrons into the capacitor. At the same time, the capacitor plate to the positive terminal will lose electrons to the storm.
Noteworthy, a capacitor will store the energy through electrical charges. Also, a charged capacitor will hinder the passage of direct current but will allow alternating current to pass through.
Lastly, capacitors are handy in stabilizing electricity in power transmission systems. Hence, their role in smoothing power supply output in analog filters. Further, they are essential in radio tuning to the desired frequencies in resonant circuits.
Factors to Consider when Choosing a PCB Capacitor
Fig 10: Different Capacitor Types
1. Leakage Current
It’s common for capacitors to leak stored current. Hence, choose one that has the least leakage rate, especially if you intend to hold a charge.
Capacitors have tolerances of between ±1% to ±20%. It is a measure of the capacitance difference from its nominal value.
It is arguably the most important parameter when choosing a capacitor. Where an electronic circuit needs the filtering of a rectified voltage, it’s advisable to use a large capacitance.
4. Voltage rating
Different capacitors have different voltage tolerances. Hence the voltage rating of a capacitor is a critical aspect to consider.
5. Operating temperature
The ambient temperature surroundings are also a critical aspect when choosing capacitors. For instance, if a PCB works in an environment of 100°C, the ideal capacitor should have a higher rating than this.
6. Life expectancy
A capacitor with an extensive lifetime will serve you longer. Hence, for permanent applications, choosing one with good longevity is best.
How To Replace A Capacitor On A Circuit Board？
Fig 10: Soldering a Capacitor
Critical steps to replacing a capacitor Include:
1. Check out for spoilt capacitor
The following are some telling signs of a malfunctioning capacitor that you should replace.
- Presence of irregular lines on your electronic device and screen flickering
- Check if there’s Irregular switching on and off the device.
- Also, check if there is an inability to restore the device from standby mode.
- Lastly, check if the device fails to switch on.
2. Assemble the Tools
You’ll require tools such as a mask, soldering iron, screwdriver, and a new capacitor.
3. Locate the capacitor
First, turn off the device and disconnect from the power supply before commencing on opening. After opening the device’s casing using a screwdriver, look for the following:
- A capacitor with a leaking brownish fluid.
- Look if there’s a corroded capacitor or one with leads disconnected from the circuit board.
3. Remove the capacitor
Now remove the damaged capacitor. But, ensure you note its temperature, capacitance, and voltage rating. Ensure you go for a like-for-like replacement and a type of capacitor with a similar rating.
4. Install the new capacitor
Lastly, solder the new capacitor using a soldering iron. Check out this soldering and desoldering guide for more directions on steps 3 and 4.
As we’ve highlighted above, a surface mount capacitor is one of the most significant passive components. For more on any capacitor, reach out to us.