This guide covers everything you need to know about PCB vs PCBA.
Whether you’re a newbie or a professional in the PCB industry, there is a lot you can learn here.
Keep reading to learn more.
- What is the difference between a PCB and a PCBA?
- What are the Key Steps in the PCBA Process?
- What Component Types are attached to PCBs to make them PCBAs?
- What are the Component Packages available in PCBA?
- How are the Components attached to a PCB during Assembly?
- What are the Components available on a PCBA?
- What are the Advantages of using Surface-mounted Components Over Through-holes on PCBA?
- What are the Limitations of Surface-mount Technology on PCBAs?
- What is the Importance of a Solder Mask on a PCB and PCBA?
- Are Surface Finishes Applied to the Traces on a PCB?
- How are a PCB and PCBA Inspected?
- Why are Conformal Coatings applied on a PCBA?
- How are the Conformal Coatings applied on a PCBA?
- What Tests are Carried Out on a PCB and PCBA?
- Is Drilling employed on PCBs and PCBAs?
- What is the Role of Silkscreen on a PCBA?
- Can you Repair Surface-mounted Components on a PCBA?
- What are the Features of Infrared Soldering on PCBAs?
- Is Hot Air Soldering possible on PCBAs?
- What are some of the Standards used for the PCB and PCBA?
What is the difference between a PCB and a PCBA?
A Printed Circuit Board (PCB) supports electronic components while electrically connecting them using conductive paths known as traces.
The traces are commonly fabricated from copper and furnished over a substrate, which is a non-conductive layer.
PCBs are fabricated in different configurations.
You will find various types such as single-sided PCB, double-sided PCB, and multilayer PCB.
The determination of type is guided by the number of conductive layers the board has.
Multiple layers are connected through channels called vias.
A Printed Circuit Board Assembly (PCBA) is used about a functional PCB with all the board attachments and peripherals.
An assembled PCB is one you find with soldered and attached components and features, allowing for the design function’s execution.
You find a Printed Circuit Board Assembly (PCBA) to be the complete agglomeration inserted into a device.
For instance, televisions and computer monitors can have a similar basic PCB structure.
However, to execute their respective functions, these PCBs will be attached with unique components to make different PCBAs.
What are the Key Steps in the PCBA Process?
The PCBA process is a sequential process that ensures a functional and effective presentation in the end.
Before embarking on a PCBA process, it is essential to carry out a design check for manufacturability.
With this check, you can establish any vulnerabilities that may hamper the board’s functionality.
The steps involved in the PCBA process are:
Application of Solder Paste
The foremost step in the assembly of a PCB is the board application of solder paste.
A stencil made from stainless steel is used to mask the board surface.
The stencil highlights only the areas you apply the solder paste, which will rest the components.
Besides, the solder paste has a grey appearance and is a mixture of solder and flux.
The solder material is composed of tin, copper, and silver elements.
You find flux is used to enhance the melting of the soda and its bonding strength.
Solder paste can be applied manually or automatically.
When applying solder paste, you need to be concerned with the paste and the amount.
The stenciled board is held firmly in place for automatic application while an applicator machine applies solder paste over the stencil.
The stencil is removed on completion, leaving solder paste in the required areas.
SMD Component Placing
The SMD component placing follows the solder application process.
The surface-mounted components are typically placed on their respective solder lands by a process called pick and place.
You can manually carry out pick and place or automatically through programmed machines.
In the manual process of pick and place, you use tweezers to pick up components.
Thereafter, you carefully place them on the solder paste at the required location.
Due to the small sizes of SMDs and the high precision requirement, conducting the process manually is tiring and slow.
The automated pick and place process is facilitated by programmed machinery in the form of robotic arms.
Using vacuum suction, these machines pick up the components and use their programmed board information to position the part precisely.
You find this automated process to be fast and accurate devoid of human deficiencies such as exhaustion and error.
Soldering of the SMD Components
Upon completing the placing process, you need to ensure the components are firmly fixed on the board to prevent movement.
You can manually solder the components or use automatic means called the reflow technique.
In soldering, you heat the solder paste to melt the solder, which will bond the board’s component on cooling.
The reflow process involves conducting the board in ovens via a conveyor system.
Inspection and Quality Assessment
You will need to check the soldered components on the PCB for their functional ability.
You might find the reflow process was hindered, resulting in connection flaws.
A common fault in the process is the occurrence of shorts compounded by component misplacement.
You can inspect manual checks, x-ray inspection, or through an automated optical process.
With manual inspection, you visually examine the board for defects.
You will find the manual inspection process to be exhausting when done continuously over a period.
Furthermore, executing a manual check for a large number of boards is impractical.
When carrying out Automatic Optical Inspection (AOI), you use powered cameras to capture various board aspects and elements.
You set up cameras to cover the entire board with a reference for the right board appearance.
For instance, you can determine the solder’s quality by examining their reflection in the captured images.
AOI is a fast process that you can efficiently and accurately administer for large board numbers.
You can also employ x-rays in your inspection efforts.
The x-ray inspection is particularly useful if you have a multilayer board construction.
Using x-rays will allow you to view the internal layer board aspects as the rays penetrate matter.
The approach to handling the flaws you identify will depend on the level of damage or defect observed.
You can rework some boards or do away with them entirely if the flaws are in abundance.
Testing your board succeeds in the inspection process and speaks to your board quality.
It gives you an overview of how your surface mounted devices respond to signals.
Board testing can involve calibration procedures or even programming protocols.
Inserting Through-hole Components
You insert through-hole components on PCBs in plated through-holes drilled through the board to provide inter-layer connection.
You find copper is commonly used to plate the through-holes allowing conductivity.
You use the soldering process to fix the component on the board.
You can manually carry out the procedure or use an automated approach referred to as wave soldering.
Ultimate Inspection and Testing
PCB component mounting
Just like after connecting the SMD components, you need to inspect and test the board on attaching through-hole components.
Since there are no other procedures, you find this to be a conclusive test before completing the assembly.
You inspect the component placements making final adjustments where necessary.
You follow the inspection by carrying out a test to evaluate the board functionality.
Your test procedures should highlight the electrical characteristics of your board, such as voltage and current rating.
You will require other fixtures and equipment to carry out a functional test, such as a flying probe.
A successful board test allows you to proceed to the package.
When a board fails a test, you can rectify the issue or discard the board.
What Component Types are attached to PCBs to make them PCBAs?
Electronic components are semiconductor-based devices that are attached to a board to execute specific board functions.
You find these PCB components are interconnected to achieve an overall design objective.
You can identify components on PCBAs in two categories: surface mounted and through-hole components.
Through-hole components have wire-like extensions called leads used to provide an electrical connection to the board via drilled holes.
Surface-mounted components lack these leads instead having metallic bases that connect to the board via landings referred to as pads.
You find various contrasts between the through-hole and surface mounted components.
For instance, surface mounted components are smaller than through-hole components allowing for a higher component density.
Contrastingly, the small size makes them difficult to attach compared to through-holes, especially in a manual application, rework, and repair activities.
Furthermore, you can attach SMT chips on either side of a PCB construction.
On the other hand, through-hole components can only be attached on one board side.
You find this is because through-hole components are fastened to the reverse board side.
Additionally, connecting SMT chips is faster compared to the through-hole component attachment.
What are the Component Packages available in PCBA?
Component packages are usually employed to provide more superficial board attachment during assembly.
They are used for integrated circuit chips and are typically standardized, allowing compatibility with different manufacturers.
Standard component packages used on PCBAs include:
· Single In-line Package (SIP)
The single in-line package is composed of a single row of connecting contacts called pins.
You can find SIPs with pin counts of up to 24.
When used for components with large thermal dissipations, the main frame body is employed as a heat sink.
· Dual In-line Package (DIP)
You find this package to bear similarity with the single in-line package but with two pin rows parallel to each other.
It is a quadrangular package commonly used for many components with a pin count that can reach 64.
You can insert the package into a socket on the board or through-holes.
· Chip Carrier
Quadrangular component packages with contacts around all the edges are referred to as chip carriers.
The chip carrier is usually plastic or ceramic derived and attached to the board via soldering.
You will find two types of this package option: leaded chip carrier and leadless chip carriers.
The leaded chip carrier has metallic leads twisted around the package’s edge.
On the other hand, a leadless chip has metalized pads rather than leads around the edges.
· Pin Grid Array (PGA)
The pin grid array package is four-sided with evenly-spaced pins located at the base of the package.
You find this package to have a high pin count than other packages like the DIP.
The pins could be populated entirely over the bottom or not and inserted through-hole or into a socket.
· Quad Flat Package (QFP)
As the name suggests, this package has four sides with flattened leads spread out from the sides like birds’ wings.
You can only surface mount this package type.
However, there are instances where this package type is socketed.
It can support high pin counts with a pin profile spacing of between 0.4 and 1.0 millimeters.
· Ball Grid Array
The ball grid array is a package type with characteristic small spherical attachments located at the package’s bottom.
You find this package type to have a high pin connection density with shorter leads enhancing its performance.
The ball grid array package is commonly used for permanent board attachments such as the microprocessor.
How are the Components attached to a PCB during Assembly?
You attach components on a PCB by using the soldering process.
The soldering process involves melting solder and cooling it to form a strong bond.
You can manually solder components to the board using a heat stick and solder.
Additionally, when faced with many panels, you can conduct the process via automated methods.
Since components on boards are of two types, SMD and through-hole, you will employ different automation processes.
You use a reflow soldering process for SMDs and a wave soldering approach for through-hole components.
· Reflow Soldering
Here, you direct the PCB on a conveyor to an oven that facilitates the reflow process.
You find the oven has several heaters that supply enough heat to initiate solder melting.
Thereafter, you pass the board through cooling heaters, which control the cooling of the solder.
When the solder cools, you notice it creates a stable joint between the surface-mounted component and the board.
You will use different approaches for the reflow process, depending on the board configuration.
For instance, in two-layer boards, you will work on one layer first before attending to the other.
· Wave Soldering
Wave soldering allows you to execute the insertion and fixing process in a single stroke approach.
The through-hole components are inserted into their hole locations and conveyed to an oven.
You find molten solder is applied in waveform across the board’s base where the component leads are attached.
You then cool the board with the solder, bonding the components to the board.
You find using wave soldering on double-sided boards is difficult as it can interfere with other electronic board aspects.
What are the Components available on a PCBA?
You find components on a PCBA to be either surface mounted or through-hole components.
These components serve specific functions that contribute to the overall performance of your board.
There are many components that you find useful on a PCBA. Some of these components include:
- The electronic capacitor that stores charges on the board.
- Various integrated circuit chips for specific functions such as memory storage.
- The electronic transistor which is used in switching applications.
- The electronic resistor that regulates the current flow.
What are the Advantages of using Surface-mounted Components Over Through-holes on PCBA?
Through-hole components have leads that you can identify as wire-like extensions extending from their bodies.
The leads can extend radially or axially.
Surface-mounted components are those you observe to lack leads.
You find these components typically have their bottom surfaces used to provide electrical attachment to the board.
Surface-mounted components find widespread use over through-hole components for the following reasons.
- You find surface mounted components to be smaller than through-hole mounted components.
Consequently, you can attach more SMDs than through-hole components for a similar sized area.
- Furthermore, when using SMDs, you can mount components on the top and reverse surfaces.
Through-hole leads are attached on the reverse side, preventing you from inserting them on both surfaces.
- When employing SMDs, you achieve a denser connection as a result of laying them on the surface.
With through-hole components, you drill holes through the board, which eat up routing channels.
- You find the connections created from using SMDs are less affected by the inductance and reduced resistance.
Therefore, you derive better performance from such populated boards in high-frequency applications.
- The electromagnetic compatibility of boards you populate with SMDs is improved as a result of their small sizes.
You find this reduces the area of radiation loop while decreasing inductance due to the leads.
- When you use SMDs instead of through-hole components, you reduce the overall board cost.
Through-hole features require drilled holes for insertion.
Drilling consumes a lot of your time while requiring specialized equipment, which adds to your cost.
- Attaching SMDs on your board is faster, especially when employing automation. You find the picking and placing routine is simple and straight forward.
- When making SMDs, you use less material compared to similar through-hole components.
What are the Limitations of Surface-mount Technology on PCBAs?
While you find surface mounted components to offer many benefits, they are also limited in specific ways.
PCB surface mount component
- You find misalignment of SMDs to be common when positioning them on the solder pads.
As a result of misalignment, you can encounter poor connections hampering performance.
- When subjected to mechanical shocks and movement, you find surface mounted components more susceptible to detachment.
Therefore, you are better off avoiding such components when employing them, along with frequently detached peripherals.
- Using surface-mounted components with potting elements will reveal to you their weak solder joints, especially under the thermal cycle.
- You find it challenging to handle repairs or rework on boards with surface mounted devices.
The small component size and tight spacing make it difficult for you to require specialized equipment and skills.
- While sockets provide simple installation of board components, you find their use with surface mounted devices limited.
Socketing is especially useful when you have to replace damaged components or upgrade features.
- Breadboards are especially useful in testing circuit designs, such as in the case of prototyping.
However, you find direct use of surface mounted components on this board type is impossible.
You have to furnish the SMD on a carrier device with pins.
You can also create a unique test board to accommodate your components, which is expensive.
- As SMDs are made smaller, you find attaching them to the board becomes more difficult. A significant problem that you find familiar is voiding.
Voiding occurs when a joint is not created between the board and component when you carry out soldering.
Voiding is harmful to your board as it can impair the joint and, consequently, the performance.
- You can identify through-hole components due to their size and visibility if markings.
Some SMDs are very small, requiring coding for identification, making it a complicated process for you.
What is the Importance of a Solder Mask on a PCB and PCBA?
You use a solder mask to protect your copper trace on a circuit board.
Besides, you appreciate the use of a solder mask when handling an automated board soldering process.
You apply the solder mask as a layer that shields the conductive path.
Also, you follow a photolithographic approach to mark out the locations of the solder pads.
You have the choice of different materials for your solder mask.
You can use epoxy compounds, photo imageable ink, and dry film materials.
There are several options you can use to lay the solder mask.
You can apply the solder mask as a silkscreen spray or through vacuum lamination and curing.
Protection is offered from oxidation, which you find influenced by the atmospheric presence of oxygen.
Additionally, you find the solder mask useful to prevent bridges between tracks by escaped solder.
Are Surface Finishes Applied to the Traces on a PCB?
You can apply surface finishes to your PCB traces.
Surface finishes are a coating you use over the conductive pattern of your board typically before soldering.
A surface finish for use on your board can be of different material compositions and applications.
Common materials you can employ for your surface finish are tin, nickel, silver, gold, and even organic preservative.
The two common reasons for your use of surface finish are:
PCB Surface Finish
- You prevent oxidation-induced corrosion to your copper track.
- You improve the ability of your board surface to adhere to components when soldering.
How are a PCB and PCBA Inspected?
The inspection of PCBs and PCBAs ensures the early identification and detection of flaws and errors.
There are several ways you can inspect your board, mainly depending on the cost and board count.
You can inspect your board through either one of the following procedures:
· Manual Inspection
In manual board inspection, you use your visual ability to identify flaws on the PCB.
You need to be attentive to details to ensure nothing escapes you.
Some of the flaws you look for when inspecting the board include misplaced and misaligned components and broken circuit paths.
Experience is a crucial useful factor to help you make correct interpretations with the required board design.
You find manual inspection to be limited to only a few boards.
Visually inspecting a board strains your eyes, resulting in fatigue after some time.
· Automated Optical Inspection (AOI)
With automated optical inspection, you employ the use of powerful cameras instead of your eyes.
You position these cameras such that they capture every board aspect and feature.
When using AOI, you identify flaws by light shade differences and programmed comparison with the required design.
You find the use of AOI is free of human fatigue, allowing its use on numerous boards.
· X-Ray Inspection
You use x-rays to conduct an inspection, especially for multilayer boards where the internal layers are obstructed from view.
X-rays can penetrate the board, allowing you a glimpse of the inner sections.
Using the captured images, you can compare with the required board design and identify any defects.
You can address the faults by correcting them or, if far too gone discarding the board.
Why are Conformal Coatings applied on a PCBA?
A conformal coating is a layer you apply over a PCBA that takes the board shape.
You find a conformal coating is useful in protecting the board from externally located elements such as moisture and dust.
Conformal coatings you employ are typically made from polymer materials such as resin.
You, therefore, find conformal coatings to be poor electrical conductors but good insulators.
Some of the conformal coatings you will find are acrylic coatings, polyurethane coatings, silicone coatings, and epoxy.
Conformal coatings are useful in the following ways:
- You benefit from preventing aging of the board via dust accumulation and moisture-induced corrosion when you use conformal coatings.
- You realize using conformal coating does not significantly impact the total weight of the board.
- Furthermore, a conformal coating ensures the performance of your board is stable.
Conformal coatings prevent the accumulation of foreign matter on your board that can hamper performance.
- Since conformal coatings are insulative, you can lay your traces much closer, allowing for a higher density. The resulting board performance can be improved when you compare it with a similar-sized board without the coating.
- The resin-based composition of conformal coatings improves the thermal performance of your board.
How are the Conformal Coatings applied on a PCBA?
There are different approaches to applying conformal coatings spray that you can use.
You can consider several factors to justify your choice of application method.
Common factors of consideration include the cost involved, the board design, the processing time, required thickness, and penetration depth.
Furthermore, you will need different equipment for each application method.
Standard application methods are as follows:
- By spray method
- By dipping
- By brushing
- By use of selective coating
What Tests are Carried Out on a PCB and PCBA?
Testing your board is necessary to ensure it attains the intended functional performance.
The tests you carry out on your board should cover its mechanical, electrical, and thermal performance.
Standard tests you can carry out on your board include:
A thermal cycling test to determine its performance at different temperature values will speak to its operating temperature.
You can carry out tests to establish the board’s mechanical strength by subjecting it to compression and pulling forces.
Tests such as the flying probe will help you evaluate your board’s electrical performance.
You can also carry out a capacitance test to check for shorts and opens in your circuit.
Is Drilling employed on PCBs and PCBAs?
Drilling is useful as it allows you to create plated through-holes for component attachment.
Leaded components are fastened to the board by inserting their leads into these holes before soldering them.
You can manually drill your PCB before assembly using drill files to guide you on the hole location.
The use of automated drill procedures is also possible where you can employ computer-controlled equipment.
You can use programmed drilling machines with information from the drill files to actualize your drilling process.
You will also find laser beams to be more effective but comes at a higher cost.
What is the Role of Silkscreen on a PCBA?
The silkscreen is an inked informative layer that helps you to identify board aspects.
You find these aspects to include: components, polarities, symbols, points of tests, and PCB parts, to mention a few.
You find the silkscreen is practically placed on the top side of the body over components.
You can find it on the reverse board side, but to keep it, there is costly.
Using a silkscreen helps you to locate the board populates quickly.
Therefore, you find the silkscreen colors to be easily identifiable such as white and yellow.
Can you Repair Surface-mounted Components on a PCBA?
Repairing a PCBA with surface mounted components is possible by employing soldering irons or a rework system with no contact.
However, you find the process to be complicated by the small component size and flat base attachment.
Successfully carrying out repair work on an SMD requires you to have refined skills and experience.
You find detaching the SMD from the board without damaging it is challenging.
What are the Features of Infrared Soldering on PCBAs?
Infrared soldering is a procedure you will find commonly employed during rework activity.
It is a non-contact method of soldering which can be used for SMD removal.
You find that to carry out a soldering process; you require induced heat.
You derive the heat from an infrared radiation source of either a short or long wave for infrared soldering.
You will find the following features associated with infrared soldering:
- You can easily set up an infrared soldering process.
- You don to require compressed air to actualize infrared soldering.
- Your costs will be reduced due to the absence of the component-specific nozzle requirement.
- Using an infrared source is fast speeding up the soldering process.
- Controlling the temperature during infrared soldering is challenging, requiring you to shield neighboring components.
Is Hot Air Soldering possible on PCBAs?
Hot air soldering is another contact soldering process you employ during PCBA rework activity.
With this method, you derive the heat energy for soldering from a flow of hot gas.
You can employ inert gas such as nitrogen or air to induce hot air soldering.
The hot air soldering process affords you the following benefits.
- You can simulate a reflow oven environment with hot air soldering.
- You can swap between hot air and nitrogen in select systems.
- When you use hot air soldering, you employ different nozzles for different components, which increases reliability.
- You can control the component temperature by adjusting the temperature of the hot air.
- You can transfer large, and even heat amounts at the concerned board areas.
- When you complete the soldering process, cooling occurs quickly, forming delicate solder joints.
What are some of the Standards used for the PCB and PCBA?
Standards are useful in helping you develop boards to the acceptable specification.
You find standards ensure board quality and dependability.
Common standards used for PCBs and PCBAs include:
You find this to be a standard for the design and use of printed circuit boards and assemblies.
The BS-EN-61191-1 is a standard you will find generally used for printed circuit board assemblies.
With this standard, you find detailed test approaches for the board assembly materials and other interconnected features.
You also find provisions for the soldering paste used in the assembly process.
You will employ the standard above when carrying out tests for electrical board materials and their assemblies.
Another standard providing guidelines for the testing of board features and composition is the IEC-61189-5-3.
You find this test useful in establishing the design and use of the printed circuit boards and assemblies.
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