PCB Assembly

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PCB Assembly Process

Our daily lives include a lot of electronics. Electronic components are found in everything, including our automobiles and smart phones. The circuit board, or PCB, is the brain of these electronics.

PCB Assembly

Printed circuit boards are typically easy to identify. These are the tiny green chips with copper pieces and lines that are in the center of disassembled electrical equipment. These boards are constructed from fiberglass, copper lines, and other metal components. Epoxy holds the components together, and a solder mask provides insulation. That distinctive green hue originates from this solder mask.

Have you ever seen those PCB boards with components firmly adhered, though? Never think of them as mere PCB board embellishments. A sophisticated circuit board cannot work until components are put on it. An assembled PCB is a PCB that has had components installed on it, while PCB assembly, or PCBA for short, refers to the manufacturing process. Traces are the copper wires that connect connections and components to one another electrically on a bare board. They transmit signals between various components, enabling the circuit board to perform in a manner for which it was particularly created. These functions range from the straightforward to the intricate, yet PCBs may be as little as a thumbnail in size.

So, precisely how are these gadgets created? The assembling of a PCB is a straightforward procedure that includes both automated and human phases. A board maker has both manual and automated choices for every stage of the process. Below, we’ve broken down each stage of the PCBA process so you can better comprehend it from beginning to end.

PCB Assembly

PCB Design

The foundation, which is made up of numerous layers and is the most fundamental component of the PCB, is where the PCBA process always begins. Each layer is important to the finished PCB’s functioning. These layers as below:


On a PCB board, the last layer is a white silkscreen. Characters and symbols are added to the PCB as labels on this layer. This aids in describing the purpose of each board component.

Solder Mask

The solder mask is placed over the copper layer to give each PCB its distinctive green hue. To prevent accidental contact between copper traces and other conductive materials, which can cause a short, it insulates them. In other words, everything is kept in its proper place by the solder. To join components to the board, solder is applied through holes in the solder mask. The use of a solder mask during PCBA manufacture is essential to prevent shorts by preventing soldering to unintended components.

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A thin copper traces add to the functional side of the PCB.


This serves as the PCB’s primary component. It ensures the stiffness of the Printed circuit board.

Except for the substrate, these components and materials are essentially the same for all PCBs. Each designer’s desired features for their completed product, like as affordability and bendability, influence the substrate layer material of a PCB.

There are three popular PCB types:


These boards provide even another choice from the standard FR4 board. These boards, which have a metal core, have a tendency to disperse heat more effectively than others. By doing this, heat is dissipated and more heat-sensitive PCB board components are protected.

Flex PCB

In comparison to its more rigid predecessors, flexible PCBs provide a little more pliability. These PCBs are often made of a flexible, high-temperature plastic called Kapton.

Rigid PCB

The majority of PCBAs use rigid PCB bases, which are the most popular variety. A stiff PCB’s solid core provides the board its rigidity and thickness. These rigid PCB bases are made of a variety of substances. The most used material is fiberglass, sometimes known as “FR4”. Epoxies and phenolics, which cost less to produce than FR4, are used to create less durable PCBs.

There are two popular assembly technology types:

THT(Through Hole Technology)

works effectively on components that require mounting on a board by putting leads or wires through holes on the board. The additional lead component would be soldered on the board’s opposite side. This method is used on PCB assemblies that must combine bulky components like capacitors and coils.

SMT(Surface Mount Technology)

Sensitive parts, some of which are quite small, like resistors or diodes are automatically positioned on the board’s surface. SMD assembly, or surface mount device, is what this is. Surface mount technique may be used with integrated circuits and tiny components (ICs).

THT and SMT are different from one another, which necessitates various assembly procedures.

Before Start the PCB assembly work

Before the actual PCBA process ever starts, a few preliminary procedures must be taken. This mostly entails a DFM examination and aids PCB producers in evaluating the functioning of a PCB design.

The PCB design file, together with any additional design notes and particular needs, are often needed to begin by PCB assembly businesses. This allows the PCB assembly firm to examine the PCB files whether exist any problems that could impair the PCB’s functioning or ability to be manufactured. This is a DFM check, or design for manufacturing ability, check.

All of a PCB’s design specifications are examined by the DFM inspection. This check specifically searches for any features that could be troublesome, redundant, or missing altogether. Any one of these problems might have a significant negative impact on how well the project works in the end. For instance, having too little space between PCB components is a typical PCB design problem. Shorts and other issues may come from this.

DFM inspections help save production costs and unanticipated expenses by spotting possible issues before manufacture even starts. This is because fewer boards were discarded as a result of these tests. Every project purchase from INTOPCB includes a free DFM assessment as part of our dedication to high quality at competitive prices. Because Valor DFM/DFA check INTOPCB rely on is an automatic system contributing to high speed and accuracy, INTOPCB offers FREE DFM and DFA check with, however, priceless values.

PCB assembly

Six Stages of PCB assembly

Stage 1. Solder paste printing

The first step in PCB construction is to coat the board with solder paste. This procedure is similar to screen printing on clothing, except instead of using a mask, the PCB is covered with a thin stainless steel stencil. Assemblers can now only apply solder paste to certain areas of the potential PCB. The final PCB will include these portions as the locations for the components.

The actual solder, commonly known as solder paste, is a gray material made up of microscopic metal balls. These minuscule metal balls are made up of 96.5 percent tin, 3 percent silver, and 0.5 percent copper. The flux, a substance used in solder paste to assist the solder melt and adhere to a surface, is combined with the solder. Grey substance known as solder paste needs to be placed to the board in precisely the proper locations and dosages.

A mechanical fixture keeps the PCB and solder stencil in place in a professional PCBA line. The correct amount of solder paste is then applied using an applicator to the desired regions. The paste is then evenly distributed across the stencil by the machine, covering all of the vacant spaces. The solder paste stays in the designated places after the stencil has been removed.

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Stage 2. Pick and place components

Surface mount components, or SMDs, are placed on a prepared PCB by a robotic device after the solder paste has been applied to the PCB board in the PCBA process. The majority of non-connector components on PCBs nowadays are SMDs. The next stage of the PCBA process involves soldering these SMDs to the board’s surface.

The machine picks up a PCB board using a vacuum grip and moves it to the pick and place station to begin the pick and place procedure. After positioning the PCB at the station, the robot starts attaching the SMD components to the PCB surface. These component parts are positioned in predetermined places.

Traditionally, assemblers had to choose and put each component by hand while using a pair of tweezers to complete this task. Thankfully, PCB makers now do this procedure automatically. This change has place mostly as a result of robots’ propensity for accuracy and consistency over people. Even while humans are capable of working swiftly, working with such tiny components tends to cause weariness and eyestrain after a while. Machines don’t become so worn out working nonstop.

Stage 3. Automatic Reflow Soldering

Surface mount components must stay in place once the solder paste is applied. In order to adhere components to the board, solder paste must harden. This is achieved during PCB construction via a procedure known as “reflow”.

The PCB board is put on a conveyor belt following the pick and place procedure. This conveyor belt travels through a huge reflow oven, resembling a commercial pizza oven in several ways. The board is progressively heated in this oven, which comprises of a number of heaters, to temperatures of around 250 °C or 480°F. The solder in the solder paste will melt at this temperature.

The PCB continues to pass through the oven after the solder has melted. The melted solder can cool and solidify in a regulated manner as it goes through a sequence of colder heaters. As a result, the SMDs and PCB are permanently connected via a solder connection.

Particularly for two-sided PCB Assembly, several PCBAs demand particular care during reflow. Each side of a two-sided PCB assembly has to be stenciled and reflowed individually. The side with the fewest and smallest pieces is stenciled, put in position, and reflowed before the other side.

Stage 4. Inspection

The finished PCBA and completed board need to be checked for operation after the surface mount electronic components have been soldered in place following the reflow process. Movement during the reflow process frequently causes a connection to be lost entirely or to have a poor quality connection. This movement can occasionally cause parts of the circuit to join that shouldn’t be connected, which can result in shorts.

One of many different inspection techniques can be used to look for these mistakes and misalignment. The following are some of the most popular inspection techniques:

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Manual Checking

Despite the approaching growth trend of automated and intelligent manufacturing, PCB assembly still relies on manual inspections. An in-person visual examination by a designer is an efficient way to guarantee the quality of a PCB following the reflow process for smaller quantities. However, as the number of examined boards rises, this process becomes more and more inefficient and incorrect. Over an hour of looking at such tiny components can cause eye fatigue, which reduces the accuracy of examinations.

AOI(Automatic optical Inspection)

For bigger batches of PCBAs, automatic optical inspection is a better inspection technique. An AOI machine, also known as an automated optical inspection machine, employs a number of powerful cameras to “see” PCBs. To view solder connections, these cameras are set up in various configurations. A lower-quality solder may be identified by the AOI because various types of solder connections reflect light differently. The AOI processes a large number of PCBs in a brief amount of time thanks to its extremely fast processing speed.

X-Ray Inspection:

X-rays are yet another examination technique. This less popular inspection technique is most frequently utilized for PCBs that are more intricate or have several layers. An observer can perceive lower levels and see through layers with the use of an X-ray to find any possible problems that may be concealed.

Depending on the PCBA company’s criteria, a defective board will either be sent back to be repaired or trashed.

The next stage then moves on to testing the component parts to ensure it performs as intended, if an inspection not found one of these errors or not. Checking the PCB connections for integrity is required. For boards that need calibration or programming, there are even additional procedures to ensure optimal operation.

After the reflow procedure, these checks may be carried out often to spot any possible issues. The the designer and manufacturer may both save time, labor, and materials by doing these routine checks to make sure that problems are identified and corrected as soon as feasible.

Stage 5. THT PCB assembly

The board may have a number of components in addition to the typical SMDs, depending on the types of PCB board covered by PCBA. PTH components, also known as plated through-hole components, are among them.

A PCB hole that has plating that extends through the whole board is known as a plated through-hole. These holes are used by PCB components to transmit signals from one side of PCB board to the other. Soldering paste won’t help in this situation since it will pass right through the hole without having an opportunity to attach.

In the final stages of PCB construction, PTH components demand a more specific type of soldering technique:

Manual insertion

Through-hole insertion by hand is a simple operation. Typically, one component will be inserted into a specific PTH by one person at a single station. When they’re done, the board is moved to the station below, where a different individual is attempting to attach a different component. For every PTH that has to be equipped, the procedure is repeated. Depending on how many PTH components must be placed during a PCBA cycle, this procedure may take a while. PTH components are still frequently used in PCB designs, despite the fact that most businesses specifically try to avoid using them.

Wave Soldering

Although it uses a totally different procedure, wave soldering is the automated equivalent of human soldering. The board is then placed on yet another conveyor belt following the installation of the PTH component. This time, a wave of molten solder is applied to the bottom of the board when the conveyor belt passes through a specialized oven. This simultaneously solders every pin on the board’s bottom. Due to the fact that soldering the whole PCB side would render any fragile electronic components worthless, this form of soldering is almost impossible for double-sided PCBs.

After the soldering procedure is complete, the PCB can go to the final inspection or, if new parts need to be added or another side has to be completed, it can repeat the previous processes.

Stage 6. Functional Test

A final inspection will test the PCB’s functioning once the soldering phase of the PCBA process is complete. This examination is referred to as a “functional test.” The test puts the PCB through its paces and replicates the conditions under which it will typically function. In this test, the PCB is exposed to power and simulated signals while testers keep an eye on its electrical properties.

The PCB fails the test if any of these properties, such as voltage, current, or signal output, exhibit unacceptable fluctuation or reach peaks outside of a defined range. In accordance with the criteria of the firm, the faulty PCB can then be trashed or recycled.

The final and most crucial phase in PCB assembly is testing, which indicates if the procedure was successful or unsuccessful. Regular testing and inspection are crucial throughout the whole assembly process for the same reason that this testing is done.

After PCB assembly

The ideal instrument for cleaning residue off of PCBs is a stainless-steel, high-pressure washing machine that uses deionized water. The instrument is unaffected by washing PCBs with deionized water. This is so that the actual water itself—rather than its ions—does not harm a circuit. Therefore, when PCBs go through a wash cycle, deionized water is safe for them.

After washing, the final PCBs undergo a brief cycle of compressed air drying before being prepared for packaging and shipping.

Some technique of PCB Assembly: Mixed Technology, SMT Assembly and THT Assembly

Mixed PCB assembly

Electronic devices are growing more and more sophisticated as a result of advances in current science and technology, which has led to PCB boards that are more intricate, integrated, and compact. It is very hard for PCBAs with just single type of components to participate.

Surface mount technology and thru-hole technology must work together since most boards contain both SMD and SMD components. However, soldering is a challenging procedure that is frequently impacted by an excessive number of factors. Therefore, improving the order in which surface mount technology and through-hole technology are introduced becomes extremely important.

Mixed technique application in PCB assembly condition:

Double side PCB Mixed Assembly

There are two options for double-sided mixed assembly techniques: PCBA with adhesive application and PCBA without. This PCBA technique requires three heating cycles, which tends to result in low efficiency. Additionally, the cost of PCB assembly as a whole is increased by the use of adhesives.

THT and SMT on each side

This method of PCB assembly is not advised since the use of adhesives will increase the PCBA cost and may cause certain soldering troubles.

Single side PCB mixed assembly

The production process for single side PCB mixed assembly is as follows: When only a few THT components are needed in this kind of assembly, hand soldering may be used instead of wave soldering.

After comparing the mixed assembly methods presented above, it can be said that hand soldering is effective for PCB assembly when there are several components required on both sides, with SMD components being more prevalent than THT components. So, when faced with a circumstance where only a few THT components are required, wave soldering is recommended.

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SMT (surface mount technology) PCB assembly

Because it includes a fully automatic mounting PCB assembly process from solder paste applying, components pick and place to reflow soldering, surface mounting stands out in terms of production efficiency when compared to thru-hole mounting.

First Step. Solder Paste Applying

A soldering paste printer is used to apply solder paste to the board. A template, also known as a stencil or solder screen, makes ensuring that solder paste can be correctly applied to the proper locations where components will be installed. Because the quality of the soldering is closely related to the quality of the solder paste printing, PCBA manufacturers who focus on high quality products frequently conduct inspections with a solder paste inspector after the solder paste printing. This inspection confirms that printing adheres to rules and specifications. If errors are discovered during the solder paste printing process, the printing must be redone, or the solder paste will be removed before the second printing.


As soon as the PCB exits the solder paste printer, it is automatically delivered to a pick-and-place machine where the components or integrated circuits are put on the appropriate pads under the influence of the solder paste’s tension. Through component spools within the machine, components are installed to PCB boards. Component reels, which revolve like film reels, pass the electronic parts to the automatic machine, which sticks those pieces to the board swiftly.

Third Step. sOLDERING

The board goes through a long furnace once every component has been assembled. Solder paste liquefies at a temperature of 500°F. The SMD electronic components are now securely fastened to the board.

THT(through hole technology) PCB assembly

The through-hole mounting process is carried out using a combination of human and automated procedures as is the case with conventional PCB assembly methods.

Step 1st  Inserting Components :

Engineers working in the field manually do this procedure. Engineers must rapidly and accurately insert components on the PCB according to the client’s circuit board design files. To ensure high-quality finished goods, component placement must adhere to the rules and operating criteria of the thru-hole mounting procedure. For instance, when working with static-sensitive electronic components like ICs, they must wear anti-static wristbands, clarify the polarity and orientation of the components, prevent operating components from affecting ambient components, and ensure that completed component placement is compatible with the relevant standards.

Step 2nd  Inspection

Once electronic components is finished placement, the PCB board is put in a transport frame that matches it, where it will be automatically checked to see if the components are correctly plugged in. If component placement problems are discovered, it is also simple to have them quickly fixed. After all, in the PCBA process, this occurs before soldering.

Step 3rd Wave Soldering

Now, carefully solder the THT components to the circuit board. In the wave soldering technology, the board glides gently across a high-temperature, 500°F-plus wave of liquid solder. All leads or wire connections may then be made effectively, allowing thru-hole components to be securely fastened to the board.

In this article, descriptions of the PCB assembly process only focus on standard PCBA practices and technology. Design files and unique client requirements play a significant role in determining and influencing the practical production process. PCB assembly is a highly technological process that requires careful consideration of many different factors. Even little changes can have a significant impact on both cost and final quality. Additionally, the production technique and manufacturer experience may have an impact on PCBA quality. As a result, clients must carefully consider how to assess a reputable PCB assembler before placing their PCBA purchase.

Why choose INTOPCB?

The leading supplier of PCB solutions is INTOPCB. We can take care of all of your PCB needs, including parts procurement and electronic assembly. We’ll be there for you every step of the way, offering you complete knowledge and quality assurance.

If you selecting us as your partner, you’re deciding to work with a firm that offers the greatest results. Our printed circuit board assembly services adhere to IPC Class 3, RoHS, and ISO 9001:2008 certification standards and satisfy the highest quality criteria. Additionally, whether the project involves a single-sided or double-sided PCB, SMT, through-hole, or mixed assembly, we are capable of handling it. We can carry out any task you need!

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From the start of the project all the way to its conclusion, we’ll stay in touch with you and keep you updated on everything, from PCB fabrication to PCB assembly. With reduced PCB prices, shorter wait times, and better goods, It would help you to save investment and reduce stress. We aim to save you effort, energy and time, so you can concentrate on designing PCBs rather than worrying about the details of production.

Related Technology of PCB assembly

Some technology would using in PCB assembly, you may want to know, then you can select a better PCB assembly service.


Transferring the layout and the PCB’s schematics onto a photo or glossy paper for final production is referred to as PCB printing. The output should be in the form of a shiny one-sided. This step is very important to ensure that the results are of good quality.

N2 System

N2 is a type of gas that’s commonly used in the production of PCBs. It’s a colorless and odorless gas that can be used in the process of selective soldering and reflow soldering. The use of nitrogen gas in the production of PCBs provides a unique method for preventing convection reflow and oxidation.


A varnish coating is a type of protective material that is applied to the surface of a printed circuit board to prevent corrosion and damage. It can also help prevent the board from getting damaged due to the environment.


Conducting tests on PCBs is an essential step in the production of electronic components. It can help manufacturers identify errors and prevent them from happening in the first place. Doing so will minimize the costs associated with reworks and ensure that the board is working properly.

Lead-free soldering

In commercial use, lead-free solders can contain various metal components such as silver, copper, bismuth, and antimony. However, they should be used with caution since they can potentially produce dust and fumes that are hazardous.

Box-Build Assembly

The term systems integration refers to a type of assembly that involves the complete integration of a product’s components. A box build community is a place where the customer’s finished product is assembled. This type of assembly can be done in a cabinet that’s full of wires and a small enclosure.

Radial Vertical Assembly

A radial vertical assembly is done on a bare PCB, and components are placed on top of one another. This method ensures that the order of the components is placed on the board. When talking about leads, they come from one end of the element.

Turnkey Assembly

A “turnkey” service or product is a ready-to-use service or product that can be purchased by the end user immediately. For instance, when it comes to the assembly of a printed circuit board, a supplier can handle the various aspects of the project.

Axial Horizontal Assembly

The axial leads protrude from the ends of boxes or cylindrical components. These are commonly used to span short distances on PCBs. They are typically shaped like wire jumpers and are ideal for use in applications where the board is short. There are two types of axial horizontal assembly: surface-mounted and right-angle through-hole.

Cable Assembly

A cable assembly is a type of component that consists of wires and cables that are arranged into a single unit. It can transmit power, as well as send and receive informational signals. These components are usually used to organize multiple cables in a convenient package.

BGA Assembly

The Ball Grid Array, also referred to as BGA, is a type of surface mount technology that is commonly used in the production of electronic components. This type of packaging is very low-cost and high-density. It is ideal for bringing out the best possible circuit boards.

Mechanical Assembly

Mechanical assembly of PCBs involves assembling components in a process known as an assembly line. It’s also a type of manufacturing that involves putting products together for a specific function.

Surface mount technology

An electrical component is mounted directly onto a printed circuit board (PCB). This method is commonly referred to as surface mount technology (SMT). Compared to through-hole components, SMT components have a surface face that’s shorter than the short leads of the PCBs.

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