Thursday, 30 June 2022 17:07

What is PCB Assembly process?

pcb assembly pcb assembly Quelle: Lizenz:

electronics is a printed circuit board commonly referred to as a PCB and it is essentially an electronic chip.

Since the majority of electronic devices will not be able to function without a PCB, there is a high demand for its manufacturing and it is a common practice to use the services of EMS providers for its production. In this article, we are going to focus on the assembly process of PCBs.

Modern technologies used for PCB assembly

Usually, a basic PCB has a layered structure with a conductive coper foil attached to the base with a solder mask, covered with silkscreen. Assembly can be conducted in two ways: through SMT and THT and, depending on the exact method, it is possible to create various types of PCBs including the ones of a flexible or rigid structure, or, for instance, a PCB with a metal core.


SMT stands for Surface Mount Technology and it is regarded to be a more up-to-date method for printed circuit board assembly. The greatest part of PCB assembly relies on SMT as it allows direct placing of pieces of electronics on the surface of a board making it easy to automate the process.

Furthermore, the components can be placed on the both sides of a board saving space and material and resulting in overall lower costs of production. SMT allows creating more complex structures than previous technologies and working with very small components such as the ones of the 01005 type which are regarded to be the smallest electronic components today.

Manufacturing with SMT is achieved through several different technologies including fine-pitch BGA, Mini BGA and pin-in-paste. The manufacturing process itself is powered by the pick-and-place technology.

To create a final product with SMT, reflow is required. Reflow can be performed with a high temperature and nitrogen with or without lead. SMT reflow can also be two-sided.


THT is an abbreviation for Automated Through-Hole Assembly. This technology had been widely used before the advent of SMT. It was initially based on assembling electronic components exclusively by attaching them to drilled holes, however, the latest modification uses solder paste and reflow, thus, utilising the advantages of SMT.

Usually, for THT, the process of PCB assembly is less automated than it is for SMT which can result in higher costs of manufacturing in the long run. That is one of the major reasons why SMT has become a domineering technology in the electronics manufacturing industry. Yet, there is still a demand for THT mainly due to its reliability of mounting based on mechanical bonds.

Step-by step PCB assembly with SMT

To understand the process of PCB assembly better, it is sensible to look at the steps of SMT manufacturing as it is the most commonly used technology today.

In its case, everything starts with machine programming for setting specific configuration according to the requirements of a project. For this purpose, an EMS provider needs Gerber files for automating the pick-and-place and inspection machines. These files as well as the bill of materials (BOM) are provided by the client.

When the manufacturing equipment is ready, the solder paste application begins. Often, the surface is covered with the paste according to a template and this process requires high precision to avoid errors. That is why, the control procedures are absolutely necessary during the manufacturing process. Depending on the exact SMT machinery used for PCB assembly, control can be achieved with either the 2D or 3D technology. This process is automated.

The next stage of SMT assembly is mounting components on the board which is usually done with the help of the pick-and-place machine. Yet, before the machine places elements on the board, they are checked automatically with machine vision. Depending on the exact equipment, the speed of the process can vary. It can reach even 120 thousand pieces mounted on the board per hour.

A certain circuit structure requires particular temperature for reflow which is necessary for soldering paste to attach the elements on the board appropriately. The manufacturing line is often divided into several zones with different temperatures to solidify solder paste connecting the elements on the board better.

A typical manufacturing procedure ends with Automated Optical Inspection or AOI checking for any faults and comparing the results to the master plate.

Manufacturing approaches

Regardless of the technology, PCB assembly can be performed according to one of the following approaches.

The first one is known as Low-Mix/High-Volume and it is a commonly used way to produce PCBs. It is suitable for mass projects with a demand for a large quantity of equal or similar goods.

While such a method is quite common for any mass production, there is a growing need for diverse versions of the same product and this trend specifically influences PCB assembly, albeit in the case of electronic manufacturing, this task becomes particularly challenging.

To create a smaller number of different products, a method known as High-Mix/Low-Volume is used and it requires a great flexibility and advanced resource management from an EMS provider.

Complex services of PCB assembly

For many companies, outsourcing PCB assembly is a sensible decision since building sufficient infrastructure for electronics production is a rather expensive investment. Using the services of professional electronics manufacturers allows enterprises to save a lot of money and time as well as helps them to avoid unnecessary technological mistakes.

There are EMS providers on the market that offer complex support for PCB assembly. Their task is to manufacture PCBs exactly according to the design of their clients.

EMS providers assist original electronics manufacturers during the initial phase of a new product introduction taking care of the entire supply chain. They pay particular attention to the project requirements and make sure the collected components are compliant with the specifications.

The introduction of a new product results in a prototype. If a client finds it satisfactory, mass production starts.

Some EMS providers, for example, Assel, go even further and offer box build and electro-mechanical integration to their clients. Depending on the expectations of a client, final products can also be packaged by an EMS provider.

Find out more on