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28 October 2026
Printed circuit boards (PCBs) are marvellous things, but they don't emerge into the world complete and ready to slot into your electronics. Good thing for us too, or everyone at J-TEQ might need to find a different job.
So how do you go from a bare PCB to a fully assembled board ready to go? Let's go through the steps we'd take when building a PCB for you.
Many people think PCB assembly and PCB manufacturing are the same, but there's a slight difference between the two. We typically use the term "PCB manufacturing" to talk about the construction of the actual bare boards, while "PCB assembly" is when we take the bare boards and mount components on them.
There are two main ways in which we do this: surface mount technology (SMT) and through-hole technology (THT).
SMT is where the components are soldered directly onto the board rather than inserted through drilled holes and soldered to pads on the opposite side. This latter is the THT process. SMT is the more commonly used of the two, but both are still widely used throughout modern PCB assembly processes. They each have their own strengths and weaknesses, and an EMS provider such as J-TEQ will be able to advise on the correct assembly process for your project.
Though no two projects may be alike, we can quite easily break down the assembly process into these stages.
The first stage of any PCB assembly process is a design review. Here at J-TEQ, we won't design your PCB for you, but we will put it through a design for manufacturability (DFM) and design for assembly (DFA) assessments. These processes allow us to identify potential manufacturing issues before production actually begins.
If there is a problem or something likely to cause an error, these reviews allow us to hopefully catch it before components end up on boards. This prevents costly production errors and delays.
With the design ready to go, we will look into component sourcing to check that we have everything we need. This includes checking component availability, specifications, and compatibility, all to ensure that we have chosen exactly the right components for your board.
We will also prepare the PCBs in this stage and ensure we have the correct solder paste and other materials best suited for your project. Procurement expertise allows us to manage supply chain risks more easily, so we can substitute an unavailable component with a suitable replacement and move the project forward without delay.
Solder paste plays an important role in creating the electrical connections between components and the PCB. It contains tiny solder particles and flux, which helps the solder flow and bond to the metal surfaces during heating. The paste is applied to designated pads using a stencil, ready for component placement.
The placement of components must be incredibly precise, especially on high-density PCBs where there may be many components arranged in a finite space. For this, we use an automated pick-and-place machine. Not only can it place components precisely where we need them, but it can also do it much faster than the average technician.
Using pick-and-place machines allows us to maintain consistency, whether you have a small run of PCBs or a large order to fulfil. For high-density PCBs, consistency is key.
When the components are correctly placed, the board is passed through a special oven. This melts the solder paste and allows connections to form between components and the board, allowing electricity to pass through the board when used as part of a wider device.
A reflow oven is not the same as a conventional oven. The board passes through a carefully controlled heating and cooling process, allowing the solder paste to melt, form secure electrical connections, and solidify without damaging the components or common defects like tombstoning or solder bridges forming.
If a through-hole component process is going to be used, this stage of production may take place at several points during the overall assembly.
Through-hole components may be inserted manually or using automated equipment. Depending on the project, soldering can also be carried out by hand, through selective soldering, or using a wave soldering machine. In wave soldering, the underside of the board passes over a wave of molten solder, creating connections between the component leads and the PCB.
Good inspection and quality control efforts should take place after every stage of the assembly process. If inspection only took place after soldering, as an example, there is a high chance that defects could be spotted that could have been corrected much earlier in the process. This results in costly mistakes, delayed production, and wasted components when a more robust quality control system would hopefully catch these issues.
A variety of inspection and quality control methods are used to ensure PCBs are up to standard. These may include visual inspection, where a trained technician will examine the board closely, and the use of machines. Automated optical inspection (AOI) checks for visible defects, including missing or incorrectly positioned components and soldering issues. Meanwhile, X-ray inspection examines hidden solder joints, particularly beneath ball grid array (BGA) components that cannot be examined by visual inspection.
Once assembly has been completed, the boards have one more core stage to go through: testing.
In-circuit testing (ICT) examines individual circuits and components to identify faults such as short circuits, open connections, or incorrect component values. Functional testing, meanwhile, checks whether the completed PCB performs as intended under specified operating conditions.
Testing can also be dictated by the end-use requirements of the PCB. A board that is going into a high-risk environment may require additional testing to ensure it meets the standards required of its intended industry. With testing complete, the PCB is ready to be delivered to its destination.
As with any manufacturing or assembly process, things can never progress as smoothly as we might first like. It is therefore important that we are realistic about some of the factors that could affect the PCB assembly process. These may include but are not limited to:
Building a good partnership with your PCB provider is key, whether you need help with just one small project or you are searching for someone to build a lasting partnership that will span over multiple projects.
J-TEQ EMS may be the assembly partner you have been searching for. We have built our assembly process on the principles of manufacturing excellence, continuous improvement, and stringent control. Our staff is committed to consistently delivering high-quality products and services to meet our customers' exact specifications, whatever they might be.
From SMT to THT to rapid prototyping and low-volume orders, our team carries a wide array of experience and specialities. Whether you have a project in mind or you just want to enquire about how our assembly processes work, get in touch today.
