From smartphones and laptops to satellite systems and medical equipment, printed circuit boards (PCBs) are the base of most electronics products. 

Today, the use of PCBs in electronics is widespread and there are various types: from single-sided or double-sided to multilayer, and they can be rigid, flexible or a mixture of both. But no matter the type of PCB, it’s always critical that the assembly process is done right the first time. A single misstep could result in malfunctions, lack of functionality or even the threat of accidents… 

So, what PCB assembly methods are available to electronics manufacturers, and how does the process work?  

What are the commonly used PCB assembly methods?

Plated through-hole (PTH) mounting is the original method for PCB assembly (PCBA). Through-hole mounting involves inserting components into plated drill holes to a bare PCB, then manually applying solder to the component to form an electronic or mechanical connection.  

But with the development of technology, electronic products are becoming increasingly complex, driving the need for smaller, more intricate PCBs. As such, through-hole mounting is now less prevalent in PCB assembly, and surface-mount technology (SMT) is the core assembly method. However, PTH application is still part of PCB assembly, as not all components are available in SMT form — particularly heavy-duty parts that require a more robust mechanical connection.  

SMT involves directly securing components onto the surface of the board by solder, as opposed to placing them into drill holes. 

Surface-mount devices (SMDs) are typically smaller — meaning more components can be fitted into a smaller space. The manufacturing of PCBA using this method is also far more efficient and reliable as it’s automated — leading to cost savings for both the electronic manufacturer and the end customer. 

How are PCBs assembled?

Before PCBA can begin, electronics manufacturers will require the manufacturing data pack, consisting of PCB Gerber data (including the specifications and fabrication notes) and the bill of materials (BOM). Not only does this allow the manufacturer to quote the project, but it also enables a thorough review of the data to ensure adequate design for manufacturing (DFM) ahead of assembly.  

Once the check is complete, the first step of assembly is applying solder paste to the bare board, processed by automatic alignment of a stencil with laser cut apertures to suit the PCB layout. Depending on the component footprint, various reductions are applied to the stencil before the solder paste is applied to the PCB using squeegee blades programmed to optimum speed and pressure.  

Next, a fully automated pick-and-place machine is used to place SMDs onto a pasted PCB. To ensure ultimate precision, the machine is programmed using X and Y coordinates generated from the supplied Gerber data.  

Once the SMDs are in place, they need to adhere to the board. To do this, the PCB is transferred to a conveyor belt through a reflow oven consisting of a series of heaters. This allows the solder to turn molten and solidify through the cooling zone. Each zone is set to a specific temperature depending on the design of the PCB — starting low and steadily increasing, which prevents thermal shock to the PCB and SMDs.  

Now that the SMDs are soldered in place, the assembled board will go through automatic optical inspection (AOI) to ensure its component values, placement alignment and solder quality are correct.  

Selective soldering

As through-hole mounting is still a requirement, selective soldering can be used for most PTH components. This allows the manufacturer to enhance and streamline the process, negating the need for manual intervention and ensuring consistency and increased throughput.  

Selective soldering operates by pumping molten solder from a reservoir through a nozzle securing the component that protrudes through the PCB’s surface.  

How can EMS assist your PCBA needs?

As a specialist PCB assembly manufacturer, EMS offers both through-hole and surface-mount technology — enabling us to provide the complete PCB manufacturing solution you require. 

Thanks to our policy of continuous investment, all our PCB assembly services are carried out using the latest, top-of-the-range equipment — like our selective soldering machine, the Kurtz Ersa Versaflow, which allows for greater flexibility, increased precision and boosted productivity. 

Need a quick turnaround time for your electronics project? No problem. At EMS, we supply PCB prototypes to volume, so no matter your requirement, we’ll work with you to achieve the best turnaround possible…   

We’re ready to meet all demands — big or small! To learn more about our PCBA services and how our manufacturing solutions can assist you, don’t hesitate to request a quote today or contact us at