PCB assembly - far from old-fashioned technology

As part of the Electronic Manufacturing Services of Leesys GmbH, PCB assembly includes the placement and soldering of various electronic components onto a raw board (unassembled PCB).


What makes the PCB Assembly?

Over the past decades, the technology which Leesys uses for the assembly of printed circuit boards has always developed further with the use of components. The trend is moving to ever smaller designs and ever higher packing densities when it comes to the requirements for high-quality PCB assembly. The smallest components that can be assembled at Leesys are those of size 01005, which requires a great deal of know-how in addition to precise, highly efficient production systems.


The most important thing when assembling printed circuit boards is to create visually and technically perfect soldering points while treating the components as gently as possible and subjecting them to as little thermal and mechanical stress as possible. In the past, it was mainly the sensitivity of the solderers that was important. Today, it is the intuition in the figurative sense that the operator has to prove during machine soldering and assembling.


State-of-the-art equipment and know-how in combination with well planned processes and responsible handling of materials make for high-quality PCB assembly - at Leesys from one piece onward. Leesys manufactures small, medium and large series. The highest quality is always guaranteed with soldering effects of only 1 dpm and placement errors of only 13 dpm.

PCB assembly


Method in the assembly of printed circuit boards

Until the 1980s, the actual assembly of the printed circuit boards was done by hand, even though many production steps had already been automated. The connecting wires of the components were inserted and soldered through holes drilled in the printed circuit boards beforehand. This manufacturing process is called THT assembly (through hole technology).
Since the late 1980s, the term printed circuit board assembly has generally been associated with (fully) automated SMT assembly (surface mounted technology).


With a stencil printing plate, a specially manufactured stencil with recesses for the individual pads, the solder paste is applied to the corresponding areas before the actual assembly using the screen printing process. The prepared plate can now be equipped with the individual electronic components.

Depending on customer requirements, both SMT and THT processes are used at Leesys.


Surface Mounted Technology

SMT assembly is usually fully automated: All small components, such as capacitors, resistors or microcontrollers, are assembled quickly and in large numbers. Leesys uses eight SMT lines from ASM for this purpose. These offer high precision and performance with minimal footprint. Up to 760,000 elements are assembled per hour, 14 million assemblies per year.

Through Hole Technology

In THT assembly, PCB fasteners, connectors and cables are usually assembled by hand. On the one hand, this prevents damage to components that have already been soldered on. On the other hand, further SMT assembly is often no longer technically possible if both sides of the PCB have already been assembled. The advantage of the THT PCB assembly process is the mechanical strength and the possibility to process even very large components.


After the PCB has been assembled, the various components are soldered. This is followed by depanelization and, if required, protective coating. Leesys offers three types of depaneling: By roller knife, with the milling machine and cutting with the saw. If necessary, a protective coating can be applied to the printed circuit board by dipping. This type of painting is used for high mechanical requirements or high environmental demands.

Finally, the assembled PCB is subjected to various automatic optical inspections (AOI) and functional tests.