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Problems Frequently Found in Complex PCB Assembly

For the final product to work as intended, the circuit board assembly process entails a number of procedures and instructions that need to be followed in the correct order. PCB producers control he way components are put and secured into place by using regulated cooling and heating systems, screen templates, as well as other methods.

Depending on the available components, you must select the appropriate technology while assembling a circuit board. This PCB design calls for precise alignment of all the components in their predetermined locations. Any divergence, no matter how little, could have a significant impact on how well the final board performs.

What Does Complex PCB Assembly Mean?

The completed board once all the entire components are soldered and mounted on a circuit board is known as the circuit board assembly (PCB). The assembly is created by using the conductive paths carved inside the laminated sheet layers of copper of PCBs inside of the non-conductive substrate. The final step in creating an electronic gadget that is fully functional is attaching all electronic components onto the PCBs.

PCB refers to the circuit board that has not yet been assembled with electronic components. This board is known as the printed circuit assembly or a PCB assembly once the electronic components have been soldered on. Throughout this process, many automatic and manual tools for PCB assembly are used.

It is important to keep in mind that complex PCB assembly differs from the process of PCB manufacturing. Several procedures go into the production of circuit boards, including PCB design and PCB prototype production. Before a PCB may be utilized in different electronic devices or equipment, Passive and Active Electronic Components must be soldered on it. This electronic component assembly depends on the circuit board type, the electronic component type, and the circuit board’s intended use.

Technologies for Mounting during Complex PCB Assembly  

 SMT (Surface-mount technology)

The primary driver for the switch to SMT was the significant increase in PCB manufacturing process speed, cost, and reliability. Despite this being the main effect of the technology’s adoption, it also has an effect on the creation of fresh electronic devices and equipment.

Fortunately, the transfer has more positive effects on circuit performance and development than negative ones. The usage of SMT has various benefits for development engineers.

Components are put directly on the PCB surface using the SMT method. The technique, which was created during the 1960s but was initially called “planar mounting,” has become more and more well-known since during the 1980s. Nowadays, SMT is used almost exclusively in the production of electronic devices.

THT (Through-hole technology)

Component leads gets inserted in drilled holes present on the blank PCB for through-hole mounting. The procedure was used until the development of SMT during the 1980s, when it was anticipated that through-hole would be totally phased out.

However, despite suffering a sharp decline in popularity through time, through-hole technology still endured in the SMT era, giving a variety of benefits and specialized applications, most notably durability.

The optimum applications for through-hole components come with high-reliability systems that call for stronger connections present between the layers. Leads for through-hole components pass through the board, enabling the leads to endure greater environmental stress than SMT components, which are only fastened by solder and on the board’s surface.

Because of this, through-hole technology can be frequently applied to aerospace and military goods that could be subjected to high temperatures, collisions, and extreme accelerations. In test as well as prototype applications, which occasionally need for manual modifications and replacements, the through-hole technology comes also helpful.

Steps Necessary for Complex PCB Assembly


Stenciling of the Solder Paste

The first stage in PCB construction is the stenciling of the solder paste. This step stays the same regardless of the PCB assembly type. Over the circuit board is a unique stencil fashioned from a metallic and thin sheet. It makes sure that such solder paste can only be utilized where the mounting of the components is intended. The stencil is removed from the board after the solder paste has been applied.

Picking and placing the components  

Component mounting can be described as a picking and placing task that can be carried either automatically or manually. Component mounting is done by hand during THT PCB assembly. An automatic machine does it in the surface-mount circuit board assembly. Automatic mounting of the components provides a swift, accurate, as well as error-free procedure.


On the Circuit board, soldering is used to connect components. Wave soldering is used in through-hole assembly. In this, a hot liquid wave solder is passed over a Circuit board with installed components. These solder balls become liquefied as a result, and the paste solidifies after cooling to room temperature. Reflow soldering would be done in the SMT PCB assembly, though. In this, a furnace with a 500°F temperature is used to process the PCB.  After melting, this solder paste cools and settles with all the components involved.


To guarantee that the gadget is operating properly, quality and inspection testing are done. It includes three separate inspection techniques, which are listed below.

Inspection (post assembly) as well as functional testing

After assembly, the PCBs undergo a second inspection and functional testing. To wrap up the process, functionality tests such as micro-sectioning test, solderability test, and contamination test are conducted.

Typical Issues with Complex PCB Assembly

PCB Assembly Control Board
PCB Assembly Control Board

Faulty PCB footprints

Just as we mentioned, it is crucial to verify the BOM so as to ensure the correct footprint is linked to the part. However, an examination of this PCB footprint must go beyond the BOM alone. Verify that this footprint is constructed correctly in accordance with the data sheet of the manufacturer as well as industry requirements.

Its footprint pads should also be examined to make sure the component will mount and solder to the PCB board properly.

Insufficient human access

Rework technicians cannot swap out parts, fix any assembly flaws, or test a board if they don’t have enough room to work. Due to the technicians’ need to maneuver around the impediments and potential for damage to other components, the limitation of space causes PCB assembly to take longer and cost more money. Additionally, if such connectors as well as other forms of human interfaces are not positioned for simple access, connecting the board to its system could be challenging.

Faulty soldering

The components must be positioned precisely to prevent soldering errors in addition to being properly spaced for the pick and place machine. The pieces must be rotated so as to enter a wave perpendicular towards it in order to use wave soldering.

Additionally, avoid placing taller components in front of shorter components in the wave since this may result in shadow effect, which may weaken the solder joint present on those pins. Make sure the two pins of the smaller 2 pin distinct items are both thermally balanced before placing them in solder reflow ovens. By doing this, you can prevent tombstoning, which is when a part gets pulled onto a pin because one side of the component heats up more quickly compared to the other.

BOM issues

Inaccurate information in the bill of materials may result in the ordering and installation of the wrong part on the circuit board. BOMs may also include information that is no longer accurate and list parts that cannot be produced.

Check the BOM of the circuit board before sending it off for manufacturing.

  • Accurate parts
  • Parts with matching part numbers and descriptions
  • PCB layouts that are accurately matched to their components
  • Parts that might not be readily available because they are end-of-life, obsolete (OBS), as well as recommended for brand new designs

DFM mistakes

One important factor for designing the circuit board is DFM – design for manufactureability. Make sure the components remain positioned with the appropriate distance between them, the board edge, and any other mechanical objects for the board.

Without this gap, it may be impossible to assemble the components using automated machinery, which would significantly increase the manufacturing cost and time of the board.

Faulty PCB footprints

Just as we mentioned, it is crucial to verify the BOM in order to ensure the correct footprint is linked to the part. However, an examination of that PCB footprints should go beyond the BOM alone. Verify that the footprint has been constructed correctly in accordance with the datasheet of the manufacturer as well as industry requirements. These footprint pads should also be examined to make sure the component will mount and solder to the pcb board properly.

PCB Inspection Methods in Complex PCB Assembly

pcba box build assembly

Visual and manual examination

Soldered connections can only be visually inspected by hand. This technique is only appropriate for small batches of Circuit boards; otherwise, optical fatigue prevents precision.

Automatic Optical Inspection

To examine PCBs, this AOI machine has high-resolution cameras which can be positioned at various angles. For the double or single-sized PCBs, this kind of examination is appropriate, however it is insufficient for multi-layer complex Circuit boards.

X-ray inspection

On complex PCB designs, X-ray inspection will be done. It is challenging to optically analyze such intricate PCBs.


More than the raw materials as well as a properly designed board are needed to put together the printed circuit board. It also needs the appropriate technologies. Additionally, there are a number of processes in the complicated PCB construction process that must be meticulously completed.




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