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A Short Guide to Different Types of PCB Assembly Processes

 May 13, 2020

The Printed Circuit Board (PCB) is at the core of every electronic device that we connect today. These PCBs. PCBs basically interconnect the electronic components by creating conductive pathways via copper pads and connecting lines. Therefore, the PCB assembly process becomes one of the most intriguing concepts in electronics. This post introduces different types of PCB assembly processes and gives insights about their functionalities.

Introduction to Traditional PCB Assembly Process

The basic PCB assembly, generally referred to as the PCBA, proceeds in the following way.

  • Solder Paste Application: The paste solder grains mixed with flux is applied on the baseboard of the PCB. The stencils of different sizes and shapes are utilized to ensure the application of paste on the specific locations only.
  • Component Placement: The small electronic components of the circuit are placed on the solder pasted board, either manually or automatically, with the help of pick and place robotic mechanism.
  • Reflow: The solidification of the solder paste is performed in the reflow process. The PCB board with mounted components is passed through a reflow oven that has over 500° F temperature. Once the solder paste is melted, it is taken back to the conveyor and solidified by exposing it to a cooler.
  • Inspection: This follows the post reflow process. The inspection is performed to check the functionality of components. This stage is important as it helps identify misplaced components, poor quality connections, and shorts. Generally, misplacements occur during the reflow process. The PCB manufacturers employ manual checks, X-ray inspection, and automated optical inspection at this stage.
  • Through-hole part insertion: Many circuit boards require the simultaneous insertion of through-hole and surface mount components. So, in this step that that is accomplished. Generally, the through-hole insertion is performed using wave or manual soldering.
  • Final inspection and cleaning: Finally, the PCB board is inspected for its electronic potential by testing it under different currents and voltages. Once the PCB board passes this inspection this stage, it is washed with deionized water as soldering leaves some residues. After washing it is dried under compressed air and a fine product is packaged.

This is the traditional PCB assembly process that is followed. As seen, most PCBs utilize Through-hole technology assembly (THT), surface mount technology assembly (SMT) and mixed assembly processes. These PCBA processes are discussed further.

Through-Hole Technology Assembly (THT): A Brief Introduction to Steps Involved

Only a few steps of PCBA differ in Through-hole technology (THT). Let us discuss the steps of THT for PCBA.

  • Components Placement: In this process, the components are mounted manually by highly experienced engineers. The manual pick and place component mounting process requires the utmost precision and speed to ensure the component placement. The engineers are expected to follow THT standards and regulations to achieve optimum functionality.
  • Inspection and Component Rectification: The PCB board is matched with a design transport frame to ensure the precise placement of components. If any misallocation of the components is found, then it is rectified at that time only. Rectification is easier before soldering, therefore component positions are rectified at this stage.
  • Wave Soldering: In THT, the wave soldering is performed to solidify the solder paste and keeping the components intact at their specific positions. In wave soldering, the component mounted PCB board moves over liquid solder, heated at the temperature over 500° F, in a slow wave motion. And then is exposed to the coolers, to solidify the connections.

Surface Mount Technology Assembly (SMT): What are the Different Steps Involved

The PCBA steps followed in SMT assembly are detailed as follows:

  • Solder Paste Application/Printing: With the reference of a design stencil, the solder paste is applied on the board, via solder paste printer. This ensures that the solder paste is printed at specific locations, in satisfactory quantity.
  • Components Placement: The component placement is automatic in the SMT assembly. From the printer, the board is sent to component mounting where components are picked and placed by the robotic pick and place mechanisms. This technique saves time as it is quicker than the manual process and also ensures the precision of specific component locations.
  • Reflow Soldering: After the component mounting, the PCB is placed in a furnace, where the solder paste melts and settles around components. The PCB is passed through coolers to fixate the components at the location.

Surface Mount Technology (SMT) is more efficient for complex PCB assembly processes.

Due to the increasing complexity of electronic devices and PCB designs, the mixed assembly type is also used in the industry. Although, as the name suggests, the mixed PCB assembly process is an amalgamation of THT and SMT.

Since the industrial significance of the PCB assembly process is gradually increasing in electronic device manufacturing, it is convenient to go for professional services. Accelerated Assemblies, Inc is the company that offers professional PCBA services to medical, municipal, lighting, electrical manufacturing, and industrial control industries and many more.