PCB Assembly Process: Step-by-Step Guide to Precision and Quality

Apr 23,2020

The printed circuit boards (PCBs) form the core of various electronic devices that we use today. These PCBs are made of several small and fine components, which are carefully designed and assembled for the desired outcome. Thus, the PCB assembly is a straightforward yet lengthy process. Not to be distracted by the simplicity of the process, it demands meticulous attention to details. If not paid attention any slightest error may have a drastic impact on the performance. Therefore, it is very important to follow the PCB assembly steps without any fail. This post discusses the steps involved in a PCB assembly.

A Discussion on Step-by-Step PCB Assembly Process

China is known as the heartland of electronics manufacturing. PCB manufacturing has been one important industry in China. Earlier Most US-based manufacturers outsourced their PCB manufacturing and assembly services to China to save on time, efforts, and money. However, in recent years, there has been a decline in outsourcing. Increasing demand for quality PCBs, raising awareness about sweat factories, and the institution of various stringent environment-friendly directives regarding the use of hazardous substances in PCBs are some factors that have contributed to this trend reversal. Today, many US-based electronics manufacturers prefer partnering with trusted PCB assembly services in the US rather than outsourcing their services to China. Now, you may ask is the PCB assembly process in the USA different from other countries. No, there are no major differences, except for a few.

As aforementioned, the PCB assembly is a step-by-step guided process. Depending on the specific type of PCB assemblies such as through-hole and surface mount, the steps may vary slightly. The following are the steps involved in the PCB assembly process in the USA.

The Solder paste is the mixture of small metallic balls called solder and the flux. Solder is the powder or tiny balls of 3% Ag, 96.5% Sn, and 0.5% Cu. This mixture is applied as a settling glue on the board. For complex PCB designs, a detailed solder paste stenciling is used.

This process is common to most PCB assembly services in the US. As said before, PCBs are integral to several electronic devices, so it is important to approach a trusted or experience PCB assembly services in the US for your next project Creative Hi-Tech is a leading provider of PCB assemblies in the US. Established in 1998, the company has been serving clients across industries such as military and defense, medical, aerospace and satellite, among others.

• Solder Paste Stenciling:

  The solder paste stenciling is the foundation step of PCB assembly. Irrespective of the types of PCB assembly, this step remains the same. A stencil made of a thin metallic sheet is placed over the board. It ensures that the solder paste is only applied to the area where the components are to be mounted. After the application of solder paste, the stencil is taken off the board.

• Pick and Place Components Mounting:

  The component mounting is a pick and place activity which can be performed manually or mechanically by an automated system. In the through-hole PCB assembly, the component mounting is performed manually. In surface-mount PCB assembly, it is performed by an automated machine. Automatic component mounting offers quick, precise and error-free process.

• Soldering:

  Soldering is performed to join components on the PCB. In the through-hole assembly, the wave soldering is performed. In this, the PCB with mounted components travels over a hot wave solder liquid. This liquefies the solder balls and then on cooling at room temperature solidifies the paste. However, in the surface mount PCB assembly, the reflow soldering is performed. In this, the PCB is passed through a furnace heated to a temperature of 500°F. The solder paste melts and on cooling settles with the components.

• Inspection:

  Inspection and quality testing are performed to ensure the functioning of the device. It involves three different methods for inspection, which are as described below.

  • Visual/Manual Inspection:

    Manual inspection is only sufficient to inspect the soldered connections. This method is only suitable for the small batch of PCBs, otherwise, due to optical fatigue, it l

    acks accuracy.

  • Automatic Optical Inspection (AOI):

    The AOI machine features high-resolution cameras that can be aligned in different angles to test PCBs. This type of inspection is suitable for single or double-sized PCBs but it does not suffice for multi-layer complex PCBs.

  • X-ray Inspection:

    X-ray inspection is performed on intricate PCB designs with multi-layer component mounting. Such complex PCBs are hard to inspect optically.

• Post Assembly Inspection and Functional Testing:

  Once the assembly is done, the PCBs are inspected again and are tested for functionality. The functionality tests like a micro-sectioning test, contamination test, Solderability test, are performed to conclude the process.

Related Blog Post: 

• How Does a PCB Assembly Process Work?