Understanding PCB Inspection Techniques for Superior Quality

Mar 10,2022

Quality and accuracy are crucial aspects of any product to remove errors, and the same applies for printed circuit boards since they are a crucial component in all digital and electromechanical devices. So, PCB inspection is a crucial aspect of PCB manufacturing and assembling. In manufacturing, blank boards are fabricated, and assembling comprises mounting circuitry and components. Ideally, PCB inspection is carried out at each step of the manufacturing and assembling processes. While a basic visual inspection may identify some flaws and is still used, there are many types of automated testing tools and techniques used by PCB manufacturers and assembly service providers. This post offers the types of PCB inspection and its significance.

Referential and Non-Referential PCB Inspection Techniques

There are three types of boards widely used- rigid, flex, and rigid flex. Flex and rigid flex boards find maximum applications across industries as they are flexible yet durable with a high bend radius and have the capacity to accommodate several components on a thin substrate. These boards have different PCB inspection algorithms based on their type and properties. As mentioned, blank PCBs are inspected thoroughly before component mounting and soldering. There are certain algorithms which separate the type of probable defects such as shorting, protruded copper spurs, dust on the board, open circuits and conductors, and so on. The following are two common inspection algorithms used to identify issues in PCBs.

• Referential algorithms:

  These algorithms are reference based, which means they have a ready model or design with which they can compare the characteristics of the new board. This type of inspection includes matching of images and templates. Circuits are also compared in this manner with a 3D model as a reference. These referential methods are widely used even now. However, they have their own set of cons. For instance, when you have a reference board or a model and comparisons are conducted, there could be false readings due to noise, image distortion, and interpretation errors. So, non-referential algorithms have also been developed and are used as much.

• Non-referential algorithms:

  Here, there is no reference model or design. So, the readings and observations of the PCB inspection performed are absolute. They are original, which means the board image is observed and its patterns, attributes, and probable defects are noted in the form of data. This is verified based on design rule verification standard. The defects are detected after applying those specific algorithms. After this, a data table or so is formed and analyzed to take further steps. Non-referential algorithms are applied to inspect external or morphological features, board boundaries, and run length encoding. When using these algorithms, it is absolutely essential to verify them against the set standards. Also, while there is no design preview or reference for comparison, one must ensure that the design requirements are met and there are no defects pertaining to the same. This is one of the challenges of non-referential algorithms. So, most times a hybrid algorithm is used which has features of referential and non-referential.

• Hybrid algorithms:

  This is an ideal combination which overcomes the cons of the above two approaches. This approach achieves two things- it prevents any violation of defects as per specific design requirements of a client. Also, it meets the required verification standards.

Among all the type of boards, flex ones may pose certain challenges in terms of accurate defect detection. This is mainly because they are thin and bendable, and may reflect distortion in their stretching capacity. These boards may show size distortion and overall non-uniformity in patterns due to which it is difficult for an algorithm to detect defects. Fortunately, there are ways to overcome these challenges.

Overcoming Defect Detection for Flexible PCBs

First, the image of the blank board is captured and it is divided into small frames or sets. While the frames of these images may overlap, the overlapping width is taken into consideration and set based on the maximum deviation between the test and reference image. This way, one can overcome issues such as distorted physical characteristics and non-uniformity contrast levels. This is achieved by processing each image frame separately. Finding defects in fine pitch patterns can be achieved through sub-pixel analysis. This is also used for defects related to edge detection and alignment of the board. There are algorithms that detect foreign particles such as dust on the board through color values, irregular size, and geometry.

All of these inspection techniques ensure or validate if the application requirements are met. They also ensure the overall structural and functional accuracy as well as quality. If you are an OEM and working on a crucial product with zero error tolerances, ensure the PCBA used for this product is just as perfect. For this, you can partner with an experienced PCB manufacturer and assembly solutions provider who has stringent testing and inspection processes in place and is capable of understanding and executing your specific or complex application requirements. Creative Hi-Tech is a well-known PCB manufacturer and assembly services provider who specializes in custom PCB designs and assemblies.

Related Blog Posts:

• The PCB Inspection Techniques You Should Know About
• An Overview of the Most Popular PCB Inspection Methods