Automated optical inspection is a key technique used in the manufacture and test of electronics board. AOI enables fast and accurate inspection of PCB PCBA and in particular PCB to ensure that the quality of product leaving the production line is high and the items are built correctly and without manufacturing faults
For Bare printed circuit boards, The AOI test verifies the finished conductor trace image for deviations from the Gerber data and finds errors that the E-Test may not discover, such as (for example) narrowed, but still unbroken conductor traces.
The AOI test is especially important for the following application areas:
1. High frequency
2. High power loads
3. High data transmission rates
4. Op-amps with high amplification factors and input resistances
The inner layers of multilayer PCB use AOI to scan before they are pressed together. This guarantees the high reliability of multilayer boards.
Automated optical inspection (AOI) is a key test method used in surface mount technology (SMT) printed circuit board (PCB) assembly to detect defects and ensure quality. This article provides an overview of AOI covering:
Understanding AOI technology and capabilities is important for quality management and process control in electronics manufacturing.
AOI machines capture high resolution images of assemblies and use image processing software to compare against a “golden board” reference to identify defects.
Image Capture
Image Analysis
Results
AOI inspection can identify a wide range of assembly-related defects:
Component Flaws
Solder Joint Issues
PCB Defects
Marking Flaws
2D AOI
3D AOI
A typical AOI inspection sequence is:
1. Setup
2. Verify Settings
3. Production Testing
4. Review Failures
5. Reporting and Analysis
There are different configurations of AOI equipment:
Inline AOI
Standalone AOI
Dual Lane AOI
Mini AOI
False calls where AOI reports a defect incorrectly reduce efficiency. Strategies to minimize false calls:
Despite advanced imaging technology, AOI has limitations including:
Compared to ICT
Compared to X-Ray
Compared to SPI
Key steps for utilizing AOI effectively:
Automated optical inspection is a critical quality control technique used throughout the SMT assembly process. This article provided an overview of how AOI works to detect surface defects on PCB assemblies. Understanding AOI capabilities as well as factors like false calls and limitations helps manufacturing engineers apply AOI optimally as part of a comprehensive quality strategy. Implemented effectively, AOI provides valuable inspection data to improve yields, reduce escapes and achieve consistent product quality.
Here are some common questions about AOI testing for SMT:
Q: What types of defects can AOI detect?
AOI detects missing, shifted or wrong components, solder defects, PCB flaws, barcode issues and more. It finds assembly-related rather than electrical defects.
Q: Does AOI replace functional PCB testing?
No, AOI complements electrical and functional testing. AOI verifies component placement while circuit tests confirm electrical operation.
Q: Can AOI be used for BGA inspection?
Yes, AOI can reliably inspect BGA solder joints. 3D AOI provides accurate measurement of solder ball heights.
Q: What is the difference between inline and standalone AOI?
Inline AOI inspects boards directly on the assembly line while standalone AOI allows off-line sampling.
Q: Does AOI completely eliminate escapes and field failures?
AOI dramatically improves defect detection but cannot find all failure mechanisms like latent defects. Multiple test methods are still required.