Automated Optical Inspection (AOI)

How does one deal with stains, scratches, and nodules that appear as surface defects in PCBs as they roll out of the production line? Your weapon, of course, is automated AOI inspection. This method will also probe and find many other defects in the PCB, such as missing parts, badly placed parts, and also open circuits, thin solders, or shorts.

Today, PCBs have modernized into more complex and miniaturized units. As a result, this has forced changes from the manual inspection system which the industry used to monitor them. In addition, the use of the Automated Optical Inspection System (AOI) in PCB testing is your assurance to a superior product.

The Necessity of Automated Optical Inspection

The modern PCB features almost countless joints, thus making the manual inspection a challenging task. Keep in mind that even in the years of simpler PCB circuit boards, manual testing was still hard and resulted in imperfect outcomes.

Think of the human factor. Human inspectors get tired, lose attention, or accidentally overlook some defects. It’s clear that with more advancement in these products, manual testing can’t keep pace with the exacting demands required. Moreover, vast quantities of PCBs are needed to satisfy the large and growing demand for electronic circuits. So, one needs more rapid and accurate methods. For all this, the only answer is an automatic optical inspection system.

How does AOI PCB accomplish its stunning results? Here we list three basic approaches

  • Template matching – this method compares the image captured with that of the “golden board,” which acts as a benchmark. So anything that is a mismatch to this board is flagged
  • Pattern matching – the system keeps a store of the image of the ideal PCB board and to match the actual output with the stored image in order to identify flawed products
  • Statistical pattern matching – This technique resembles pattern matching but uses large numbers of board images. Following this, It then applies methods of statistics to identify flaws. Consequently, this method will also not reject all board errors, as some are too minor to need flagging. 
AOI, AXI, and ICT in The Major Defect Detection Capabilities

How does the automated optical system (AOI) compare with other systems such as AXI and ICT? Here are the performance parameters contrasted with the AOI PCB inspection.

Soldering defects    
Solder bridgesYesYesYes
Open circuitsYesYesYes
Insufficient solderYes (not heel or joint)NoYes
Excess solderYesNoYes
Solder shortsYesYesYes
Solder qualityNoNoYes
Solder voidNo  
Component defects   
Missing componentYesYesYes
Lifted leadYesYesYes
Misaligned or misplaced componentYesYesYes
Faulty componentNoYesNo
Incorrect component valueNoYesNo
BGA and CSP defects   
BGA open circuit connectionsNoYesYes
BGA shortsNoYesYes
When Do We Use AOI During PCB Manufacturing

We do a 3D automated optical inspection of PCBs at a very early stage of the production run. After the soldering stage is done, we deploy the technique. The value of this is that we can detect flaws early enough and correct them. Since these defects are detected early rather than later in the production process, the savings in cost and time are great.

Also, the automated optical inspection system benefits from a feedback process. When defects emerge, they are promptly detected and relayed back to earlier stages. Therefore, we are able to catch and remove flaws so that not too many boards with the same defects appear

Attributes and Working of AOI

The AOI PCB inspection uses a high definition camera.

Below we detail the attributes that we achieve based on the model VCTAB486 that we use

  • Automatic Optical Measuring Instrument VCTAB486
  • Positioning Accuracy < 0.15mm
  • Measurable minimum element: 0201
  • Moving speed: 700 mm/s
  • Measurable PCB range:25*25mm – 349*480mm
Your PCB Order Will Comes with AOI Inspection Service

MOKO Technology has made quality a top concern in what we deliver to you. Therefore, we always include automated optical inspection with all PCB orders that you bring to us. This is a solid guarantee for you to receive products of incredible quality. Coupled with this, you will receive your order speedily and at a low price.

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