ML-TN-003 — AI at the edge: visual inspection of assembled PCBs for defect detection — Part 1

Info Box Applies to Machine Learning Applies to Machine Learning Technical Notes

History

Version	Date	Notes
1.0.0	March 2021	First public release

Introduction

In [ML-TN-001_-_AI_at_the_edge:_comparison_of_different_embedded_platforms_-_Part_1 this series] of articles, different embedded platforms suited for building "[Edge AI]" solutions are compared from the point of view of inferencing capabilities/features, development tools, etc. In principle, such platforms can drive a bunch of different applications in the industrial world and other fields as well.

This series of Technical Notes illustrates a feasibility study regarding a common problem in the manufacturing realm that supposedly Machine Learning (ML) algorithms can address effectively: defect detection by automatic visual inspection. More specifically, this study deals with the inspection of assembled Printed Circuit Boards (PCBs). The ultimate goal is to determine if it would be possible to design innovative machines exploiting ML algorithms and able to outperform traditional devices today employed for this task. This is a blatant example of AI at the edge as the application requirements include the following:

• Data — images in this case — must be processed where they are originated
• Processing latency has to be minimized in order to increase the manufacturing line efficiency.

Currently, the problem of latency is what is driving many companies to move from the cloud to the edge, along with the fact that it is not reasonably feasible to afford a GPU for all the use cases. This has led to the birth of a new computational paradigm called "Edge AI" that combines the efficiency, speed, scalability, and the reduced costs of edge computing with the powerful advantages offered by the use of Artificial Intelligence and Machine Learning models. "Edge AI", "Intelligence on the edge", or "Edge Machine Learning" means that data is processed locally — i.e. near the source of data — in algorithms stored on a hardware device instead of being processed in algorithms located in the cloud. This not only enables real-time operations, but it also helps to significantly reduce the power consumption and security vulnerability associated with processing data in the cloud.

While moving from the cloud to the edge is a vital step in solving resource constraint issues, many Machine Learning models are still using too much computing power and memory to be able to fit the small microprocessors available on the market. Many are approaching this challenge by creating more efficient software, algorithms, and hardware or by combining these components in a specialized way. To this end, a new generation of purpose-built accelerators is emerging as chip manufacturers work to speed up and optimize the workloads involved in AI and Machine Learning projects from training to performing inference. Faster, cheaper, more power-efficient and scalable, these accelerators promise to boost edge devices to a new level of performance. In this work, a modern system-on-chip (SoC) embedding a configurable hardware accelerator of this sort was analyzed in view of using it as a core building block of such devices. Also, it was studied its applicability in a real-world scenario characterized by issues that are common to a large class of problems in the industrial realm.

Articles in this series

• Part 1 (this document)
• Part 2 talks about the classification of surface-mounted components on printed circuit boards.
• Part 3 deals with the issue of data scarcity.

Models

ResNet50

	Train and validation accuracy trend over 1000 training epochs for ResNet50 model		Train and validation loss trend over 1000 training epochs for ResNet50 model

lorem ipsum lorem ipsum lorem ipsum

Host machine, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.95740 0.89900 0.92728 1000 capacitor 0.97278 0.96500 0.96888 1000 diode 0.88558 0.95200 0.91759 1000 inductor 0.97006 0.97200 0.97103 1000 resistor 0.98882 0.97300 0.98085 1000 transistor 0.92262 0.93000 0.92629 1000 Weighted avg 0.94954 0.94850 0.94865 6000

lorem ipsum lorem ipsum lorem ipsum

Target device, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.96384 0.85300 0.90504 1000 capacitor 0.99068 0.95700 0.97355 1000 diode 0.83779 0.94000 0.88596 1000 inductor 0.94839 0.97400 0.96103 1000 resistor 0.97211 0.97600 0.97405 1000 transistor 0.89960 0.89600 0.89780 1000 Weighted avg 0.93540 0.93267 0.93290 6000

lorem ipsum lorem ipsum lorem ipsum

	[[]]		[[]]

ResNet101

	Train and validation accuracy trend over 1000 training epochs for ResNet101 model		Train and validation loss trend over 1000 training epochs for ResNet101 model

lorem ipsum lorem ipsum lorem ipsum

Host machine, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.96375 0.95700 0.96036 1000 capacitor 0.96373 0.98300 0.97327 1000 diode 0.96425 0.94400 0.95402 1000 inductor 0.98500 0.98500 0.98500 1000 resistor 0.98504 0.98800 0.98652 1000 transistor 0.96517 0.97000 0.96758 1000 Weighted avg 0.97116 0.97117 0.97112 6000

lorem ipsum lorem ipsum lorem ipsum

Target device, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.96288 0.88200 0.92067 1000 capacitor 0.95898 0.98200 0.97036 1000 diode 0.93965 0.90300 0.92096 1000 inductor 0.93719 0.95500 0.94601 1000 resistor 0.90428 0.99200 0.94611 1000 transistor 0.93896 0.92300 0.93091 1000 Weighted avg 0.94033 0.93950 0.93917 6000

ResNet152

	Train and validation accuracy trend over 1000 training epochs for ResNet152 model		Train and validation loss trend over 1000 training epochs for ResNet152 model

lorem ipsum lorem ipsum lorem ipsum

Host machine, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.94553 0.97200 0.95858 1000 capacitor 0.95538 0.98500 0.96997 1000 diode 0.98298 0.92400 0.95258 1000 inductor 0.98584 0.97500 0.98039 1000 resistor 0.99390 0.97800 0.98589 1000 transistor 0.92899 0.95500 0.94181 1000 Weighted avg 0.96544 0.96483 0.96487 6000

lorem ipsum lorem ipsum lorem ipsum

Target device, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.91182 0.91000 0.91091 1000 capacitor 0.94460 0.98900 0.96629 1000 diode 0.96464 0.87300 0.91654 1000 inductor 0.94124 0.94500 0.94311 1000 resistor 0.94038 0.97800 0.95882 1000 transistor 0.90358 0.90900 0.90628 1000 Weighted avg 0.93438 0.93400 0.93366 6000

InceptionV4

	Train and validation accuracy trend over 1000 training epochs for InceptionV4 model		Train and validation loss trend over 1000 training epochs for InceptionV4 model

lorem ipsum lorem ipsum lorem ipsum

Host machine, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.94524 0.86300 0.90225 1000 capacitor 0.98051 0.95600 0.96810 1000 diode 0.88384 0.87500 0.87940 1000 inductor 0.95575 0.97200 0.96381 1000 resistor 0.96847 0.98300 0.97568 1000 transistor 0.83670 0.91200 0.87273 1000 Weighted avg 0.92842 0.92683 0.92699 6000

lorem ipsum lorem ipsum lorem ipsum

Target device, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.78158 0.89100 0.83271 1000 capacitor 0.99220 0.89000 0.93832 1000 diode 0.88553 0.82000 0.85151 1000 inductor 0.88973 0.94400 0.91606 1000 resistor 0.97319 0.98000 0.97658 1000 transistor 0.83282 0.80700 0.81971 1000 Weighted avg 0.89251 0.88867 0.88915 6000

Inception ResNet V1

	Train and validation accuracy trend over 1000 training epochs for Inception ResNet V1 model		Train and validation loss trend over 1000 training epochs for Inception ResNet V1 model

lorem ipsum lorem ipsum lorem ipsum

Host machine, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.98274 0.96800 0.97531 1000 capacitor 0.97571 0.96400 0.96982 1000 diode 0.94889 0.98400 0.96613 1000 inductor 0.98085 0.97300 0.97691 1000 resistor 0.98211 0.98800 0.98504 1000 transistor 0.97278 0.96500 0.96888 1000 Weighted avg 0.97385 0.97367 0.97368 6000

lorem ipsum lorem ipsum lorem ipsum

Target device, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.84127 0.95400 0.89410 1000 capacitor 0.99787 0.93600 0.96594 1000 diode 0.94346 0.90100 0.92174 1000 inductor 0.95275 0.98800 0.97005 1000 resistor 0.94852 0.99500 0.97121 1000 transistor 0.93348 0.82800 0.87758 1000 Weighted avg 0.93622 0.93367 0.93344 6000

Inception ResNet V2

	Train and validation accuracy trend over 1000 training epochs for Inception ResNet V2 model		Train and validation loss trend over 1000 training epochs for Inception ResNet V2 model

lorem ipsum lorem ipsum lorem ipsum

Host machine, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.97872 0.96600 0.97232 1000 capacitor 0.99177 0.96400 0.97769 1000 diode 0.98963 0.95400 0.97149 1000 inductor 0.97931 0.99400 0.98660 1000 resistor 0.98213 0.98900 0.98555 1000 transistor 0.93365 0.98500 0.95864 1000 Weighted avg 0.97587 0.97533 0.97538 6000

lorem ipsum lorem ipsum lorem ipsum

Target device, confusion matrix & classification report

Class Precision Recall F1-score Support IC 0.91735 0.89900 0.90808 1000 capacitor 0.99466 0.93200 0.96231 1000 diode 0.98793 0.90000 0.94192 1000 inductor 0.92066 0.99800 0.95777 1000 resistor 0.96970 0.99200 0.98072 1000 transistor 0.87887 0.93600 0.90654 1000 Weighted avg 0.94486 0.94283 0.94289 6000

Useful links

• Young-Gyu Kim, Tae-Hyoung Park, SMT Assembly Inspection Using Dual-Stream Convolutional Networks and Two Solder Regions, July 2020.
• Hangwei Lu, Dhwani Mehta, Olivia Paradis, Navid Asadizanjani, Mark Tehranipoor, Damon L. Woodard, FICS-PCB: A Multi-Modal Image Dataset for Automated Printed Circuit Board Visual Inspection, July 2020.
• Kaiming He, Xiangyu Zhang, Shaoqing Ren, Jian Sun, Deep Residual Learning for Image Recognition, December 2015.
• Christian Szegedy, Sergey Ioffe, Vincent Vanhoucke, Alex Alemi, Inception-v4, Inception-ResNet and the Impact of Residual Connections on Learning, August 2016.