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CompactRIO Delivers Major Impact in the World of PCB Assembly Inspection

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"The CompactRIO system has proven to be a dependable, reliable, and cost-effective solution for this high-performance, ground-breaking application. Using CompactRIO as the product management system significantly reduced our development time and helped us get the various autonomous state machines of the multiple product control cells running with far tighter timings than the normal 1 ms tick of most PLCs."

- Alan Smith, Amfax Limited

The Challenge:
Designing and developing a revolutionary XYZ measurement-based inspection technology to help companies improve the quality of their manufactured PCB assemblies.

The Solution:
Combining the benefits of CompactRIO and FPGA and the user interface qualities of LabVIEW software to develop the world’s most accurate PCB assembly inspection system, enabling OEMs and CEMs to reduce their lifecycle PCB assembly inspection costs.

Author(s):
Alan Smith - Amfax Limited

Amfax, a global NI Platinum Alliance Partner of 23 years, designs and manufactures test engineering solutions for customers worldwide. Our extensive customer base includes blue chip companies in the aerospace, rail, transport, energy, telecommunications, and consumer electronics market sectors.

Many PCB manufacturing companies have struggled to solve a problem that has been going on for many years, which is accurately and repeatedly inspecting PCB assemblies to ensure correct component placement and good quality solder joints to improve reliability in use. We addressed this challenge by developing the a3Di PCBA inspection system.

 

Figure 1. The Amfax a3Di Development Team

 

Historically, the mark 1 human has been used to visually inspect PCB’s at the end of the production line. This became uneconomical and prone to poor repeatability due to the short concentration time of human inspectors, so many companies switched to automated optical inspection (AOI) systems. These automated systems use cameras in place of the inspectors to capture images of the board and then compare these images against a gold reference standard to check if the PCB assemblies have any faults. These systems can provide significant benefits over the human inspection method.
AOI systems work by comparing recently acquired images against gold reference images. Any difference between the images results in the system reporting a failure. Many of these failures are not legitimate failures, but are flagged by the AOI as potential failures. The local system operator then makes the final decision as to whether the board has failed or not. These potential failures are known as false calls.

The rate of false calls on 2D and 3D AOI systems means that an operator must always be present when the PCB assemblies are inspected. This incurs additional operating costs, and the operator must halt the machine every time a potential fault is identified so that he/she can visually inspect the PCB assembly before deciding of it is a true failure or not.

What Makes a3Di Unique?

The Amfax a3Di system takes a completely different approach to address these challenges. It uses a twin laser-based metrology technology to take millions of XYZ measurements with accuracies of under 3 microns. The system scans the whole of the PCB assembly being inspected in a few seconds. We can then test these measurements against the original CAD data to identify any problems with solder joints, component location and orientation, foreign objects, or board warpage. As a3Di performs real measurement testing, we do not need an operator as there are zero false calls—either the board passes the test or not. That is the benefit of testing against real 3D measurements instead of relying on a comparative methodology such as AOI.

This means that a3Di users save the cost of at least one operator and significantly improve their product throughput as they can continuously test without pausing the machine. One consumer electronics manufacturer in Asia is testing over 18,000 boards per day on one a3Di, a significant improvement on their previous solution.

 

Figure 2. 3D Image of a3Di’s Measurement Data: The colours shown represent height, with Z resolution down to less than a micron. The blue section at the top indicates signs of board warp. Laser etched component information can be seen on some of the ICs.

 

CompactRIO: The Heart of the Machine

The a3Di control system manages all aspects of the machine’s operation. We chose a CompactRIO control system for a3Di that includes FPGA and NI-9375 digital I/O hardware. This CompactRIO solution can control all of the following I/O and sensors on the a3Di:
• Machine motors
• Control switches
• Optical position sensors
• Inverters
• Up and downstream SMEMA (Surface Mount Equipment Manufacturers Association) conveyor control
• Light tower
• Pneumatics
• Operator manual controls for width PCB control
• System emergency stop

The a3Di was a brand new design for Amfax. As an NI Platinum Alliance Partner, we immediately considered using CompactRIO. The CompactRIO system has proven to be a dependable, reliable, and cost-effective solution for this high-performance, ground-breaking application. Using CompactRIO as the product management system significantly reduced our development time and helped us get the various autonomous state machines of the multiple product control cells running with far tighter timings than the normal 1 ms tick of most PLCs.

 

Figure 3. CompactRIO at the Heart of the a3Di Control System

 

Our developers, who are CLD- and CLA-level engineers, partnered with the technical support teams in the local NI UK & Ireland office. They helped the team overcome some of the detailed control issues raised in the system design.

LabVIEW: The Obvious Choice for User Ergonomics

We decided early in the a3Di product specification phase to use LabVIEW software to not only provide the control code but to control the system from the user interface perspective also. The ability to design product quality operator interfaces and the flexibility of LabVIEW for creating an engaging user interface environment for the operator makes the software front end of a3Di a unique selling point.

 

Figure 4. Main a3Di System User Interface Developed Using LabVIEW

 

We used NI components within the a3Di product so we could deliver a world class, unique, and well supported solution to those OEMs and CEMs looking to improve their PCB assembly inspection process and significantly reduce their operational costs.

The a3Di is also revolutionizing the way PCB assembly manufacturers compete for business. By using a3Di, these manufacturers have a unique selling proposition to their own customers. They can pass on savings made by using a3Di and guarantee that the boards being manufactured are tested by the most accurate system available.

The importance of this exciting technology has not gone unnoticed. The British government’s innovation department recognised a3Di as a significant step forward in manufacturing. The Amfax a3Di was a finalist at the 2016 Innovate UK awards hosted at the British Houses of Parliament.

 

Figure 5. Case Study and UK Innovation Award Details Shown on UK Government Website

Author Information:
Alan Smith
Amfax Limited
Clump Farm Industrial Estate
Blandford, Dorset
United Kingdom
Tel: +44 (0) 1258 480777
alans@amfax.co.uk

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