INSPECTION - Think you only need AOI? Think again.
14 January 2011
Only Automated First Article Inspection plus AOI covers all the bases as Mike Judd reports.
When talking to Production or Quality Managers about Automated First Article Inspection, chances are the first thing they’ll say is: 'We don’t need it, we already have AOI.'
Presumably, your process includes checking first off boards despite having AOI, doesn’t it? Whether or not that is the case, consider this scenario, and decide for yourself if there’s a better way:
You’ve completed the first production run of 5,000 boards for a new customer, or an updated board for an existing contract. They’ve passed QA, been shipped on time and fitted in your customer’s new gizmo. Everybody’s happy.
Happy, that is, until the worst possible thing happens. There’s a failure, and it’s down to an incorrect component being placed – on your line. You’ve potentially lost untold revenue and days of rework or remanufacturing time. To say nothing of your reputation, and your sanity!
But how could this possibly have happened? Every unit passed AOI with flying colours against your golden board.
The problem happened because the ‘golden’ sample wasn’t assembled correctly, and the whole idea of AOI is to help ensure that what’s coming off the line is exactly the same as the original with which it’s being compared. ‘Rubbish in, rubbish out’, as the saying goes... the AOI probably did its job just fine. Or maybe not: there is a known or expected false call and escape rate with the AOI process, which by the way is why it can’t be used for first article inspection.
First article inspection is used to ensure that the first board off the line is populated and assembled perfectly and provides a master to benchmark against.
As a discipline, it has been around as long as the PCB, and typically works like this:
(1) Set-up SMT machine
(2) Load feeders
(3) Load program
(4) Build first board
(5) Get two trusted people to inspect board using bill of materials, drawing and microscope or magnifier lamp
(6) Get same two trusted people to complete detailed documentation correctly for traceability purposes
That’s how it’s been done for years, but for better or worse, the world has moved on. Moved on because of the complexity of electronic design and packaging. Moved on because of budget pressure and tightening resources. And moved on because of more expensive penalty clauses. There’s also human error to factor in, but that’s never changed!
Apart from chronic inaccuracy, the really serious issue with conventional first article inspection is that it’s slow and laborious... and therefore very expensive. If you have two dozen parts on the board, it’s not a problem, but if you have a 300 x 360mm board with 1200 components on it or, in the case of a smartphone even worse with a 100mm x 55mm board with a similar number of parts, it’s going to take many hours to conduct a thorough inspection against the BOM and the drawing, with two people trying to communicate with each other and fill in the paperwork at the same time. As the SMT line is one of the most expensive investments in your factory, to have it sitting idle whilst boards are being inspected by eye is, in effect, seriously depleting your profit margin and competitiveness.
Accurate, quick first article inspection, fast ROI
Automated First Article Inspection is, quite simply, a virtually foolproof, computerised method of inspecting that first board which saves substantial time and money and gives you confidence that your production boards are as intended. It is a logically validated, semi-automatic system that integrates visual inspection with document or data file control and traceability reporting. Boards are checked for errors against a platform of strictly controlled procedures to eliminate risk of failure. Here’s how:
The CAD and machine placement files and BOM are loaded into the system. First of all, the system automatically verifies the pick and place file against the BOM to ensure that no extra, missing or changed parts exist. The first-off, completed PCB is loaded into the system’s scanner and the digital image file is displayed on a monitor ready for inspection. That’s the first major practical benefit... the time saved because the FAI system doesn’t require manual programming. There are a number of AOI systems on the market that also import BOM and CAD data, but unlike Automated First Article Inspection, they require time consuming (and potentially flawed) programming.
All of the BOM data is reviewed in respect of the image on the monitor, bringing up an expanded view of the part being inspected. There’s no need to check off parts in the system because the BOM data is 100% accurate, having come from the placement machine or further upstream if validation of the placement program is also required. The location of individual parts on the PCB is automated too, as the coordinates are also from the pick and place files or the original CAD data set. This combination of all the data and the image file into a unified, digital system makes the first article inspection task much more efficient and effective, while the operator is free to focus on visual inspection of the parts in a systematic, unpressured way. Talking of operators, there’s no danger of losing track of progress in the event of a coffee break.
Once inspected, the first board is saved as a master. Any boards from subsequent production runs may be compared to it to ensure no parts have been added, deleted, rotated or moved. Used in this way, the system is used not only as a first article inspection tool, but also great for production audits, ECO implementation and as a diagnostic tool to verify components on boards that fail at test. Of course, the data set is also saved for future production runs. The system interfaces with common Windows-based programs to provide traceability reports in a format of the user’s or customer’s choice.
More than ever, flexibility is an essential element of successful manufacturing, whether in-house or contract. That’s flexibility to implement design modifications as well as being able to chop and change from one assembly to another – and back again – with the minimum disruption. The system easily accommodates the need for such flexibility because of its speed and accuracy. In fact, it’s sometimes referred to as an ‘Automated Production Engineering System’ as the people with the most to gain from buying it are production managers who know how many hundreds or thousands of pounds it costs when their SMT line is waiting for the go ahead from the first article inspector.
Making a business case
Of course, thinking back to the beginning of this article, the other person most likely to say “We don’t need it, we already have AOI” is the Finance Director. Implementing a significant new process always involves financial justification, and fortunately with this one it isn’t difficult.
Labour costs associated with inspection will be significantly lower. This will vary according to the complexity of the board and number of components, but to take an example, the actual inspection time for a board that takes two to three hours is reduced to around 30 minutes. That’s relatively easy to put a cost against. Even more significant, however, is the reduction in production line downtime during product changeover. Say the opportunity cost for an idle production line is £500 per hour. Multiply that £500 by the number of hours by the number of lines and setups carried out in a week, and potential for saving costs becomes massive. Experience shows that ROI for this system can typically be achieved in weeks or months rather than years. It could be the FD who’ll be pressing you to invest in the system, not the other way around.
This has been a very brief, top line introduction intended to explode the myth that if you have AOI, you don’t need Automated First Article Inspection. There will be more detailed technical information and application stories published over the coming months.
Mike Judd writes on behalf of Cluso Vision Systems
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