AOI systems

Some AOI manufacturers require you to put in a GOLD PCB. Gold PCB is a perfectly manufactured board - Correct placements, correct polarity, no solder short, a "GOOD" PCB. With the vision limitations of some AOI equipment components that have variations in color can cause false errors. Thus causing down time or false rejects. This is a programming step or false read eliminated with UV-OS.

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Phil, I have got a couple of CR Technology machines also. We have handed off our "learning" to the operators, but you must have confidence in those people! The must be well trained! The AOI machine will flag the things it feels is "bad" and the operator will need to review these to determine if they are bad or not. Like any other inspection, a good eye is needed!

Larry

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The CAD data is the centroid data, x,y location. I developed an Excel macro in which we import the data as a text file and convert it to the CR Technology format.

Rates for false failures varies, but is ~10 - 20%. The operators are given an oportunity to review the failed parts. The false failures are simply parts that don't match the template, so they are able to dismiss them. The true failures are assigned a failure code and a rework sheet can be printed out that is routed with the board.

The extra time to review the false failures is minimal. Bottom line is that you can't leave the AOI alone. Whether in-line or off-line, an operator will need to be stationed at the machine.

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Have you had bad experiences?

We have a paste checker on line, and all components are verified at receiving and again when loaded on the machines.

The purpose of AOI ( for us anyway ) is to reduce the time spent after reflow visually checking the boards for defects such as missing parts, shorts and skews. ( I'm not saying we have lots of trouble with this, our yields are around 95% currently ) What we want to eliminate is the human element involved with visual inspection. On a good day, an inspector is only going to catch 85% of the errors, and it goes down from there ( ie Friday afternoons are the worst!)

Would we not benefit if that person, instead of checking the whole board, only had to check a few locations that the machine reported back, and verify if they are actually failures? ( accounting for false failures )

In my mind, any process that can be automated to do ( or assist ) a task previously done by a person is a step forward. The biggest issue is ensuring the machine performs as expected.

Phil

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We are already using ICT on the PCB, which should catch most missing components, also components installed backwards, or the wrong value(to a point - we do RF so we have lots of very small value caps and inductors which can't be measured), and in some cases, faulty components. To enhance the yield we are seeing from ICT, we have been looking at two additional inspection methods - X-ray, and AOI.

We have had several small builds of a new OEM product that is scheduled to become very high volume(for us). We have had yields ranging from 60-90% first pass test. We looked at the faults we've seen and for us over 90% were things like insufficient solder and not soldered, shorts, misaligned components and rotated components. The rotated components should be picked up by ICT (our CM is still working out a few bugs in the fixture) but the other items should be picked up by X-ray. We were told that X-ray strengths are evaluating solder issues on the board, solder patterns, shapes and volumes. It can also evaluate hidden joints. The fault spectrum(the number of different types of faults) picked up by X-ray is the smallest of the three test types, however the percentage of those faults it finds in most cases is higher than AOI and ICT, and the percentage of faults occurring on our products that fall into the categories for X-ray is quite high for us. Also, whereas ICT requires a fixture, X-ray doesn't, and the programming time is supposed to be about the same for both. The main cost is the actual x-ray equipment. Our CM tried to tell us that the only thing x-ray was really needed for was BGA's of which we aren't using any. However, we have a surface mount SMA connector that you can't see the pin, so AOI would not be able to determine a good connection. It can't be probed from the bottom, so ICT would not work. X-ray is the only thing that can determine if we have a problem before actually hooking up the board and finding no signal going thru.

We were also told that ICT gets stopped by every fault it finds, shorts opens, etc. The board must be reworked and rerun thru the test. Put X-ray in front, and it will catch 90% of opens and shorts. Then ICT time will be much faster as it will primarily need to test only values and functionality of components.

All of this stuff is brand new to me - I had never even heard of ICT 8 months ago. So, very little of this is personal experience, it is what I have been told by my research and talking to people who are supposed to know. If there are errors in my info, please let me know.

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