AOI for defect detection at soldering process

Sorry, I have not read the article. However, I do have five years experience constantly tweaking an AOI system that ran ONE product! The strength of the machine was solder inspection. The biggest problem was component color variation and shadowing from other components.

Pro: One machine replaced 5 inspectors and yields increased. Inspection time went from several minutes to 12 seconds. It was definitely a good investment.

Cons: Your dealing with a machine that is analyzing light reflected off a joint. Look at a single PCBA and compare the differences from joint to joint. Shift the board slightly, shift a component slightly... you'll get a different image. Shift a nearby component and create a new shadow. Then look at those same joints over a period of time. One week, the component leads may be perfect prior to soldering, the next, they may have poor solderability. Now consider lead diameter tolerances, board tolerances, varying degrees of acceptable joints, placement accuracy. Consider all the variables that occur throughout the process from recieving inspection, to lead forming, component placement, fluxing, soldering, etc... Then teach a machine what is good and bad!

It all adds up to one result and that result is that you will end up tweaking the inspection program indefinitely. Yes, as time goes on, the tweaking will lessen, but you will never get away from that machine!

In my experience, solder inspection using AOI is only worthwhile in high volume.

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For solder joint inspection you cannot beat AXI. That's what is was designed for. AOI machines were designed for component inspections and solder joint checking was an add-on. In transmission AXI you can get a measurement of the whole solder joint. AOI is just looking at what it can "see" and is making asumptions. For more info, go to this link:

http://www.teradyne.com/axi/

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