The Importance of Non-Destructive Testing
Non-destructive testing is a type of test which causes no permanent change to the chip or electronic component under ideal conditions. Conversely, destructive testing destroys the chip and renders it useless for anything after that. Of course, there are times when you have to destroy the chip in order to make the analysis. For example, decapsulating a chip (removing the plastic package material to expose the silicon circuit) will prevent it from being used in a system again - the very nature of the procedure mandates it.
Of course, there are cost reasons to prefer Non Destructive Testing (NDT) but there are others reasons too. After all, chips can be mass manufactured and the loss of any one chip is unlikely to be a disaster unless it's a costly prototype. When a test is non destructive, we can perform it several times to see if we reach the same conclusions. In addition, we can perform many different kinds of tests using various methodologies to check our conclusions.
One other reason to prefer NDT techniques is that a particular flaw may not be easy to find in any other chip. Electronic systems are made up of thousands or millions of tiny components and sometimes finding an unusual error can help us identify flaws in the manufacturing process which we would not normally uncover. In such cases, preserving the malfunctioning component becomes very important indeed.
Many techniques fall under the umbrella of NDT. For example, all procedures which rely on electromagnetic radiation such as emission spectroscopy and optical microscopy are non destructive. Procedures such as acoustic microscopy are also the same. Microthermal imaging techniques using either infrared radiation or liquid crystal imaging and even fluroscent imaging all preserve the chip for further analysis.
These techniques are tried first before any destructive testing commences. After all, it's easy to find a chip that works properly. Finding one that doesn't is a rarity!