When determining the cause of a malfunctioning chip, failure analysis engineers have access to a wide range of procedures. Some of these like radiography, don't harm the chip and leave it usable for further examination. This is called "Non Destructive Testing" or NDT for short. Such operations are highly prized because of their flexibility. Since the chip isn't destroyed, it can be preserved for future reference or as a test case. Many times however, we have to perform a more intrusive test where the chips is rendered useless afterwards. These destructive tests involve opening up the chip to isolate the source of the error. The technical term for this is decapsulation and can be performed in a variety of ways. Laser decapsulation is just one example and we'll be examining it in this article.

The basic principle behind laser decapsulation is simple. We expose the package to laser radiation in a specific way. The properties of the laser are such that the substances exposed to it "burn" away. This is either a process of evaporation or sublimation. Unlike other techniques which require the package to be exposed to acid, laser decapsulation is dry and there is no danger of exposing the person conducting the procedure to dangerous chemicals.

This type of decapsulation of an IC package is also more structured than the alternatives. Using CAD specifications, we can automate the process by entering the coordinates of the area requiring decapsulation into a computer. By contrast, in procedures where we need to carefully control the flow of acid, human intervention is indispensable.

Depending on the properties of the laser, the effects on the surrounding substances can be minimal. This means that a laser can be configured to only effect that part of the chip which needs to be scoured away leaving the rest intact. No undue heat is transferred due to the speed and the short duration of the laser pulse.

Additionally, manufacturing trends are tilting towards the use of copper bonding which makes techniques such as acid etching dicey and imprecise. Laser decapsulation on the other hand has no side effects and only removes what is required.

Decapsulation is usually performed only after other tests have been tried. The final act of opening the IC package can be to confirm or disprove a hypothesis - though you only get one chance at it, after which the chip is useless for further testing. Laser decapsulation is a valuable tool in the hands of experienced failure analysis engineers and helps make our electronics safe and reliable.

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