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Can laser engraving damage IC's through photoelectric effect?

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Terminator3

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I want to buy HD video camera modules PCB. I got one sample and was very surprised that all ICs including FPGA, DSP and even power supply are engraved very precisely with some laser technology, and under magnifying glass ICs surface now have equally spaced melted plastic dots. I am sure that main purpose was to make IC component names totally unreadable to make reverse-engeneering much harder. What i am concerned of is reliability of ICs after such engraving. Silicon inside IC is usually very small and placed in the center of the entire chip. What if laser beam goes through plastic and cause photoelectric effect in some places with current enough to damage or degrade silicon circuit? I read story about some power supply IC noise that was affected by camera flashes, which is light source too. Although IC plastic is black, high intensity light can go through it and couse ome photoelectric effect. Please comment.
 

bigdogguru

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The short answer to your question is, typically no.

Laser engravers can usually be set to a specific depth of penetration, which would normally leaves a sufficient amount of material between the outer package and the chip die. The photons of the laser are normally unable to penetrate the remaining material, typically some form of plastic, and contact the silicon die.

I might also add, several chip manufactures routinely use laser engraving to inscribe both their logo, part number and date code on the package in an attempt to thwart attempts at counterfeiting their products. Obviously, the technique would not be employed if there were a significant chance of damaging the silicon die of the device.

I suspect the story to which you are referring, concerns the core processor voltage regulator which is incorporated into the design of some Raspberry PI 2s. In that particular case the package type of the device in question was a Wafer Level Chip Scale Package (WL-CSP), which is essentially an inverted bare silicon die with BGA like solder balls affixed directly to the silicon, when mounted the WL-CSP package leaves, albeit small, a significant gap remaining between the PCB and silicon die, sufficient for light to enter the void between the silicon die and the PCB. A very strong light source, in this case a Xenon flash from a camera, produces enough of a intense short burst of photons to trigger a cascading photoelectric effect on the surface of the inverted die, which in turn triggers a momentary failure of the voltage regulator circuit and hence the processor core. Normal ambient light does not yield sufficient quantity nor energy photons to trigger such an event. In this case, the WL-CSP package utilizes no plastic encasement, it typically consists of only the bare silicon die with the possible exception of very thin protective coating or silk screening print on the top side, but far more often, nothing at all.

Wafer Level Chip Scale Package (WLCSP)

As the devices to which you originally refer are completely encased in opaque black plastic, there is little merit to your concerns.

BigDog
 
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