when a product is released, the great unwashed masses will find some really, really weird bugs. The first one to crop up is a light-sensitive reset of the Raspberry Pi 2.
U16, a small chip located in the power supply part of the Raspi 2, is sensitive to light. Putting enough photons will cause the Pi to shut down or restart.
This is the chip that is responsible, and this is not an EMP issue. This is a photon/light issue with the U16 chip. The solution to this bug is to either keep it in a case, or put a tiny amount of electrical tape over the chip.
In February 2015, early users of the Raspberry Pi 2 noted that the single-board computer would reboot if you took a flash photograph. Wags soon dubbed this phenomenon the Xenon Death Flash, in the spirit of the Blue Screen of Death, and the Click of Death predecessors. In a class act, and to show companies they don’t have to hide behind PR people, the Raspberry Pi folks soon verified the problem
Thanks to many hands making light work, it didn’t take long for users to narrow down the problem to a power supply chip. That chip was in a CSP (chip-scale package), what I used to call a flip-chip. It is a bare die, and the smallest way to package a silicon chip.
There was a lot of speculation and many were incredulous that a burst of light would cause the chip to go bonkers. Soon after, users noted that a laser pointer directed at the chip would also cause a reboot.
I am surprised any chip company would sell a CSP part to a customer without warning them of the potential susceptibility to light.
The speculation on the Internet was amusing since nobody really seemed to understand the exact problem. Every silicon P-N junction is a photo-diode. When light hits that diode it generates a photo current, a reverse current. You can think of it as the leakage of the diode going way up. Those currents inject into high-impedance nodes, where it affects the chip. Currents can also get injected into the substrate. That really screws things up. Amplifiers will stop working for seconds, until the free carriers get swept out of the substrate or recombine. Modern IC processes are so clean, there are few impurities to serve as recombination sites, hence the seconds of not working.
The real problem with any coating on a silicon die is ionic contamination, especially chlorine ions.
semiconductor companies go to extreme lengths to wash off any trace of the photo-resist that may contaminate subsequent steps in the process.
Most of those proposed solutions in the Raspberry Pi blog post would work for a long time as a one-off fix for this problem. But be aware how much semiconductor companies worry about long-term contamination of their parts.
Another misconception in the comments of the Rasberry Pi blog post was that the only reason that they used a flip-chip is low cost. CSP parts can cost more than conventional plastic-packaged parts. The real reason you use CSP parts is for space. Cell phone engineers love them
Silicon die area is far more expensive than plastic packaging, which can cost less than a penny a part.
Another cost increase in CSP parts comes from testing. If you drop probe needles on the bare pad, you can damage them, and then the solder balls won’t stick.
To me the lesson here is to use a well-respected IC supplier, and listen to the their apps people when they warn you about photo-electric effects. In the blog post about the problem, commenter Lada notes: “Yes, and the manufacturer of the (I presume switching regulator) warns about shining light on the package (chip). Maxim, Analog Devices, Texas Instruments, all do.”
Meanwhile don’t despair, the Raspberry Pi 2 is doing great, and has found many neat uses.
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2 Comments
Tomi Engdahl says:
Photonic Reset of the Raspberry Pi 2
http://hackaday.com/2015/02/08/photonic-reset-of-the-raspberry-pi-2/
when a product is released, the great unwashed masses will find some really, really weird bugs. The first one to crop up is a light-sensitive reset of the Raspberry Pi 2.
U16, a small chip located in the power supply part of the Raspi 2, is sensitive to light. Putting enough photons will cause the Pi to shut down or restart.
This is the chip that is responsible, and this is not an EMP issue. This is a photon/light issue with the U16 chip. The solution to this bug is to either keep it in a case, or put a tiny amount of electrical tape over the chip.
Tomi Engdahl says:
Xenon death flash for the Raspberry Pi 2
http://www.edn.com/design/systems-design/4441502/Xenon-death-flash-for-the-Raspberry-Pi-2?_mc=NL_EDN_EDT_EDN_today_20160229&cid=NL_EDN_EDT_EDN_today_20160229&elqTrackId=9ae61357ecf84a20b125aaab436a0299&elq=edb34f689fce417a8a85f4c04c6d5805&elqaid=31079&elqat=1&elqCampaignId=27172
In February 2015, early users of the Raspberry Pi 2 noted that the single-board computer would reboot if you took a flash photograph. Wags soon dubbed this phenomenon the Xenon Death Flash, in the spirit of the Blue Screen of Death, and the Click of Death predecessors. In a class act, and to show companies they don’t have to hide behind PR people, the Raspberry Pi folks soon verified the problem
Thanks to many hands making light work, it didn’t take long for users to narrow down the problem to a power supply chip. That chip was in a CSP (chip-scale package), what I used to call a flip-chip. It is a bare die, and the smallest way to package a silicon chip.
There was a lot of speculation and many were incredulous that a burst of light would cause the chip to go bonkers. Soon after, users noted that a laser pointer directed at the chip would also cause a reboot.
I am surprised any chip company would sell a CSP part to a customer without warning them of the potential susceptibility to light.
The speculation on the Internet was amusing since nobody really seemed to understand the exact problem. Every silicon P-N junction is a photo-diode. When light hits that diode it generates a photo current, a reverse current. You can think of it as the leakage of the diode going way up. Those currents inject into high-impedance nodes, where it affects the chip. Currents can also get injected into the substrate. That really screws things up. Amplifiers will stop working for seconds, until the free carriers get swept out of the substrate or recombine. Modern IC processes are so clean, there are few impurities to serve as recombination sites, hence the seconds of not working.
The real problem with any coating on a silicon die is ionic contamination, especially chlorine ions.
semiconductor companies go to extreme lengths to wash off any trace of the photo-resist that may contaminate subsequent steps in the process.
Most of those proposed solutions in the Raspberry Pi blog post would work for a long time as a one-off fix for this problem. But be aware how much semiconductor companies worry about long-term contamination of their parts.
Another misconception in the comments of the Rasberry Pi blog post was that the only reason that they used a flip-chip is low cost. CSP parts can cost more than conventional plastic-packaged parts. The real reason you use CSP parts is for space. Cell phone engineers love them
Silicon die area is far more expensive than plastic packaging, which can cost less than a penny a part.
Another cost increase in CSP parts comes from testing. If you drop probe needles on the bare pad, you can damage them, and then the solder balls won’t stick.
To me the lesson here is to use a well-respected IC supplier, and listen to the their apps people when they warn you about photo-electric effects. In the blog post about the problem, commenter Lada notes: “Yes, and the manufacturer of the (I presume switching regulator) warns about shining light on the package (chip). Maxim, Analog Devices, Texas Instruments, all do.”
Meanwhile don’t despair, the Raspberry Pi 2 is doing great, and has found many neat uses.