from Hacker News

The Xenon Death Flash: How a Camera Nearly Killed the Raspberry Pi 2

by DamonHD on 5/24/25, 12:06 PM with 89 comments

  • by K0balt on 5/24/25, 1:52 PM

    Photosensitivity in WLCSP parts is not something that was “discovered” by the community.

    The data sheets for WLCSP parts specify that the part is photosensitive and often give data on how light can affect the part.

    This has been known since the inception of WLCSP, and is treated as a design parameter by responsible engineers.

    Chip manufacturers know that bare silicon chips are light sensitive, they are literally made of thousands/millions/billions of tiny solar panel junctions. CMOS imaging tech evolved from exposing cmos memory chips to a focused image. WLCSP chips are basically unpackaged silicon chips.

    None of this is a “discovery”. People have been decapoing transistors to use them as photodetectors or solar cells since people started putting metal covers on transistors to protect them from light interference. Early photo transistors were a standard npn part with a windowed can.

    If you put WLCSP parts on a PCB that will be unprotected, and photosensitivity is not an acceptable design feature, you are either a hack, or making mistakes like a NOOB and should be supervised by a senior engineer.

    It’s called reading the data sheet, before integrating a part into millions of devices. Maybe understanding what a silicon chip is made of and how semiconductor junctions work. It’s a basic engineering responsibility, and failing to do so is an abdication of your duties and responsibilities as an engineer.

    Anyway, cool story except I get the definite feel that the article was written or heavily influenced by LLM output, by the pedantic cadence and constant summarization.

  • by skrebbel on 5/24/25, 5:18 PM

    In case the author reads HN, I just wanted to share that I was rather irked by the writing style, the way it adds all kinds of weird irrelevant bits of info that don't actually clarify anything (eg "the same phenomenon Einstein won a Nobel Prize for explaining") and ways to make things sound more spectacular than they are (eg "Blu-Tack (yes, really)" or the whole story about "community trust").

    I read on your about page that you use LLMs to assist your writing. Consider this comment a suggestion to depend on them less, or at least be more critical with their output. I've never been so frustrated reading a blog post as when I read yours as I flashed from interest to annoyance and back again many times.

  • by Sharlin on 5/24/25, 1:42 PM

    Another classic hardware glitch: iPhones Are Allergic to Helium [1]

    [1] https://www.ifixit.com/News/11986/iphones-are-allergic-to-he...

  • by geerlingguy on 5/24/25, 3:51 PM

    Every even numbered Pi model had some kind of interesting quirk requiring a hardware change to 'fix':

      - Pi 2 had the camera flash reboot issue
  - Pi 4 had improperly implemented USB-C charging circuit, causing many PD adapters to not power it[1]
    (I still have and use both of the original models — the hardware flaw was only a problem in certain circumstances.)

    The Pi 5 has it's funky 5V / 5A requirement (though 5V / 3A works fine if you're not using high power USB accessories, if you have a decent power adapter), but it's otherwise not had any hardware-level odd quirk on the scale of Pi 2/4.

    So the question is: what will it be on the Pi 6?

    [1] https://hackaday.com/2019/07/16/exploring-the-raspberry-pi-4...

  • by itishappy on 5/24/25, 4:36 PM

    Fun fact: semiconductor effects are often reversible! A light emitting diode is an inefficient photovoltaic panel, and vice versa. This is relevant here because the same effect that allows you to stimulate the junctions using high intensity IR light happens in reverse: a stimulated junction emits IR light which can be detected through a thin enough package. With the right camera you could in theory take a video of specific junctions activating on chip. Efficiency makes this difficult in practice. I don't know how many photons you get per junction per clock cycle but it's not many, and those photons still need to make their way out of the package and be picked up by your sensor. I suspect getting a useful signal involves seriously overvolting the chip and/or underclocking it, so I'm not sure how "functional" of a test it would be.

    Wish I could remember the name of the company that was working on commercializing this...

  • by nickdothutton on 5/24/25, 1:37 PM

    Reminds me just a little of the "SPARC CPU cache corruption by radioactive decay of impurities in chip packaging" which cost me many hours in my first job.

  • by rini17 on 5/24/25, 1:30 PM

    I had same issue with fancy translucent cover for my hearing aids. Sunlight at certain angles and flashes caused noise. Nobody believed me.

  • by RajT88 on 5/24/25, 8:00 PM

    I am reminded of a strange issue I had with a DV Cam which I took on a "tiger cruise". The TC is where you visit your family aboard an aircraft carrier on the way back from a tour - in our case we rode the boat from Honolulu to San Diego.

    When on deck, the video would get scrambled every 3 seconds. It was a weird issue! I soon figured out it lined up with the sweep of the radar array - makes sense.

    Knowing I was dealing with radiation of some sort, I reasoned if I kept my phone angled so the battery (filled with heavy metals) between the radar array and magnetic heads, the video would no longer stutter every 3 seconds. Worked like a charm.

  • by pvg on 5/24/25, 12:10 PM

  • by xeonmc on 5/24/25, 1:21 PM

        The intensity threshold was crucial. Regular LED camera flashes didn’t produce enough photons, but xenon flashes and laser pointers packed sufficient punch to trigger the malfunction. Even more interesting, the effect required silicon’s specific bandgap energy—meaning infrared and visible light could potentially cause problems, but only at extreme intensities.
    Article is confusing intensity with wavelength. Unless they’re talking about nonlinear multiphoton absorption which could inly be achieved by intense ultrafast laser pulses

  • by pclmulqdq on 5/25/25, 12:46 AM

    Post-silicon debug of flip-chip parts is sometimes done by shining a laser on the chip at a very specific spot and detecting backscatter from the laser spot to determine if a transistor is on or not. If you turn the laser power up, you can switch specific transistors open or closed. Semiconductors in general are pretty sensitive to light, which is why they are usually packaged in a way that keeps them dark during operation.

  • by johnea on 5/25/25, 2:15 AM

    This also happened to me. I guess it was the late 1980s.

    I was programming UV erasable microcontrollers in quartz-windowed ceramic packages. Once I had the whole multi-processor distributed system up and running, I snapped a photo with my flash (film) sports camera.

    Everything crashed! I also had to repeat the process reliably a couple of times before I was convinced it was the flash that caused it.

  • by tallanvor on 5/24/25, 2:10 PM

    I can't find a link now, but I remember a story about AT&T (I think) proudly showing off their new digital switching technology recently installed at an exchange and having the system crash when the flashes were strong enough to erase the EEPROMs they used in the system.

  • by prpl on 5/25/25, 1:06 AM

    I used to use xenon flashes to calibrate latencies to calibrate data streams. I had a few different SDR devices hooked up to consumer hardware, and a high resolution/accuracy (50ns) time device I could control a xenon flash with. I’d trigger the xenon flash and basically just inject the flash in the data.

  • by jdbs_alter_ego on 5/24/25, 7:20 PM

    Ugh, this article smells of AI slop.

    For starters the "jdb" "forum user" (with a Raspberry Pi Engineer tag - i.e. an employee) never claimed to have tested the board with any sort of Samsung camera.

    The actual post referencing Samsung is here: https://forums.raspberrypi.com/viewtopic.php?f=28&t=99042#p6... - which has a couple of broken nested quotes.

    And literally the next post has jdb's replication with a Canon compact handheld.

  • by tedunangst on 5/24/25, 5:40 PM

    Conclusion seems rather forced. Like if trends continue, in ten years you will 1024 babies.