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.
[1] https://www.ifixit.com/News/11986/iphones-are-allergic-to-he...
It was interesting and remarkable because many engineers, despite solid diligence, might have missed the possibility unless they were well versed in MEMS manufacturing processes which were not very widely known before publication.
Still, it wasn’t at all surprising to the manufacturers of the parts, since using a calibrated gas mixture for initial adjustment is a standard design step.
Really. It's in the article linked.
> If that happened before the publicised discovery, it is a very impressive example of attention to detail.
The article seems to imply it was, but I don't know timelines because links are broken and I don't feel like doing archaeology. It is a known issue with that MEMS component before it made its way into the iPhone, so I don't find it very impressive. I don't know about Apple in particular, but it is very standard for electronics user manuals and spec sheets to list operating envelopes and known issues and limitations exhaustively.
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.
> Light-sensitive circuit protection, as claimed in literatures, is not a reality concern since silicon is only transparent to long wavelength light, which is rarely encountered in broad applications of WLCSP.
https://web.archive.org/web/20150210111428/https://www.fairc...
The article doesn’t make that claim. There’s an entire section titled “This Wasn’t Actually Unprecedented”. It links to another article containing stories about previous examples. It discusses the root cause of WLCSP photosensitivity.
> None of this is a “discovery”.
The discovery was that the Raspberry Pi 2 was photosensitive, not that WLCSP parts are photosensitive. Most PCBs aren’t distributed to consumers as bare PCBs, so this issue rarely appears to end users.
> 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.
You’re exaggerating. WLCSP photosensitivity is an uncommon phenomenon that requires a very strong and specific light source (Xenon flash, in this case) and the combination of an exposed PCB. I know there’s something about the Raspberry Pi that makes armchair quarterbacks want to find ways to call their engineers “hacks” and “NOOBS” but this is really a rare edge case. I wouldn’t be surprised if the photosensitivity was not even mentioned in the part’s data sheet.
This vulnerability, where present can be (and is commonly) exploited in alarm systems, access control devices, and other electronics that may face adversarial incentives. Light-protective covers are a very standard feature in construction of any kind of critical device that uses WLCSP parts.
In the case of the raspberry pi, the fact that it is a hobby device is a pretty good excuse for leaving the devices unprotected, but I definitely would have included the fact that the design incorporates WLCSP parts in critical roles and that the PCB should be in a case if being used in mission critical applications, since presumably, designers integrating RPI are less likely to be experienced board-level engineers.
My comment about being a hack or a noob really wasn’t meant for the RPI designers, though I can see how it would be easy to read it that way. I may be a bit of a literary hack, myself lol.
In terms of hobby/maker electronics, embedded systems, etc., which the Raspberry Pi falls under, yes they absolutely are. The entire Arduino ecosystem is like this.
But it also has lots of users for whom it is simply a cheap computer to plug into a screen / mouse / keyboard, people for whom the only interesting things about the hardware are its price and size.
(I've no idea what the ratio is, but I would guess the majority of customers are the latter type; though possibly not the majority of Pi's sold, since the former group contains people much more likely to buy multiple devices, whether someone like me who's bought a few for tinkering with, or someone actually doing something interesting and needing either 100s for their own project, or 1000s to go into something they're selling.)
So what you said is true for some, but far from all, Pi consumers.
Perhaps some kids can circulate a list of those commercial products incorporating a Pi, and campaign to liberate and repurpose them. Win-win?
"In 1967, Dawon Kahng and Simon Min Sze at Bell Labs proposed that the floating gate of a MOSFET could be used for the cell of a reprogrammable ROM (read-only memory).[3] Building on this concept, Dov Frohman of Intel invented EPROM in 1971,[3] and was awarded U.S. patent 3,660,819 in 1972. Frohman designed the Intel 1702, a 2048-bit EPROM, which was announced by Intel in 1971.[3]"
"The programming process is not electrically reversible. To erase the data stored in the array of transistors, ultraviolet light is directed onto the die. Photons of the UV light cause ionization within the silicon oxide, which allows the stored charge on the floating gate to dissipate. Since the whole memory array is exposed, all the memory is erased at the same time. The process takes several minutes for UV lamps of convenient sizes; sunlight would erase a chip in weeks, and indoor fluorescent lighting over several years.[8] Generally, the EPROMs must be removed from equipment to be erased, since it is not usually practical to build in a UV lamp to erase parts in-circuit."
Deep deep archived memory that one...
> sunlight would erase a chip in weeks
Been there, done that. When I wasn't in a hurry, I'd stick some EPROMs in a foam & put 'em under a window. Usually took a bit under 3 weeks. But no point trying in the midst of winter; probably works but could take months.
Loved those windowed ceramic packages. Especially microcontroller parts like (iirc) 87C52. Lovely patterns to have a look at with magnifier.
Because they are hacks and noobs? Who puts a WLCSP part on a board which is more commonly zip-tied to a piece of wood than it is placed into a case, and is more likely to be driving some wild contraption shooting RF and UV and god knows what else everywhere, than it is sitting inside some nice little commercial device like an office labelmaker?
Their hardware is almost always immediately superceded by cheaper, faster, better boards because they're not trying to give Qualcomm blowjobs clearing out shitty SoCs nobody wanted to buy because they were buggy, underperformant, overpriced, or all three...and they don't have the market advantage of everyone buying whatever garbage they spit out. Other companies have to start on the back of their heels so their products can't suck.
Their hardware designers are inept with every generation of every product they've made having issues and/or promised features not making it into production.
Their QA is non-existent despite seeding test boards widely where either they're not catching problems before doing into production or they're intentionally not fixing stuff because it would increase their costs and they know people will just snap up whatever garbage the Pi Foundation ships. The problems are so bad that you have to ask how they even got past internal testing and validation.
Seriously: if a bunch of college EE students worked for a semester they could probably build a better product.
Each generation of the Raspberry Pi has had basic hardware design flaws showing that their hardware engineering was not up to the task of producing the dominant hobbyist (and increasingly commercial/industrial, somewhat frighteningly) SBC.
Then they fucked up the RP2040, a wildly simpler product. When when they released a revised version that fixed the ADC issue, they fucked up GPIO. How do you fuck up GPIO and not notice?
I don't know who the Raspberry Pi foundation employes as hardware enginers but whoever their head of engineering is should have been fired a long, long time ago.
* "I'm mad because there's not an open source hardware/software/gpu/schematics/BOM" so I can't hypothetically make a clone of it
* If (1) above is not the motivation, then it's because there's some specific use-case that doesn't work that the rage-post precipitates, and crucially - includes zero links to bug reports or a log of efforts that the OP has attempted
* "All the designers are idiots because minor fault X is indicative of systemic failure Y" - with no supporting evidence
* General assertions that all these faults are catastrophic and should bankrupt the company (often conflated with the Foundation, which is a completely separate legal entity)
There's been about 80 million units sold so far. They must be doing something right.
Disclaimer: I own RPI.L stock. It's one of the few tech stocks on the LSE that have actually performed OK and not tanked since IPO.
“Real” engineers understand this and that is why they are often seemingly irrational about their selective attention to detail.
Hacks and noobs are just unintentionally dumping plane loads of gum wrappers over our cities, nominally increasing human misery by tiny amounts without even realizing it… but in a population of billions, and more transistors than grains of sand on the planet, the overall effect is cumulative and significant.
That’s why people that understand their civic responsibility to do their job to the best of their ability look upon hacks and noobs with concern or sometimes active hostility.
Introducing even a tiny spark of misery into the world that will be experienced millions or billions of times makes you a world class asshole that has actively contributed to making the world a shittier place in a significant way. It’s like you just dumped a c130 load of gum wrappers over a city from high altitude.
You can see how this would be overlooked: a given board may have many parts, and data sheets can be long. Usually you get good at picking out the important parts: Protocol description, pin maps, ref layouts, voltage tolerance etc. Reading the fine print certainly would have prevented this, but you can justify skipping it. Maybe less justifiable for a device like this that's produced in huge quantities though!
Also, Pedantic Cadence (r), the acerbically sarcastic EDA software where AI critiques all of your design decisions for the best possible engineering result! Only an extra $199 a month!
Right. Who put a bare chip on an open board and expected it to work?
There have been cases of photosensitive parts in the past, where the plastic encapsulation didn't have enough carbon black. Some old parts were packaged in brown plastic that wasn't opaque enough. That's a problem from decades ago.[1]
[1] https://electronics.stackexchange.com/questions/217423/ics-c...
I don't think "makers" should be brought into this - to me, "makers" include individuals who may not have any formal engineering education just putting ideas together.
Of course it's a different story for actual companies selling a product such as Raspberry Pi - the engineering standard should rightfully be higher.
[1] https://www.onsemi.com/download/data-sheet/pdf/ncp6343-d.pdf
Not all WLCSP parts have substantial or even noticeable photosensitivity issues. The vast majority of CSP devices have a backside coating which protects the top of the chip from most light, which leaves the majority of the photosensitivity to the edges of the device (or, reflections to the underside).
Some do, but in my view that’s largely a design flaw rather than an issue endemic of all WLCSP devices. Also depends on the type of device you’re building. Most basic digital logic, processors, and power parts shouldn’t have meaningful issues with light. The problem usually is band gap or oscillator light sensitivity, which can be alleviated by chip layout changes.
Depends... if you have an input that isn't driven externally (tri-state or nc), and there's just a weak pull-up or -down on the pin, you could have issues. An unexpected reset here, a bitflip there...
Also there's high-impedance ADC inputs on some parts. Wouldn't take much to send readings waayy out of spec.
Note that affected signal might be inside the IC (not going to an IO pin). More likely to be driven though (low-impedance).
If you meant 'EPROM' the story is almost certainly made up as the same company that sold you the EPROM sold you the sticker to put over the window.
- 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]
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...
I've tried explicitly to avoid it, but usually the subs will rewrite all headings.
Jeff shouldn't be doing it here: there is no sub to blame and we're not a mouth-breathing audience...
Jeff: I may have misjudged your intent, but know that that style may not work on British technical pendants, obviously a valuable segment of your audience... %-P
In penance I offer: every person who confuses correlation and causation dies...
One thing common to all models of Pi is that the onboard power circuits are either rather simplistic, or missing altogether. I think I saw somewhere that this may have to do with EU/UK regulations that otherwise forbid the bare board sold as a consumer product. Anyone read/heard similar?
Wish I could remember the name of the company that was working on commercializing this...
Another fun example: Manually rotating a DC motor produces current! Might make sense if you start out with generators I suppose, but as someone who used a DC motor "the other way" first, it was kind of counter-intuitive.
* Electromagnetism (motors/generators)
* Photoelectricity (LEDs/PVs)
* Thermoelectricity (TEGs/Peltier coolers)
* Piezoelectricity (crystal oscillators)
Anybody got others?
Ceramic capacitors can have similar issues: apply voltage, part warps a tiny bit. @ the right frequencies some (mechanical) resonance effects might come into play. Yay! But I have a hard time imagining this to be a real-world problem.
Edit: "microphony" or "microphonics"
https://en.wikipedia.org/wiki/Microphonics
Just an idea: coil whine might be reversible too. Vibrate coil, get some (noise in) inductor current.
Oh yeah: don't yell too loud at your (spinning) harddrives.
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.
As long as it's clear it's the machine or UI, I don't mind LLM output that much.
I enjoyed the post more as a story more than as a report.
Everything is starting to sound the same, and it's becoming monotonous
The initial part was fine but when it got to the conclusion it was incredibly monotonous.
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.
https://magnus919.com/2025/05/what-i-learned-about-agi-at-a-...
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.
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.
pvg•8mo ago
DamonHD•8mo ago