Re: CSP light sensitivity / google groups

the first Raspberry pi 2 would reset if photographed with flash light, turned out to be the power supply chip package that was transparent to the light from a photo flash, and the light upset it

Some early germanium transistors were potted in hazy epoxy inside a bullet shaped glass envelope with matt black paint on the outside. OC71 being a notable Mullard part that is still curiously popular in guitar fuzz circuits even today. You could convert the cheaper part into a fair approximation of the more expensive phototransistor just by scraping off the black paint. This no longer worked when transistors came in metal cans. The latter went with a much bigger bang when they blew.

A fair number of consumer LCD digital watch circuits were photosensitive in that they could not survive a photoshoot flash gun at close range.

If you have a really bright light, you might even get a chip to latch up. If there is a pnpn structure e.g. formed by some grounded n-well in a p-substrate process, that can be basically a SCR across the power rails. If there are enough substrate contacts grounding the p substrate near the grounded n-well then that can be ok (it's like putting a low value resistor from the gate to cathode on the SCR making it hard to trigger), but if there aren't enough substrate contacts and the light is bright enough, you can turn it on, and possibly destroy the chip, or at least make it need power-cycling.

This used to happen to me quite a lot when I was debugging chips on a probe station, and I was cutting off tracks with a pulsed laser (to determine which ones were coupling RF from one part of the chip to another). To be safe one would turn off the power before cutting, and turn it back on afterwards to see the effect, but sometimes I didn't turn it off, because I was cutting a track that was necessary to start up the chip and after the track was cut it would no longer be possible to configure the chip registers to the desired state, and so sometimes I triggered latchup.

Once I noticed this, out of curiousity I defocused the laser and scanned around the chip to find all of the other places where I could make it latch up easily, and then on the next mask revision I improved the substrate contacts and/or removed the need to have grounded n-wells in those places, and made the chip much less prone to latch-up.

In theory, when we were doing electron beam probing on unpackaged chips, we could have run into this problem, but the chip was running under vacuum in an evacuated chamber to let the electron beam get at it.

The chamber didn't have to be light-tight all the time, but we detected the secondary electrons by letting them hit a scintillator (Everhart–Thornley detector) so it did have to be light-tight when we were using the electron beam to look at the chip.

I have an OC3 somewhere. (Early Philips germanium transistor. Before germanium were called AC### ). I thought the enclosure was glass, painted black and the paint was removable. If the enclosure was plastic, it could easily be made black plastic. Need it check it though.

All electronic devices are sensitive for EM radiation as long as it enters the crystal.

A lesson learnt as a technician when fixing an old outside broadcast mixer at the BBC. Terrible mains hum, but try to see it on a 'scope and it disappeared. Took a while to realise that leaning over with a 'scope probe was shielding the Germanium transistors with worn paint from the overhead fluorescent striplights.

Separately, some of the RF Germanium transistors, eg OC44, used some sort of blue putty to protect the junctions. I believe, on very little evidence, that it was what came to be known as 'Silly Putty', or at least was very similar.

That blue stuff was silicone gel.

No but the light after travelling through our atmosphere and any air currents in the room can have a fair bit of variation. The amount of variation twinkling in stars (less for planets) can be used to infer the diameter of unresolved objects by finding the separation between two scopes at which they cease to be correlated. Hanbury-Brown and Twiss first made the intensity interferometer work in the optical.

Michaelson & Peas beat them too it with a steel girder add-on in front of the Mt Wilson 100", but it required an experimentalist of Michaelson's calibre to make it work properly. They measured the diameters of several of the brighter nearby stars with it.

AF116 and AC128 were the ones in my first electronics kit.

Followed closely by BC107 and Ferranti e-line tinning failures that merely required patient application of a soldering iron to fix them.

I've seen watches that could not withstand direct sunlight. It was 1978 or something like that, I think they were being given away at "Pauls camera House" or similar shop as part of some promotion.