Black dots on the back of my camera module - what are they actually for?

I tear down old phones for parts and those dots show up on pretty much every module I've handled. On the two Galaxy boards and an old OnePlus I've got in a drawer, they sit in the same sort of pattern you're describing, right around where the lens barrel mounts. My understanding after asking around a while back is that they're alignment marks for the factory robots, so the pick and place head can line the module up perfectly when it's being assembled. Some of them also end up holding a dab of adhesive under the lens assembly, wich is why a few look like they've aged strangely once heat and time get at them.

The mate who reckons glue isn't far off the mark for at least some of them, but the regular pattern is the giveaway that it's from manufacturing rather than somthing going wrong.

As for poking at them, I scrubbed one with isopropyl once on a dead unit out of curiosity and it didn't change a thing, camera still focused fine. But that was a board I never planned to reuse. On a phone you actualy want working I'd leave them exactly as you have. The coating on those modules scratches easier than people expect, and a stray fibre or fingerprint inside the stack ends up as a shadow in every photo, which is a far more annoying problem than a few mystery dots ever were.

I'd push back a bit on the robot alignment theory. When I rebuilt the camera on a Pixel 4a after it started doing that annoying wobble in videos, I got deep into how these lens stacks go togehter, and those little dots are most likely cured glue. Modern camera modules get the lens adjusted against the sensor while a camera is running, then a few tiny drops of adhesive are hit with UV light to lock everything in place. The dots you see on the back are where the glue squeezed through or where the dispensing head touched down.

I saw this firsthand on the module I had apart. The dots sat exactly where the lens carrier meets the mounting frame, and when I warmed one gently with a hot air station at low temp, it went soft and shiny like adhesive does, which a solder pad or printed mark would never do. That actually matches your glue theory more than the test point idea, so your mate might be onto something. As for wheather they're on every phone, I've checked modules from an old Moto and a Xiaomi and both had them, though the patterns differed a bit between manufacturers. Either way, leaving them alone was the right call. Scrape at them and you can shift the lens slightly out of position, and that's how you end up with photos that are sharp in one corner and mushy in the other.

I've seen those dots on the newer ones where the surrounding plastic housing is really tight. It makes me think they might be tied into heat management, which is always an issue with these high-res camera setups these days. If those marks are holding the assembly in place, it's pretty wild how much delicate glass they cram into there. I wonder what material those dots are actually made of; I've seen some that looked like solid epoxy, but maybe they're silicone.

I always figured those dots were just some kind of tack, but looking closer at old boards, the plastic housing right around those spots seemed really fragile. It got me thinking about whether they might be designed to act like tiny stress reliefs for the sensor chip itself. If you drop the phone, that specific area is always the first place for microfractures to start. definately something to keep in mind when dealing with these delicate camera assemblies.

I've noticed those dots more often when phones are recovered from moisture damage. I once opened a unit that had been submerged for six months and found that nearly every dot had oxidized slightly, which suggests they might be micro-seal points designed to prevent water from getting into the sensor array. When I was looking at one of the newer models, I counted about 12 contacts around the perimeter of the lens. It seems like a surprisingly low number for a component that relies on such delicate optics, but it makes sense if they are serving a sealing function rather than a complex electrical one.