I’m working on a CE to try to make it very, very thin. I bought some thin calculators on Amazon to teardown to understand what sort of “minimum required parts” there are for something basic like a calculator (input/output, memory storage, processor to compute values, etc).
I took some photos and was wondering if anyone could help identify some aspects of the parts:
What are these globs of black rubber material for? They add a good bit of thickness (like 1-2 mm).
The blue part is the rubber keypad, and there are these tiny black pads on the back of each button that I guess complete the circuit on the circuit board. Is this just conductive rubber? I sliced it open to see if there was anything special inside, but no dice.
A similar system employed with black dots on the back of a thin sheet of coated paper:
Some additional questions:
Also, does anyone with knowledge on batteries know how thin they can get these days? I’ve found paper-thin batteries in research settings, but are there alternatives to watch batteries or Lithium ion batteries currently found in smartphones?
How thin can an induction coil get for induction charging? I haven’t had a chance to buy something that has induction charging that I can afford to tear down. Tips on using that in a very thin CE would be appreciated!
Thank you so much!
Globs of black rubber: This is an insulator. When producing very large quantities of a board, it’s cheaper to solder a uninsulated chip onto the board and drip a plastic coating onto it than buy a chip with the insulation like this one:
The keypads use a carbon pad to make the contact. I’m not sure what the material is that completes the circuit, but I’ve always heard it referred to as a carbon pad.
As for batteries, it depends on the load you have on it. Obviously, there are some very thin lithium-ion and lithium polymer cels available (4-5mm). However, the size of the cel is often driven by the demands of the product. Talk to your electronics engineer.
Thanks for the tips! Unfortunately, this is a side project and where I work doesn’t have any EEs. The power demand is very little, basically a day’s use of calculator level type input, with ability to store values to sync later on via BT or NFC (haven’t decided).
the thing under the big blob is a ASIC or application specific IC and is really really tiny. The board thickness is dependent on how many layers, the physical loads expected some are even flexible. Induction coils can be very small, they are just 1/2 of a air gap transformer after all. That said you still need a battery to store the juice because as soon as you move that coil out of its design air gap its induced current go’s by by. Thin batteries, its a hot topic with lots of money in R and D being spent, on thin commercially available thin batteries just do a google and then call around. I have seen them off the shelf as thin as 1/8" .
The black things on the backs of the keys are carbon pucks. They are just silicone with a high carbon content to trigger the capacitive circuits on the board.
Battery thickness. Depends heavily on your requirements. Coin cell batteries can usually be found that are ~3mm thick. You’ll find those in things like the Apple remote controls. Li-ion or Li-po packs like those used in the iPhone or Ipod touch are usually only about 5-6mm thick.
For the induction coil, see if you can find any of those commercial cell phone charger packs. The coil itself is probably very thin, but requires a large amount of surface area.