How small can a circuit board be? - Page 1
Forum section: electronics / general

author: Connecteur
author_rank: Frequent Contributor
timestamp: April 15, 2023, 06:57:44 am
content: We all know about MEMS and the decreasing die thickness of IC chips, but what are the practical limits of a circuit board with soldered components? I'm sure there are pick and place machines made down to a certain size for making implantable medical devices and such, but how small can they eventually go? It would be interesting to know if microscopic circuit boards can be made some day.

author: helius
author_rank: Super Contributor
timestamp: April 15, 2023, 08:54:20 am
content: Small circuit boards can always be processed on the panel level and separated after assembly.The smallest I have seen so far are in laptop power adapter plugs. A circle 8mm in diameter.

author: Infraviolet
author_rank: Super Contributor
timestamp: April 15, 2023, 05:04:54 pm
content: For typical FR4 like boards I would imagine the method of cutting the boards out of the sheet would have an influence on the minimum size physically possible. I'd suspect you couldn't get boards with length or width dimensions smaller than the thickness of the board manufactured anywhere. Also, for very small circuit boards, what would the application be, too small and there wouldn't be room enough for any components, much less any way to connect from those components to things off the board. I did once make some circuit boards of about 4mm by 5mm to adapt from two pins (2.54mm spacing) of a tiny microswitch straight in to a header for a 1.27mm pitch two wire cable assembly, it was nicer than soldering long wires directly to the switches' pins.

author: abeyer
author_rank: Frequent Contributor
timestamp: April 15, 2023, 09:05:49 pm
content: At what point does the special process and equipment to support soldering discrete components that small stop making sense vs just putting whole thing on a single asic? It feels like there might be use cases for it, but niche enough that it doesn't seem likely to become common unless you really need it.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 15, 2023, 09:31:26 pm
content: Part of this depends on how you define pwb. If you include ceramic substrates you can inter-connect ic die and passives at very small dimensions. They were a hot technology back in the late 70s to the 1980s, but only get used in specialized applications.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 15, 2023, 09:44:57 pm
content: The smallest commercial parts are probably interposers (silicon mounts directly to it) and certain examples of flex and whatnot. And yeah, ceramic and hybrid sorts of construction are probably good contenders as well.Regarding flex, I recall one application that was something like, 2-4 long chips bonded side by side ("| | | |" orientation) onto a flex then curled into a rough cylinder. Then swallowed. It was a medical sonar receiver (or transponder?) system or something like that, and under 1mm dia. or something like that. Cool beans!Tim

author: Someone
author_rank: Super Contributor
timestamp: April 15, 2023, 11:09:48 pm
content: As with the above answers, it gets blurry as you transition from wire bonded "discrete" chips through to bump bonded (like tiny BGA packages). This was all done for electro-optic systems where the chips were made on different processes (Ge, III-V, now SiC) but a more recent example with good pictures and promotion is AMD:https://www.pcgamer.com/amd-infinity-links-rdna-3/https://www.anandtech.com/show/17288/universal-chiplet-interconnect-express-ucie-announced-setting-standards-for-the-chiplet-ecosystem0.009mm pitch packages!https://videocardz.com/newz/amd-3d-v-cache-uses-9-micron-pitch-bonds-the-future-of-3d-stacking-is-circuit-slicing

author: Gribo
author_rank: Frequent Contributor
timestamp: April 17, 2023, 06:05:20 pm
content: If you can accept horrible yields, It is possible to route ~1cmx1cm, 1mm thick FR4.I had such PCB made as a patch for another board, it had a 6 bump BGA device on it. Yields were <50%.

author: AndyC_772
author_rank: Super Contributor
timestamp: April 17, 2023, 08:25:19 pm
content: What was the yield problem due to? The board being thin or small shouldn't be an issue in itself; did the chip have very small solder joints? Was it subject to bending forces when separating the individual PCBs from the panel?

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: April 18, 2023, 04:12:40 am
content: Quote from: Gribo on April 17, 2023, 06:05:20 pmIn addition to above questions, how thick of copper?

author: NorthGuy
author_rank: Super Contributor
timestamp: April 18, 2023, 01:40:18 pm
content: TI sells power modules like this one (2.3 x 2.9 mm PCB):https://www.ti.com/product/TPS826716

author: lamabrew
author_rank: Regular Contributor
timestamp: April 18, 2023, 02:38:06 pm
content: Maybe not the smallest, but certainly very dense:https://octavosystems.com/octavo_products/osd335x-sm/

author: AndyBeez
author_rank: Frequent Contributor
timestamp: April 18, 2023, 04:18:00 pm
content: Another teeny solderable PCB example in daily use, the (dreaded) Apple lightning cable validator circuit.https://www.techinsights.com/blog/apple-lightning-cable-teardownThere are plenty of other diminutive examples such as wireless devices crammed into USB dongles. I assume there is a point where the PCB gets too thin to remain robust without same form of encapsulation?

author: rfclown
author_rank: Frequent Contributor
timestamp: April 18, 2023, 06:49:36 pm
content: I worked on an implantable neurostimulator that was placed in the body through a needle, so it was long and very thin. The circuit was on a flex with an ASIC (done by iSinehttps://isine.com/portfolio/medical-device/) and a handful of 0201 parts. The flex was only wide enough to accommodate one 0201 part in that dimension. There might have been about 20 flex circuits on a panel.

author: Connecteur
author_rank: Frequent Contributor
timestamp: April 20, 2023, 06:26:21 am
content: I had a procedure a few years ago, where they put a camera inside my circulatory system and made an inspection.Although it makes me cringe to think about, I didn't feel a thing and it just felt like spending some time relaxing and lying comfortably.

author: dukelec
author_rank: Contributor
timestamp: April 21, 2023, 08:56:07 am
content: The smallest PCB I've made is 5 x 7.3 mm (It is a core board for Latice iCE40UL FPGA):https://github.com/dukelec/cdpga/blob/master/cdpga_a/files/cdctl_a_component.pngThe other iCE40UL FPGA core board I made is slightly larger at 5.5 x 8.3 mm:https://github.com/dukelec/cdbus/tree/master/examplehttps://github.com/dukelec/cdpga/blob/master/cdpga_b/img/cdctl_bx.jpg

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 21, 2023, 09:08:20 am
content: The first limiting factor is how easy it is to break them out of the panel.At some point, you may need to CNC rout them out after assembly, and maybe use a jig for support - the limiting factor on this will be the precision of the routing process.

author: sinewave
author_rank: Unknown
timestamp: April 21, 2023, 10:48:46 am
content: Quote from: mikeselectricstuff on April 21, 2023, 09:08:20 amThere actually are laser-based machines that will do this with a C02 or UV laser