Manufacturing process of things similar to EEVblog #1078 "World's Thinnest Calc" - Page 1
Forum section: electronics / projects

author: Meerkat
author_rank: Newbie
timestamp: May 28, 2018, 10:57:05 am
content: Hi all,Would any of you know how to start putting together a device like that calculator?The usual board I've seen are of the 1.6mm FR4 variant, and looking at that calculator, it's obvious that producing an FR4 and mounting components on it is not the way that was made. Rather, multiple layers of copper, plastic, and then print on top probably involved more than one company, including ones that specialized in pcb, and another in plastics.A similar problem (probably a much easier start) to designing something like that is an RFID card, with its embedded antenna and controller. See example card on ebay for what I'm talking about:https://www.ebay.com/itm/3X-CUID-UID-Changeable-Block-0-Writable-13-56Mhz-RFID-Card-Support-NFC-App-MCT/263521746331?hash=item3d5b1ebd9b:g:4Y0AAOSwDNdVniUUSo a better question from me might be how would one go about designing and getting a passive RFID card manufactured?My guess (that can be totally wrong) is that the copper antenna first gets modeled in some simulation package, then transferred to Altium (or other similar software) along with a footprint for an IC die (which you purchases from chip manufacturers???). Then, the whole lot gets brought to a pcb manufacturer for a flat flex type pcb, then that whole lot gets shipped out to some sort of plastics facility to mold into a card. After that, some other place probably made a sticker that goes on top, or the cards just get sent off to a printing facility that stamps the design and graphics on the card.Perhaps discussion can be tagged in four different categories - copper design, plastic design, copper manufacture, and plastic manufacture.I'm interested in knowing names of companies who would do this type of design as well, in case I do pursue a similar project.Thanks!-Mk

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 28, 2018, 02:30:31 pm
content: Flex is pretty normal these days, whether rigid-flex (thin FR-4?) or the film based stuff.Altium actually has limited facilities for CoB wirebonding. The process is something like, make a footprint showing the die pad locations; make a footprint with the bond pads; and make a map of jumpers between the two, which goes into the wirebonder table somehow.Flip chips, of course, you just do whatever. Either it's directly bonded (requires high precision!), or it's a CSBGA or something like that.I've done boards before with planar RFID coils; in that case, I estimated the inductance and put in enough extra capacitor footprints to allow for adjustment by assembly variant. On one, the coil filled the board outline (bigger is better), so the electronics had to go in the middle. I poured ground plane over the circuit area -- well stitched -- to try and minimize whatever self-interference it might induce in the circuitry. The ground shorts out some field, reducing the inductance (and Q factor, but that's probably not a big deal), so the ground pour should be minimized as well. Everything needs to be crammed in tightly, then wrapped with just enough ground to protect it, no more.Tim

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 28, 2018, 03:00:16 pm
content: To build a credit-card-like device (similar thickness), you could use flex, but FR4 could work too. 4-layer, 0.36 mm FR4 PCBs are common these days. A lot of manufacturers can make them. They are just rather expensive, but more than 2 layers with flex can be *very* expensive. Then you could over-mold it in plastic or so to get something like 1 mm overall thickness. You would probably have to use COBs. Sounds doable. Now that would be thin.