0.8mm PCB Flexibility - Page 1
Forum section: electronics / projects

author: Twistx77
author_rank: Regular Contributor
timestamp: May 29, 2013, 10:12:45 am
content: Hi,I'm working in a prototype of something where I need some flexibility in the PCB. I need the PCB to get the PCB to adapt a little bit to my forehead . It will be a 50x50mm PCB. I know I could use flexible PCB but that is much more expensive.So I want to know how flexible is a 0.6mm or a 0.8 mm standard FR4 PCB compared to the 1.6mm.Any other ideas are welcome.Thank you.

author: Rerouter
author_rank: Super Contributor
timestamp: May 29, 2013, 10:14:21 am
content: your best bet would be to ask the manufacturer for a minimum bend radius, FR4 only stands for the fire resistance rating, the actual materials used can vary greatly,

author: EEVblog
author_rank: Unknown
timestamp: May 29, 2013, 10:17:00 am
content: I've folded back 0.8mm board (a thin strip) on itself within maybe 50cm diameter IIRC, so probably not doable on a forehead?0.4mm would be much better.I've also sourced pre-preg before, the stuff they use for the inner layer on multilayer boards. That stuff is practically a flex board.Go with the thinest of whatever your manufacturer will do.

author: Twistx77
author_rank: Regular Contributor
timestamp: May 29, 2013, 10:21:02 am
content: Thanks to both.I'll try to get a 0.4mm. But I've also found out that iTead makes now 10 flexible PCBs of 5x5cm for 65$ which isn't much.I will give it a try to both.Btw Dave, I just got my 555 gray t-shirt!! Good quality!

author: Ryu.Hayabusa
author_rank: Contributor
timestamp: May 30, 2013, 02:03:17 am
content: A heatgun would assist in curving it, though I would imagine too much of a curve and you'd start ruining traces or pads.

author: Corporate666
author_rank: Unknown
timestamp: May 30, 2013, 04:09:50 am
content: 0.8mm is much more flexible than 1.6mm... I have a thin strip (1cm height, 20cm long) that would conform to the curve of a forehead - but bear in mind that any board, FR4 or flex, will only bend in one axis, never two. And the longer the "joint" of the curve (axis perpendicular to the curve direction), the stiffer the board will be and harder to curve in that direction. In other words, a 200mm x 50mm board will be much harder to bend along it's length compared to a 200mm x 5mm board, which will be very flexible.I have also used 0.4mm boards and they are *very* flexible. My fabricator also does 0.2mm which is like flex, as Dave said.Also keep in mind longevity if this is designed to flex often (longevity of the PCB as well as the connections to components mounted on it).

author: David_AVD
author_rank: Super Contributor
timestamp: May 30, 2013, 04:36:05 am
content: I've wondered about the stress on the components and the joints. I guess flexible designs need to avoid components that span too much of the curve?

author: Twistx77
author_rank: Regular Contributor
timestamp: May 30, 2013, 08:42:53 am
content: Thanks to everyone.Corporate666 great advices. Thanks. I'll keep that in mind. I think I will go for the flex this time and maybe I will do one 0.4mm later on to compare but for this first prototype I want it to be flexible enough to test it well.It has to bend in both directions but since the vertical bending will not be much, I don't think that will be a problem.

author: Mike Warren
author_rank: Unknown
timestamp: May 30, 2013, 12:02:57 pm
content: Quote from: Twistx77 on May 30, 2013, 08:42:53 amI think it probably will be a problem. As soon as you put a curve in one direction, the other become massively stronger.

author: Twistx77
author_rank: Regular Contributor
timestamp: May 30, 2013, 12:17:23 pm
content: And what would you think is the best option to adapt the PCB to the forehead?

author: Mike Warren
author_rank: Unknown
timestamp: May 30, 2013, 12:27:07 pm
content: How wide does the board need to be? As an experiment, get a piece of cardboard cut to the same size and see if you can get away without the second curve.How are you planning to hold the curve in place anyway?One possibility is that you might be able to cut slots in the board to weaken it, but not knowing what components and traces you need, that may not be practical.

author: fcb
author_rank: Super Contributor
timestamp: June 01, 2013, 09:30:01 pm
content: What is the radius of your forehead..?0.8 is pretty flexible, but I don't fancy the chances of you being able to flex it in-use routinely. If you deformed it during manufacture it might be better - personally I'd go with a flexi board or even flexi-rigid.

author: Corporate666
author_rank: Unknown
timestamp: June 02, 2013, 01:42:57 am
content: Quote from: Twistx77 on May 30, 2013, 08:42:53 amIt will bend in one direction and will have zero flexibility in the other direction. The only way to make it bend in two directions would be to cut slots in the board perpendicular to the direction of the first curve - but this can make routing traces more difficult.The problem is that once you bend in the first direction, in order to bend in a second direction, the material would need to fold in on itself. There is actually physical material in the way that prevents the second curve - you need to cut slots.As an example, take something as flexible as a sheet of paper and curve it into a cylinder and tape it in place. Then curve it in the second direction - you can't, not unless you cut slits in the paper and fold it over on itself. Same with the PCB.Even a flex PCB will have zero flexibility in two directions at once unless it has slots cut in it to fold over on itself.

author: Twistx77
author_rank: Regular Contributor
timestamp: June 02, 2013, 11:53:01 am
content: Thanks but since the PCB will be shaped like a star with 4 spikes I think there will be no problem.Anyway, this is my first FCB, is there anything special I should know? I know that there are probably many things to take into account but since the PCB is not complex and the soldering will be made by hand I don't think it will be much different.Is too difficult to hand solder the components or is it just like the regular PCBs?

author: Corporate666
author_rank: Unknown
timestamp: June 02, 2013, 10:27:52 pm
content: Quote from: Twistx77 on June 02, 2013, 11:53:01 amStar shaped should be OK - each "leg" of the star will flex in one direction which should be fine for your application.As for solderability - do you mean using flex PCB or thin FR-4 laminate? I haven't had a problem hand soldering either, although I am careful to keep the soldering iron on the pads and solder quickly when I am using flex (I do that for laminate as well, just a habit I guess). keep in mind that regardless of how flexible your PCB is, your components generally aren't... so use some consideration to where you place the components, especially the larger and heavier ones (you don't want the board below a TQFP-100 chip to be bending, for example, or it will bend/break the wires).

author: safarir
author_rank: Regular Contributor
timestamp: August 13, 2013, 12:55:49 am
content: Sorry to Relaunch this topic, but I got the exact same question ...Did you finally try to bend some 0.6mm pcd ?Dave, do you have more information about those prepreg board ?

author: Twistx77
author_rank: Regular Contributor
timestamp: August 14, 2013, 11:49:11 am
content: Hi,I finally got the flexible PCB which is way more flexible than we needed. Anyway, I got the 0.15mm FCB and the 0.3mm and the 0.3 mm. I think that the 0.4 mm PCB will be still very very flexible even when the sustrate has changed. If you can get the 0.6mm or even better 0.4mm for a reasonable price, I would suggest doing that, If you don't need very high flexibility that will be ok for you I think.Regards.