How to assemble flexible PCB with Pick and place machine. - Page 1
Forum section: electronics / general

author: luiHS
author_rank: Frequent Contributor
timestamp: February 23, 2023, 03:27:56 pm
content: Hello.I have a Neoden4, and I want to make my first circuit with aflexible PCB, but I don't know what is the ideal way to assemble it in my Pick and Place machine.I suppose that I will have to put the flexible PCB on a conventional rigid PCB board, but it will also have to be fixed and always in the same position so that the Neoden4 can detect the fiducials.Anyone with experience mounting flexible PCB boards with their pick and place machine?

author: sinewave
author_rank: Unknown
timestamp: February 24, 2023, 11:14:41 am
content: Don't have experience, but place either a rigid bit of FR-4 or sturdy plastic underneath, probably better to be blank, as for fiducials, wouldn't your flex PCB have fiducials as you can just use those. Securing it may be challenging, but you could just use kapton or packing tape.

author: 48X24X48X
author_rank: Frequent Contributor
timestamp: February 24, 2023, 11:17:09 am
content: I can only imagine having some holes at few corners on the FPC panels with pins on a rigid PCB. Holes must be tight. This way it can be repeatable.

author: SMTech
author_rank: Frequent Contributor
timestamp: February 24, 2023, 12:36:05 pm
content: Quote from: 48X24X48X on February 24, 2023, 11:17:09 amThat is essentially how it is done. Customised carriers that take your flex from print right through to reflow. See this thread for examplehttps://smtnet.com/Forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=22277&mc=13And then cobble up a homebrew equivalent.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 24, 2023, 12:49:23 pm
content: Quote from: 48X24X48X on February 24, 2023, 11:17:09 amaccuracy isn't usually a big deal as the fiducials will normally be on the flex pcbWhen I do thin boards I usually just tape them to a FR4 carrier with kapton tape

author: luiHS
author_rank: Frequent Contributor
timestamp: February 27, 2023, 09:50:30 pm
content: Thank you all for the answers.I'll try putting a rigid PCB under the flexible PCB, so the Neoden4 can place the components.Does using kapton tape have any advantages over using normal adhesive tape? It is to avoid spending more money, if it is not necessary.The only advantage that kapton tape could have is being able to put the board directly into the oven without removing the tape, although it is no longer necessary once the Neoden4 installs the components on the PCB.I have never made flexible PCB boards, can someone confirm that they are designed the same as normal PCBs, that is, I can route tracks on both sides and use vias. I guess they can't be done with more than two layers.

author: thm_w
author_rank: Super Contributor
timestamp: February 27, 2023, 10:54:16 pm
content: Why would you say its no longer necessary to have the flex PCB on a rigid plate when putting it in the oven?I mean if you can get the flex off the FR4, without bumping any of the parts, and your oven has a flat surface or enough support, I'm sure its fine. But most cases I can't see that easily being done. Kapton tape is very cheap.Quote from: luiHS on February 27, 2023, 09:50:30 pmYes flex PCBs can have two or more layers with vias. You should read about them before you design anything:https://www.pcbway.com/blog/News/What_is_Flex_PCB____An_Overview_of_Flex_and_Rigid_Flex_PCB.htmlhttps://neuronicworks.com/blog/flex-pcb/

author: SMTech
author_rank: Frequent Contributor
timestamp: February 28, 2023, 08:56:05 am
content: If you google around, there's a free book about flex circuits too.One of the most problematic things about them is they are very hygroscopic, and more sensitive to reflow temps. This increases the risk with lower end setups that perhaps how weaker reflow control and zero climate and storage moisture control. If it goes wrong, the flex delaminates during reflow.

author: luiHS
author_rank: Frequent Contributor
timestamp: March 01, 2023, 04:31:44 am
content: Quote from: SMTech on February 28, 2023, 08:56:05 amThx.Does this mean that the flexible PCB could be damaged in the soldering process in the oven, does it require any temperature or special soldering curve?

author: Psi
author_rank: Super Contributor
timestamp: March 01, 2023, 06:14:26 am
content: The only one I've seen (rigid flex panel) was placed on a carrier plate and a metal cutout sheet (like a solder paste stencil) placed on top.This metal sheet had cutouts for all general areas with parts and was solid everywhere else, so it held down the pcb against the carrier plate everywhere there was no parts to be placed.

author: luiHS
author_rank: Frequent Contributor
timestamp: March 01, 2023, 09:59:57 pm
content: Quote from: thoven on March 01, 2023, 12:18:40 pmThank you.Can you send me a link to the video? I'm very interested to see how it's done.

author: PCBprototyping
author_rank: Contributor
timestamp: March 03, 2023, 01:13:31 am
content: Quote from: luiHS on February 23, 2023, 03:27:56 pmSince you use Neoden 4, I assume you are assembling prototypes, so automated process is not that important for you.Therefore, you can use 3M 75 adhesive spray or t-shirt silkscreen printing spray to temporarily fix the flex board to rigid FR4. Kapton won't fully fix the flex PCB which can cause you some issues with p&p heights and printing. Using spray will eliminate this and it will be very simple to remove the flex after the reflow as these sprays are just low strength temporary adhesives for light fixing. If flex is too sticky after removal, spray it with some alcohol and wipe off the adhesive.

author: luiHS
author_rank: Frequent Contributor
timestamp: March 03, 2023, 01:58:07 am
content: Quote from: PCBprototyping on March 03, 2023, 01:13:31 amIs the surface of a flexible PCB not perfectly straight and smooth? This would be a problem for the Neoden4 to put the components on the PCB, they could be out of place. Specifically, it will be to place WS2813 LEDs sizes 2020 and 3535, precision is needed so that they are well placed, a roughness on the flexible PCB can ruin the task.

author: PCBprototyping
author_rank: Contributor
timestamp: March 03, 2023, 12:33:17 pm
content: It is smooth, but if you put kapton tape over or under the flex, it won't be perfectly flat anymore. Spray is a better option.Upload the photo of flex PCB, so it will be easier to help you.