First rigid-flex design  - Page 1
Forum section: electronics / general

author: Halide
author_rank: Contributor
timestamp: February 11, 2021, 05:50:15 pm
content: Hi everyone,I want to make my first rigid-flex project. I send gerber files to some manufactures but the price which they provide is very high - around 1500$ for 5 PCBs.Can someone how have experience with designing rigid-flex PCBs can advise me what should I change to make price better?I have very complex built, I mean:-trace 3/3mils with 2.5/2.5mils partly-no blind via-all vias 0.15/0.30-WLCSP package with 0.4mm pitch and 0.2mm pads-flex part is very short ~3mm, and thin ~2.5mm-rigid part rigid part is design as circle(radius 5mm) with 0.4mm thickens.If some information is no clear, pleas let me know. I try explain it further.

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: February 11, 2021, 08:18:49 pm
content: because ridig-flex IS so expensive, is there any reason why you can't use 2 regular boards and have connecting cables?

author: GerardG
author_rank: Regular Contributor
timestamp: February 12, 2021, 08:23:54 am
content: Hello @Halide,You describe a very hard to build Flex-Rigid board.$1500 is not a very high price for what you describe.For flex boards you need some extra punching tools or laser cutting.~2.5mm flex part?Crucial for these kinds of boards is the stackup. This will dictate the steps in production, punch tools needed and price.You can make a 2 layer flex rigid in a lot of different ways, so making a multilayer will result in even more possibilities.When starting to design a multilayer, go to the manufacturing company and ask them for the design rules of the flex-rigid with your stackup.My suggestions:-Go to the supplier that will do the series production.-Ask the supplier to help you with a stackup that they prefer. (most will have a few different options)-Then ask for the design rules for this stackup. (Flex on inner layers or outer layers will make a difference)-Do not forget to ask the minimum bending radius for this stackup !!!-For a multilayer, keep the flex as an inner layer.-Move your via's away from the transition area.-Make the flex a little longer, 2mm is a very high cost. If you can't make the flex longer, move it a few mm into the outline of the PCB. See the narrow flex part in attached picture.

author: mon2
author_rank: Frequent Contributor
timestamp: February 12, 2021, 12:22:38 pm
content: Hi. Was quoted $7k usd for our very small fpc from a USA mfr. Must have been a joke.Got the same fpc made for around $300 usd but took some time to dig for the proper supplier. Many could not support our design as-is.Try the following, they supply Apple and have the proper knowledge in this arena:dawei.cui@lk-tek.com <dawei.cui@lk-tek.com>For us, they are our goto supplier for fpc boards.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 12, 2021, 12:53:24 pm
content: Quote from: Halide on February 11, 2021, 05:50:15 pmThat's going to be expensive anyhow, flex or no...

author: mon2
author_rank: Frequent Contributor
timestamp: February 12, 2021, 06:16:18 pm
content: Try the vendor we have referenced - you may be pleasantly surprised. Our recent project was a WLCSP bridge cable.

author: supperman
author_rank: Regular Contributor
timestamp: February 12, 2021, 06:35:16 pm
content: I agree with others here.. that is probably a correct price. tends to be 2x what you may pay for a Flex only.. AND 4x or so more than lesser tolerances.. So 8x a basic flex design which is probably 16x to 32x a standard PCB?You don't mention the number of layers.. Keep flex layers to two if you can since that makes a Big difference. Keep in mind that the flex is the same size as the Flex + rigid... but I think area is not so critical as the 20 some manufacturing steps needed. (I bet going from 5 to 10 boards makes no difference in price). Don't specify stack up on the Flex if you can.. just ask them for cheapest. (hitting a specific thickness costs lots of money and effort)In general my experience has been the Flex itself is super expensive once you get to 3/3 or 2/2 trace/gap. When you add rigid they have to align the boards at high tolerances and that makes it super complex. I think they price in a high failure rate. In my case they have had to redo boards which caused delays and cost them money.

author: Halide
author_rank: Contributor
timestamp: February 16, 2021, 01:02:33 pm
content: Hi everyone,Thank you for your answers.Quote from: Rat_Patrol on February 11, 2021, 08:18:49 pmHi Rat_Patrol, That i said this is very complex built. I don't have enough space to put some pads to solder flex cable.Quote from: GerardG on February 12, 2021, 08:23:54 amHi GerardG,I tried to talk with some Chinese suppliers but it is very difficult to get some clear information from they - for example they suggest to change pad size to 0.4mm. But for this design it is impossible.Bending radius is no problem for me. This project will be single bended.Yes, I put flex as inner layers - i have 4 layer board.This is good idea, i try to cross the elements to make something like in this picture.Quote from: mon2 on February 12, 2021, 12:22:38 pmHi mon2, I will try to contact with this company.Quote from: supperman on February 12, 2021, 06:35:16 pmHi supperman,I have 4 layer boards, inner layers are flex part.If I understood you right, only flex board can be cheaper than rigid-flex?

author: supperman
author_rank: Regular Contributor
timestamp: March 09, 2021, 12:27:47 am
content: Sorry, Just saw this. YES. my understanding is that flex is much cheaper than rigid flex.. certainly at small quantities since with rigid flex they have a lot of alignment to do. I take it the board has two sided components? If not then a stiffener on the bottom is MUCH cheaper than a rigid flex and has the same properties.