JLCPCBA standard assembly rails: Confused, support conflicting with website. - Page 1
Forum section: electronics / general

author: Whales
author_rank: Super Contributor
timestamp: July 12, 2025, 02:51:39 am
content: I am having a very confusing time discussing edge rails with JLCPCB support. I feel like we might be discussing completely different things or using different definitions. If anyone here has dealt with this or similar before I'd appreciate your thoughts or advice.Note: JLCPCBA only requires edge rails for "standard" PCBA, not "economic" PCBA. If you have not seen or heard of these edge rails then you have probably used their economic service.I am testing out their "standard" PCBA offering because it's a trial order for a larger production run.My understanding of edge rail requirementsBased onJLCPCB's edge rails guideand other info given during checkout:1. The "rails" are a 5mm region on two opposite sides of the pcb for handling the PCBs during assembly. Components and component pads cannot go in this rail region, it must be flat PCB.2. At least 4 fiducials must be added. They can be put inside the edge rails as long as they meet specific distance-from-edge requirements.3. Removal of these rails after assembly requires extra milling and is an extra cost.I decided to add the rails and fiducials to my design so that (1) I could ensure the design fits the case, (2) I can ensure JLC doesn't add them to the wrong sides causing my right-angle HDMI connector to be unusable and (3) so I can use the rail space for silkscreen text.Lots of things have gone wrong after I submitted this order1. Online DFM view showed that JLC had added a second set of rails to the outside of my rails.2. I asked if my edge rails were inadequate, their answers suggested they cannot see the rails on my design:QuoteQuote3. I sent them the annotated pictures (shown above) with the rails circled and numbered. They talked to their engineers and replied with:QuoteVcuts? I have not seen v-cuts mentioned anywhere to do with assembly rails. That sounds like panelisation, not edge rails.Perhaps they now v-cut the assembly rails prior to assembly so the customer can remove them? But then it would be really hard for them to de-panelise other nearby v-cuts, unless they do assembly on a whole panel at once, but then these edge rails would be completely 100% useless so that doesn't make sense.4. I asked them to clarify where they want these v-cuts to go, with the following diagram:I will await their reply, but I'm worried that we're on completely divergent tracks and are thinking about different things.I am hesitant to ask them technical questions without labelled images. I tried that in my first email (numbered the questions too) but they ignored both of them. I suspect the customer support is middle-manning between me and the engineers, possibly with an extra layer of translation too.

author: Smokey
author_rank: Super Contributor
timestamp: July 12, 2025, 03:03:02 am
content: The two ways to detach assembly rails are v-groove and mouse bites. You need to call that out on your panel/fab drawing.V-groove is much preferred since it's automated and way faster and less labor to break away but if you put parts too close to the edge then they can't cut the rails off with the v-groove parting machine. In that case you need to use mouse-bites, which is a whole other topic. Here is a thing talking about mousebites:https://cdn.sparkfun.com/assets/home_page_posts/4/4/0/0/Mousebites_Whitepaper_Final.pdfIf you just let them handle it then they will add the rails. Make sure you select that you want to approve the final design files and you can see what they did and either approve it or send it back for revision.

author: Whales
author_rank: Super Contributor
timestamp: July 12, 2025, 03:09:06 am
content: They expect the rails to be designed to be removable??? They only show asilkscreen lineon their online guide and mention nothing about v-grooves, mousebites or anything else. I designed assuming the same thing (non-removable rails only denoted by silkscreen). They mention that removal processes are optional extras costing more, so I assumed v-grooving would too.https://jlcpcb.com/help/article/How-to-add-edge-rails/fiducials-for-PCB-assembly-orderMaybe that's the source of the confusion. Thankyou Smokey, I'll try and follow up with them.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 12, 2025, 06:46:52 am
content: They assume rails will be v-cut to make them removable. The extra cost is only if you want them to remove them.I think they are getting confused by you wanting to use part of your active pcb as the edge rail, and may have a problem with the ends of the rail not being square - could be issues with conveyor etc.IME the people doing the data prep know very little about the actual process and just follow the rules they are given, so anything that's a little outside their normal process can be a real pain to commmunicate.They may also want to have tooling holes basically they want to be in charge of the edge rails so they can put what they want there

author: Whales
author_rank: Super Contributor
timestamp: July 12, 2025, 08:05:33 am
content: Quote

author: tooki
author_rank: Super Contributor
timestamp: July 12, 2025, 09:54:05 am
content: Quote from: Whales on July 12, 2025, 08:05:33 amFor what it’s worth, I would have interpreted their documentation the same way you did. Whoever wrote the web page clearly did not understand what the fabrication side was asking them to say.

author: Whales
author_rank: Super Contributor
timestamp: July 12, 2025, 11:27:55 am
content: After I receive & confirm the boards I might make some changes to that page and send it to them as a suggestion. If it helps even one more person then it would be worth it.

author: asmi
author_rank: Super Contributor
timestamp: July 12, 2025, 06:48:36 pm
content: Hmm, it never even occured to me to use parts of actual final PCB as tooling railsWhich is why I got confused just like JLC did. I'm used to the notion of tooling stips as something that gets ripped away and discarded after assembly.

author: Smokey
author_rank: Super Contributor
timestamp: July 14, 2025, 05:57:51 pm
content: Unless you have unusually large boards, production runs are typically done with panels of board arrays of a single design (for example 2x3 for a 6up panel). In this case you save panel space by having break away assembly rails.Not to be too harsh here, but it sounds like you are just not familiar with how boards are made and assembled. There are pretty well established systems and processes for all this stuff that are pretty close to optimal for the vast majority of boards. You should always coordinate your board designs with your assembly company but following the typical processes and procedures will make everyone happy most of the time without surprises.

author: krzysssztof
author_rank: Contributor
timestamp: July 17, 2025, 07:24:33 pm
content: Guide on their website is very poor.I second what Smokey just said:- For a small to medium sized PCBs, it is very inefficient to assemble each board separately- For this reason, it is a common practice to create panels with multiple copies of the same PCB placed next to each other, with just a small spacing for final separation (breakout/milling/etc.)- Because of the above, edge rails are usually added to the panel/array of boards, not to the single PCB (what you have tried to achieve)- Edge rails often also contain some process-related features, (like already mentioned fiducials, but sometimes also QR codes for production tracking or other markings)There are three possible approaches here:1) Design an array and edge rails by yourself. But then you need to stay in a VERY close cooperation with assembly company and know their requirements in details, which is clearly not the case here.2) Design and array by yourself, but ask them to add whatever edge rails they need.3) Design and send just the single PCB and ask them to handle both panelization and edge rails by themselves. Much easier, because their process engineers know their equipment and requirements. Just need to specify if you need a final delivery to be whole panel or single PCBs.You probably shouldn't bother designing panel by yourself unless you have some further steps in your production process which require multiple boards to be handled together.

author: Accu-Sembly
author_rank: Contributor
timestamp: July 21, 2025, 05:58:49 pm
content: I am in agreement with what Smokey said.If you are interested, our recommended panelization is available on our website and a bit more detailed.https://accu-sembly.com/downloads-forms-statements-clauses-terms-conditions-instructions/

author: Smokey
author_rank: Super Contributor
timestamp: July 23, 2025, 09:27:15 pm
content: Quote from: Accu-Sembly on July 21, 2025, 05:58:49 pmThat's a good document. I'll add it to my list of links. Thanks!One thing that's not on there that maybe should be is the minimum component spacing to a v-groove cut.

author: mtwieg
author_rank: Frequent Contributor
timestamp: July 27, 2025, 12:16:01 pm
content: Quote from: asmi on July 12, 2025, 06:48:36 pmQuote from: Smokey on July 14, 2025, 05:57:51 pmYeah I've done a couple designs where we decided on no tooling rails, for exceptional reasons. The boards were somewhat large (like 8x8") and had heavy components on them, so we knew the CM would want to assemble them 1-up (not in an array). Adding tooling rails to each PCB would have reduced the number of boards made from a single panel significantly (increasing cost). So instead we designed the board such that along two parallel edges there were no components within 1/4" of those edges, and added tooling holes and fiducials. We did not see these edges as "rails," and they are not separated from the board after assembly. But they fulfill the role of tooling rails during assembly.In our fab notes we simply said "boards are 1-up, no tooling rails" and the fab didn't put up any fuss. That wasn't JLCPCB though.

author: Accu-Sembly
author_rank: Contributor
timestamp: July 31, 2025, 08:55:47 pm
content: Quote from: Smokey on July 23, 2025, 09:27:15 pmThat's something we always cover during DFM, but I agree, it should definitely be on that document especially since our recommendations change based on component material and orientation to the v-score line. Thanks.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 31, 2025, 10:17:18 pm
content: The only reason rails are needed is where there are parts too close to the edge to go through the conveyor. If your board has 5-10mm component-free areas on 2 edges, and you don't mind putting fiducials and tooling holes there, that's all that is needed.

author: SMTech
author_rank: Frequent Contributor
timestamp: August 01, 2025, 08:57:58 am
content: Quote from: mikeselectricstuff on July 31, 2025, 10:17:18 pmAnd how many SMT machines these days need tooling holes, I don't think its many? Some machines now move and track the board through the machine so its always as close as possible to the parts being picked and can combine that with full edge clamping so printing and placement can work all the way up to the edge.Different manufacturers and machine generations have very different requirements which can be affected by the machine options they chose when ordering. We don't run a conveyor, so we have 10mm borders on our panels - the machine needs 3mm and I need somewhere to put my fingers! Its also easier if the borders are on all sides to make sure the board can't move in the fixtures. Our SMT machine essentially insists on fiducials on every individual circuit, so we don't really need fiducials in the rails. Its infinitely better if the centroid file includes the fiducial co-ordinates so that you are not measuring their location with the top down camera or using the measurement tools in a Gerber viewer.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 01, 2025, 10:48:53 am
content: Quote from: SMTech on August 01, 2025, 08:57:58 amI have a component called "Fid", with the required pad & pick/place point so it automatically gets included in the pick/place file.This seems such an obvious solution that I'm really surprised how rarely I come across this being done in other people's processes.

author: Smokey
author_rank: Super Contributor
timestamp: August 05, 2025, 05:55:46 pm
content: Quote from: mikeselectricstuff on August 01, 2025, 10:48:53 amI also do this

author: SMTech
author_rank: Frequent Contributor
timestamp: August 06, 2025, 12:09:49 pm
content: Quote from: Smokey on August 05, 2025, 05:55:46 pmI've had customers say they can't possibly do it. Or they don't know how to make a part that has a pad but no paste layer or they can only do it if they generate it as ODB++ and all sorts of bollocks. I think it should be a std DFM rule in CAD software and a standard part in a default library - but what would I know I don't track up PCBs.

author: loki42
author_rank: Frequent Contributor
timestamp: August 06, 2025, 04:05:46 pm
content: I assumed everyone included the fiducials in the position files as all my machines assume they are. Setting up my inspection machines is via SRF files which are super annoying.Tooling holes i assume depends on process. They are handy if the board is going into a carrier like for selective soldering or for testing / flashing.

author: Smokey
author_rank: Super Contributor
timestamp: August 09, 2025, 04:30:18 am
content: I usually add some extra mounting holes (usually 4-40 size) on the rails since they are "free", but I've never used them and I've never seen any assembly house guidelines for their size or shape for use during actual assembly as tooling holes. Only time I've used a solder palette, it didn't use any holes on the board. It just located on the edges.