PCB slot thickness and cost - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: August 13, 2023, 01:51:06 pm
content: Hi,On SMPS PCBs, often a slot is put between the pins of, say, an opto to accord with creepage distance.Though is a 1mm wide slot more expensive than a 2.5mm wide slot?We are told it is, but eg, JLCPCB website says you can have 1mm slot and doesnt say its more costly.

author: jpanhalt
author_rank: Super Contributor
timestamp: August 13, 2023, 05:17:28 pm
content: Quote from: Faringdon on August 13, 2023, 01:51:06 pmGo to JLCPCB, if cost is an issue.

author: Faringdon
author_rank: Super Contributor
timestamp: August 13, 2023, 06:08:01 pm
content: Thanks, though is it cheaper (2.5mm vs 1mm)?

author: HwAoRrDk
author_rank: Super Contributor
timestamp: August 13, 2023, 07:27:23 pm
content: Think about this critically. Why would it cost more? Because it must be something that causes the PCB manufacturer additional costs. Why would that be? Because it's something that they don't normally do. Why don't they normally do it? Perhaps because quality or yield is not so good, and so they expect to have to apply special measures during production, or are factoring in additional wastage. Or perhaps because they don't normally carry that size of tooling on their CNC milling machinery, so incur more costs through extra labour to perform tool changes. Or perhaps such small tool bits break more easily, so they factor in the greater cost of additional tool replacement.Or it could be other reasons. Why not just ask them why?

author: floobydust
author_rank: Super Contributor
timestamp: August 13, 2023, 07:33:47 pm
content: Electrical safety standards specify a minimum width for slots. Check yours.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 13, 2023, 07:34:21 pm
content: Quote from: Faringdon on August 13, 2023, 01:51:06 pmBecause smaller routers need to be run more slowly, and can't cut through as many panels in one go.1.6mm is generally the smallest slot that doesn't cost extra, though different manufacturers will have different limits.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 13, 2023, 07:36:14 pm
content: Quote from: floobydust on August 13, 2023, 07:33:47 pmNo they don't - , they specify creepage and clearance distances - on a PCB, creepage is usually the issue, especially in higher contamination situations.It is up to the designer to decide how to use slots to increase creepage where necessary.

author: floobydust
author_rank: Super Contributor
timestamp: August 14, 2023, 04:37:02 am
content: I had a certifier explain my slots were too thin, he wanted 1.5mm it was with CSA and UL was the same stance on another product.Creepage or clearance is not always simple, as you say depending on Pollution Degree. But I find a minimum spec table X= 0.25, 1, 1.5mm depending on PD1,2,3 and this is what I am referring to, or at least I recall this one clause the certifiers pointed out- as well as the spacings table requirement, as it was a PD2 design.The measurement/assessment is not always a logical one. What is your background in this because my experience is counter to your statement.I do laugh at OP's cost concern on the slot though, after the labour-intensive heatsinking of the InnoSwitch IC

author: Faringdon
author_rank: Super Contributor
timestamp: August 20, 2023, 05:34:45 pm
content: Thanks, and say you have 4mm gap between primary and secondary copper and you need 6mm....then presumably you can have a slot of 1.6mm between them?....because the slot is better than a groove......and as long as the length along any surface (creepage) between them is >6.5mm then its ok?

author: Gyro
author_rank: Super Contributor
timestamp: August 22, 2023, 02:07:26 pm
content: Quote from: Faringdon on August 20, 2023, 05:34:45 pmNo!A slot doesnothingfor clearance, you need to meetboth, and all the slots in the world aren't going to turn a 4mm clearance into a 6mm one.Pleasethink!Do you agree?

author: Infraviolet
author_rank: Super Contributor
timestamp: August 22, 2023, 08:24:42 pm
content: Its only for big volume production where you get charged per operation and extra fees for slot milling and such. JLC and equivalents charge enough fixed price for a smal run of boards that they can avoid complicating the ordering process by having to introduce extra charges for extra operations, with the exception of a few extreme cases (they say they'll charge extra if vias are at an extreme density all over the board for example).

author: abeyer
author_rank: Frequent Contributor
timestamp: August 22, 2023, 09:12:22 pm
content: Quote from: Gyro on August 22, 2023, 02:07:26 pmQuote from: Gyro on August 22, 2023, 02:07:26 pm

author: Faringdon
author_rank: Super Contributor
timestamp: August 23, 2023, 05:49:26 am
content: Thanks, though 90 degree "L" shaped slots are going to cost more?

author: JLCPCB Official
author_rank: Regular Contributor
timestamp: August 23, 2023, 08:38:49 am
content: Thank you immensely for your valuable contribution to the forum on this subject.In order to ensure seamless alignment between your designs and JLCPCB's exceptional capabilities, I recommend consulting our comprehensive JLCPCB capabilities page available at:https://jlcpcb.com/capabilities/pcb-capabilities. This resource will empower you to discern the viable options for slot creation that best suit your needs.In the context of your particular case, it's noteworthy that milling fees for slots smaller than 5mm will not incur any additional charges. Should you wish to ascertain the specific scenarios that might incur extra costs, I invite you to explore the detailed information provided in section 3, "Milling Fee," on the following webpage:https://jlcpcb.com/help/article/15-In-what-cases-will-there-be-charged-extra.Kindly don't hesitate to reach out if you require any further elucidation or details. Your continued engagement is highly appreciated.

author: floobydust
author_rank: Super Contributor
timestamp: August 23, 2023, 09:27:11 pm
content: What happened to the URL's? They were there yesterday. I can't find a Section 3 Milling Fee.

author: tooki
author_rank: Super Contributor
timestamp: September 05, 2023, 01:23:01 am
content: Apparently adding “www.” to the URL targets fixes the links! (Probably a forum software issue.)Quote from: JLCPCB Official on August 23, 2023, 08:38:49 am

author: tooki
author_rank: Super Contributor
timestamp: September 05, 2023, 01:25:41 am
content: Quote from: Faringdon on August 23, 2023, 05:49:26 amWhere do you get this nonsense?And what prevents you from reaching out and asking the PCB makers yourself? Why this learned helplessness? Why ask strangers instead of the manufacturers?