Footprint orientation and pick and place machines - Page 1
Forum section: electronics / general

author: TomS_
author_rank: Frequent Contributor
timestamp: September 11, 2024, 03:14:50 pm
content: Hi all, this question occurred to me recently...In the footprint library for various projects of mine I have a lot of custom drawn parts. The orientation of these parts in the library isnt consistent.For some IC footprints for example, I have pin 1 in the bottom left corner of the footprint, while in others pin 1 is top left (rotated 90 degrees clockwise from the first, for example).This doesnt matter to me since I have hand assembled everything to date, but I wondered what this would do to a pick and place machine - if I had a selection of these footprints on the board, would it pick up some of the parts and rotate and place them correctly, while others would be picked up and either rotated too much or not enough due to the differences in the footprint orientation?Naturally I suppose some tweaking of the machines instructions would fix this, but I wondered if there was a standard orientation that parts should be drawn in to maximise "success by default" and minimise the amount of tweaking that needs to be done?Thanks

author: nctnico
author_rank: Super Contributor
timestamp: September 11, 2024, 05:43:33 pm
content: Most of the assemblers I have worked with can deal with any orientation just fine. Biggest difference I have encountered so far is that most want the body center as point of origin and some like pin 1. The PCB software I use can export body center (automatically determined), part origin or pin 1. IMHO it is a good habit to draw footprints with the body center as the orientation point.

author: AndyC_772
author_rank: Super Contributor
timestamp: September 11, 2024, 06:07:28 pm
content: There's no standard. I draw all my own library symbols, and they end up in whatever orientation was in the particular manufacturer's data sheet. Part of the process for any commercial assembly house is to manually go through and set the orientation (and position) for each part. None have ever complained about the data I give them, nor can I remember anyone ever getting the placement wrong (very occasional human error aside).I did have an interesting discussion at the Southern Manufacturing show earlier this year, with a vendor trying to sell a simple deskop pick & place machine. Obviously it needs to know the (x,y) position of each part, which I can easily export from my CAD software.It also needs to know the rotation, and of course, that can't possibly be known in advance, because I don't necessarily know which way round they'll be loaded onto the machine. I've also no intention to go into my library and edit every footprint just for the benefit of one P&P machine.I asked the seller about this and he became defensive. He was very keen to sell the machine on the basis of its (surprisingly) low cost, but didn't like being asked revealing questions about the time it would take to set up vs the time it would save me doing manual assembly. Plus, of course, it would need a pizza oven adding too, which would have significantly increased the cost of a minimum usable setup.I walked away. If it's too much work to do with a soldering iron, then it's off to a commercial assembly house.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 11, 2024, 06:46:49 pm
content: Quote from: AndyC_772 on September 11, 2024, 06:07:28 pmUnless you count:https://xkcd.com/927/Some PCB assemblers use the tape orientation as their standard, but that is inherently faulty because tape orientation can vary, at least between different manufacturers of parts, but sometimes, already with different ordering codes from the same manufcaturer. Try to get all manufacturers of 0805 sized LED's to use the same tape orientation, Well, good luck with that.I don't know what software you use, but KiCad has it's own KLC (KiCad Library Conventionhttps://klc.kicad.org/) There is no "worldwide" standard, but at least this makes footprint orientation consistent in KiCad's own libraries. When you use other libraries all bets are off.This lack of standards is a constant nuisance for SMT placement, and it pretty much makes manual verification a necessity. SMT machines usually have a built in system to "fix" rotation issues, similarly to how they can fine tune X, Y placement. One thing you can do while designing a PCB, is to make sure that all footprints that need a certain orientation have a clearly visible pin one mark.

author: TomS_
author_rank: Frequent Contributor
timestamp: September 12, 2024, 07:16:36 am
content: Thanks for the responses, I guess the gist is "dont worry about it".Im not drawing any symbols or footprints for addition in to the KiCad libraries, so Im not really worried about following their standards, just my own preference and taste.Im more of a "origin is centre of the part" than "origin is pin 1" kind of person, and draw them all this way or adjust them to be this way. Thats an EAGLE carry over I guess, but I feel like it makes more sense in my own mind - as in Im placing the part at a coordinate, not a pin...The tape orientation was probably what I was thinking about, and whether there was an appropriate orientation to draw the components in relation to how they are oriented on tape. But if even that isnt consistent then all bets are off. And I hadnt considered the fact that some machines let you mount tapes on both sides, which would throw things out by 180 degrees anyway making this whole exercise null and void...Thanks all

author: selcuk
author_rank: Frequent Contributor
timestamp: September 12, 2024, 07:47:46 am
content: Diode directions are generally from right to left on the reels.Assembly houses always check the orientation and other parameters. If they don't, they will have issues. The coordinates and orientation are written on your manufacturing files but the step distance between the components on the reel isn't for example. So they compare all related data with physical items.There is no global standard for each part but I can recommend you to draw footprints on the same direction written on the datasheet. Each datasheet has a figure depicting the orientation in the package and even pick point if it is different than the center point. This way assembly technician will have less job to do. That leads less errors. If you want to be close to perfect, you can define different footprints for reel, tube and tray versions because they can have different orientations for the same part. I personally don't do this to keep my footprint library less crowded.

author: tszaboo
author_rank: Super Contributor
timestamp: September 12, 2024, 07:51:19 am
content: Quote from: AndyC_772 on September 11, 2024, 06:07:28 pmThe standard is IPC 7351.Unfortunately IPC charges money for the standard from the users, which stands in the way of wide industry adaptation.There is also IEC 61188-7.Unfortunately IEC charges money for the standard from the users, which stands in the way of wide industry adaptation.And unfortunately the standards differ in terms of their content and where the marking should be placed.

author: langwadt
author_rank: Super Contributor
timestamp: September 12, 2024, 08:17:51 am
content: Quote from: selcuk on September 12, 2024, 07:47:46 amseen from where?

author: tszaboo
author_rank: Super Contributor
timestamp: September 12, 2024, 11:41:05 am
content: Quote from: langwadt on September 12, 2024, 08:17:51 amUpside down from inside out of the monitor, bottom view, but mirrored.

author: langwadt
author_rank: Super Contributor
timestamp: September 12, 2024, 01:13:01 pm
content: Quote from: tszaboo on September 12, 2024, 11:41:05 amand right is the one that's opposite left?

author: selcuk
author_rank: Frequent Contributor
timestamp: September 12, 2024, 01:14:29 pm
content: Quote from: tszaboo on September 12, 2024, 11:41:05 amIt is when assembly technician sees the components feeding into the machine. You may check "Figure 25. SMA, SMB, SMC" on page 24 here:https://www.digikey.com/htmldatasheets/production/778632/0/0/1/Tape-Reel-Packaging-Spec.pdf

author: tszaboo
author_rank: Super Contributor
timestamp: September 12, 2024, 02:30:29 pm
content: Quote from: langwadt on September 12, 2024, 01:13:01 pmIt's circularly polarized in 3D, but the third dimension is not Z but W.

author: Feynman
author_rank: Regular Contributor
timestamp: September 12, 2024, 09:07:08 pm
content: The bottom line is: Zero component orientation standards are a real mess, because over the years there were many different...There was IPC-SM-782, IEC 61188-7, IPC-7351A, IPC-7351B and the whole shit-show with IPC-7351C, which has been ultimately thrown in the trash can by IPC although the industry started applying it based on some preliminary documents floating around on the internet.Because of this mess, assembly shops are used to check every single BOM item.If I would set up a fresh library from scratch, I would use the "Pin 1 bottom left" convention consistently. But I don't think it's worth overhauling an existing library.Where the fun really starts is with components on the bottom side. Because then it depends on your CAD tool: Is Pin 1 on the left in the bottom-view or on the left in the through-board-viewLike I said: It's a mess. But as a consequence assembly shops are used to clean up your data.The important thing is to have an assembly drawing that makes it crystal clear how your components should be oriented on your board.

author: tszaboo
author_rank: Super Contributor
timestamp: September 13, 2024, 10:00:10 am
content: Quote from: Feynman on September 12, 2024, 09:07:08 pmI though the IPC-7351B was thrown away, and the IPC-7351C accepted?

author: Feynman
author_rank: Regular Contributor
timestamp: September 13, 2024, 04:35:11 pm
content: Quote from: tszaboo on September 13, 2024, 10:00:10 amNope, IPC-7351C never made it.