^^^ Direct cut and paste of the article title^^^
Here is the link to the article:
Hackaday
Anyone know of any detail the article may have not gotten 100% right?
Thanks in advance, as this could be costly for me if it is not 100% right.
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In that article, this remark struck me immediately as the KiCAD library convention has a different rule:
“… it’s our responsibility to design all of our footprints such that the footprint orientation matches that of the reel, relative to that of the reel feed direction. In a nutshell, we just need to make sure that pin 1 on our footprint design matches the same quadrant as pin 1 on the reel when it runs through the machine.”
I checked the KiCAD library convention, and is says (rule 7.2):
“Pin-1 should be placed at the top-left. Where this is impractical, it should be placed closest to the top (IPC-7351)”
(See: https://github.com/KiCad/kicad-library/wiki/Kicad-Library-Convention)
It might be, in practice, that pin 1 is in the first quadrant (read the hackable article to see what I mean) in the reel most of the time, but that is not guaranteed.
The article also says:
“Sometimes, an IC’s primary datasheet may not contain the reel orientation. For that info, they sometimes refer you to a different datasheet with reel information for a specific package type.”
Should the library convention be adapted to include the reel orientation in rule 7.2? (I would hate that!)
Does anyone have any ideas on that?
m
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My experience is that tape orientation can change depending on where the final test and taping was done, often subcontracted out in multiple countries
I would say unless your using a quite low volume pick and place, focus more on having the same relative orientation, Pick and place machines rarely have the feeders only on 1 side, so they need to rotate the parts depending on what reel feeder they use.
By at least keeping your polarised in the same direction, the guy camming it in can just set them all the same.
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Don’t try to keep your footprints pin 1 orientation according to a datasheet, it’s no worth the effort.
The same part from a different manufacturer might have a different orientation. Try to keep it to a standard (there are even more than one to choose from), “pin 1 is top left and positive if applicable” is pretty good for a start.
“Component Zero Orientations for CAD Libraries.pdf” is my primary crutch if I’m in doubt how to orient a footprint, I’m sorry I can’t remember where I got this file from, Google should help finding it.
No assembly house I worked with had enough trouble with my part orientation to ask for clarification or change, they are used to check and correct rotations as it seems.
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See this:
and this from the same topic:
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Thanks. I had missed the earlier thread.
m
Definitely not, designing to a specific part is a bad idea. Makes me wonder about the rest of the advice in that article. Rather than “best practice” or even “good practice”, hackaday stuff is often in the “we literally just learned this stuff yesterday, and here is a hack that seems to work for us” category.
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To put it in a nutshell: Bullshit.
While the article is right that having the part centroid correct is essential, what does the footprint orientation in the library have to do with the orientation of the part on the belt/wheel? Exactly nothing. Else you could never design a board with parts rotated to satisfy the need of your design.
If you are aiming for low-cost high-volume products, the fly time of the pick&place head may become a consideration for calculating production costs, but I think this is an issue far out of the average hackaday reader’s scope.
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Seeed studio has a PCB design for manufacturing document: https://statics3.seeedstudio.com/fusion/ebook/PCB+DFM+V1.0+.pdf
This is about board design, not the pick and place files. Seeed doesn’t ask for a pick and place file for their assembly service; they generate that from the board Gerbers.
That is the usual way. Different assembly processes vary enormously
I suppose there is some good advice here. Having recently had my first ever PCB made, the only serious issues I had were with bad footprints. I should have done a better job checking them rather than trusting they were correct.
The problem on both bad footprints was drill holes too small for the part’s thru hole pins. I was able to make the boards work by filing hundreds of pins with a Dremel tool! Visual inspection of a footprint isn’t enough, you must measure, and check the drill hole sizes with a gerber viewer.
I also had to edit some footprints where they were centered on Pin 1 rather than the center of the part. How could I position a switch at a precise location when the center is pin 1?
By the way, I used PCBWay and was very impressed with their cost, communication, speed and quality. I just had them populate the SMT parts, because it was cheaper in small volume to supply my own thru hole parts. When I make an order for 300 boards, I’ll have them assemble all of the parts. They did ask for a Centroid file, and they asked for clarification on a SMT diode orientation.
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There is an updated version of that document, with a few significant changes, at Seeedstudio DFM Handbook ver 1.1
Dale
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