General > General Technical Chat
Do tables of XY coordinates tarnish the souls of engineers?
VK3DRB:
Some footprints are disgusting, most are medicore, some are excellent.
To be frank, many footprint drawings are made by people who have never done PCB design. Altium is by far the world's most popular professional PCB design tool. Better footprint dimensions that are Altium-friendly should start from a datum reference point, such as the centre of Pin 1 and everything is dimensioned from that point. Manufacturer's should realise helping the electronics designer helps sell their product as does a decent website.
I tend to avoid vendors who provide crap datasheets or don't think you are worthy enough to have a 3D step file for their component. 3D models help me verify footprints and mitigate risk from mistakes. You can get a hint of the bad brands when Digikey has no link to the 3D models. For some 3D models, you have to register or even email some sales department. I won't use a part (especially connectors!) if there is no 3D model, whether it be from the OEM, SnapEDA, 3D Content Central, Octopart or elsewhere. There is no excuse not to use 3D component models in a PCB design these days. Building crappy extruded models for components is a poor man's approach and is a recipe for errors. It tells me the designer was time desperate or is lazy. Besides, PCB layout is ARTWORK that should be created by a skilled craftsman with pride in their work, not by a slap-dash tradesman.
I often modify recommended footprints for improved reliability or manufacturability. I NEVER use those Altium default footprint library component from last century, but I do sometimes use their footprint generators for things like BGA's, but I always use a small filled triangles for pin 1 markers. The triangle is superior to the round dot in a number of practical ways, especially on high density boards. There is no valid argument why the old round "fly-vomit" dot should be used over a triangle for a pin 1 marker.
Why a triangle? It is an inherent arrow head that points to where pin 1 is, reducing ambiguity, unlike a dumb arse dot or circle. For those with poor vision, a triangle stands out out clearly even if a lot smaller than a dot, where a dot looks like a via, fly vomit, a spec of dust or a solder ball. A triangle helps debug technicians and manufacturers easily verify pin one without resorting to a separate a drawing or using a magnifier. Everyone I know who has used triangles never go back to circles unless they inherit someone else's library. Not having pin 1 markers or hiding IC orientation information under a populated IC, or omitting a ground testpoint could almost justify a sentenced of installing Windows 95 floppy disk version ten times a day for one year onto an old PC with a noisy fan.
Rerouter:
I kind of agree there, 3D models for connectors, and any large throughole components are a strong contender for if I will consider a part or ignore it. footprints I am still more leniant seeing as there are so many different cad packages, and they won't have an easy means to export them, but they will have 3D models in house, and those can be easily / automatically exported
ConKbot:
I'll take a table if they stop sticking with mechanical drawing tradition of no redundant information. Connectors are especially bad at this. Have to find how to get from one feature to another via adding, subtracting, dividing 3-4 other dimensions to get the one I need. Just mark the convenience ones as reference only, so the tolerance stack up can still be unambiguously calculated, and everyone is happy.
Nominal Animal:
--- Quote from: Siwastaja on March 01, 2021, 07:07:52 am ---
--- Quote from: Benta on February 28, 2021, 08:13:45 pm ---"Is there any reason manufacturers prefer this way rather than giving you a table with the XY coordinates of the centers of the pads?".
Yes there is, but you need to know a bit about mechanical engineering to understand why:
Dimensions need to refer to measurable points. An imaginary "center" is not one.
--- End quote ---
Why not? You just came up with a completely arbitrary rule.
Your post is an excellent example of the sadism I described.
--- End quote ---
This is ubiquitous. Humans love arbitrary rules. Benta is not evil or sadist, just being an ordinary human behaving as normal humans do.
My favourite example of this is how browsers nowadays no longer let you choose UTF-8 as the default character encoding.
Why? "Because it is not a legacy encoding." Who decided that? "It's obvious, isn't it? Everything except Unicode is legacy."
Yep, the reason boils down to someone making up a new rule, and now that it exists, it is wrong to break it. All current browsers now follow this rule, even though it is a rule the browser users have no use for, and that only causes friction and troubles, solving nothing.
Terry Bites:
It's good that there is a reason why manufacturers like to be difficult. Why don't they just convert their mechanical production drawings into simpler formats that are engineer friendly? I've got to say electromechanical are the worst offenders of all in this racket. ARRRGH!
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