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Do tables of XY coordinates tarnish the souls of engineers?
daqq:
I'm drawing a footprint from a datasheet. There's a recommended footprint - which I'll base my own on - and of course you have to calculate the position of the pads from the drawing. Because reasons.
Is there any reason manufacturers prefer this way rather than giving you a table with the XY coordinates of the centers of the pads? OK, sure, if there's some weird shaped pad then OK, but this is a bunch of rectangles with easily defined centers. Why is this preferred? Is there something awesome about this that I'm missing?
Siwastaja:
You are not missing anything. That has been requested for at least three decades straight. It's a tradition. Additionally, it's pure sadism.
Because every manufacturer does that, no one can vote with their money.
Also it's small enough problem so no one will base their competitive edge on such small detail.
Some managers and engineers fear change; some may actually get satisfaction out of bullying their customers. In any case, it sucks, and continues to suck.
Actually, you don't even need an xy table to implement what you suggest: sanely chosen reference lines (at part origin) and measurements drawn to this line suffices. This strategy could be used to satisfy those who require things not to change, yet provide a readable drawing. The fact that 99% of the datasheets do not do this IMHO proves that it's just a case of bullying for no other reason than satisfaction stemming from sadistic soul.
And it's not only about how to represent the data. In 97% of datasheets, part of important data is missing, namely the origin, which is highly important for SMT components. It's the place where the P&P nozzle is supposed to touch. The drawing should have a crosshair there, all measurements shown relative to this. Now it's up to the designer to guess where the P&P origin is, and up to the CM to use their experience in modifying their customer's files to increase the yield based on testing. This is absolutely unbelievable.
Benta:
"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. You also need a reference point for the dimensions (there are several ways to define this)
Edges, corners, diameters, angles etc. can all be measured physically for tolerance and quality control. A "centre coordinate" can not. You can derive it, but that's not the same.
Kremmen:
--- 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.
[...]
--- End quote ---
Maybe so but this only shifts the responsibility from the one manufacturer to the numerous individual users. Because in many EDA programs you just cannot use the dimensioning style chosen by the manufacturer. So such strict principle is quite useless in practice.
I fully agree with the previous sentiments, although i would add, quoting Hanlon's razor: Never attribute to malice that which can adequately be explained by stupidity.
If not actual stupidity or sadism, then certainly hidebound tradition and inability to listen to the paying customer.
tom66:
I think it's a mechanical engineering tradition. In my day job I deal with several mechanical engineers and none of them like these diagrams. They're drawn to have only one set of measurements for every possible dimension, which eliminates rounding/precision/typographical errors (in theory) but they can make finding some dimensions incredibly difficult.
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