General > General Technical Chat
Do tables of XY coordinates tarnish the souls of engineers?
daqq:
Thanks, I assumed as much. I'm familiar with mechanical drawings and I understand that there it makes sense. But these are drawings that have one purpose - to be fed into a PCB design tool, the bulk of which simply work with centers.
It's not a huge issue, I can work with that, but it's an annoying issue that would cost nothing to fix.
/rant
VK3DRB:
--- Quote from: daqq on March 01, 2021, 08:32:10 pm ---...But these are drawings that have one purpose - to be fed into a PCB design tool...
It's not a huge issue, I can work with that, but it's an annoying issue that would cost nothing to fix.
--- End quote ---
But like I said, those who made the footprint know no better. They need to be made aware, ie: education.
Maybe a new format needs to be created where the footprint dimensions are in a table, something looking like an Excellon drill file. Then, irrespective of the CAD package, the footprint dimensions are simply imported with one click and converted to a footprint with accurate dimensions.
nctnico:
--- Quote from: daqq on February 28, 2021, 02:20:40 pm ---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?
--- End quote ---
Like others said: it is how mechanical engineers work. Sometimes I get drawings like that for PCB outlines :scared:
BTW: your example isn't the worst footprint drawing I have come across. Some can be real puzzles in order to reference pads to eachother and the package outline. Having a CAD package which supports 3D models is a big plus. At least you can fit the 3D model on the footprint.
CatalinaWOW:
I worked in a mixed engineering environment. Those of us with EE degrees were called sparkies by those with ME degrees, who we called tin benders. Both kinds were sure they knew how to do the others job better. Me too, possibly with more justification than most since dad was an ME, and I switched from ME to EE after sophomore year at university. Weird to think that I thought that contour integrals and Poynting vectors were easier than Hamiltonians and stress tensors.
The point of this is that it is easy to disdainfully say the other guy is being lazy. That centers are easy, that is how centers of holes are specified, the nominal place that it is. But there are real problems involved, and I suspect that verification of performance occurs far more frequently than creation of CAD models. How do you measure the center of a real hole. If the drilled hole is actually round there are geometric ways to infer the center, but real holes have imperfections including taper, barrel and higher order diameter vs depth variations and many types of eccentricity. How do you define te center of an egg shape hole, or one not orthogonal to the surface? It makes sense to make the more common job the easier one. Supplying both is an option, but then you get the issue if which one is the controlling document. Would you like a set of X, Y with an accompanying note with weasel words like "typical" or "refer to ... for true dimensions".
The suggestion on pick up crosshairs seems a good one, but I can also imagine problems with process variations.
Finally, there was a move as I retired to move away from paper based specifications to model based specs. Would a model of a part (a very fancy list of x,y s) make your job of designing footprints easier? It promised to make the mechanical side easier.
gnuarm:
I don't really mind too much the goofy ways parts are notated. But what I really hate is when the drawings were taken from a CAD package that thinks lines are infinitely thin. Seems the "official" PDF rendering is to draw them as 1 pixel wide no matter how much you blow them up. The result is often lines that are so faint they can barely be seen.
Some PDF viewers allow you to set a minimum line thickness in some way. Others feel this is a problem with the author of the data sheet. Obviously the people making the data sheets don't use the same PDF viewer I do.
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