RANT: datasheets, drawings, and footprints. meh! - Page 1
Forum section: electronics / general

author: djacobow
author_rank: Super Contributor
timestamp: August 14, 2014, 05:18:22 pm
content: <opinion rant_mode="on">This is a very sophisticated industry, on the leading edge of so much -- literally inventing the future.So why the hell is it so very, very, VERY, ASTOUNDINGLY backward when it comes to basic CAD support for parts? Sure, you might get your knickers in a twist about YourPCBSoftware vs. OtherGuysPCBSoftware, but that is nothing compared to the pure hell of the way footprints are disseminated.Because they are disseminated in drawings. On datasheets. That have been xeroxed and mimeographed since the dawn of writing. And even on the drawings there are no standards. mm or mil? How about a mix in the same drawing? Should measurements be edge-to-edge or center-to-center? I know, how about mix it up, edge-to-center and center-to-edge? You want to know how far from Pin-foo to Pin-bar? Sorry, you can't get there from here. You'll have to stop by Pin-baz and Pin-qux first, and then past the third notch on the top of that crescent-shaped doohickey. But don't worry, the 9 dimensions you need for this calculation are conveniently listed in a table with Chinglish headings two pages away.We're pretty good at standards in electronics. Resistor values and tolerances, temperature ratings, protocols, etc. Why can't we have a half decent standard way to disseminate patterns that every cad program could easily adopt? Something simple, like a bit of JSON or XML that describes the shapes needed and maybe even has some useful metadata like pin names and types. (NB: I'm not even going to Google it, but I know there must be multiple mostly failed attempts at this out there.) And if manufacturers really want to continue with the PDF, they can put it all in a great big QR code on the last page of the datasheet.In a perfect world, CAD packages would not even have libraries. What is the point of them if they are mostly full of obsolete crap that is "not recommended for new designs." Anything new is not going to be in there. What would be nicer is if CAD packages had a short database of URLs, one for each part manufacturer, where you could launch a search for a part number and it returned the manufacturer's component/pattern/whatever, right into your CAD program, and you could choose to add /that/ do your design or local library.How about at least a naming convention for standard footprints that actually uniquely identifies them rather than just giving a general idea of the shape -- something which is damn near close to useless unless you only daydream about PCBs?Come, ON!</opinion>

author: free_electron
author_rank: Super Contributor
timestamp: August 14, 2014, 08:57:33 pm
content: that does exist. it is called JEDEC and IPCserious datasheets list the numbers you need. plug in the IPC footprint wizard. click ok and out comes the correct footprint

author: djacobow
author_rank: Super Contributor
timestamp: August 14, 2014, 09:05:34 pm
content: Quote from: free_electron on August 14, 2014, 08:57:33 pmWow, how does it work? I've googled on IPC footprint wizard and IPC footprint expert and its hard to tell. There appears to be some file format .fpx that most PCB packages can import. But I don't think I have seen such files for download.Can this handle irregular footprints, like from oddball connectors and the like? I seem to be dealing with a lot of "unserious" datasheets these days.

author: tszaboo
author_rank: Super Contributor
timestamp: August 14, 2014, 09:16:15 pm
content: We are really really bad at making and following standards. Just think about it, a standard which is made for everyone to follow, well, why does it cost money? Can I get IPC specifications? Or Jedec? Or anything?And there has been various attempts to standardize this. Check out the complete garbage called Ultra Librarian. They even got TI onboard they sinking ship.Not to mention you have the same footprints for different densities, wave soldering, hand soldering, IR reflow, and so on.I'm fine drawing my footprints. At least I know who to blame if it is wrong.

author: free_electron
author_rank: Super Contributor
timestamp: August 14, 2014, 10:12:19 pm
content: Quote from: djacobow on August 14, 2014, 09:05:34 pmthe datasheets nomrally list a dable of numbers inidcated with letters e,E d, D , F H A B b and so on. uppercase and lowercase. the IPC wizard shows you the table with these letters. simply type in the numbers . the datsheet will also list the tolerances for these numbers. you can enter those as well. the wizard then does its magic and spits out 3 footprints ; one for dense boards ( machine population ) one for medium boards ( machine population but reworkable ) and one for low densitiy ( easy for hand soldering )done.not everything can be described. stuff is categorized in classes of parts. a connector with pins on an arc for example cannot be described. but any ic package with 2 sides of 4 or qfn or bga can be described.Many PCB CAd packages have a wizard that can handle this.

author: djacobow
author_rank: Super Contributor
timestamp: August 14, 2014, 10:23:53 pm
content: Quote from: free_electron on August 14, 2014, 10:12:19 pmYeah, those are the easy ones. But with a nice file format that everyone published for their parts we could handle just about anything. And we could have names for the pins -- automatically! And we might even get a smidge of metadata like input/output/tristate/open drain/collector which would make ERC a bit better.But as NANDBlog points out, it ain't going to happen. And that /is/ an embarrassment, IMHO.

author: marshallh
author_rank: Unknown
timestamp: August 15, 2014, 02:32:47 am
content: Big vendors have orcad files for the parts. Some have Ultra Librarian files (absolute garbage)In the end it always comes down to making your own.

author: Dago
author_rank: Frequent Contributor
timestamp: August 15, 2014, 01:44:32 pm
content: Check out Library expert (used to be Footprint expert):http://www.pcblibraries.com/LibraryExpert/It's literally the best software I've found in a long while. It creates IPC-7351 compliant footprint files for tens of different CAD-packages when you enter the package dimensions and tolerances in the datasheet. Literally takes like thirty seconds for any package. There is a free lite version which does not have any huge limitations (just can't do "batches" afaik).Only problem with it is that it does not work in Wine or a virtual machine because it somehow detects its running inside a VM and refuses to start which is ridiculous.