Package Mechanical Drawings

That's Geometric Tolerancing. Basically, that denotes a radius that the ball can be off by. Instead of a X,Y tolerance.

Cheers

Start with

I have read part mechanical drawings for some time now, but it seems there is a lot more information than I am able to get out of them. For example,

There are also designators I don't understand at all which seem to be an arrowhead projection from the side of a line with another line from the point to a letter in a box. These seem to be marking reference lines, but I don't see where they are used anywhere in the drawing.

There are also "aaa" and "ccc" designators which aren't clear. The "aaa" designator might be indicating how much the balls squish when soldered, but I have no idea what the "ccc" designator is for.

I poked around on the Internet, but couldn't find anything useful about this.

Page 93 defines aaa fff etc.

Cheers

That helps a lot, thanks. I'm still not completely clear on the difference between eee and fff. Both use the same symbol which refers

which I thought meant diameter (which wouldn't apply if referring to position) and both use the C datum as a reference... but they have two different values. How can both values mean the same thing???

I dont know what it means when there is a 2nd row, it has something to do with the datum reference plane C. I only see examples that call out Concentric and pararellism for the second line. It's obvious it has something to do with the ball height.

My knowledge of GDT is limited, The guru in the next cube may know, I can find out Monday.

Cheers

Thanks. It's probably not important to me. I'm just trying to understand what dimensions I need to use for routing a board. I think the VF256 might just let me use 6/6 design rules or damn close to it. I can't find an actual escape routing example for this part. That would make me very happy. :) I need to check with other manufacturers and that means I have to check all the package specs. lol Hard to do if I don't know what they mean or maybe not...

BTW, is the world ever going to get away from using inch measurements for PCB layout? I see many fab houses still spec their capabilities in terms of mils.

On 10/4/2015 3:04 AM, rickman wrote: [...]

Most components are still based on 0.1" pitch - as nature intended. Possibly. I think it's in the Declaration of US American Stuff, also.

There's a lot of inertia. I'd specify a 5 mm hole with a tight tolerance (achievable with 5 mm drill fed smoothly) so a split bushing (standardized throughout an international company) would press in properly. The purchasing people would send it off to their "preferred" supplier. The part would come in undersize, QA would bounce it, I'd get a call from the tearful supplier facing financial ruin, I'd point out that a #9 drill is really not the same as a 5 mm drill and there's no difference in price or availability "so get some metric drills".

- lather rinse repeat.

They are??? The board I designed back in 2008 used 2 parts that were inch based, a couple of debugging connectors. Everything else was metric, even the mounting hole was for a metric screw.