I've been thinking about this... and reading all of the responses... and
hesitate to reply, but decided to go ahead and stick my head out of the gopher
hole - and hope it doesn't get hit too hard.
I'm an old-timer, I suppose. I started doing CAD layouts (and don't forget
Schematic capture) years ago. Many years ago. (I don't think Bishop Graphics
had their 'dots' and 'tape' in metric.)
When I create Patterns, I usually use the units that the part was created in.
As we all know, the DIP packages were created in Imperial units. I use that
for those parts. The newer parts (most - but not all), now use metric. So, my
CAD software allows me to switch to Metric units, and viola! I create the
Patterns in metric units.
I then switch back to Imperial units to place and route the boards.
One bit that I haven't seen addressed is the Schematic. I create all on my
Schematic symbols using Imperial units, and place the Symbols using an
Imperial Grid, onto Titleblocks that are set up as either A-size, B-size, or
C-size. Guess what? I print these on paper that is in Imperial units, too.
8-1/2x11, 11x17 or 17x22 inches. (Occasionally, I still need to use D-size
paper, but I really try not to go that large for schematics, unless I need a
new tablecloth.)
Here in the States, I cannot go into the local office supply store and
purchase Metric paper for printing my schematics on (yet), and so am going to
buy the A, B or C-sized paper.
Now. My point? I try to use the same units from start to finish for the entire
design.
Getting back to the PCB layout, I noticed that it was mentioned that the
Imperial units are 'rounded' (either up or down) to the nearest 1-mil. I dunno
if I agree with this practice. I remember in the early days, the CAD software
that I was using at the time could not do sub-mil grids for layout. There were
some parts (if I recall correctly), where we had to 'fudge' the Pad placements
to achieve that 1/2-mil.
Most modern CAD systems can now do sub-mil in the layout. I always allow it. I
guess I am concerned that there may be an issue with the layout and drill not
quite matching up.
In my experience, I have had more issues with inherited designs, and the
original designer not keeping his output data (Gerber & Drill) in the same
resolution for whatever units that they chose to use.
This is my biggest 'gripe'. When I generate Gerbers, I use 4.4 (or 2.4), which
means that I can have 4 places to the right of the decimal place. Sub-mil.
I'll use it.
Same with the drill files.
On occasion, I've seen the designer use 2.4 for the Gerber, and 2.3 for the
drill files. When pulled into a CAD viewer, it becomes apparent rather quickly
that this is not the best thing to do.
So... my concern is not with what units to use. It is more to do with keeping
the data integrity for the fellas in fabrication - to make their jobs easier,
and to be sure that we get good boards produced.
Now. Pad naming. (No - I'm not through ranting...)
Through the years, I've toyed with naming conventions that not only make sense
to me, but can be easily remembered (I don't have enough wall space to tape up
all sorts of charts), and used each time.
So, for naming my padstacks, I use a simple method for naming.
I start with the diameter of the drilled hole. No hole? The drill hole is '000'.
Here is an example...
D035X0650Y0650EA
D000X0591Y0512RT
Why do I do this? Well, through the years, I've found that I look first for a
pad in my list (which can get long), by the drill hole. Second by the X & Y
dimensions. Lastly, I look at the shape of the pad.
I use simple shapes like Ellipse, Rectangle, Oblong, Polygon, Mounting Hole.
Sometimes, I have to get creative with the naming, but I can usually come up
with something that still fits into my naming conventions.
I also try not to make the Padstack name so long, either. I mean... jeepers!
What are you doing spending all of your time typing out some cryptic Padstack
name? I have a design to finish. Plus, there are still some CAD systems that
are limited as to the number of characters that they allow. My CAD software
limits me to 20 characters. That should be plenty for any PadStack name. You
may need to rethink this if you're trying to create a 'standard' that you want
others to follow, as I seem to remember counting over 30 characters in one of
those Padstack names in your presentation.
Also - you may notice that I use the zeros - leading and following. This helps
align the Padstack names in a neat little list that then gets sorted by my CAD
software, and making it easier for me - an old fogey - to scan down the list
quickly, looking for the correct Padstack to use or edit, if I am trying to
change the Drill holes to consolidate the Drill table to less than 10 or 11
Drills.
I also have some thoughts that are similar on Pattern naming, but I've
probably ticked off enough folks for one e-mail.
Thanks for letting me rant.
Regards,
James Jackson
Oztronics
Quoting Tom Hausherr <[log in to unmask]>:
> All,
>
>
>
> Our web-server crashed so you'll have to wait until it comes back on-line.
> Nick Ban and our web team are hot on it.
>
>
>
> Thanks for the fantastic feedback and excellent dialog. In the IPC world,
> Jack Olson & Mike Buetow are correct that the term Footprint is the
> component package dimensional data and Land Pattern is what the Footprint
> solders to. The term "Land" is what the component lead attaches to.
> However,
> no one uses the term "Land" because all the CAD vendors call it a "Pad".
> It's what we deal with every day.
>
>
>
> At IPC APEX "Designer's Day" I made an announcement -
>
> "This is my last presentation... that I will ever give using Metric Only
> dimensional data in my Power Point files. From now on I will always
> include
> both Metric and Imperial dimensions side by side with Imperial being the
> dominant number and (metric) secondary until there is clear evidence that
> the industry has successfully transitioned. And I will always use the term
> Footprint when referring to PCB library parts because that is the term
> most
> widely used. And I will refer to Chip components using the EIA Imperial
> names of 1206, 0805, 0603, 0402 until the component manufacturer's refer
> to
> them using the IPC metric names 3216, 2012, 1608, 1005."
>
>
>
> Some of you reported typos in the Power Point Presentation. I updated the
> website last night -
> http://www.pcblibraries.com/Forum/ipc-apex-expo-2012_topic6.html
>
>
>
> The updates also affected the "Proportional Through-hole Padstacks" chart
> -
> Proportional_Through-hole_Padstacks.pdf
> <http://www.pcblibraries.com/Forum/uploads/1/Proportional_Through-hole_Padst
> acks.pdf> (you can still access this file on our server)
>
>
>
> People have been asking me off-line to explain the Proportional
> Through-hole
> Padstacks and I will post the explanation of the mathematical formulas
> here
> (once the server is back on-line) -
>
> http://www.PCBLibraries.com/forum/forum_posts.asp?TID=15
> <http://www.PCBLibraries.com/forum/forum_posts.asp?TID=15&PID=60#60>
> &PID=60#60
>
>
>
> One more thing, PCB Libraries, Inc. is 6 weeks away from launching the 5th
> generation IPC Calculator and after hearing your feedback we officially
> named it "PCB Footprint Calculator". This is brand new "coded from
> scratch"
> over the past 8 months and the Designer's Day Power Point Presentation is
> the blueprint for the new tool. Example: The user can insert the component
> dimensions in metric and then switch to mils and all the Footprint
> dimensions are converted to 1 mil increments, the Footprint & Padstack
> names
> are generated in Mil units. However, if you stay in metric units, the
> Footprint (Land Pattern) dimensions and library name will be in Metric
> Units. Example: you enter the component dimensions for a 3216 using metric
> dimensions and when you switch to Mils the Footprint name automatically
> changes to 1206 and all the Footprint dimensions are in 1 mil increments.
> The new tool boosts many new features including rotation to create the
> IPC,
> IEC or EIA Zero Component Orientation. Coming May 1, 2012 when the
> official
> PCB Libraries.com website opens. This is a Free download without any
> registration required, it will have regular updates that will have an
> auto-update notification and it will come with the Texas Instruments
> "Standard Parts" product line which includes over 35,000 TI part numbers.
> It's our gift to the electronics industry. No strings attached.
>
>
>
> Tom
>
>
>
> Tom Hausherr
>
> President
>
> PCB Libraries, Inc.
>
> 13730 Sorbonne Court
>
> San Diego, CA 92128
>
> 858.592.4826 Office
>
> 858.859.5371 Cell
>
> [log in to unmask]
>
>
>
>
>
>
>
> ______________________________________________________________________
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>
>
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