1. Use Metric Units through-out the PCB design process (Metric Padstack Names)

2. Use Mil Units through-out the PCB design process (Mil Padstack Names)

3. Use a mix of Metric and Mil Units through-out the PCB design process (Metric & Mil Padstack Names)

 

#1 & 2 are no brainers and that is what we expected the industry to do.

 

We have to take a close look Option #3 and add an identifier at the end of the Mil padstack name and let the Metric Padstack Name be the default because that is wehere the industry is headed long term.

 

I will discuss this issue with our programmers so that when auto-generating Mil Padstack Names it produces c60h35_mil. c= circular pad, 60 = 60 mils, h = hole, 35 = 35 mil hole size, _mil = mil units.

 

For the Land Pattern Name, the pin pitch is always the first numeric identifier in the name and there are no Inch or Metric pin pitches that match. So SOP50P = 0.5 mm pitch and the land pattern name in in metric units. The same land pattern name in mils would be SOP19.685P = the same exact 0.5 mm pitch but was built in mil units. i.e.: 0.5 mm = 19.68 mils. 

 

The Land Pattern Names are obvious unless you can present a scenario where the mil land pattern name could be confused with a metric land pattern name. It is obvious that a 3216 Chip Capacitor is metric and the equivelent 1206 is Mils.

 

But this subject needs to be carefully examined to insure that no conflict is possible. Our estimates are that over 50% of the PCB design industry is stuck in the Mil Unit category and they don't understand metric units or metric numbers or metric speak. They would if they transitioned but they don't because they are being held back by their PCB Fabrication shops and / or mechanical engineers who provide all constraint drawings, mounting holes, enclosures, etc. in Inch Units.

 

I have been designing in metric units for the past 10 years and I burned all references to the Imperial measurement system. But that is because I controlled my destiny. When I was laid off Mentor Graphics and tried to get employment back in the "real world", the only thing that's available is Mil Unit PCB layout and the #1 reason why is being driven by the PCB fabrication shops and PCB material providers and CAD Vendors where all the training and education to use the CAD tool in based on Inch Units.

 

We really don't want to do this, but it's more like we have to do it until PCB fabrication transitions to the metric system. Then every one will transition along with them. I can't wait for that day.

 

 

Thanks for your reply. I agree with you that ICs probably do not present a problem. Where I forsee problems in admitting different units are passives. Consider an 0603 device. Browsing through a library, unless the library is clearly annotated with units, there is no way of knowing if this part is metric or imperial. From a library user's point of view, design flow efficiency requires a clearly recognizable indicator of units so that it takes seconds to make a decision on a part, instead of having to place a part and make measurements of the land pattern to verify it is indeed the appropriate one.

 

So the question is, can a land pattern designator as currently defined in IPC-7351B be modified in a simple fashion so as to convey measurement system? A simple-minded example being: CAPC0603X01 for the metric part, and CAPC(I)0603X01 for the imperial part?

 

However, those people who are entrenched in the mil unit system and don't understand metric units and have no intention on ever using metric units can output everything in mil units.

 

Pick one unit system or the other and run with it. My advice is to not mix metric and mil units in the same library. If you must use both measurement systems, create a separate metric and mil PCB library. And do the same for your PLM system. Create a metric .fpx library and a mil .fpx library.

 

On their own, PCB designers are currently creating library names like CAPC1608X90N-0603.

 

I will discuss this issue with the programmers and explain all the concerns. I'm sure that once we release PCB Footprint Calculator in beta test the week of April 16, that people will voice their concerns and they will be addressed in on-going software releases.

 

Remember that this is a brand new product that will have a 10 - 15 year lifespan depending on the direction of the component package industry.