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Height difference between different AMLs

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Nightwish View Drop Down
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    Posted: 06 Mar 2012 at 1:24am
Hi Tom,
 
When I am creating a cell for a connector which has two different AML's spec and I find they have much difference in Height value. One is 15.5mm and the other one is 19mm. In this case is it good to create a single cell for the part? I am not sure if there is a standard or IPC guide on in which range the difference between Height can be acceptable. Sometimes the EE missed this and they prefer to have 3 or 4 AMLs in one part number but this may give us CAD librarian much difficulty.
 
Thanks,
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar 2012 at 8:46am
In the near future, we'll be mapping 3D Models with Footprints and several things need to line up and one of them is "Height". The Footprint and 3D Model must have the same rotation, name, origin, height, etc. They are synced together.
 
One of the main things that IPC is considering for Footprint Name creation is to add a 2 - 3 character suffix at the end of the name to indicate the component manufacturer. I will be posting an Excel spreadsheet list of all component manufacturers and the recommended suffix characters. This will distinguish the variances between the component manufacturer's tolerances.
 
We are trying to resolve having 2 components with the same "nominal" dimensions but different tolerances and therefore different pad sizes and spacing that result in the same footprint name. But in our viewpoint, "Component Height" does require different footprint names primarily because of the emerging 3D Model technology in the electronics industry.
 
There is an exception to this rule for people who are using enterprise CAD tools like Expediton, Allegro and CR-5000 which can handle component height differently than a normal PCB layout tool like PADS or Altium. The enterprise tool has the ability to use the same footprint but have different attributes for different heights. I guess PADS Layout has the same feature in that a "Decal" is the footprint with pads and 2D Lines and the Part Type has all the attributes like Height, component family, gates, apha-numeric pin assignments and Decal Mapping. So a single "Decal (footprint)" can have hundreds of logical "Part Types" with different component mfr. part number names. i.e.: the Part Type name is totally different than the Decal name. This was intended to reduce duplication of Decals, however it does get rather complex when some Decals have a thousand Part Types with different names while other Decals are one-of-a-kind and the Part Type and Decal name are identical.
 
In my humble opinion, every Decal and Part Type name should be the same. There will be some duplication but at least it's clean and less confusing to the PCB designer and EE engineer.
 


Edited by Tom H - 06 Mar 2012 at 9:03am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nightwish Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2012 at 9:44pm
We are using Mentor Graphics Expedition flow so it is easy for me to create alternate cells with different Height value for one part but the PCB designer may be confused when they place the part on board because they don't know which one to choose.
 
I agree with you that the Component Height does rerquire different cell names but their may be some limit or restrictions on this. For chip components like 0603 or 0805 resistor, there may be some differences between different manufactures, for example KOA, Vishay, Rohm or Sumsung, but very tiny difference and we usually ignore. In this case we only have one cell in library called RES0603 and the height is using the worst case.
 
But for other components like connector, if the components engineer or hardware engineer have many different AMLs for one part number and they have difference in body outline or height, this will be a big challenge for us. If we export emn or emp file to mechanical engineer to check in 3D and may be there will be some confilict. I think I will have to persuade them to make some changes to the AML.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 08 Mar 2012 at 1:09pm
I agree that for 2 pin passive footprints, having one that fits all and use the max height is a good idea.
 
But IC's and connectors are a different story and I would use unique footprints for each different component vendor's tolerances and heights. And make both the Decal & Part Type the same name, or in your case, don't use the Cell + Alternate Cells concept as it may cause confusion.
 
Simplicity makes our job easier and reduces errors.
 
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