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Manufacturer's Boundary Recommendations

Yoda5939

All,

I'm in the need of information. I work in an environment that is geared toward the automotive industry. Typically, when I build a part, I'll also include a PLACE_BOUNDARY_XXX, which has a height attribute built in as well as making it more convenient for stuffing.. In previous job, multiple boards were built to fit in the same enclosure so height was very important. (<2'' boards). While having a discussion today, I was told by the ME that components will also spec a recommended boundary as opposed to just a recommended footprint. This revalation willl killl any library I might have, What information would the community have regarding the assertation that there are recommended boundaries are the norm? Brinf me out of the dark.

-Ron Scott 

  •  There is what IPC Standards refer to as the Placement Courtyard, which one would typically assign as the PLACE_BOUDARY_XXX.  Some manufactures may specify that area, but more commonly, if it is being used, it is derived from the IPC standards IPC-7351B or driven by your manufactures requirements.  The height attribute can be added to this PLACE_BOUNDARY, or in my case, height is driven from my part table files or component database.

     Here is a link to a blog that might explain it a little better.

     http://blogs.mentor.com/tom-hausherr/blog/2010/11/18/pcb-design-perfection-starts-in-the-cad-library-part-6/

     I don't understand why you think it will kill your current library though.

    Chad

  • Chad, The folks I work with insist that all components come from the manufacturer with a recommended boundary. I explained that the boundaries are driven by the manufacturing necessities and I had even sent them the same link you had sent me. For layout purposes, I have always measured out 10 mils from each surface, rather simplistic but it works for me. I then started putting the height attribute on all my symbols. I guess what I need was someone to tell me the library is a living, movable thing and it's up to each group to figure out what works for them. I think the company that these guys left had made a library , just like we are talking about and calling it a standard. The hardest thing I have to do is answer the external, "Where did you get that spec?" -Ron Scott

  •  I rarely ever see manufacturer recommended boundaries.  I would ask them to provide you the data when questioned.

    As for the spec, I assume you are referring to the IPC-7351B  spec.  It is available for purchase from IPC.org.  Thay have many specs related to almost every aspect of PCB design, fabrication and assembly and is a pretty much widely accepted industry standard. My company has copies of a few of them.

    I use Library Expert Lite from PCBLibraries.com.  It is the free version of PCB Library Expert available on their website.  The free version will let me input the component dimensions and will give me back the dimensions of the footprint based in IPC standards.  I then build the footprint in Allegro manually.  This works for most standard type components (there will always be exceptions). With this, I don't have to always refer to the spec or memorize it.  I am way too old for the latter.

    Chad

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