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IPC-7351 SMD & PTH Reference Calculators

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Nick B View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nick B Quote  Post ReplyReply Direct Link To This Post Topic: IPC-7351 SMD & PTH Reference Calculators
    Posted: 07 Jan 2013 at 2:35pm

Here are the latest Reference Calculators. Please note there are TWO (2), one is Surface Mount, and the other Plated Through Hole, also referred to as TH. (you need to be logged in, registration is absolutely free!)

IPC-7351 SMD Reference Calculator


Below is the is the PCB Library Expert PTH Reference Calculator:
 
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jk-999 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jk-999 Quote  Post ReplyReply Direct Link To This Post Posted: 02 Apr 2014 at 9:00am
Which equation is correct? Zmax=Lmin +2JT + SQRT((CL)² + (2*F)² + (2*P)²)   or 
                                        Zmax=Lmin +2JT + SQRT((CL)² + (F)² + (P)²)
 
IPC 7351A  uses the second equation. I believe the calculator is using the first equation.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jeff.M Quote  Post ReplyReply Direct Link To This Post Posted: 02 Apr 2014 at 12:44pm

Both are correct.

The difference is due to the definitions of the 'Placement' (P) and 'Fabrication' (F) tolerances.

IPC-7351 demonstrates them as a single value.  For example in their publication they use 0.10 mm for F and 0.20 mm for P (this is your 2nd equation).

We use plus-or-minus values where an equivalent F would be +/- 0.05 mm and P would be +/- 0.10 mm so they're doubled before squaring (this is your 1st equation).

Either way, the tolerances are the same and the result is the same.
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Nick B View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nick B Quote  Post ReplyReply Direct Link To This Post Posted: 20 Oct 2014 at 12:53pm

Please note the IPC-7351 Reference Calculator was just updated! There is now an Inserted Mount "IMD" (TH) Reference Calculator. Download it from this forum thread, or from www.PCBLibraries.com/downloads

Nick

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