IPC7351 SMD & PTH Reference Calculators 
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Nick B
Admin Group Joined: 02 Jan 2012 Status: Offline Points: 1512 
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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!) IPC7351 SMD Reference Calculator Below is the is the PCB Library Expert PTH Reference Calculator: 

jk999
New User Joined: 12 Dec 2012 Status: Offline Points: 1 
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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.


Jeff.M
Admin Group Joined: 16 May 2012 Location: San Diego Status: Offline Points: 353 
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Both are correct. The difference is due to the definitions of the 'Placement' (P) and 'Fabrication' (F) tolerances. IPC7351 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 plusorminus 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.


Nick B
Admin Group Joined: 02 Jan 2012 Status: Offline Points: 1512 
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Please note the IPC7351 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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