IPC-7351 SMD & PTH Reference Calculators

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   Hello guys,

I start to create footprints with IPC-7351.
Could you tell me what are Thermal ID and Thermal OD for PTH?

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dfournier Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 06 Jul 2018 Status: Offline Points: 2	Post Options Post Reply Quote dfournier Report Post Thanks(0) Quote Reply Posted: 09 Jul 2018 at 12:09am
	Hello guys, I start to create footprints with IPC-7351. Could you tell me what are Thermal ID and Thermal OD for PTH?



Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(1) Quote Reply Posted: 09 Jul 2018 at 7:32am
	Thermal Relief is for all PTH pins that connect to a Plane. A PTH lead with a direct connection to a GND or VCC Plane can have a cold solder joint because the plane can dissipate all the heat from that connection. ID = Inside Diameter of Plane Pad OD = Outside Diameter of Plane Pad The thermal ID & OD are connected with Spokes from the pad to the copper plane.
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dfournier Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 06 Jul 2018 Status: Offline Points: 2	Post Options Post Reply Quote dfournier Report Post Thanks(0) Quote Reply Posted: 10 Jul 2018 at 5:24am
	Hello Tom, Thank you for informations. Does IPC define Thermal ID and OD? I don't find explanation that define these diameters. I use CADSTAR software and Thermal ID and OD are differently defined.

Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 10 Jul 2018 at 7:35am
	IPC-2221 and IPC-2222 are the only documents with through-hole pad stack info. IPC-7351C is stalled in committee and will not be released for another year or so. Every CAD tool defines Thermal Relief patterns differently. Library Expert has over 100,000 users worldwide and no one has ever complained about this issue in the past 6 years. We use best practice math that we have tested and tried in a CAD tool library since 1982.
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stanleycayochok Members Profile Send Private Message Find Members Posts Add to Buddy List Active User Joined: 04 Apr 2016 Status: Offline Points: 23	Post Options Post Reply Quote stanleycayochok Report Post Thanks(0) Quote Reply Posted: 15 Feb 2021 at 9:14pm
	There is a difference on the Smax[RMS] formula between IPC7351 and from the "PCB Library Expert SMD Reference Calculator.xlsx" IPC7351 RMS Smax formula: Smax[RMS] = Smin + Stol[RMS] Library Expert RMS Smax formula: New Smax = Smax - (Stol -Stol[RMS])/2 Both will result in a different output value. May I know why Library Expert used such formula?

Jeff.M Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 16 May 2012 Location: San Diego Status: Offline Points: 477	Post Options Post Reply Quote Jeff.M Report Post Thanks(0) Quote Reply Posted: 16 Feb 2021 at 11:10am
	I believe the formula you're referring to (Smin + Stol[RMS]) dates back to the IPC-SM-782 document from 1993. IPC revised this about 2005. Please refer to IPC-7351B section 3.1.1 (should be page 11) shown as follows. This example is demonstrated in our free SMD Reference Calculator for Excel.
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stanleycayochok Members Profile Send Private Message Find Members Posts Add to Buddy List Active User Joined: 04 Apr 2016 Status: Offline Points: 23	Post Options Post Reply Quote stanleycayochok Report Post Thanks(0) Quote Reply Posted: 25 Feb 2021 at 5:17am
	Hi Jeff, There is no image on your post. I was referring to this Smax[RMS] formula in the 2005 IPC7351, please refer to attached image: In the "SMD Reference Calculator for Excel" the formula is this: New Smax = Smax - (Stol -Stol[RMS])/2

Jeff.M Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 16 May 2012 Location: San Diego Status: Offline Points: 477	Post Options Post Reply Quote Jeff.M Report Post Thanks(0) Quote Reply Posted: 25 Feb 2021 at 11:18am
	You should try to get a more recent copy of IPC7351. What follows is a direct quote from IPC-7351B, June 2010. Note the line for Smax. (All the values in the Excel Reference Calculator match the example given in that document, allowing for rounding). "Therefore, the calculations for ‘‘S’’ minimum and maximum dimensions are as follows: Smin = Lmin - 2Tmax = 5.8 mm - 2 (1.27 mm) = 3.26 mm Smax = Lmax - 2Tmin= 6.2 mm - 2 (0.4 mm) = 5.40 mm Stol = Smax - Smin = 5.4 mm - 3.26 mm = 2.14 mm" Section 3.4.1 discusses the reason for creating New_Smax. New_Smax is ultimately used to produce Gmin. Not Smax.
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stanleycayochok Members Profile Send Private Message Find Members Posts Add to Buddy List Active User Joined: 04 Apr 2016 Status: Offline Points: 23	Post Options Post Reply Quote stanleycayochok Report Post Thanks(0) Quote Reply Posted: 26 Feb 2021 at 12:47am
	Will definitely get the latest version. Thank you Jeff for the detailed explanation.

Aaronbat Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 11 May 2023 Status: Offline Points: 1	Post Options Post Reply Quote Aaronbat Report Post Thanks(0) Quote Reply Posted: 12 May 2023 at 4:46pm
	Hello, I have the calculator but I'm new reviewing this kind of stuff, from where I can get the information is question on the fields: Fabrication Tolerance Placement Tolerance Toe Goal Heel Goal Side Goal Place Round Size Round Some of them I don't know what it means.