PCB Libraries Forum Homepage
Forum Home Forum Home > Libraries > PCB Library Construction Guidelines
  New Posts New Posts RSS Feed - IPC-7351 SMD & PTH Reference Calculators
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

IPC-7351 SMD & PTH Reference Calculators

 Post Reply Post Reply Page  12>
Author
Message Reverse Sort Order
stanleycayochok View Drop Down
Active User
Active User


Joined: 04 Apr 2016
Status: Offline
Points: 21
Post Options Post Options   Thanks (0) Thanks(0)   Quote stanleycayochok Quote  Post ReplyReply Direct Link To This Post Topic: IPC-7351 SMD & PTH Reference Calculators
    Posted: 26 Feb 2021 at 12:47am

Will definitely get the latest version.

Thank you Jeff for the detailed explanation.
Back to Top
Jeff.M View Drop Down
Admin Group
Admin Group


Joined: 16 May 2012
Location: San Diego
Status: Offline
Points: 371
Post Options Post Options   Thanks (0) Thanks(0)   Quote Jeff.M Quote  Post ReplyReply Direct Link To This Post 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.


Stay connected - follow us! Twitter - LinkedIn
Back to Top
stanleycayochok View Drop Down
Active User
Active User


Joined: 04 Apr 2016
Status: Offline
Points: 21
Post Options Post Options   Thanks (0) Thanks(0)   Quote stanleycayochok Quote  Post ReplyReply Direct Link To This Post 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     


Back to Top
Jeff.M View Drop Down
Admin Group
Admin Group


Joined: 16 May 2012
Location: San Diego
Status: Offline
Points: 371
Post Options Post Options   Thanks (0) Thanks(0)   Quote Jeff.M Quote  Post ReplyReply Direct Link To This Post 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.
Stay connected - follow us! Twitter - LinkedIn
Back to Top
stanleycayochok View Drop Down
Active User
Active User


Joined: 04 Apr 2016
Status: Offline
Points: 21
Post Options Post Options   Thanks (0) Thanks(0)   Quote stanleycayochok Quote  Post ReplyReply Direct Link To This Post 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?
Back to Top
Tom H View Drop Down
Admin Group
Admin Group
Avatar

Joined: 05 Jan 2012
Location: San Diego, CA
Status: Offline
Points: 4839
Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post 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. 

Stay connected - follow us! Twitter - LinkedIn
Back to Top
dfournier View Drop Down
New User
New User


Joined: 06 Jul 2018
Status: Offline
Points: 2
Post Options Post Options   Thanks (0) Thanks(0)   Quote dfournier Quote  Post ReplyReply Direct Link To This Post 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.


Back to Top
Tom H View Drop Down
Admin Group
Admin Group
Avatar

Joined: 05 Jan 2012
Location: San Diego, CA
Status: Offline
Points: 4839
Post Options Post Options   Thanks (1) Thanks(1)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post 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. 
 

 
Stay connected - follow us! Twitter - LinkedIn
Back to Top
dfournier View Drop Down
New User
New User


Joined: 06 Jul 2018
Status: Offline
Points: 2
Post Options Post Options   Thanks (0) Thanks(0)   Quote dfournier Quote  Post ReplyReply Direct Link To This Post 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?
Back to Top
Tom H View Drop Down
Admin Group
Admin Group
Avatar

Joined: 05 Jan 2012
Location: San Diego, CA
Status: Offline
Points: 4839
Post Options Post Options   Thanks (1) Thanks(1)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 2018 at 2:55pm
IPC-7351 has no recommendation on using circular pad shape for Chip Components. 

The best source for this recommendation would be the Assembly Shop source that you are currently using. 

Stay connected - follow us! Twitter - LinkedIn
Back to Top
 Post Reply Post Reply Page  12>

Forum Jump Forum Permissions View Drop Down



This page was generated in 0.078 seconds.