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0402 Min Size Land Pattern

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Tom H View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 29 Mar 2015 at 2:32pm
The Free Library Expert Lite provides all the Land Pattern dimensional data for 144 different component families - www.pcblibraries.com/downloads
 
You can also switch between IPC-7351 Density Levels.
 
Since the V2015.09 Library Expert Lite has all the latest IPC-7351C mathematical formulas for packages less than 0603, you'll be able to see distinct differences between 0603, 0402 and 0201 chip components.
 
It also has all the rules for Molded Body Tantalum Capacitors and Diodes.
 
The Free Library Expert Viewer can load FPX files and if you purchase the IPC-7351B you get a special Viewer that comes with 5,000 different component package dimensions.
 
 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote jayx Quote  Post ReplyReply Direct Link To This Post Posted: 20 Apr 2015 at 3:54pm
Hi Tom,

 OK, as advised I've downloaded Library Expert Lite and entered 1005 (EIA 0402) dimensions (based on Kemet: D=1±0.05, E=0.5±0.05, A=0.5±0.05. L/L1=0.3±0.1mm) and land pattern results are: L/L1=0.59, W=0.6, S=0.22mm. Very similar to your recommendations apart from S which is two times smaller (it's 0.5mm in your recommendation).

It's quite big difference for such a small component, and in fact Kemet recommends S=0.28mm so close to the above calculations. Reducing tolerance or change density level don't get me close to your recommended S dimension, could you comment please?
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 21 Apr 2015 at 5:48am
I don't think you understand Library Expert. The initial settings are IPC-7351 compliant but the user has several options.
 
1. You can select the Footprint tab and enter the mfr. recommended pattern dimensions.
 
2. You can open the "Terminal Settings > Density Level" and change the Toe, Heel and Side solder joint goals.
 
3. Or, what some users are starting to do is in the Terminal tab is change the Placement and Fabrication Tolerances to 0 (zero) due to the accuracy of the machines and processes in 2015.
 
I would not take the IPC-7351 default settings as the holy gospel as the "Standard" was recently downgraded to a "Guideline". And new updated solder joint goals are currently in testing. So maybe the mfr. recommendation is the way to go. Then you can blame any problems on the mfr.
 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote DenisFr Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2016 at 3:58am
Hi Tom,

I try to understand how the footprints are calculated with Library expert. Especialy "S". In IPC, i saw that Sm=Lm-2xTM, but i don't find the same result than in the calculation tab. For example, for a 0805 resistor, i will have Sm=1.85+2x0.65=0.55 while i obtain 0.816 in library expert. Did i miss a parameter ?

Thank you very much

Denis
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2016 at 7:49am
You should download the Surface Mount Reference Calculator and it will allow you to change all the values so you can see how the IPC mathematical model works.


If you're using V2016.14 it's in this folder -
C:\Program Files (x86)\PCB Libraries\Library Expert 2016\Documents

The IPC math considers the Component Package and Terminal Lead Tolerance and adds a Fabrication and Assembly Tolerance plus a Toe, Heel and Side solder joint goal.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote DenisFr Quote  Post ReplyReply Direct Link To This Post Posted: 09 Nov 2016 at 1:20am
Great, thank you very much. I see the formula used so it can be more precised i believe.
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