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Tom H View Drop Down
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Joined: 05 Jan 2012
Location: San Diego, CA
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    Posted: 06 May 2019 at 2:22pm

All solder joint goal default values for Toe, Heel and Side are best industry guidelines derived from IPC-J-STD-001 Standard for Assembly Acceptability. The calculator mathematical model for land pattern calculation is derived from IPC-7351, which uses the Terminal Lead Tolerance, a Manufacturing Tolerance and the default Solder Joint Goals derived from IPC-J-STD-001 (not IPC-7351). If you want to use the IPC-7351B solder joint goals, then you should select the IPC-7351B_DefaultPreferences.dat Preference file and then save as your personal Preference file to edit all the Drafting Outlines, Rules and Pad Shapes. In the new upcoming V2020 of Library Expert, we will drop the Manufacturing Tolerance to 0.00 as this only has a slight impact on the resulting pad size. But the user can add the Manufacturing Tolerance back if you want to use it. Also, all negative solder joint goals will be changed to 0.00 as the negative values were created to compensate for the Manufacturing Tolerance.

Note: The Library Expert default values have been used to create millions of land patterns worldwide without any complaints from any user. We believe that the values provide best industry practice for pad size and spacing calculations. However, every user, has the opportunity to change any of the solder joint goal values for toe, heel and side, the manufacturing tolerances and the terminal lead tolerance to calculate a land pattern that best fits their unique assembly process. We urge all Library Expert users to consult with your assembly shop to evaluate all the numbers that they need for the best package attachment to the PCB.


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