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There are 2 Calculation Modes, Min/Max & Nominal.
1. To select between the two options, select "File > Calculation Mode", then either "Min/Max" or "Nominal".
2. The Min/Max Mode uses package and terminal tolerances. Solder joint goals in this mode are based on the IPC J-STD-001 standard.
3. The Nominal Mode does not use package and terminal tolerances. Chose this option if you use Manufacturer Recommended patterns, or if you use hard coded solder joint goals. Solder joint goals in this mode are based on the FED Volume 18 standard.
4. The Min/Max calculator settings are based on the IPC-7352 mathematical model. The resulting pad stack size uses the Terminal Tolerances and Toe, Heel and Side Solder Joint Goals. This concept was created by IPC in the 1980s and is still used today. This concept depends on the component package tolerances to create Min/Max dimensions that are used for pad stack calculation. However, the question of package tolerances is being questioned by the FED standards organization in Berlin Germany. For the IPC-7352 Mathematical Model documentaiton, in the Footprint Expert, go to "Help > Important Documents" and see the "IPC-7352 Mathematical Model.pdf".
5. The FED Vol 18 standard uses nominal package dimensions. This greatly simplifies dimensional data entry and users control the Toe, Heel and Side for every terminal shape. Solder joint goals are created by using the nominal package terminal lead height or lead frame thickness. Below are 2 examples that illustrate the percentages used to calculate the Toe, Heel and Side.
The new Nominal calculation mode allows users to hard code the Toe, Heel and Side solder joint goal values and the results are predictable and repeatable.
Note: Modern machines and manufacturing processes for electronic components and PCBs are highly accurate, producing components and assemblies that closely adhere to nominal dimensions. Most component manufacturers recommend solder patterns in their datasheets based on Nominal package dimensions with pre-defined solder joint goals. Few component manufacturers use the IPC-7351 mathematical model, which incorporates manufacturing tolerances. Component package tolerances differ widely between manufacturers, complicating footprint standardization. This raises questions about the necessity and accuracy of these tolerances. Are they practical and realistic?
EXAMPLE 1 - Rectangular End Cap (Chip) Leads:
Common Chip Component Packages have different 3D STEP models:
Chip Capacitor  |
Chip Resistor  |
Chip Inductor  |
Polarized Chip Capacitor  |
Chip Diode  |
Chip LED  |
EIA Standard Chip Component Package Sizes with no Standard Height reference
Table of Chip Package Size Codes and Dimensions |
|||
EIA (inch) Name |
Inch Dimensions |
IEC (metric) Name |
Metric Dimensions |
01005 |
0.0157 in x 0.0079 in |
0402 |
0.4 mm x 0.2 mm |
0201 |
0.024 in x 0.012 in |
0603 |
0.6 mm x 0.3 mm |
0402 |
0.039 in x 0.020 in |
1005 |
1.0 mm x 0.5 mm |
0603 |
0.063 in x 0.031 in |
1608 |
1.6 mm x 0.8 mm |
0805 |
0.079 in x 0.049 in |
2012 |
2.0 mm x 1.25 mm |
1008 |
0.098 in x 0.079 in |
2520 |
2.5 mm x 2.0 mm |
1206 |
0.126 in x 0.063 in |
3216 |
3.2 mm x 1.6 mm |
1210 |
0.126 in x 0.098 in |
3225 |
3.2 mm x 2.5 mm |
1806 |
0.177 in x 0.063 in |
4516 |
4.5 mm x 1.6 mm |
1812 |
0.18 in x 0.13 in |
4532 |
4.5 mm x 3.2 mm |
2010 |
0.197 in x 0.098 in |
5025 |
5.0 mm x 2.5 mm |
2512 |
0.25 in x 0.13 in |
6332 |
6.4 mm x 3.2 mm |
2920 |
0.29 in x 0.20 in |
7451 |
7.4 mm x 5.1 mm |
EXAMPLE 2 - Gullwing Leads:
PCB Libraries, Inc. added the Nominal Calculation Mode to Footprint Expert V25.02 as an alternative land pattern calculator, released in January 2025. Footprint Expert users can easily switch back and forth between Min/Max (IPC-7352) and Nominal (FED Vol 18 "New Proportional Land Dimensioning Concept").
