BGA Terminal Size Mil to mm Rounding

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   Hello,
When I change the solder mask expansion preference for the terminals of BGA family from 0 to 2 mils and change the preferences to mm, it changes every value on the size matrix to rounded off error values. 

Example :
0.60 mm to 0.599
0.55 mm to  0.551
0.35 mm to 0.351
0.25 mm to  0.249

Why is the program changing all the preferences if I only want to change the solder mask expansion?

This caused a footprint error with a BGA, the default preferences said the pad should be .41mm diameter and the program with our preferences (just by changing the solder mask expansion) made it 0.36 mm diameter...

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Eng. Jesus Mora Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 11 Jul 2013 Status: Offline Points: 56	Post Options Post Reply Quote Eng. Jesus Mora Report Post Thanks(0) Quote Reply Topic: BGA Terminal Size Mil to mm Rounding Posted: 14 Jul 2017 at 5:05pm
	Hello, When I change the solder mask expansion preference for the terminals of BGA family from 0 to 2 mils and change the preferences to mm, it changes every value on the size matrix to rounded off error values. Example : 0.60 mm to 0.599 0.55 mm to 0.551 0.35 mm to 0.351 0.25 mm to 0.249 Why is the program changing all the preferences if I only want to change the solder mask expansion? This caused a footprint error with a BGA, the default preferences said the pad should be .41mm diameter and the program with our preferences (just by changing the solder mask expansion) made it 0.36 mm diameter...



Eng. Jesus Mora Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 11 Jul 2013 Status: Offline Points: 56	Post Options Post Reply Quote Eng. Jesus Mora Report Post Thanks(0) Quote Reply Posted: 14 Jul 2017 at 5:06pm
	here is the diference in pad size with the same values entered...

Eng. Jesus Mora Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 11 Jul 2013 Status: Offline Points: 56	Post Options Post Reply Quote Eng. Jesus Mora Report Post Thanks(0) Quote Reply Posted: 14 Jul 2017 at 5:07pm
	Here are the preferences before changing the solder mask expansion...

Eng. Jesus Mora Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 11 Jul 2013 Status: Offline Points: 56	Post Options Post Reply Quote Eng. Jesus Mora Report Post Thanks(0) Quote Reply Posted: 14 Jul 2017 at 5:08pm
	here are the preferences after changing the soldermask expansion... notice how size values and Var+ values change by themself

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 Jul 2017 at 7:05am
	That's the way it works for grid arrays. The preference values are stored in Micrometers. When a table is loaded the stored values are converted to the selected units for display and when you just switch between them they remain consistent. But once you commit a change, as you have, all the table values are converted from selected units to micrometers and saved. There's no way to ignore values that haven't changed. Due to rounding (1 decimal place for mils, 4 dp for inches, 3 dp for mm and 0 dp for microns) in many cases this results in a lack of exact conversion. If you switch your unit preference you should stick with that preference and not go back and forth. Note that if you will be designing in several different unit types you can have different preference files to compensate. Or, if you wanted to enter a mil equivalent into a mm preference, use the units conversion tool.
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