IPC-7351 Collapsing and Non-Collapsing BGA Balls

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   IPC has a rule for BGA pad size tolerances. They take a Nominal Ball and reduce or increase the pad size by a percentage, then add a pad size tolerance (variation). IPC-7351 recommends using the Maximum Material Condition of the Variation. 
All BGA balls collapse. Non-collapsing BGA balls are created by the PCB librarian by solder mask defined pads or making the pad size larger than the Ball. 

Collapsing Ball.

Non-Collapsing Ball defined by Solder Mask.

IPC-7351 BGA tables for pad size reduction for collapsing balls and pad size increase for non-collapsing balls. The pad size increase is normally used for fine pitch BGA's that require via-in-pad technology for fanout. 

There are 3 Density Levels A, B and C that indicate the percentage amount for pad size calculation.

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Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5774	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Topic: IPC-7351 Collapsing and Non-Collapsing BGA Balls Posted: 07 Apr 2024 at 1:31pm
	IPC has a rule for BGA pad size tolerances. They take a Nominal Ball and reduce or increase the pad size by a percentage, then add a pad size tolerance (variation). IPC-7351 recommends using the Maximum Material Condition of the Variation. All BGA balls collapse. Non-collapsing BGA balls are created by the PCB librarian by solder mask defined pads or making the pad size larger than the Ball. Collapsing Ball. Non-Collapsing Ball defined by Solder Mask. IPC-7351 BGA tables for pad size reduction for collapsing balls and pad size increase for non-collapsing balls. The pad size increase is normally used for fine pitch BGA's that require via-in-pad technology for fanout. There are 3 Density Levels A, B and C that indicate the percentage amount for pad size calculation.
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Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5774	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 07 Apr 2024 at 1:39pm
	The Solder Mask Defined BGA pad helps secure the pad to the prepreg. This helps during drop tests.
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mking Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 28 Mar 2025 Status: Offline Points: 6	Post Options Post Reply Quote mking Report Post Thanks(1) Quote Reply Posted: 28 Mar 2025 at 11:39am
	For the collapsing BGA ball with a diameter between the values listed what is appropriate reduction? My example is a 0.242 mm diameter. Is the recommended reduction 15%, 20%, or 19.2% (linear interpolation)?

Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5774	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 28 Mar 2025 at 1:38pm
	If the Ball diameter is on the dividing row between percentages the new ball size will take the lower values. Here is a sample BGA terminal option table where the 0.24 mm Ball Diameter was added.
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