Collapsing vs: Non-Collapsing BGA Balls

Non-collapsing BGA's normally are 0.50 mm pitch or less.

There are various Chip Scale Packages where the mfr. calls the package a BGA but instead of a Ball there is only a bump. This is also a non-collapsing BGA.

All other BGA's are Collapsing Balls.

This is what a Collapsing BGA Ball looks like -

 

Here is a non-collapsing BGA ball with a solder mask defined pad. IPC has guidance to avoid this, but it's impossible for pin pitches below 0.65 mm if there are traces on the same layer.

 

 

 

The pad size is larger because you need to do via-in-pad and you need an annular ring. 

The solder mask swell = 0 or even -0.05 mm to solder mask define. 

Even if you can use 2 mil trace/space to escape the second rows, the solder mask must always cover the trace to avoid solder bridging between trace and pad. 

A 0.50 mm pitch non-collapsing ball size average is 0.25 mm diameter with a pad of 0.33 mm diameter. This leaves a 0.17 mm gap between pads. 0.05 mm trace/space = 0.15 mm but you must consider a 0.025 mm tolerance on the solder mask registration. 

Non-Collapsing BGA pads are bigger then collapsing BGA pads to allow an annular ring for the drilling process. 

Also, if you need to solder mask define the BGA pad to pass drop tests, the solder mask will help with the pad attachment to the prepreg. During drop tests, the ball to pad joint will withstand a drop test, but a non solder mask defined pad could rip away from the prepreg causing the device to malfunction.