uBGA 380 Solder ball to pad

Hi, we used to have a RoHS package with uBGA 380 Solder ball's 0.8 mm pitch approx 15x15 mm, bump size is 0.4mm on a 0.33mm pad. Suddenly we need to use another vendor for various reasons. However, the new bump size is 0.45mm according to specs and they also tend to be at upper size of the specs after measurements, meaning closer to 0.5 than 0.4 mm. The old ones alwas stayed within the max 0.4mm bump size. Is it ok to still use the same landpatern 0.33 mm and still get the right performance in speaking of solderjoint strength?

I saw that the IPC recommend 0.35-0.40mm solder pad? 2 hundreds of a mm doesn't look very big, but hey, what about if the numbers is all wrong from the beginning, then these 0.02 mm starts counting...?? Process window you know...

Or, we got it all wrong from the beginning... /Mika

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