How do i make this formula not case sensitive?

so im using this formula to return a value based on the letter U in a cell:

=SUM(LEN(BO5:BO14)-LEN(SUBSTITUTE(BO5:BO14;"U";"")))

but how do i make it not case sensitive, as it stands now, it only registers capitals, and its the other way around, if i make the u small in the formula, can you come around this?

thanks