take a example, if Ib=+, this means Vin flow to Op, or Op flow to Vin?
IB’s direction depends on the input structure and more. NPN goes in, PNP comes
out, CMOS and JFET is just leakage and its direction is unknown. Bipolar op
amps where IB cancellation is done, direction can be either way. + is going in
and – is coming out.