every trace of corrosion must be neutralized and removed.
even the via's must be cleaned out. no use removing the top and bottom corrosion unless you remove the via corrosion. and the corrosion under the headers.
and if it has made its way as far as the housings for the switch rows / columns then these will have to be replaced also
on 2 occasions i have had to cut and replace several inches of row / column  wire because when you stripped the insulation back the conductor was green / white with corrosion