Within surface mount technology processes -- joining IC chips to an interconnect package -- coplanarity is a measurement of the height of interconnect leads and/or C4 bumps, to see if they will solder uniformly when mated.
The measurement of coplanarity of separate points in space, as in measuring whether or not flip chip components are coplanar, is difficult. The difficulty arises because of the relative wideness of spacing of the interconnects or C4 bumps, the planarity of which must be compared to each other independent of the substrate, because substrate flatness is not an essential component of the coplanarity parameter.
