TCNCP requires OSP surface finish (low cost, fine pitch process margins v/s Sn based finishes, controlled solder wetting v/s EPIG finish). However this requires use of fluxing agents in NCP material, to remove oxides during thermal compression bonding. Also it is critical to remove any residual OSP from the pad, since the OSP can combine with by-products of the fluxing reaction and lead to NCP entrapment. This therefore, requires an OSP pre-clean step, which comprises of plasma-treatment & chemical deflux, ahead of TCB.
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