In order to overcome the problems facing Cr-Cu-Au metallization, such as discoloration, diffusion of Cu into Au, a four-layer metallization Cr-Cu-NiP-Au is demonstrated on alumina substrate for microwave integrated circuit (MICs). A amorphous and nonmagnetic NiP barrier layer is used to avoid the diffusion of Cu into Au through the grain boundaries, which are the low activation energy path for diffusion at moderate temperature.
In this view, properties of Cr-Cu-NiP-Au metallization, such as sheet resistance, solderability, bondability and adhesion strength, are evaluated. Further integrity of Cr-Cu-NiP-Au structure is evaluated by subjecting to this structure to multiple temperature cycles test. Visual observation is carried our before and after the thermal cycling test. No degradation is observed as the consequence of thermal cycling test. Test and evaluation are carried out for a multi-section broadband power divider (1 : 2) on this metallization (metal thickness 12-12.5 microns) in the 0-6 GHz frequency range. Insertion loss, return loss and isolation are comparable with Cr-Cu-Au (metal thickness 5.0-6.0 microns). Performance of the power divider and properties of this metallization system reveal its novelty over the existing.
Rakesh Kumar Sharma,
Kamlesh C. Pargaien,
"A Novel Four Layer Metallization for Microwave Integrated Circuits," Progress In Electromagnetics Research Letters,
Vol. 29, 175-184, 2012. doi:10.2528/PIERL11120607