## 3 Results
### Palladium Chemical Plating Characterization  
To obtain an adherent deposited layer, is not sufficient that the copper substrate be cleaned, it should also be not damaged by the PCP. The same PDP procedures employed for samples #6, #8, and #10, were used as pre-deposition for PCP (obtaining samples #6C, #8C and #10C, respectively) to evaluate which one was the most protective one towards Cu base material, since copper is severely attacked by the high concentration of ammonia present in the PCP solution. In addition, the effectiveness of the PCP is valuable for application in which deposits in the micron range are requested. Each PDP pre-deposition was carried out immediately before PCP. The PCP depositions were performed without stirring at a temperature of 55 \({}^{\circ}\)C and for a duration of 60 min. In Figure 5, it is possible to observe the samples 7 days after the deposition. The copper substrate, which was not covered with a protective PDP, although it was not immersed in the solution, was strongly corroded by the ammonia vapours. In the bottom part of the samples, where the pre-deposition was carried out, a homogeneous and shiny palladium deposit is visible. After one week, sample #6C underwent a strong exfoliation, while the other two samples appeared intact to the naked eye. As can be seen from Figure 5, PCP sample #6C showed the copper substrate under the palladium exfoliation. Our hypothesis on the failure of this sample regards the poor stability of the PDP pre-deposition performed on this sample. As already observed for PDP sample #12, the relaxation of residual internal stresses developed by Pd thin film on copper was the origin of the detachment of the PDP+PCP palladium coating on sample #6C, and occurred in a time range longer than the 7 days during which the PDP pre-depositions were monitored.  
The deposits obtained were analysed using XRF [49; 50], the total palladium film thicknesses obtained summing PDP+PCP processes are shown in Table 5. The average values and the standard deviations were the result of three measurements carried out in different spots that were randomly chosen.  
Figure 5: Palladium chemical plating samples after 7 days of aging. Sample number is reported on the uncoated part of each sample (from left to right, samples #6C, #8C, #10C).  
In Figure 6 it is possible to appreciate the deposits analysed using OM, 7 days later in the deposition process. Deposit #10C was the most homogeneous, free of defects and even the thickest, while sample #6C presented extended exfoliations which brought to light the characteristic colour of the copper substrate; sample #8 showed cracks.  
Sample #10C, obtained by the combined process of PDP + PCP applying the PDP and PCP solutions already exploited by [PERSON] and [PERSON] [PERSON] and [PERSON] (2008) was the best result in terms of Pd film adhesion, homogeneity, and absence of surface defects (cracks, blisters or exfoliations). In the work of [PERSON] and [PERSON], the authors stated a deposition rate of over 2.5 \(\upmu\)m/h for the PCP on copper. In the present work, applying the same conditions of the aforementioned work, the authors obtained a growth of 1.78 \(\upmu\)m of Pd in 1 h. The discrepancy between the two values can be due to two main factors. In [PERSON]'s work, the PDP pre-treatment was longer and another pre-treatment based on a tin electroless bath was anticipated, which altered the catalytic activity of the surface on the oxidation of hypophosphite in the PCP bath. Second, the thickness determination method used in the present work for the PDP+PCP samples (X-ray spectroscopy) was more accurate than the gravimetric method applied by [PERSON] and co-worker.