Results and Discussions
Prior to the contact co-firing process, the average finger widths, as presented in Table I, fall within the range of 51µm to 55µm. Post-firing, the width of the Ag+Cu bi-layer stack notably expands to 56µm due to most likely ductile behavior of copper, while concurrently attaining a height of 10µm. Although the widths of the fingers shrink for each contact types, there is no ghost finger formation on the surface after firing process as shown in Fig. 2. In comparison, the width of the conventional screen-printed Ag contacts is slightly narrower. However, the metal fractions of the contacts, which are related to glass frit used in this study, are similar, measuring 5.1% for Ag, 5% for in-house Ag, 5.4% for the Ag+Ni bi-layer, and 5.7% for the Ag+Cu bi-layer, respectively. These are closely aligned with the approximated 5% metal fraction of commercial Ag contacts [23], [24]. As tabulated also in Table I, the width of the fingers varies depending on the metal used, a phenomenon potentially attributable to disparities in wetting and concentration within each paste. The Ni contact exhibits the narrowest average width of 47µm post-firing, having commenced at 55µm prior to the firing process. This highlights the increased tendency for Ni fingers to sinter and compact, forming into a continuous line. For the finger height of the printed fingers, contacts with in-house prepared Ag paste gives the tallest finger which suggests that the surfactant and thixotropic agent used in the paste, although the same type is used in each paste, correlate with Ag particles better than the others.
Table I The average finger widths and height before and after contact co-firing process