pull the ribbon off in an angle of 180° and measure the force by a force meter. The industrial requested peel-off
force in this test is Fpeel > 1 N/mm of ribbon width. A slight decline of the peel-force is visible towards lower
silver content. However, all pastes down to a silver content csilver = 36 % reach a sufficient peel-off force Fpeel > 1
N/mm.
2.2.2. Glass frit as a sintering aid
Reducing the silver content the sinterability becomes more and more important for the internal stability of the
bus bar paste. As a sintering aid, the glass frit starts wetting the particle surface already at temperatures T 450
C. The wetting affects the diffusion flow between the particles and thus, increases the sintering by lowering the
starting temperature of the sintering. We combine different oxides in our glass frit which fulfill the function of
contacting the substrate, the wetting of the surface and the lowering of particle oxidation for a paste including base
metals. In this study we optimize a metal paste with an Ag content cAg = 30 % starting with a peel-off force Fpeel =
1 N/mm containing glass frit A and glass frit B.
Fig. 4: Measured peel-off force for a variation in the compounding of the glass frit. Our frit contains two parts, Frit A and Frit B. Frit A is
necessary for the contact of the bus bar to the substrate whereas Frit B lowers the wetting temperature of the glass frit. Thus the surface
diffusion on the metal particles starts at lower temperatures and the sintering increases. The optimum frit setup increases the peel-off force to F
= 1.7 N/mm with cFrit A = 3 % and cFrit B = 3.5 % relative to the weight of the paste.
Figure 4