Issue link: https://iconnect007.uberflip.com/i/1156271
86 PCB007 MAGAZINE I AUGUST 2019 it is also a concern for the fine traces by any process. Higher height geometry always needs higher adhesion against the same amount of force (Figure 9). Advantage of LMI Ink This unique layer structure of LMI palladium provides uniqueness for the catalyst. Table 2 shows a comparison of the types of catalyst. The colloidal tin-palladium is deposited over the substrate as a particle with stannous hy- droxide. The particle size is approximately 50 nanometers. Then, the stannous hydroxy layer is removed by acidic solution and the tin-pal- ladium alloy particles reside over the surface. This tin-palladium particle size is about 2–5 nanometers. The absorption amount of the tin- palladium particles is about 20–65 microgram per square decimeter. Next, the particle sur- face area to the deposited surface area (surface area ratio) becomes about 0.2 to 1.6. The tin- palladium alloy particle does not have 100% of the active point compared to the pure palladi- um because of alloying with tin and residual of stannous hydroxide. The effective active point is considered less than 50%. Also, the whole particle surface could not work for the deposi- tion. It is considered about half of the surface area. Therefore, the effective surface ratio of the tin-palladium catalyst becomes 0.05 to 0.4 or less. The ionic palladium is deposited over the substrate as 5–10-nanometer particle size. The absorption amount of the palladium particle is about 10 to 35 microgram per square deci- meter. Then the particle surface area ratio be- comes about 0.1 to 0.4. The LMI palladium layer weight is 6 micro- grams per decimeter when it is deposited 5 nanometers over the substrate. The surface ar- ea ratio is obviously 1.0. And this ratio would not be changed when the deposited catalyst layer thickness is changed. This is a great ad- vantage to get stable catalytic activity and to reduce the catalyst cost. When the particle is a sphere, and the top half hemisphere of the particle is considered the active area for the copper deposition, the active particle surface area ratio is 1.57 for the primitive cubic pack. A surface area ratio less than 1.6 means the palladium catalyst particles are not 100% covered over the substrate, and this indicates that the conventional processes do not cover the entire substrate surface. By contrast, if the particles are packed as hex- agonal close-packed, then the active particle surface area becomes 2.03 (Figure 10). This supports the deposition theory that is sche- matically described in Figure 2. The organic solvent system of the palladi- um ink improves wettability to the substrate compared to conventional water-based sys- Figure 9: Force difference by trace height. Table 2: Catalyst comparison by type. Figure 10: Particle pack types.