2,808
edits
Changes
no edit summary
<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s6">Preparation</p></td><td><p class="s6">Substrate</p><p class="s6">Material</p></td><td><p class="s6">Application by</p></td><td><p class="s6">Firing Temperature [°C]</p></td><td><p class="s6">Properties</p></td><td><p class="s6">Silver Content [wt%]</p></td></tr><tr><td><p class="s6">Argonor N92</p></td><td><p class="s6">glass, ceramics</p></td><td><p class="s6">paint brush, spray gun</p></td><td><p class="s6">530 - 650</p></td><td><p class="s6">Viscosity</p><p class="s6">500 – 1.000 mPa·s, good solderability</p></td><td><p class="s6">65</p></td></tr><tr><td><p class="s6">Argonor</p></td><td><p class="s6">glass,</p><p class="s6">ceramics</p></td><td><p class="s6">screen</p><p class="s6">printing</p></td><td><p class="s6">530 - 650</p></td><td><p class="s6">Viscosity</p><p class="s6">10 – 15.000 mPa·s, good solderability</p></td><td><p class="s6">65</p></td></tr></table>
Fig. 8.2: Solar cell with print pattern of ARGONOR N920
===8.2.2 Conductive Paints and Adhesives===
Conductive paints are precious metal preparations in liquid or paste form. They contain the metal filler material, fine silver particles as conductive pigments mostly in flake form, a paint compound on artificial resin basis, and an organic solvent ''(Table 8.3)''. The solvent evaporates during drying in air or by aging at slightly elevated temperatures. This allows the silver particles to connect metallically and form conductive paths ''(Fig. 8.3)''.
Conductive adhesives are used mostly for mechanical bonding with low thermal impact. As the adhesive components high-polymer organic substances such as epoxy resins and mixed polymers are mostly used. They are made electrically filler materials such as flake shaped silver powders (70 – 80 wt%). Silver based conductive adhesives are available as single or two component adhesive systems. Both types are hardening without the application of pressure.
Table 8.3: Silver Paints, Conductive Pastes, and Conductive Adhesives
<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s6">Preparation</p></td><td><p class="s6">Substrate</p></td><td><p class="s6">Application</p></td><td><p class="s6">Drying</p></td><td><p class="s6">Properties</p></td><td><p class="s6">Usage</p></td><td><p class="s6">Area</p></td></tr><tr><td/><td><p class="s6">Material</p></td><td><p class="s6">by</p></td><td><p class="s7">[°C]</p></td><td/><td><p class="s6">Amount</p><p class="s7">[g/100 cm²]</p></td><td><p class="s6">Resistance</p><p class="s7">[<span class="s10">S </span>/m²]</p></td></tr><tr><td><p class="s7">AROMAL 38</p></td><td><p class="s6">glass, plastics</p></td><td><p class="s6">spraying, immersion,</p></td><td><p class="s7">RT,</p><p class="s7">30 min</p></td><td><p class="s6">hard well conducting</p></td><td><p class="s7">0.5 - 2</p></td><td><p class="s7">< 0.1</p></td></tr></table>
Conductive paints and adhesives have broad applications in electrical and electronic engineering. They are used for example for the contacting of film resistors, mounting of terminal wires, conducting electrostatic electricity, or contacting components at low temperatures.
The mechanical strength of the bond connections depends mostly on the selected hardening temperature ''(Fig. 8.4)''.
Fig. 8.3:
Flexible keyboard contact pattern
printed with AUROMAL 170
Fig. 8.4:
Shear force of an adhesive joint
(silver adhesive AUROMAL K 20) as a function of
the hardening temperature
===8.2.3 Precious Metal Flakes===
To obtain certain desired physical properties of preparations the dispersed precious metals in flat flake-like particles (generally called “flakes”) are needed. These are produced by milling fine metal powders in the presence of milling additives or agents. The properties of these metal flakes, i.e. silver flakes (ability to disperse easily, flow characteristics, electrical conductivity) are strongly dependent on the particle shape and size as well as on the type of milling agents used. Fig. 8.5 illustrates through SEM photos a type of rather fine silver flake (medium particle size 4 – 6 µm) (a) and another one with relatively large flat but thin flake shapes (particle size 8 – 11 µm) (b). Typical commercial silver flake types are listed with their respective properties in Table 8.4. Gold and platinum can also be produced as powder flakes. By volumes used they are however of lesser commercial importance.
Fig. 8.5: SEM photos of silver flakes (a) fine grain (b) large flat
Table 8.4: Typical Commercial Silver Flake Types
<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s6">Type of Flake</p></td><td><p class="s6">F56</p></td><td><p class="s6">B190</p></td><td><p class="s6">ES4</p></td></tr><tr><td><p class="s6">Main characteristics</p></td><td><p class="s6">Low tap density</p></td><td><p class="s6">Very fine</p></td><td><p class="s6">Pure, wide grain size distribution</p></td></tr><tr><td><p class="s6">Silver content [wt%]</p></td><td><p class="s6">>99.0</p></td><td><p class="s6">>99.0</p></td><td><p class="s6">>99.7</p></td></tr><tr><td><p class="s6">Med. Grain size [µm] Tap density</p></td><td><p class="s6">3 - 8</p></td><td><p class="s6">4 - 6</p></td><td><p class="s6">9 - 13</p></td></tr><tr><td><p class="s6">DIN/ISO 3953 [g/cm<span class="s8">3</span>]</p></td><td><p class="s6">0.7 - 1.1</p></td><td><p class="s6">2.1 - 2.7</p></td><td><p class="s6">2.7 - 3.6</p></td></tr><tr><td><p class="s6">Spec. Surface area B.E.T. [m<span class="s8">2</span>/g]</p></td><td><p class="s6">0.7 - 1.1</p></td><td><p class="s6">0.3 - 0.7</p></td><td/></tr><tr><td/><td/><td/><td/></tr></table>