Silver flakes

Metal flakes in a suspension are common. For example, aluminum paint is actually aluminum flakes suspended in paint. Upon application, the flakes orient themselves parallel to the surface and give very good coverage. Similarly, silver flakes can be applied to give good electrical conductivity. 

UV curable flexo ink for RFID antennas Radio frequency identification (RFID) devices and contactless smart cards are capable of uniquely identifying an individual or object when they are interrogated by an external radio frequency signal. Recently, a process of printing with the use of UV curable conductive flexo inks has been introduced. The inks are based on polyfunctional acrylates with silver flakes added for the electrical conductivity. The advantages of these inks are ... 

Names silver powder, silver flakes, atomized silver powder, silver/palladium powder and flakes... 

A model was developed to analyze the conductivity of materials filled with conductive particles. This model was compared with experimental data for four commercial adhesives containing silver flakes. It was discovered that the resistivity is higher in the planar direction (thin films) than in three-dimensional space. Figure... 

Solution processable conductors come in three main elasses metals, metal oxides or organics. Printed metals, most notably as eleetrodes or RFID antennae, are mainly obtained by using partiele-based inks. Silver or gold partiele inks are eommercially available. Evonik has developed silver printing pastes, sueh as Silver 30 SN, a formulation of silver flakes in organie solvents, optimized for screen printing (Figure 2.6). 

Silver epoxies consist of silver flakes suspended in an adhesive carrier. The materials are designed so that the silver flakes touch each other when cured and provide an electrically conductive path. Generally, silver epoxies have lower conductivity than solder paste, but usually have the advantage of a reflow temperature lower than the temperature required for solder paste. 

Thixotropy occurs when clusters of filler particles break up and fluidity increases. At rest, fillers exist in clusters and their strength, size, and shape determine the static viscosity of the adhesive. The total surface area of the filler particles also contributes to static viscosity. Shear thinning occurs when the clusters, such as silver flake in silver-filled epoxies, break apart and viscosity decreases then, as stress is removed, the clusters form again and viscosity increases. ... 

In adding conductive filler to an insulating resin, the volume resistivity changes slowly until a critical level of filler is reached, called the percolation point. The percolation point occurs when the resistivity drops abruptly, then continues to drop slowly (Fig. 2.11). " Almost continuous linkage of metal particles occurs at the percolation point where typical filler volumes for silver flakes are 25-30%. According to the percolation theory, there is a minimum critical volume of filler required for electrical conductivity in a polymer at which each filler particle must contact two other particles. A misconception in the use of silver flakes is that increasing the number of contacts lowers volume resistivity. Actually, the converse is true because, once the percolation point has been reached, each additional contact adds resistance. Thus, increasing the particle size can increase conductivity since the total number of contacts for a fixed volume decreases." ... 

McNeilly K, Pemice RF. Silver flake increases performance of conductive adhesive. Adv... 

Leong WH. Developing an underfill process for dense flip-chip apphcations. In Proc. 1996 lEEE/CPMT Int. Electronics Mfg. Technol Symp. Oct. 1996 10-17. lost EM, McNeiUy K, Sexton P. Silver flakes for state of the art conductive adhesive apphcations. Proc. Seventh Int. Microelectronics Conf. 1992 442-8. 

The processing and surface preparation of silver particles is critical to their performance as a filler. The first step in manufacturing silver flakes is to produce silver powder. Powdered silver may be produced by chemical precipitation, electrolytic precipitation, or melt atomization. Most commercially available silver powders are precipitated by reducing silver from a silver nitrate solution. Particle sizes of powdered silver range from submicron to 5 pm." Silver powders are selected based on size and... 

Ferro silver flake with mid-range with good rheological 0... 

The type of lubricant used may have a major effect on the volume resistivity of a cured epoxy. In one example, a conductive epoxy formulated with silver flakes using a thiol lubricant in a proprietary solvent showed consistently higher volume resistivity (4—5 orders of magnitude) than a similar composition where the silver flakes were coated with a fatty acid lubricant. ... 

The surface area of the filler has a pronounced effect on viscosity. As the surface area of silver-flake filler increases, the frictional forces between particles increase... 

Add silver-flake flUer (Ferro s 26LV) to the resin mixture at 80% by weight and blend in a three-roll mill until homogeneous. 

Technical Data Sheets for Adhesives, Ablestik Electronic Materials Dec. 2003. McNeilly K, Pemice RE. Silver Flake Increases Performance of Conductive Adhesive. Advanced Packaging. Jun./Jul. 1999. 

Pandiri SM. The Behavior of Silver Flakes in Conductive Epoxy Adhesives. Adhesives Age. Oct. 1987. 

Jost EM, McNeilly K, Sexton P. Silver Flakes for State of the Art Conductive Adhesive Applications. Proc. 7th Inti. Microelectronics Conf. 1992 422-428. 

Silver Flake 84/ Ferro, Degussa Fligh-purity silver flake low viscosity and non-ionic lubricant 4.5-5.6 0.15-0.30 <0.10 <0.50 20.0 10.0 5.0... 

Silver Flake 80/ Ferro, Degussa Fligh-purity silver flake handling characteristics of flake and powder 3.2-5.0 0.40-0.70 <0.10 <0.50 ... 

Silver Flake 65/ Ferro, Degussa Fine silver flake with high-surface area 3.0-4.5 0.80-1.40 <0.10 <0.70 30.0 11.0 3.0... 

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