SPI Silver Paste Plus™
Some physical property values of this product
SPI Silver Paste Plus is a suspension of a specially prepared silver powder
combined with a proprietary organic binder system. The product is designed
to produce electrically conductive paths, patterns, or films over
nonconductive surfaces. The product is designed for either air drying or
low temperature curing for applications on substrates which will not
generally tolerate high-temperature firing. The product can be used to
produce electrically conductive paths on paper, plastic, rubber, cloth,
wood , etc. and may be applied by dip, spray, brush, stylus, syringe or even
screen printing.
The selection of an air drying composition, such as SPI Silver Paste Plus
is dependent on the application and the performance of any other silver
composition should not necessarily be used as an extrapolation of what to
expect from Silver Paste Plus. The final properties of the end product,
after application can themselves depend to some degree on the method of
application.
Generally speaking, higher metal contents result in maximum conductivity
and load carrying capabilities, and are more easily soldered. The paste
can be diluted somewhat with SPI # 5004-AB
Silver Paint Thinner
Bonding Substrates to Heater Heads
SPI Silver Paste "Plus" was developed to provide optimum adhesion of substrates to heater heads
for thin film superconductor research. In order to obtain optimum properties, we suggest the
following procedure as a starting point for "fine tuning" your own protocol:
- Begin at room temperature. In this stage, all volatile organics are beginning to evaporate.
The silver particles are beginning to forma uniform network which permits the continuous escape
of any trapped vapors.
- Additional heating from 60 to 150 °C. The organic binder depolymerizes without carbon or
graphite formation and is expelled from the system without disruption of the uniform network
of silver particles.
- Final annealing in the range of 150 to 200 °C. At this point the uniform network of silver
particles sinters together, producing the superior adhesion properties for which this product
was developed.
Note: Larger substrates my require use of higher temperatures.
Proper preparation of the bond will provide uniformity in heat transfer characteristics
throughout the silver layer along with easy release of the substrate from the heater head
using minimum mechanical stress.
Storage and shelf life
Normally speaking, this kind of product can be stored at room temperature.
However, there is a thermodynamic phenomenon that tends to cause a
separation of the silver solids from the extender in the vicinity
of the high radius of curvature near the nozzle. The result of this
separation is that when the tube is used, the first to some out is a
thinner (extended) rich "squirt" and while this is not going to caused
the demise in properties of this product for most uses, the point is that
this is a problem and the way to help mitigate the impact of this separation,
is to store the tubes upside down on their heads, refrigerated.
The refrigeration results in a significantly slow down of the tendency
of the silver colloid to separate out and migrate away from the high radius
of curvature end (e.g. the nozzle) . And standing the tube on its head
makes possible the use of gravity itself to help reduce the rate of colloid
separation.
The main point of caution here is that after retrieval from the
refrigeration, one must be certain to wait until the product has warmed
to room temperature to avoid any moisture condensation into the product.
The SPI Silver Paste Plus will exhibit, in addition to a reasonably fast
drying rate, even at room temperature, good adhesion to most substrates
and high conductivity. It can be used to produce electrically conductive
patterns on surfaces of paper, film, plastic, rubber, or wood as well as
on conventional ceramic substrates. The product, when sold in bulk, has
found acceptance in the manufacturing of tantalum capacitors to metallize
the anode, making it a good electrical contact and solder receptive surface.
The product is one of the highest silver content paste products available
anywhere and is free of any glass frit, and is suitable for brush, stylus
or machine banding application where its somewhat higher conductivity is
desired. It is also widely used in the printed circuit board repair
industry where again, the high viscosity, high silver solids and better
solderability make it an attractive product.
In order to reduce the viscosity and percent silver solids, the paste
product can be thinned down with butyl acetate.
Safety and handling:
This product contains organic solvents and materials. It
should be handled using the following precautions:
- Use with adequate ventilation
- Avoid prolonged contact with skin
- Avoid prolonged breathing of vapor
- Keep away from sparks and open flame
Other characteristics of SPI Silver Paste Plus:
%Silver Solids in paste: 70%
Viscosity at 25 °C:
Pa.S 38-54
Brookfield HBF
Spindle 4
RPM 10
Thinner: n-butyl acetate
Cure: Room temperature or 1 hour at 100 °C / 212 °F
Sheet resistivity: < 0.05 ohms/square (25 µm film thickness)
Coverage: 72 cm2/gram (When wet film thickness is 50µm)
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Friday February 03, 2012
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