Conductive adhesives that can attach at low temperatures instead of solders
We are developing uniquely shaped silver powder, which is called TK silver powders and silver paste which utilizes them with our original technologies in the world. The TK PASTE® is a conductive adhesive with a variety of characteristics, taking advantage of the unique features of TK silver powder, such as "forming a conductive path with a small amount of silver," "having a light apparent specific gravity," "having a uniform particle size," and "sintering at low temperatures."
Why conductive adhesives are required?
In miniaturization of electronic devices and development of wearable devices, the use of resin components and mounting of components on FPCs (flexible boards) are increasing.
Conventionally, solder has been used exclusively for conductive bonding of parts, but some resin parts and FPCs have low heat resistance and are damaged by heating during soldering. Therefore, there is a growing need for conductive bonding materials that can be used in place of solder.
Conductive adhesives have long been used as conductive bonding materials that can be bonded at lower temperatures than solder. Conductive fillers are dispersed in epoxy or urethane binder resins, and after bonding, these fillers form conductive paths to achieve conductive bonding.
The conductive fillers used include metal powders such as copper, nickel, and silver, and carbon-based materials such as graphite and carbon nanotubes (CNTs).
Conductive adhesives using these fillers, which use carbon-based materials, have higher resistance values than those using metal powders, and may not provide the desired conductivity.
In addition, if metal powders such as copper and nickel are used, the electrical conductivity may gradually deteriorate due to oxidation or corrosion of the filler, which may impair the long-term reliability required for electronic devices.
For the above reasons, silver, which is a precious metal, is often used as a filler for conductive adhesives, and conductive adhesives (silver pastes) containing silver of various particle shapes and particle sizes are on the market.
Characteristics of our conductive adhesives
Since the cost of the adhesive increases in proportion to the content of silver, the amount of silver powders to be blended should be as small as possible. However, in order to form a stable conductive path and to develop conductivity, it is necessary to blend a certain amount of silver powder or more.
Conventional silver paste using silver powder having a general shape such as a spherical shape or a flaky shape requires about 70 to 80% of silver powder by weight, which raises the problem of high price of pastes.
With its proprietary patented technology, we are able to produce specially-shaped silver powder (TK silver powder) that includes the shape of chest-nut like and large flake.
These silver powders are characterized by a bulk specific gravity of about 5g/cm³ of common silver powders, whereas the bulk specific gravity of TK-silver powders is as low as 2g/cm³. In other words, when TK silver powder is used as a filler, even if the amount of silver mixed (weight) is small, a large amount of silver powder can exhibit high conductivity by efficiently forming a conductive path.
The silver paste containing this specially shaped silver powder is TK PASTE®. Even if the silver content is as low as 50% by weight, the silver paste exhibits the same conductivity as conventional silver paste, and therefore cost reduction can be achieved while maintaining conductivity and reliability.
For example, if a silver paste containing 80% by weight silver (density of about 4g/cm³) is replaced with a TK PASTE® (density of about 2g/cm³), the running cost of TK PASTE® can be halved if the unit price of silver paste (price per kilogram) is the same.