Alumina PCBs Resistant
Alumina PCBs are circuit boards made with alumina ceramic instead of the more common FR-4 laminates. They are used in applications requiring high thermal conductivity, electrical insulation and durability in harsh environments. Unlike other types of PCBs, alumina substrates can operate at very high temperatures. They also have superior mechanical strength. The combination of these attributes makes them a popular choice for demanding electronics, radar modules, guidance systems and radio equipment in land, air and sea applications where reliability is essential.
The corrosion resistance of alumina ceramics depends on the structure, microstructure and phase composition. The corrosion behavior is governed by a complex interaction between the ions and oxides. Alumina is a multicomponent system consisting of three phases, namely alumina, aluminum hydroxide and silicon dioxide (Al2O3). The corrosion mechanism of alumina pcbs varies with the concentration and temperature of the solution, which affects its reactivity.
Corrosion of alumina pcb can be divided into two stages: cold isostatic stress corrosion and hot corrosion. Cold isostatic stress corrosion is characterized by the formation of a corrosion layer on the surface, which slows down the penetration of acid into the interior. On the other hand, hot corrosion is a result of the oxidation of alumina by hydride species at elevated temperatures. The oxidation of alumina is promoted by oxygen and nitrogen, which form a complex with alumina oxides at high temperatures.
Are Alumina PCBs Resistant to Corrosion?
Another factor that determines the corrosion resistance of alumina is the presence of rare-earth ions. The addition of La2O3 improves the resistance of alumina to acid solution by delaying the corroding process. The corrosion resistance of alumina is also influenced by the microstructure, phase composition and crystallographic orientation.
Despite their robustness, alumina substrates are vulnerable to cracking due to excessive tensile stresses, grinding damage and component overloading. Cracks reduce the insulating properties and may compromise the integrity of the circuit board.
Alumina substrates permit vacuum brazing of metal walls or covers to contain and hermetically seal sensitive components, which improves resistance to environmental ingress. Moreover, they can be soldered to other materials using active brazing alloys that chemically bond with the substrates. In addition, their low thermal expansion coefficient minimizes thermal stresses between alumina and contacting components, thereby reducing the likelihood of thermomechanical stress cracking. This feature enables alumina circuit boards to withstand cyclic heating and cooling. The insulating property of alumina also protects components from shocks and vibration.