Eutectic die attach is a reliable bonding method that uses a eutectic alloy to join a semiconductor die to a substrate. This page explains how eutectic bonding works and which silicon wafers and gold-coated wafers are commonly used by researchers in eutectic die attach trials.
What Is Eutectic Die Attach?
Eutectic die attach is a bonding technique used in microelectronics to attach a semiconductor die to a substrate. In this process, a eutectic alloy is used to join the die and the substrate, forming a strong and reliable bond.
A eutectic alloy is a mixture of two or more metals or alloys that has a single, well-defined melting point and solidifies as a single phase. When the eutectic alloy is heated above its melting point, it becomes a low-viscosity liquid that can flow and fill the gaps between the die and the substrate. As the alloy cools and solidifies, it forms a strong bond between the die and the substrate.
Eutectic die attach is often used in high-temperature applications, as eutectic alloys can withstand elevated temperatures without degradation of their mechanical or electrical properties. It is also commonly applied in the assembly of high-power devices, where the strong bond and low thermal resistance of the eutectic alloy help to efficiently dissipate heat generated by the device.
What Substrate Specifications Are Commonly Used in Eutectic Die Attach Trials?
The substrate used for eutectic die attach can vary depending on the specific application and performance requirements of the device being assembled. However, several substrate specifications are commonly used in eutectic die attach trials, including the following:
Material
The substrate material is often a ceramic, such as aluminum oxide (Al₂O₃) or beryllium oxide (BeO). Other materials, including silicon, glass, or metal substrates, may also be used depending on the application.
Size
The substrate size is typically selected to match the size of the die being attached, or to be slightly larger than the die.
Surface Finish
The surface of the substrate is usually polished to provide a smooth and flat surface for proper die attachment.
Thickness
Substrate thickness can vary but is typically in the range of 100 to 500 micrometers.
Thermal Conductivity
Thermal conductivity is a critical parameter, as it affects the ability of the eutectic alloy to dissipate heat from the die. High-thermal-conductivity substrates, such as diamond or copper–tungsten, are commonly used in high-power applications.
Coefficient of Thermal Expansion (CTE)
The coefficient of thermal expansion of the substrate is an important consideration, as it should closely match the CTE of the die to minimize stress and prevent cracking during thermal cycling. CTE matching can be achieved either by selecting a substrate material with a similar CTE or by introducing an intermediate layer, such as a thin metal foil.
Metallization
The substrate may be metallized to provide electrical contacts for the die and to ensure reliable electrical connectivity between the die and the substrate.
