Applications of Copper Foil in Chip Packaging

Copper foil is becoming increasingly important in chip packaging due to its electrical conductivity, thermal conductivity, processability, and cost-effectiveness. Here is a detailed analysis of its specific applications in chip packaging:

1. Copper Wire Bonding

• Replacement for Gold or Aluminum Wire: Traditionally, gold or aluminum wires have been used in chip packaging to electrically connect the chip’s internal circuitry to external leads. However, with advances in copper processing technology and cost considerations, copper foil and copper wire are gradually becoming mainstream choices. Copper’s electrical conductivity is approximately 85-95% that of gold, but its cost is about one-tenth, making it an ideal choice for high performance and economic efficiency.
• Enhanced Electrical Performance: Copper wire bonding offers lower resistance and better thermal conductivity in high-frequency and high-current applications, effectively reducing power loss in chip interconnections and improving overall electrical performance. Thus, using copper foil as a conductive material in bonding processes can enhance packaging efficiency and reliability without increasing costs.
• Used in Electrodes and Micro-Bumps: In flip-chip packaging, the chip is flipped so that the input/output (I/O) pads on its surface are directly connected to the circuit on the package substrate. Copper foil is used to make electrodes and micro-bumps, which are directly soldered to the substrate. The low thermal resistance and high conductivity of copper ensure efficient transmission of signals and power.
• Reliability and Thermal Management: Due to its good resistance to electromigration and mechanical strength, copper provides better long-term reliability under varying thermal cycles and current densities. Additionally, copper’s high thermal conductivity helps rapidly dissipate heat generated during chip operation to the substrate or heat sink, enhancing the thermal management capabilities of the package.
• Lead Frame Material: Copper foil is widely used in lead frame packaging, especially for power device packaging. The lead frame provides structural support and electrical connection for the chip, requiring materials with high conductivity and good thermal conductivity. Copper foil meets these requirements, effectively reducing packaging costs while improving thermal dissipation and electrical performance.
• Surface Treatment Techniques: In practical applications, copper foil often undergoes surface treatments such as nickel, tin, or silver plating to prevent oxidation and improve solderability. These treatments further enhance the durability and reliability of copper foil in lead frame packaging.
• Conductive Material in Multi-Chip Modules: System-in-package technology integrates multiple chips and passive components into a single package to achieve higher integration and functional density. Copper foil is used to manufacture internal interconnecting circuits and serve as a current conduction path. This application requires copper foil to have high conductivity and ultra-thin characteristics to achieve higher performance in limited packaging space.
• RF and Millimeter-Wave Applications: Copper foil also plays a crucial role in high-frequency signal transmission circuits in SiP, especially in radio frequency (RF) and millimeter-wave applications. Its low loss characteristics and excellent conductivity allow it to reduce signal attenuation effectively and improve transmission efficiency in these high-frequency applications.
• Used in Redistribution Layers (RDL): In fan-out packaging, copper foil is used to construct the redistribution layer, a technology that redistributes chip I/O to a larger area. The high conductivity and good adhesion of copper foil make it an ideal material for building redistribution layers, increasing I/O density and supporting multi-chip integration.
• Size Reduction and Signal Integrity: The application of copper foil in redistribution layers helps reduce package size while improving signal transmission integrity and speed, which is particularly important in mobile devices and high-performance computing applications that require smaller packaging sizes and higher performance.
• Copper Foil Heat Sinks and Thermal Channels: Due to its excellent thermal conductivity, copper foil is often used in heat sinks, thermal channels, and thermal interface materials within chip packaging to help quickly transfer heat generated by the chip to external cooling structures. This application is especially important in high-power chips and packages requiring precise temperature control, such as CPUs, GPUs, and power management chips.
• Used in Through-Silicon Via (TSV) Technology: In 2.5D and 3D chip packaging technologies, copper foil is used to create conductive fill material for through-silicon vias, providing vertical interconnection between chips. The high conductivity and processability of copper foil make it a preferred material in these advanced packaging technologies, supporting higher density integration and shorter signal paths, thereby enhancing overall system performance.

2. Flip-Chip Packaging

3. Lead Frame Packaging

4. System-in-Package (SiP)

5. Fan-Out Packaging

6. Thermal Management and Heat Dissipation Applications

7. Advanced Packaging Technologies (such as 2.5D and 3D Packaging)

Overall, the application of copper foil in chip packaging is not limited to traditional conductive connections and thermal management but extends to emerging packaging technologies such as flip-chip, system-in-package, fan-out packaging, and 3D packaging. The multifunctional properties and excellent performance of copper foil play a key role in improving the reliability, performance, and cost-effectiveness of chip packaging.