1.What are the core requirements for a chip carrier board?
Excellent electrical insulation: The substrate contains extremely precise circuits (linewidth/spacing can be below 10 micrometers), requiring insulation between each line. Steel, being a good conductor, is completely unsuitable for this insulation requirement.
Controllable dielectric constant and low loss factor: These affect the quality of high-speed signal transmission. Steel's electrical properties are completely unsuitable.
Matching thermal expansion coefficient with the chip: Chips are silicon-based materials with a very low coefficient of thermal expansion. Steel's coefficient of thermal expansion is much higher than silicon and ordinary PCB materials, generating enormous stress during temperature changes, leading to chip damage or solder joint cracking.
Extremely high dimensional stability and flatness: It does not deform during repeated high-temperature processes (such as welding and lamination). While cold-rolled steel is flat, its thermal stability at the micrometer scale is far inferior to that of specialized substrate materials.
Suitable for micro-hole processing and electroplating: Laser drilling of extremely small through-holes followed by copper electroplating is required to achieve conductivity between layers. Stable micro-hole metallization processes are difficult to achieve on steel.
Lightweight: Chip substrates prioritize lightness and thinness. Steel has a much higher density than commonly used materials.
2.What are the core properties of ultra-thin cold-rolled coils (such as "tearable steel")?
Excellent metallic strength and toughness: maintains good mechanical properties even in extremely thin states.
High flatness and surface finish.
Good electrical conductivity and electromagnetic shielding.
A certain degree of corrosion resistance (achievable through coating).
3.What are the typical high-end applications of ultra-thin cold-rolled coils?
Consumer electronics structural components: such as smartphone frames, battery backplates, and support plates for foldable screen hinges.
Precision components: such as shielding covers for precision instruments in aerospace, lithography machine parts, and high-precision spring sheets.
New energy field: such as metal substrates for flexible solar cells and bipolar plates for fuel cells.
4.Why do we say "no"?
Insulation vs. Conductivity: This is the most fundamental contradiction. The substrate of a chip carrier board must be an insulator (such as BT resin, ABF film, ceramics, or special engineering plastics), while steel is a conductor.
Thermal Expansion Matching vs. High Thermal Expansion: Steel's CTE is approximately 11-13 ppm/°C, while silicon's is approximately 2.6 ppm/°C. This severe mismatch means that direct use in packaging will lead to thermal failure.
Microcircuit Fabrication Compatibility: Chip carrier boards utilize lithography, etching, and electroplating processes employed in the semiconductor/PCB industry. These processes have extremely poor compatibility with steel substrates.
5.What are the potential relevance and technological implications?
Components for manufacturing equipment: These can be used to manufacture precision parts in semiconductor or substrate production equipment, such as shielding covers, components within vacuum chambers, and conveyor arms.
Packaging perimeter and heat dissipation: In advanced packaging (such as 2.5D/3D packaging), metal frames or reinforcing sheets may be used to enhance the overall structure or aid heat dissipation. Ultra-thin high-strength steel may find applications in these "non-core circuit" components.
Lead frames: Traditional chip packages (such as QFN) use copper-based or iron-nickel alloy lead frames. Ultra-thin precision steel strips could theoretically compete in this market, but issues related to electroplating, etching, and thermal matching need to be addressed. Currently, copper and Alloy 42 (an iron-nickel alloy) remain the mainstream.