Leadframe
Leadframe is one of the core components of semiconductor packaging, mainly used to support the chip and establish its electrical connection with the external circuit.
1. Leadframe Overview
1) Core Composition
Die Paddle: Provide mechanical support for the chip to ensure the stability of the chip during the packaging process.
Lead Finger: Divided into inner pins (connected to the chip pad through bonding wires) and outer pins (connected to the PCB board) to achieve electrical signal transmission.
2) Main Function
Mechanical Support: Fix the chip and prevent the molding compound from overflowing.
Electrical Connection: Bridge the chip and the external circuit through bonding wires (gold, aluminum, copper wire).
Heat Dissipation Path: Use the thermal conductivity of metal materials to transfer chip heat.
2. What is the Manufacturing Process of Leadframe?
Stamping Method
High-speed stamping of metal strips through precision molds is suitable for low-density packaging with a pin count of <100, with low cost but limited precision.
Etching Method
Use photolithography and chemical etching (such as FeCl₃) to form high-precision graphics, suitable for high-density packaging (such as QFN), low equipment cost but high material consumption.
3. What are the Material Properties of Leadframe?
1) Common Alloys
Copper-based Alloys (such as Cu-Fe-P, Cu-Ni-Si): conductivity>80% IACS, strength>450MPa, taking into account both conductivity and mechanical strength.
Iron-nickel Alloys (such as Alloy 42): The thermal expansion coefficient is close to that of silicon (4.8-5.2ppm/℃), reducing package cracking caused by thermal stress.
2) Performance Requirements
Must meet tensile strength, electrical/thermal conductivity, softening temperature resistance (>500℃), and etching/stamping processability.
4. Development Trend of Leadframe
High Density: The pin pitch is reduced from 1.27mm to 0.15mm, supporting higher integration packaging.
Pinless: QFN and DFN packages replace traditional exposed pin designs to increase PCB layout density.
Material Innovation: Develop high-strength and high-conductivity copper alloys (such as tensile strength > 600MPa and conductivity > 80% IACS) to meet ultra-thin requirements.
5. What is Leadframe Used for?
Mainly covers consumer electronics, automotive electronics, and industrial control fields, suitable for low- and medium-complexity chip packaging with I/O count < 300.
Consumer Electronics: such as QFP and SOP packages in mobile phones and home appliances;
Automotive Electronics: TO packages for power devices and DFN packages for sensors;
Industrial Control: DIP, PLCC, and other scenarios with high reliability requirements.
6. Leadframe FAQs
1) What are the common failure modes of Leadframe?
Delamination: Interface separation due to mismatch of material thermal expansion coefficient (CET);
Pin Oxidation: Copper alloys are easily oxidized and require surface coating protection;
Mechanical Fatigue: Pin bending or package stress causes fracture.
2) What is the difference between Lead Frame and substrate packaging (such as BGA)?
Structure: Lead Frame is a single-layer metal frame, and substrate packaging uses a multi-layer wiring substrate;
I/O Density: Lead Frame is suitable for medium and low density (300 pins);
Cost: Lead Frame has a lower cost, and substrate packaging has high complexity.