The Role of Baking in IC Packaging
IC packaging involves connecting the circuit pins on a silicon wafer to external terminals for connection with other devices. The packaging form serves as the housing for installing, fixing, sealing, and protecting the semiconductor integrated circuit chip, enabling the connection between the internal chip and external circuits via wires from the chip's contact points to the package's pins, which then link to the printed circuit board's wires.
After IC packaging, baking is typically performed to ensure the integrity of internal components and structures, and to eliminate moisture, solvent residues, and other volatile substances.
Ⅰ.Functions of Post-Packaging Baking
1.Moisture and Volatile Substance Removal:Chips absorb moisture and other volatile substances during manufacturing, storage, and transportation. These impurities can cause bubbles during high-temperature soldering, leading to defects. Baking effectively removes them, reducing soldering risks.
2.Soldering Quality Enhancement:Baking activates the flux in solder paste, improving its wetting properties and ensuring a smoother soldering process. It also preheats components, reducing thermal shock and stress during soldering for greater reliability.
3.Oxidation Prevention:Oxides on chip surfaces and pads reduce metal activity and soldering effectiveness. Baking minimizes oxidation, ensuring good metal contact during soldering.
4.Cleaning and Decontamination: High-temperature baking removes oils, dust, and other contaminants from components and PCBs, lowering the risk of soldering issues.
5.Performance Improvement: Baking relieves internal chip stresses, reducing micro-cracks and defects. This enhances conductivity, durability, and for some MOS devices, carrier mobility and lifetime.
Ⅱ.Baking Process for IC Packaging
The baking process includes preheating, sintering, cooling, and cleaning:
1.Preheating: Chips are heated to a preset temperature in a preheating furnace to prepare for sintering, reducing defects like bubbles and cracks.
2.Sintering: High-temperature sintering causes material crystallization and bonding, forming the desired structure. Temperature, time, and atmosphere are critical to chip performance.
3.Cooling: Chips are removed from the sintering furnace and cooled to room temperature.
4.Cleaning: Chips are cleaned in deionized water to remove residues and ensure surface cleanliness.
Temperature, time, and atmosphere must be strictly controlled during baking. Pre-treatment like ultrasonic cleaning and vacuum drying is essential for a clean chip surface. Post-baking, chips should be promptly removed to eliminate surface oxides and ensure proper electrical performance.
Ⅲ.Appropriate Oven Types
Ovens for post-IC packaging baking must offer high-precision, high-stability heat treatment:
1.Nitrogen Atmosphere Oven: Designed for semiconductor chip baking and encapsulation curing, nitrogen prevents oxidation and improves product quality.
2.Nitrogen-Charged Precision Hot Air Oven: Uses nitrogen and controlled hot air circulation for uniform heating. It offers precise temperature control, uniform heating, and oxidation prevention, ideal for strict baking conditions.
3.Vacuum oven:Suitable for removing internal gaps and moisture in chips. Vacuum baking lowers the boiling point of moisture and volatiles, facilitating their removal while preventing oxidation and contamination.
When selecting an oven, consider chip material, size, structure, and baking requirements. For example, MOS devices need ovens with precise temperature and atmosphere control to enhance carrier mobility and lifetime.
Post-packaging baking of ICs is crucial for stability and reliability. It removes moisture and residues, improves soldering, prevents oxidation, and enhances internal structure and performance. Choosing the right oven based on specific IC requirements ensures optimal performance and reliability during baking. High-precision, nitrogen, and vacuum ovens are all suitable options.
