Post-Encapsulation Baking of ICs

IC encapsulation involves connecting the circuit pins on a silicon wafer to external leads via wires, enabling connection with other components. The encapsulation format refers to the housing used to mount the semiconductor integrated circuit chip. It not only serves the functions of mounting, fixing, sealing, and protecting the chip, but also connects the chip's contact points to the pins of the encapsulation housing via wires. These pins are then connected to the conductors on the printed circuit board, linking the internal chip to the external circuitry. Upon completion of IC encapsulation, baking is typically performed to ensure the integrity of its internal components and structure, and to remove any residual moisture, solvent, and other volatile substances.

I. Functions of Post-Encapsulation Baking

1.Removal of Moisture and Volatiles: During manufacturing, storage, and transportation, chips inevitably absorb moisture from the air and may contain other volatile substances. During high-temperature soldering processes, these impurities can cause bubbling, leading to soldering defects that affect the stability and lifespan of the circuit board. Baking effectively removes this moisture and volatile matter, reducing soldering risks.

2.Improvement of Soldering Quality: Baking aids in activating the active components within solder paste, enhancing the wetting performance of the solder, and facilitating a smoother soldering process. It preheats the components, reducing thermal shock and stress during soldering, thereby enhancing soldering reliability.

3.Prevention of Oxidation: Oxides on the chip surface and solder pads reduce metal activity and can impair soldering effectiveness. Baking reduces oxidation on component and pad surfaces, ensuring good metal contact during soldering.

4.Cleaning and Decontamination: High-temperature baking aids in removing contaminants such as oil, grease, and dust from components and PCBs, reducing the risk of poor soldering.

5.Enhancement of Product Performance: Baking can relieve internal stresses within the chip, reducing the formation of micro-cracks and defects, thus improving the chip's conductivity and durability. For certain Metal-Oxide-Semiconductor (MOS) devices, baking can also improve carrier mobility and lifetime.

II. Post-Encapsulation Baking Process

The baking process primarily includes preheating, sintering, cooling, and cleaning stages. Specific steps are as follows:

1.Preheating: The chip is placed in a preheating furnace and heated to a preset temperature to prepare for the subsequent sintering process. Preheating helps reduce the formation of defects like bubbles and cracks in the materials during sintering.

2.Sintering Treatment: Sintering is performed at high temperatures to crystallize and polymerize the materials within the chip, forming the desired structure. The temperature, duration, and atmosphere during sintering significantly influence the chip's structure and performance.

3.Cooling: After sintering, the chip is removed from the furnace for cooling until it reaches room temperature.

4.Cleaning: The chip is cleaned in deionized water to remove any residual impurities and contaminants, ensuring a clean surface.

During baking, parameters such as temperature, time, and atmosphere must be strictly controlled to ensure effectiveness. Prior to baking, chips often undergo pre-treatment steps like ultrasonic cleaning and vacuum drying to guarantee a clean, dust-free surface. After baking, chips should be promptly removed, and any residual surface oxides should be cleaned to ensure normal electrical performance.

III. Applicable Baking Ovens

Ovens suitable for post-encapsulation baking of ICs require high-precision, high-stability thermal processing capabilities to meet the demands of large-scale semiconductor packaging and assembly production for clean processes, low oxidation, and efficient curing.

1.Nitrogen (N₂) Inert Atmosphere Ovens: These ovens are designed specifically for high-precision, high-stability thermal processing tasks like semiconductor chip baking and encapsulation curing. Introducing nitrogen during baking effectively prevents chip oxidation, enhancing product quality.

2.Nitrogen-Purged Precision Convection Ovens: These ovens provide uniform heating by purging with nitrogen and controlling hot air circulation. They offer advantages like precise temperature control, even heating, and oxidation prevention, making them suitable for applications requiring stringent control over baking temperature and atmosphere.

3.Vacuum Ovens: Vacuum ovens are used when removing internal voids and moisture from chips is necessary. Baking in a vacuum environment lowers the boiling points of moisture and volatiles, making their removal easier. The vacuum also prevents oxidation and contamination of the chip.

When selecting an oven, factors such as chip material, size, structure, and baking requirements must be considered. For instance, for certain MOS devices, ovens capable of precise temperature and atmosphere control are necessary to improve carrier mobility and lifetime.

Post-encapsulation baking is a critical step for enhancing the stability and reliability of ICs. Through baking, moisture and residues within the IC can be effectively removed, soldering quality improved, oxidation prevented, and the internal structure and performance of the IC enhanced. When selecting a suitable oven, the specific requirements of the IC product and baking conditions must be comprehensively evaluated. High-Precision Ovens, inert atmosphere ovens, andvacuum ovens are all types suitable for post-encapsulation baking. By employing appropriate baking processes and selecting the right oven type, optimal performance and reliability of the IC during and after baking can be ensured.