The Impact of Baking Process in Die Bonding on Chip Performance

During the semiconductor packaging process, die bonding is the step where the chip is fixed onto the packaging substrate. The baking process in die bonding mainly serves to solidify the adhesive between the chip and the substrate through heating. Baking also removes moisture absorbed by the chip during manufacturing, transportation, and storage, as well as volatile impurities within the chip. If these moisture and impurities are not removed, they will rapidly vaporize in subsequent high-temperature processing steps, generating internal pressure that can damage the internal structure of the chip, causing cracks or delamination, thereby affecting the electrical performance of the chip and even leading to chip failure. The primary purpose of baking is to remove moisture and volatile impurities from the chip, prevent oxidation, stabilize metal particles, and improve the accuracy of testing.

Impact on Chip Performance

1. Electrical Performance

● Removal of Moisture and Impurities: Chips can absorb moisture during manufacturing, transportation, and storage, and may also have residual volatile impurities. These substances will vaporize or release in subsequent high-temperature processing, increasing the internal pressure of the chip, causing cracks or delamination, and thereby affecting the electrical performance, and even causing chip failure. For example, the pressure generated by the vaporization of moisture at high temperatures can damage the internal structure of the chip and affect its conductivity.

● Preventing Oxidation: In high-temperature environments, the metal leads and pads of the chip are prone to oxidation. The oxides can affect the welding effect, reduce the conductivity and weldability of the metal, and thereby affect the connection quality between the chip and the external circuit. However, heating in an inert gas atmosphere during baking can effectively prevent the oxidation of the chip surface.

● Stabilizing Metal Particles:Baking can redistribute and solidify the metal particles inside and on the surface of the wafer through heat treatment, reducing the phenomenon of electromigration, lowering the risk of voids forming inside the metal wires and causing open circuits, and enhancing the service life and reliability of the integrated circuit.

2. Mechanical Performance

● Enhancing Connection Strength: Through baking, the adhesive can fully cure, enhancing the connection strength between the chip and the substrate. This helps the chip better resist mechanical stress in subsequent processing and use, preventing damage caused by mechanical impact.

● Optimizing Packaging Structure Stability:The baking process can also optimize the stability of the packaging structure. For example, in plastic packaging, baking at the appropriate temperature and atmosphere can ensure good adhesion between the packaging material and the chip, preventing the packaging material from separating from the chip under subsequent high-temperature or mechanical stress conditions.

3. Reliability

● Removing Internal Stress: Baking can eliminate internal stress in the chip, reducing the generation of microcracks and defects. These improvements can enhance the reliability and stability of the chip, extending its service life.

● Improving Test Accuracy: For the CP (wafer-level test) process of the chip, baking can remove moisture and impurities from the wafer surface and inside, avoiding changes in the conductivity of the wafer surface and internal circuits caused by moisture or other pollutants, which can affect the accuracy of the test results, ensuring the reliability of the test data.

Solutions

1. Precise Control of Baking Parameters

● Temperature Control: Different packaging materials and chip structures have varying temperature requirements. Excessive temperature can cause thermal damage to the packaging material, while insufficient temperature may fail to effectively remove impurities or achieve material solidification. It is necessary to precisely control the baking temperature according to the specific materials and process requirements.

● Time Management: The length of baking time directly affects the performance of the packaging material and the stability of the packaging structure. Too short a time may not be sufficient to fully remove moisture and organic impurities from the material, while too long a time may lead to excessive changes in material properties, and even damage the chip. It is necessary to precisely control the baking time.

● Atmosphere Selection: The atmosphere used in the baking process is crucial to the process effect. Common atmospheres include nitrogen and vacuum environments. A nitrogen atmosphere can effectively prevent oxidation reactions from occurring, protecting the surface of the packaging material and the chip from oxidative damage. A vacuum environment can help further reduce the residual impurities and improve the reliability of the packaging.

2. Optimizing Baking Environment

● Cleanliness Requirements: Die bonding baking needs to be carried out in a high-cleanliness environment. The cleanliness level of this environment needs to reach 100,000 grades or higher to ensure that factors such as dust, microorganisms, and static electricity in the production environment are effectively controlled. This requires the workshop to not only have an air purification system but also to precisely control environmental parameters such as temperature, humidity, and air pressure to ensure the stability and consistency of the production environment.

Applicable Ovens

● Nitrogen-Charged Oven: By introducing nitrogen into the oven, the oxygen content is reduced, minimizing oxidation reactions. This type of oven is suitable for chips that are sensitive to oxidation, effectively protecting the chip surface from oxidation.

● High-temperature oven: Suitable for chips that require short baking times at higher temperatures, these ovens typically feature rapid heating and cooling capabilities, enhancing baking efficiency. The temperature and time can be set according to the chip's moisture protection level and material characteristics.

● Oxygen-free oven: By introducing inert gas to create a high-temperature, low-oxygen, and clean baking environment, this oven is particularly suitable for chips with extremely high baking environment requirements, such as precision electronic components and semiconductor chips, effectively preventing contamination and oxidation of the chips during the baking process.

● Vacuum Oven: Baking in a vacuum environment can lower the boiling points of water vapor and volatile substances, making it easier for them to escape from the chip. This accelerates the evaporation of moisture and the decomposition of organic materials, further improving the baking effect. It also prevents chip oxidation and contamination, making it suitable for chips with particularly high baking quality requirements or those needing to remove internal gaps and deep moisture from the chip.

The baking process in die bonding has a significant impact on chip performance. By precisely controlling baking parameters, optimizing the baking environment, and selecting the appropriate Oven equipment, it is possible to effectively remove moisture and impurities from the chip, prevent oxidation, stabilize metal particles, and enhance the electrical performance, reliability, and stability of the chip. This not only helps to improve the quality and service life of the chip but also meets the modern electronic devices' demand for high-performance and highly reliable chips.