Detailed Explanation of Chip Packaging Materials

Packaging materials are key materials used to wrap and protect integrated circuit chips from damage caused by external environments such as moisture, dust, chemicals, and mechanical shocks.

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1. The Status and Advantages of Plastic Packaging

According to the different types of packaging materials, electronic device packaging is mainly divided into three categories: plastic packaging has become the absolute mainstream packaging form due to its unparalleled cost-effectiveness and mass production capabilities.

Packaging Type	Characteristics	Application Scenarios
Metal Packaging	Good airtightness, strong shielding, excellent heat dissipation	High-reliability military and aerospace
Ceramic Packaging	Good airtightness, high temperature resistance, good high-frequency characteristics	High-end processors, RF devices, optical communications
Plastic Packaging	Low cost, small size, lightweight, suitable for mass production	Over 90% of civilian and commercial integrated circuits

Plastic packaging has become the absolute mainstream packaging form due to its unparalleled cost-effectiveness and mass production capabilities.

2. Classification and Composition of Packaging Materials

Packaging materials can be divided into two main categories:Solid Packaging Materials and Liquid Packaging Materials.

2.1 Solid Packaging Materials – Epoxy Packaging Materials

This is the most mainstream packaging material.

• Physical State: Solid at room temperature (usually in cake or granule form).

• Main Components:

• Epoxy Resin: Serves as the matrix and provides adhesion. Commonly used are phenolic epoxy resin or bisphenol A epoxy resin.

• Curing Agent: Reacts with the resin to form a three-dimensional network structure. Commonly used are amines or organic anhydrides.

• Inorganic Fillers: Mainly silica micro-powder. Its role is to reduce the thermal expansion coefficient, improve thermal conductivity, lower costs, and reduce curing shrinkage.

• Other Additives: Includes curing accelerators (to speed up reactions), release agents (to facilitate demolding), colorants (usually black, for light shielding and identification), flame retardants, etc.

• Packaging Process (Transfer Molding):

1. Preheating: Microwave heating the EMC before placing it in the mold to soften it.

2. Injection Molding: Under pressure and high temperature, injecting the molten EMC into the cavity where the chip and lead frame are placed.

3. Curing: Under heat and the action of the curing agent, the epoxy resin reacts with the curing agent to undergo a cross-linking curing reaction, forming a hard, stable thermosetting plastic shell.

Technical Development Trends – High Performance and Functionality:

• Fast Curing Type: Increases production efficiency.

• High Temperature Resistant Type: Meets the high reflow soldering temperature requirements of lead-free solder.

• Low Stress Type: Prevents excessive stress that can lead to chip cracking or warping.

• Low Moisture Absorption Type: Reduces the risk of the “popcorn” effect caused by moisture absorption.

• Green and Environmentally Friendly Type: Halogen-free, antimony-free, compliant with environmental regulations.

2.2 Liquid Packaging Materials

Mainly used in specific packaging scenarios.

• Physical State: Liquid at room temperature.

• Main Components: Similar to EMC, containing epoxy resin, curing agents, inorganic fillers, etc., but formulated to remain liquid at room temperature.

• Types and Uses:

• Epoxy Underfill:

• Uses: Mainly used for Flip-Chip packaging. It fills the gap between the chip and the substrate.

• Function: Flows into the gap through capillary action, and after curing, effectively absorbs and disperses stress, compensating for the difference in thermal expansion coefficients between the chip and the substrate, significantly improving solder joint reliability.

• Epoxy Encapsulant:

• Uses: Used to protect the chip surface.

• Process: Applied directly to the surface of the chip fixed to the lead frame or substrate through dispensing or spraying, and then cured by heating. Commonly used for sensors, power devices, or certain CSP packages.

3. Advantages of Packaging Materials

1. Excellent Electrical Performance: Low dielectric constant, low dielectric loss, high insulation strength, which helps improve signal transmission speed and quality.

2. Good Mechanical Performance: High toughness, protecting the chip from mechanical vibrations and shocks.

3. Lightweight: The weight of plastic packaging is about 50% of that of ceramic packaging.

4. High Packaging Density and Miniaturization: Enables smaller and thinner packaging structures, meeting the demand for lightweight, thin, short, and small electronic products.

5. Low Cost and High Efficiency: Very suitable for large-scale, automated production, greatly reducing the manufacturing cost of individual IC devices.

4. Disadvantages and Challenges of Packaging Materials

Despite their prominent advantages, packaging materials also have inherent defects that limit their application in extreme environments:

1. Non-Airtight: Unlike metal/ceramic packaging, plastic materials have tiny pores that cannot completely isolate gases and moisture.

2. Moisture Absorption: Packaging materials absorb moisture from the environment. During high-temperature processes like reflow soldering, internal moisture can rapidly expand, potentially causing cracks inside the package (the “popcorn” effect).

3. Relatively Poor Temperature Resistance: Long-term operating temperatures and peak tolerance temperatures are usually lower than those of ceramics and metals.

4. High-Temperature Outgassing: In vacuum or high-temperature environments, packaging materials may release volatile substances, contaminating sensitive optical or MEMS devices.

5. Poor Radiation Resistance: Weak shielding capability against radiation such as alpha particles, which may lead to soft errors, making them unsuitable for high-radiation environments (e.g., space, nuclear industry).

Packaging materials, especially epoxy packaging materials, are the cornerstone of the popularization and development of the modern electronics industry. Through continuous technological innovation, they achieve the best balance between cost, performance, and size. However, their non-airtightness and sensitivity to moisture are inherent Achilles’ heels, making airtight packaging (metal/ceramic) an irreplaceable choice in fields requiring high reliability and extreme environmental applications.