Understanding Common IC Plastic Packaging Molds

Here's the translation of your text into English:In the manufacturing process of modern electronic products, IC (integrated circuit) packaging technology plays a crucial role. With the advancement of technology and the growth in market demand, IC packaging technology has been continuously developing and evolving. IC packaging is mainly divided into three major categories: metal packaging, ceramic packaging, and plastic packaging. Although metal and ceramic packaging have advantages in high reliability and special applications, they are not widely used in consumer electronics due to their high costs. In contrast, plastic packaging has become the most popular packaging technology due to its cost-effectiveness and wide adaptability, making it the mainstream in microelectronic packaging today. Therefore, this article will focus on understanding the process technology of plastic packaging.

Transfer Molding

Transfer molding is the process of injecting preheated solid molding compounds (such as EMC) from the loading chamber into the runners and mold cavities through a plunger. This method involves placing the resin material into a loading chamber, and then under pressure, the resin material passes through the runner system into the mold cavities, filling and curing to form the shape. Transfer molding is the most commonly used method for encapsulation in semiconductor packaging materials. It is used for various packaging types, from traditional lead frame packages to BGA (Ball Grid Array) packages. Hence, it is mainly used for IC packaging, such as DIP (Dual In-line Package), SOP (Small Outline Package), and QFP (Quad Flat Package), and is suitable for electronic products requiring high reliability and consistency.Why is transfer molding the most widely used method? The main advantages are high product consistency and precise control of material usage. Compared to traditional injection and compression molding, the flowing pressure is lower, which makes it less likely to damage fragile structures, such as gold wire bonding. Therefore, it can be widely applied. However, transfer molding also has the following disadvantages:

• Difficulties in Large-Volume Packaging: When preheating EMC, the reaction rate increases rapidly at high temperatures, leading to a shorter gel time and poor fluidity. As a result, the EMC viscosity rises sharply before the cavity is fully filled, increasing the flow resistance and preventing good filling, which results in incomplete filling. This phenomenon is more likely to occur in ultra-large-scale integrated circuit packaging because these large-scale circuits often require a large amount of EMC per mold. Additionally, the relatively high temperature set for uniform heating in a short time can easily lead to incomplete filling.To address this issue, which is primarily due to insufficient EMC fluidity, several adjustments can be made: increasing the preheat temperature of the EMC to achieve uniform heating, increasing the injection pressure and speed to raise the EMC flow rate, and lowering the mold temperature to slow down the reaction rate. However, this would also require extending the curing time to achieve complete filling.
• Material Blockage Issue: Especially in small-volume packaging, due to relatively small gates and vents, it is easy for mold gates to become blocked and for vents to become clogged, preventing effective injection of EMC. The unfilled areas in the mold are often irregular. To address this situation, tools can be used to remove blockages, and mold release agents can be applied. Additionally, after each molding process, it is necessary to clean the cavities and remove EMC curing agents from the mold. Therefore, if production volume reaches a certain level, automated systems become very necessary.
• Overflow Control: In the packaging process, the issue of voids is often encountered. The formation of these internal voids is mainly due to the mold surface temperature being too high, causing the EMC on the cavity surface to cure prematurely. Combined with an excessively fast injection speed, the vents are quickly filled, and some internal gases cannot overcome the cured surface layer, resulting in voids forming inside. These void defects are typically more common in large-volume packaging, especially at the gate end and in the middle positions.To effectively reduce the occurrence of such voids, it is essential to first appropriately lower the mold temperature. Additionally, it may be considered to increase the injection pressure appropriately, but excessive pressure can lead to defects such as overflow. Therefore, a post-treatment station using laser trimming to remove overflow material may be necessary.
• Material Waste: Current transfer molding processes require the use of runner structures, similar to the principles of injection molding. The runner itself represents material waste. However, unlike injection molding, transfer molding cannot use a hot runner valve gate system to eliminate the runner and thereby reduce material waste.

The key point in transfer molding lies in the material. Most issues arise from the material itself, such as damaged EMC ingots or poor preheating control leading to inadequate flowability, resulting in problems like voids and blemishes. Therefore, the cost of preserving materials is high, as damaged EMC ingots cannot be used. In such a scenario where the material is precious, effectively matching the resin's characteristics with the molding parameters to achieve optimization is a significant area of expertise.

Injection Molding

Injection molding is a process that uses an injection molding machine to inject molten resin material into a mold cavity, where it cools and solidifies to form a shape. This method typically includes steps such as material heating, injection, cooling, and demolding. In the field of semiconductor packaging, the injection molding used is different from traditional injection molding. To protect the structure of gold wire bonding to the substrate, low-pressure molding (LPM) is adopted.So, what are the benefits of using injection molding? There are three main advantages:

• Fast Molding Speed: Compared to traditional potting or transfer molding, the time from injection to cooling and curing is significantly shortened, and multi-cavity molds can be designed, which clearly enhances production speed, making it suitable for mass production.
• Material Savings: Injection molds can achieve complex structural forms, making it easier to "encapsulate only the desired areas" in packaging design, without the need for extensive potting. Additionally, injection machines can more precisely control the amount of resin used, effectively managing material consumption.
• Suitable for High Precision and Complex Shape Packaging: This process can precisely control the injection volume and pressure, making it suitable for producing components with complex shapes and precise dimensions.

But in the application of injection molding, there are very obvious disadvantages:

• High Equipment Investment:Injection molding machines and related heating and cooling equipment are expensive, resulting in high initial investment. Additionally, mold design and manufacturing costs are also high, especially for molds with complex shapes.
• High Requirements for Process Parameters:Injection molding requires precise control of the molten material's temperature, injection pressure, and cooling time. Any slight mistake can lead to product defects such as warping, bubbles, or incomplete filling.
• Difficulties in Large-Volume Packaging: Due to the use of low pressure, LPM may have difficulty ensuring sufficient precision in larger volume packaging. The uniformity and integrity of the packaging may be affected.

Would you like to learn about plastic injection degating, ultrasonic shearing, and related design knowledge?
Further Reading :《Principles and design of ultrasonic de-gating for plastic parts》

Compression Molding

Compression molding is a process where resin material (such as granular molding compounds) is placed in a mold, and then formed by heating and pressing. This method typically involves placing preformed resin granules directly into the mold cavity, then closing the mold, applying pressure, and heating until the material cures. It is more suitable for packaging high-power components and manufacturing high-strength structural parts, such as high-power transistor packages and industrial components that need to withstand high temperatures and pressures.Therefore, if the product has a larger volume or thicker walls, compression molding can be chosen. Compared to transfer molding, compression molding only requires enough material to fill the cavity, without the additional waste from runners, resulting in better material utilization. Compression molding also has an advantage for small-scale verification, as the compression mold is a good choice. The mold structure is simple, with fewer mechanical requirements compared to injection molds or transfer molds, which have runner mechanisms and ejection mechanisms respectively, making it cost-effective and easier to manufacture. However, it is not suitable for overly complex mold structures.In addition to these points, there are a few other issues:

• Longer Molding Cycle:Due to the longer heating and curing time required, the cycle for compression molding is longer, resulting in relatively lower production efficiency.
• Material Feeding and Quantity Control:Compression molding requires precisely placing the exact amount of material into each cavity. In the case of multi-cavity molds, each cavity must be filled individually, unlike the other two methods which have a material hopper. Accurate control of the material quantity in each cavity is necessary to ensure that after compression, the material forms exactly to the specified shape. If there is a significant size difference between the mold cavities, it becomes difficult to control the molding quality. Additionally, if extra material is added to compensate for these differences, it will result in overflow and flash issues.

Common Materials for Plastic Packaging

In transfer molding and compression molding, epoxy resin is the most common material. Epoxy resin is a thermosetting material and has the following characteristics:

• Excellent electrical insulation: Capable of effectively preventing electrical short circuits and leakage.
• Good mechanical strength: It has high tensile strength and hardness, providing reliable protection.
• Excellent chemical resistance: It has good resistance to most chemicals, preventing components from corrosion.
• Low moisture absorption: It has a low moisture absorption rate, effectively preventing moisture from corroding electronic components.

Epoxy resin, due to its excellent comprehensive performance and cost-effectiveness, has become the primary material for plastic packaging.

Low-pressure injection molding mainly uses hot melt adhesives. These materials are usually based on polyolefin or polyamide (PA) formulations. Polyamide can be both naturally occurring and synthetically produced. Commonly known as nylon in Taiwan, it is an engineering plastic. Polyamide has the following characteristics:

• High mechanical strength and toughness: Polyamide has excellent mechanical strength and toughness, capable of withstanding high loads and impacts.
• Good heat resistance: Polyamide has excellent thermal stability and can maintain its performance in high-temperature environments, typically usable at 140°C or even higher temperatures.
• Chemical resistance: Polyamide has good resistance to many chemicals, including oils, aliphatic compounds, and weak acids and bases, and can maintain its performance even in some harsh chemical environments.
• Low friction coefficient and wear resistance: Polyamide has a smooth surface and a low friction coefficient, reducing wear.
• Good electrical insulation properties: Polyamide has excellent electrical insulation properties, making it an ideal material for electrical and electronic applications, retaining its insulation characteristics even in high-temperature and high-humidity environments.
• Water absorption and dimensional stability: Polyamide has some water absorption, but this can be controlled through appropriate design and treatment to improve dimensional stability.
• Good thermal conductivity:It has good thermal conductivity, facilitating heat dissipation in electronic products.
• Low-temperature impact resistance:It can maintain a certain level of strength even at -40°C.

Overall, polyamide, due to its excellent mechanical strength, heat resistance, chemical resistance, and good processing performance, is widely used not only in the electronics field but also in various industrial and consumer applications. It is a highly versatile and high-performance engineering plastic.

Would you like to learn about stainless steel manufacturing and surface treatment methods?
Further Reading :《5 Common Stainless Steel Sheet Surface Finishing Techniques》

Future Challenges

Demand for High Performance and Miniaturization
As electronic products develop towards higher performance and miniaturization, plastic packaging technology needs to adapt to increasingly higher performance requirements and smaller package sizes. This requires the development of higher-performance materials and more sophisticated process technologies.Existing plastic packaging materials may experience performance degradation under high temperature, high pressure, and high-speed operating environments. Additionally, as chip sizes continue to shrink, packaging technology requires higher precision and more complex processes, such as 3D packaging and wafer-level packaging (WLP).

Thermal Management
As the power density of electronic components continues to increase, thermal management becomes increasingly important. Plastic packaging needs to provide effective thermal solutions to ensure the stable operation and longevity of components. Traditional plastic packaging materials have poor thermal conductivity, making it difficult to meet the thermal demands of high-power electronic components. There is a need to develop packaging materials with excellent thermal conductivity, such as epoxy resin with added thermal fillers, and to design advanced thermal structures and technologies, such as built-in heat sinks and thermal channels.

Environmental Protection and Sustainability
With the increase in environmental awareness and stricter regulations, the manufacturing process of electronic products needs to be more environmentally friendly and sustainable. For example, many products need to comply with halogen-free specifications. However, traditional plastic packaging materials are mostly non-biodegradable thermosetting plastics, which have a certain impact on the environment. Therefore, some manufacturers have developed environmentally friendly epoxy packaging materials that do not contain bromine or antimony elements.

Conclusion

Plastic packaging technology occupies a significant position in IC packaging, with its excellent performance and cost-effectiveness making it a widely adopted packaging method. By selecting suitable materials and processes and accurately controlling each manufacturing step, the quality and reliability of packaged products can be improved. With ongoing technological advancements, plastic packaging technology will play an increasingly important role in future electronic product manufacturing. However, it will also face challenges such as high-performance and miniaturization demands, thermal management, environmental protection, and sustainability. Through continuous technological innovation, material development, and process improvement, plastic packaging technology can continue to play a vital role in addressing these challenges while meeting the evolving market demands and technological advancements. Future plastic packaging technology will be more efficient, environmentally friendly, and flexible to meet the changing market needs and technological requirements.