The sandwich structure design greatly improves the application reliability of MLCC products-EEWORLD

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1. Introduction

Chaozhou Sanhuan (Group) Co., Ltd. is located in Chaozhou City, Guangdong Province. At present, the company's industrial base covers an area of 180,000 square meters, the plant area is 110,000 square meters, there are 2,500 employees, 200 technical personnel of various types, and total assets of RMB 450 million. The company is a well-known brand manufacturer in my country that specializes in the production of a full range of chip multilayer ceramic capacitors (MLCC); alumina ceramic substrates for HIC and chip resistors, ceramic ferrules for optical fiber connectors, microwave dielectric ceramic devices, plastic encapsulated chip inductors, various film fixed resistors, resistor ceramic substrates and other basic electronic components. In recent years, the company has successively undertaken and completed a number of national and provincial scientific research projects, developed a number of high-tech products, and innovated a large number of high-precision special equipment integrating optics, machinery and electricity. Many scientific research results have won the Guangdong Provincial Science and Technology Progress Award. The company has been recognized as a national and Guangdong Excellent High-tech Enterprise, a National 863 Achievement Industrialization Base, and the first batch of innovative enterprises in Guangdong Province.

The main series of products developed and produced by Chaozhou Sanhuan (Group) Co., Ltd. - chip-type multilayer ceramic capacitors (MLCC) have the characteristics of small size, high precision, light weight and good stability. They are currently widely used in various IT electronic information equipment and products such as mobile phones, tablets, computer motherboards, PCB control boards, etc.

However, due to the brittle ceramic material itself, multilayer ceramic capacitors (MLCC) products often have technical quality problems such as leakage, no capacitance, short circuit and even burning due to improper operation during product application. After long-term tracking and analysis of such problems, the scientific and technological personnel of Chaozhou Sanhuan (Group) Co., Ltd. finally confirmed that the failure mode leading to the above-mentioned defects is product breakage.

2. Failure Mode Analysis of Multilayer Ceramic Capacitors (MLCC)

Failure mechanism

The main reason for product breakage is that the product is subjected to bending stress during use, which causes microcracks to form in the product and expand over time or with secondary stress, eventually leading to breakage.

In recent years, customers have found that product breakage can be avoided through PCB design and process control. However, there are still some products that have a small proportion of breakage problems during use, and most of these products are small-capacitance products made of X7R material. The fundamental reason why X7R small-capacitance products are prone to breakage is their poor mechanical strength.

Product Strength Comparison

According to the mechanical strength comparison chart above, it can be seen that the mechanical strength of X7R small capacitance products is poor, while COG materials are excellent. However, due to its extremely low dielectric constant, COG materials can only be used to produce products with lower capacitance, and because the material is expensive, it is not suitable to replace X7R products of the same specification.

3. Commonly used improvement methods

To solve the problem of X7R small capacitance products breaking, we often use:

①Increase product thickness;

②Increase the number of internal layers of the product;

③ Improve product strength in three ways, such as changing to higher-strength materials, to improve product production adaptability. However, judging from the anti-bending comparison chart, increasing product thickness and the number of layers have little effect on improving product anti-bending. In addition, since small-capacitance products have low capacity themselves, there is limited room for increasing the number of layers.

4. New improvement methods

Improving the mechanical strength of products by changing materials is obviously an effective method.

Through continuous research on materials in recent years, our company has finally developed a material with high dielectric constant, but the product made purely of this material has high cost and small capacitance range. In order to better promote the improvement of this work, the company's project team proposed the idea of adding high-strength ceramic bodies on the upper and lower surfaces of the product to improve the overall product strength. Finally, in November 2012, our company confirmed the feasibility of this method and completed the verification of various product performances in early May 2013. This new design method can greatly increase the mechanical strength of 0603X7R104K, 0805X7R104K and below capacitance products. Our company named this new product a sandwich structure product.

The structure of the sandwich structure product is as follows:

Performance comparison

1. Comparison of flexural strength

2. Comparison of bending strength

3. Capacitance distribution comparison

4. Loss tangent comparison 5. Insulation resistance comparison

6. Voltage Withstand Comparison

7. Temperature characteristics comparison

8. Resistance to welding heat

9. Steady-state damp heat

10. Moisture load resistance

11. Durability

12. Rapid temperature cycle

5. High and low temperature cycle verification

In order to further confirm the reliability of sandwich structure products, 0805X7R104K500D and 0603X7R104K500C products were subjected to 300 high and low temperature cycle tests (temperature cycle test conditions: 40℃/15min→25℃/15S→125℃/15min→25℃/15S). The verification results are shown in the following table:

Verification results show that the high and low temperature cycle characteristics of the products before and after improvement are similar and can meet customer needs.

VI. Comparative Summary

Through the above performance comparison, the sandwich structure product is compared with the original product:

1. Mechanical strength is greatly increased;

2. The temperature characteristics are slightly worse, but still meet the X7R characteristics and can meet customer needs;

3. Other products have similar performance;

VII. Research Summary

Through the above analysis, we can see that the performance of products with sandwich structure design has been greatly improved, specifically:

1. Can significantly increase the mechanical strength of the product;

2. It can greatly reduce the probability of product breakage during normal use;

3. Able to adapt to relatively harsh conditions of use (such as unique production processes such as monolithic stone);

4. The price will not be much different from traditional products;

Finally, it should be noted that the sandwich structure design can significantly improve the strength of X7R products, but the following points should be noted:

1. The problem of product breakage cannot be solved by component manufacturers alone. The fundamental solution lies in the control of the client;

2. The product range covered by sandwich structure products is relatively narrow, generally with a capacitance of 104 and below. For high-capacity products, do not casually propose the idea of a sandwich structure.