Hidden Cracks in MLCCs A Silent Reliability Risk

Multilayer ceramic capacitors (MLCCs) are ubiquitous in modern electronic systems. Thanks to their small size, stable electrical performance, and cost efficiency, they are widely used across consumer electronics, industrial control, automotive electronics, and communication equipment.

However, from the perspective of laboratory reliability testing and failure analysis, MLCCs can appear electrically normal in standard tests while still carrying latent reliability risks.

Among these risks, micro cracks are one of the most common and most difficult to detect failure mechanisms. They may not be detected during routine outgoing inspection or initial functional testing, yet may evolve into serious failures after prolonged field operation under environmental or electrical stress.

1. What Are MLCC Micro Cracks and Why Are They Hard to Detect

Micro cracks in MLCCs typically refer to microscopic fractures within the ceramic dielectric or on the surface of the component. These cracks are often only a few micrometers in size, invisible to the naked eye, and usually do not cause abnormalities in standard electrical tests such as capacitance, ESR, or dielectric withstand voltage.

The real danger of micro cracks lies in the fact that they are not immediate-failure defects, but latent reliability risks. Under conditions such as temperature cycling, mechanical vibration, or electrical stress, these cracks may gradually propagate, eventually leading to:

a) Capacitance drift or sudden capacitance change

b) Increased leakage current

c) Decreased insulation resistance

d) In extreme cases, short circuit or open circuit failures

In failure analysis cases, micro cracks are frequently identified as a contributing factor in intermittent or seemingly random field failures.

2. Main Causes of MLCC Micro Cracks Not Just a Soldering Issue

In practical engineering discussions, micro cracks are often simplistically attributed to poor soldering. However, laboratory investigations show that their causes are usually more complex and often result from multiple stress factors accumulating across different stages.

PCB Assembly and Soldering Stress

During the reflow soldering process, differences in the coefficient of thermal expansion between the PCB and the MLCC generate mechanical stress during cooling. If pad design is improper, solder volume is excessive, or cooling rates are too fast, tensile or shear stress may be applied to the ceramic body, leading to the formation of micro cracks.

Board Flex

PCB bending during assembly, depaneling, screw fastening, or transportation is a common and critical contributor to MLCC micro cracks. Even minimal board flex can create stress concentration at the interface between the termination and the ceramic body.

Component Size and Dielectric Structure

As MLCCs continue to shrink in size, such as 0402 and 0201 packages, the ceramic dielectric layers become thinner and mechanically weaker. Under identical external stress conditions, smaller MLCCs are therefore more susceptible to micro cracking.

Temperature Cycling and Environmental Stress

In environments involving temperature cycling or high humidity, repeated expansion and contraction of materials can cause existing micro cracks to gradually extend, eventually developing into measurable electrical performance degradation.

3. How Are Micro Cracks Detected Common Laboratory Methods

Due to their highly concealed nature, micro cracks often require a combination of inspection and test methods to be reliably identified and confirmed.

X Ray Inspection A Rapid Screening Tool

X ray inspection is one of the most commonly used non-destructive methods, allowing visualization of internal electrode structures and obvious cracks. However, its ability to detect very fine cracks or cracks propagating along electrode layers remains limited.

Cross Section Analysis

Cross sectioning is the most direct and convincing method for identifying micro cracks. By precisely cutting the component and examining it under a microscope, the location, orientation, and interaction between cracks and electrodes can be clearly observed. This method is destructive and is typically used for failure confirmation rather than large-scale screening.

Scanning Acoustic Microscopy SAM

SAM uses ultrasonic reflection characteristics to detect internal interface defects. In certain cases, it offers high sensitivity to micro cracks and is particularly suitable for inspection after board-level assembly.

Electrical Stress Testing

By applying temperature cycling, voltage stress, or damp heat aging while continuously monitoring electrical parameters, potential micro cracks can be indirectly revealed. These methods are more focused on accelerating risk exposure rather than direct imaging.

4. Engineering Impact of Micro Cracks Why They Matter

From a laboratory standpoint, micro cracks do not necessarily lead to immediate failure in every product. However, they significantly increase uncertainty in system reliability. This uncertainty is precisely what industrial and automotive electronics aim to minimize.

Micro crack risks are particularly critical in applications such as:

a) Industrial equipment operating continuously over long periods

b) Automotive electronic systems with strict safety requirements

c) Devices exposed to wide temperature variations and frequent vibration

d) Power and signal circuits highly sensitive to leakage current and stability

Therefore, micro cracks should not be viewed as an isolated component issue, but as an important factor in overall system reliability management.

MLCC micro cracks highlight an important reality: passing factory inspection by itself does not guarantee long-term reliability. True reliability assessment requires a more systematic evaluation that considers material properties, assembly processes, environmental stress, and laboratory verification methods.By understanding the causes and detection logic of micro cracks early in the design, manufacturing, and quality control stages, engineers can better reduce related risks.

Rapid Rabbit Lab consistently focuses on the behavior of devices under real-world application conditions during its daily testing and analysis.  Through multi-dimensional experimental methods, they help identify potential reliability issues and provide more valuable data support for engineering decisions.