The Impact of Relative Humidity on the Storage of Electronic Components

As the core components of electronic equipment, the stability of the storage environment for electronic components directly determines the performance, service life of the components and the operational reliability after subsequent installation. Relative humidity, as one of the most critical environmental indicators in the warehousing environment, together with temperature, cleanliness and electrostatic protection, constitutes the core control system for the storage of electronic components. Different from the linear impact of temperature, excessively high or low relative humidity will trigger a series of physical and chemical reactions, causing varying degrees of damage to different types and packages of electronic components, and even leading to direct scrapping of components, resulting in unnecessary economic losses for enterprises. Therefore, in-depth understanding of the specific impact of relative humidity on the storage of electronic components and mastering scientific storage humidity control methods are of great practical significance for the electronic manufacturing industry, warehousing and logistics industry and related practitioners.

Relative humidity refers to the percentage of the actual water vapor content in the air to the saturated water vapor content at the same temperature, which reflects the humidity of the air. The storage of electronic components has clear standard requirements for relative humidity. The suitable storage humidity for most conventional components is 40%～60%, while the requirements for precision humidity-sensitive components and high-reliability devices are more stringent, usually controlled at 30%～50%. When the relative humidity of the storage environment exceeds this reasonable range, whether it is too high or too low, it will have an irreversible negative impact on electronic components, and this impact is often hidden. Some damages are difficult to detect during incoming inspection, and only exposed after installation and use or long-term storage, bringing great hidden dangers to subsequent production and equipment operation.

When the humidity of the storage environment is too high (usually referring to relative humidity exceeding 70%), the damage to electronic components is the most common and serious, and its impact is mainly reflected in three aspects: chemical corrosion, physical damage and performance degradation. First of all, chemical corrosion is the most common form of damage in high-humidity environments. The pins and pads of electronic components are mostly made of metal materials such as copper, tin and silver, which are prone to oxidation reactions in humid environments——water vapor in the air will form a water film on the metal surface, and the oxygen, carbon dioxide and other gases dissolved in the water film will undergo electrochemical corrosion with the metal to form an oxide layer (such as copper rust, tin oxide). The oxide layer will increase the contact resistance of the pins, leading to problems such as difficulty in soldering, cold soldering and false soldering during subsequent welding. In severe cases, it will cause pin breakage, making the components unable to be normally connected to the circuit. For surface mount devices (SMD), pad oxidation will also affect the mounting accuracy, leading to device offset and poor contact after mounting, increasing the production rework rate.

Secondly, high-humidity environments will cause internal moisture absorption of components, leading to physical damage. For plastic-encapsulated components (such as plastic-encapsulated integrated circuits, plastic-encapsulated resistors and capacitors), their packaging materials (such as epoxy resin) have tiny pores. When placed in a high-humidity environment for a long time, water vapor will invade the interior of the device through these pores and accumulate at the interface between the chip, pins and packaging materials. When the components are subsequently welded (such as wave soldering and reflow soldering), the internal water vapor expands sharply when heated, generating huge internal stress, leading to bulging, cracking and delamination of the packaging shell, and even chip detachment, directly causing the components to be scrapped. For ceramic-encapsulated devices such as ceramic capacitors and quartz crystals, water vapor intrusion will cause the ceramic material to absorb moisture, affecting its dielectric properties and vibration characteristics, leading to capacitor capacity drift and crystal frequency deviation, which cannot meet the use requirements of the equipment. In addition, high-humidity environments will also accelerate the moisture absorption of PCB boards. After the glass fiber cloth and resin materials in the PCB board absorb moisture, their insulation performance will be reduced. Long-term storage may lead to leakage and short circuit between lines, and even cause PCB board delamination and warpage.

Furthermore, high-humidity environments will breed mold and corrode insulating materials, further exacerbating the damage of components. A humid and warm environment is a suitable condition for mold growth. Mold will grow on the surface of components and PCB board lines, and its metabolites will corrode metal contacts and insulation layers, damaging the electrical performance of components. At the same time, high humidity will accelerate the aging and softening of insulating materials (such as the insulating sheath of components and the solder mask of PCB boards), leading to a decrease in insulation resistance. For high-voltage components, it may cause insulation breakdown and pose safety hazards. Especially for precision sensors, optoelectronic components, MOS tubes and other sensitive devices, high-humidity environments will not only affect their electrical performance, but also may damage the internal sensitive structures, making them lose their detection and conversion functions and unable to work normally. For example, humidity sensors themselves are extremely sensitive to environmental humidity. If the storage environment humidity is too high, it will lead to sensor calibration deviation, and the humidity data cannot be accurately detected during subsequent use; the photosensitive characteristics of photodiodes and triodes will decrease in high-humidity environments, and the response speed will slow down, affecting the photoelectric conversion efficiency of the equipment.

Contrary to high-humidity environments, when the humidity of the storage environment is too low (usually referring to relative humidity below 30%), it will also cause serious damage to electronic components, and its core impact is concentrated in two aspects: electrostatic accumulation and material aging. First of all, low-humidity environments are prone to electrostatic accumulation, which is extremely harmful to electrostatic sensitive components. Dry air has poor conductivity. During the handling and storage of electronic components and packaging materials (such as plastic packaging bags and foam buffer materials), static electricity will be generated due to friction. However, the dry environment cannot conduct static electricity in time, leading to static electricity accumulation on the surface of components, forming a high electrostatic voltage (up to several thousand or even tens of thousands of volts). Electrostatic sensitive components such as MOS tubes, integrated circuits (ICs), optoelectronic components and quartz crystals have extremely precise internal circuit structures and very thin insulation layers. Once electrostatic discharge (ESD) occurs, the instantaneous high voltage will break down the internal insulation layer, causing short circuits and open circuits in the internal chip circuits, leading to direct failure of the components. More notably, some electrostatic damages are hidden damages. The appearance of the components is not obviously abnormal and cannot be detected during incoming inspection, but sudden failures will occur after installation, and even affect the normal operation of the entire equipment, bringing great troubles to production and use.

Secondly, low-humidity environments will cause water loss and aging of the plastic and packaging materials of components, leading to physical damage. The shells, pin sheaths and packaging tapes of electronic components are mostly made of plastic materials. Such materials will gradually lose water in a long-term dry environment, leading to brittle, easy to crack and deform. For example, the shells of plastic-encapsulated resistors and capacitors may crack, which cannot effectively protect the internal chips and pins, and are vulnerable to the invasion of dust and impurities, affecting the device performance; after the pin sheaths crack, the pins will be exposed, which are prone to oxidation and wear, increasing the difficulty of subsequent welding; after the packaging tape loses water, it will lose its viscosity and cannot effectively fix the components, leading to collision and damage of components during storage and handling. In addition, low-humidity environments will also cause water loss of the PCB board substrate, making the PCB board brittle and prone to breakage and delamination, affecting its mechanical strength and electrical performance.

In addition to the above direct impacts, abnormal relative humidity will also indirectly affect the storage life and storage quality of electronic components. For example, high-humidity environments will accelerate the aging speed of components and shorten their service life. Even if subsequent drying treatment is carried out, their original performance cannot be fully restored; electrostatic accumulation in low-humidity environments will not only damage the components themselves, but also adsorb dust and impurities in the air, attach to the surface of components, and affect their heat dissipation performance and electrical contact performance. At the same time, the synergistic effect of relative humidity and temperature will further exacerbate the damage to components——high temperature and high humidity environments will accelerate metal oxidation and mold growth, while low temperature and low humidity environments will exacerbate electrostatic accumulation and material embrittlement, bringing greater challenges to the storage of electronic components.

In view of the impact of relative humidity on the storage of electronic components, there are clear control standards and response measures in the industry. For conventional electronic components, the relative humidity of the storage environment needs to be controlled at 40%～60%, the temperature at 15℃～25℃, and the environment should be kept clean to avoid the invasion of dust and impurities; for precision humidity-sensitive components (such as humidity-sensitive resistors, precision sensors, and some integrated circuits), moisture-proof storage methods should be adopted, such as placing them in a moisture-proof cabinet (which can accurately control the humidity at 30%～50%), vacuum moisture-proof bag packaging, and placing desiccants (such as silica gel desiccants) in the packaging, and replacing desiccants regularly to ensure the moisture-proof effect; for electrostatic sensitive components, in addition to controlling humidity, anti-static protection should also be done well, such as using anti-static packaging, anti-static pallets, anti-static floors, and operators wearing anti-static clothes and anti-static wristbands to avoid static electricity generation and accumulation. In addition, regularly detecting and recording the relative humidity and temperature of the storage environment and adjusting the environmental parameters in a timely manner are also the key to ensuring the storage quality of electronic components.

In summary, relative humidity has a decisive impact on the storage of electronic components. Excessively high humidity will cause problems such as metal oxidation, internal moisture absorption and mold growth, while excessively low humidity will lead to damages such as electrostatic accumulation and material aging. Both will reduce the performance of components, shorten their service life, and even lead to component scrapping. Therefore, strictly controlling the relative humidity of the electronic component storage environment and following scientific storage standards and protective measures are important prerequisites for ensuring component quality, reducing storage losses, and ensuring the reliability of subsequent production and equipment operation. Whether it is electronic component manufacturers, warehousing enterprises or user units, they should pay attention to the control of relative humidity to avoid unnecessary economic losses caused by abnormal humidity.