Protection Processes of Electronic Components

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1		Jiantao Qi	--	2640	2023-09-07 08:17:14	\|
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This entry is adapted from the peer-reviewed paper 10.3390/met13091508

As a necessary part of all electronic devices, equipment and systems, electronic components play a vital role in the global economy. Since the corrosion of a single electronic component may directly affect the normal operation of the entire electronic system, the failure of electronic components has now become the most important cause of electrical system failure and has become a major obstacle to China’s transformation into a scientific and technological power. Therefore, it is urgent to study the corrosion failure process of electronic components and the means of effective protection.

electronic components corrosion manufacturing encapsulation physical protection chemical electrochemical protection InSb chips IC chips Sn–Zn solder chips

1. Introduction

“The 14th Five-Year Plan” emphasizes the need to “accelerate digital development and build a digital China” ^[1]. In the process of transformation and upgrading of the global manufacturing industry towards intelligence, the basic equipment control system, especially the electronic components, bears an unshirkable responsibility, and has become the key to structuring the digital economy. Electronic components include common electromechanical components, semiconductor discrete devices, optoelectronic devices, electric vacuum devices, microwave devices and components, and integrated circuits. Among them, the chip is the basic carrier of the integrated circuit and is also the collective name for semiconductor electronic components.

The ongoing development of electronic components towards miniaturization and a high degree of integration is now placing higher demands on the reliability of single components. The degree of corrosion of electronic components determines their electrical functional characteristics, including the safety as well as the reliability of the system. Currently, the failure of electronic components accounts for 70% of the causes of failure in electrical systems ^[2]. The corrosion of electronic components is mainly due to atmospheric corrosion; the corrosion types include uniform corrosion, pitting corrosion, galvanic coupling corrosion, intergranular corrosion, corrosion under stress, crevice corrosion and microbial corrosion. In hot and humid climates, such as the South China Sea islands and other special environments, high temperature, high humidity, and high salt spray together constitute harsh conditions that can cause serious corrosion effects on electronic components. The same batch of navigational equipment operating in the islands and reefs of the Cangzhou environment showed three times greater levels of corrosion than when used in less harsh environments ^[3]. The intensification of corrosion means that the probability of failure of electronic components increases. Zhang et al. ^[4] found after three years of field research that the failure rate of electronic equipment in aircraft serving in coastal airport environments was two to three times that of aircraft serving inland. As a key component of electronic components, chips play an important role in the national economy and play an important role in the country’s economic development. So, in order to improve chip life and reduce product costs, chip corrosion protection technology is in urgent need of development. In view of this, the study of the mechanisms of corrosion damage of electronic components, and the taking of protective measures to improve the service life of electronic components for the development of the electronic components industry has important economic as well as social benefits.

2. Protection Processes for Manufacturing and Packaging Processes

The protection process used in the manufacturing and packaging of electronic components determines the final corrosion resistance of the overall device. Considering the chip manufacturing process as an example, chip manufacturing is mainly divided into chip design, wafer production, packaging production, cost testing, and other major links, while crystal manufacturing and packaging manufacturing is the key to the final performance of the chip. In the manufacturing and packaging process whether the process performance is good or bad will ultimately lead to the chip corrosion effect of fast or slow; the above two processes impose certain anti-corrosion measures, which can effectively slow down the degree of chip corrosion later.

2.1. Manufacturing Protection

The processes of chip manufacturing are exposed to the environment, and pollutant particles in the environment can adhere to the chip surface and cause chip corrosion at a later stage, so environmental pollution control techniques need to be strictly enforced. The control technology includes indoor and outdoor air pollution control technology, pollution control technology, etc. Meanwhile, with the continuous rapid development of ultra-large-scale integrated circuit production technology, the scientific and technological community has imposed more stringent requirements for the production environment chemical pollution control index. Therefore, the following measures are focused on protection in the chip manufacturing process:

(1): When designing the passivation layer for the bonding of the chip to the packaging material, attention should be paid to improving the resistance to water vapor corrosion in the pressure zone of the IC while not affecting the bonding quality.
(2): Controlling the etching process of the aluminum layer in the bonding area, extending the chemical cleaning time after etching, and reducing the residue of fluorinated compounds on the surface of the aluminum layer ^[5].
(3): The storage and transportation environment of the chips in the post-etching period must not be too humid, and packaging materials must not use materials containing fluorine and halogen elements.

In industrial practice, the chip manufacturing protection process for the final corrosion resistance of the finished product plays a crucial role; however, current actual production and manufacturing factory corrosion awareness is not strong—the protection process needs to be upgraded.

2.2. Encapsulation Protection

As a common integrated chip protection technology, plastic-sealed chips have contributed to the size, lifetime, and functionality of chips. In a study by Zhou et al. ^[6] on plastic-sealed integrated circuits, it was pointed out that the non-enclosed nature of the plastic seal makes the chip subject to water vapor intrusion corrosion as well as airborne contaminant corrosion. Hermetic packages rely on a solid enclosure made of impermeable material, and are sealed to protect electronic components by keeping them in an environment with low relative humidity. Internal water content can come from stagnant water within the package before and during sealing, as well as from outgassing of adsorbed molecules. Therefore, the following controls can be implemented on the chip package:

(1): Choosing a suitable environment for placing the chip after opening the package and controlling the time it is exposed to purified air;
(2): Prevention of delamination and moisture absorption problems in the plastic seal is the key to packaging chips.

Yu et al ^[7] found that at the same potential, the N_Dr value of solder in alkaline solution is lower than that in acidic solution (as shown in Figure 1), which means that the passivation film in alkaline environment has better corrosion resistance. The environmental conditions of chip storage will affect the corrosion resistance of the solder on the chip, which in turn affects the overall performance of the chip.

Figure 1. MS curves of solder Sn-0.7Cu in different environments (acidic (a) and alkaline (b) artificial sweat) ^[7].

At the same time, the packaging material serves as a barrier to isolate the chip from the surrounding environment. By choosing green, highly adhesive, low-stress, and low-moisture absorption packaging materials, the contact between the chip surface and water, dust, and other substances in the environment, can be effectively reduced, thus reducing the strength of corrosion, and extending the life of the chip ^[8].

For common sealing materials, the encapsulation material must have high purity to reduce the concentration of Na⁺ and Cl⁻ plasma impurities in the plastic sealing materials to avoid the impurity ions leading to accelerated corrosion; for the filler material, higher adhesion is required to prevent corrosion of the aluminum layer in the molded area due to moisture intrusion ^[9]. Moreover, the addition of ion trapping agents during the production of plastic sealing materials has the same effect on the control of encapsulation materials ^[10].

The bio-implantability of new chips has now developed into a research “hotspot” in medicine, electronics, materials, and their interdisciplinary aspects. As implantable chips typically remain in the body for decades, their corrosion resistance needs to be further developed and tested for high-accuracy predictions to mitigate chip corrosion or adverse tissue effects. The key to improving the corrosion resistance of implantable chips is to ensure their implantation integrity (Anne et al. ^[11]), which must ensure that the chip functions properly for its expected lifetime and does not damage the organism after implantation. Common materials used to encapsulate biomaterials are metals, glass, ceramics, and polymers, with polymeric encapsulants, particularly poly(parylene), often used for their corrosion resistance and stability ^[12]. However, the containment properties of polymers are limited relative to other plastisol materials ^[13]. On this basis, Hogg et al. ^[14] proposed polymer multilayer stacks for implantable chip packaging materials, where the lack of molecular density of the polymer and the low permeability of the SiO_X layer form a stack as a means to achieve the required closure for chip protection. Therefore, for implantable chip packaging materials, the choice of polymer multilayer stacking applications is preferable.

3. Types of Protection Processes

Electronic component protection processes can be divided into physical and chemical-electrochemical protection, depending on the principle of protection. Physical protection is achieved by adapting the process to the characteristics of the environment in which it is used, while chemical-electrochemical protection extends the chemical or mechanical properties of the material by applying protective coatings to increase the degree of protection.

3.1. Physical Protection

Physical protection mainly considers the environmental effects outside the electronic components and protects them from harmful effects, such as moisture and electromagnetic radiation. In terms of physical protection, the following protective measures can be carried out:

(1): Improve the encapsulation hermeticity: choose high-quality encapsulation substrates, sealants, and filling media as encapsulation materials, and, at the same time, strictly follow the encapsulation process requirements to execute each encapsulation step, such as curing and hot-pressing welding, to ensure the stability and consistency of the process parameters. A strict inspection system should be established during the encapsulation process to screen and deal with possible defects in a timely manner to ensure that each encapsulated part is defect-free and hermetically sealed.
(2): Post-treatment of the welding and assembly process: The post-treatment of the welding and assembly process refers to the relevant treatment carried out at the end of the welding or assembly process. For example, the use of cleaning solutions, ultrasonic cleaners, and other cleaning methods to remove the surface of electronic components, such as oxides, oil, solder slag, and other impurities ^[15]; the need to encapsulate the components through drying, vacuum drying and other ways to ensure the dryness of their internal features, so as to extend the life of electronic components. The purpose of post-treatment of the soldering and assembly process is to eliminate impurities, such as condensation and chemical substances, that may have a negative impact, thus achieving a protective effect.

3.2. Chemical Electrochemical Protection

Chemical electrochemical protection mainly uses the coating of protective coatings to increase the corrosion resistance ^[16]. Electrochemical corrosion protection is a method of preventing or mitigating metal corrosion by applying measures to metal equipment based on electrochemical principles to make it the cathode in a corrosion cell. In the application of electronic components, chemical electrochemical protection technology needs to take into account the physical and chemical properties of the protective coatings, the device, the environment, and other factors to ensure that the protective effect is reliable. Special attention needs to be paid to the thickness of the protective coating on the surface and consideration should be given to the tolerance fit between the components to prevent the coating from being too thick, leading to component sealing failure and resulting in accelerated corrosion.

In addition, in hot and humid climates, the South China Sea islands and other special environments, taking into account the high temperature, high humidity and high salt spray environmental conditions, condensation evacuation technology, terminal sealing technology, space rust inhibitors, flow sealing technology, etc., can be used to prevent chip surface condensation and, thus, achieve the purpose of protection.

4. Protection Processes for Several Common Chip Materials

The corrosion protection process for electronic components needs to be determined with respect to the specific type, material selection, and application scenario of the electronic components. Considering the application range and frequency of various types of electronic components under actual circumstances, the commonly used indium antimonide chips, microelectronic devices (IC chips), and Sn–Zn solder chips are analyzed for the protection process, respectively. Indium antimonide (InSb) chips are widely used in military applications, such as infrared detectors, astronomical observation, and missile positioning, due to their unique physicochemical properties and excellent compatibility, as well as their outstanding performance in infrared detection ^[17]. IC chips are widely used in everyday home appliances, televisions, computers, stereos, and cameras as a type of chip that integrates a large number of miniature electronic devices in an integrated circuit. In the manufacturing process of semiconductor chips, soldering technology plays a crucial role. Sn–Zn solder is a lead-free solder, which is widely used in the manufacture of Sn–Zn solder chips in electronic products because of its low melting point and good fluidity ^[18].

4.1. InSb Chips

Considering PCB failure analysis techniques, Zhou et al. ^[19] conducted a study of the surface after corrosion. When a chip undergoes corrosion, its surface becomes uneven. Similarly, when an InSb chip undergoes corrosion, the roughness of its surface makes the current on the chip cause an increase in leakage current and a decrease in chip performance. Using the opposite idea, the surface roughness of the chip can be repaired as a way of implementing a re-healing technique for corroded chips ^[20]. However, due to the low hardness of the material of this chip, it is not easy to master the strength required when performing polishing ^[21]. Bouslama et al ^[22] experimentally verified that the repair of corroded chips can be solved under the following conditions: when the pressure is lower than 4.5 N, the speed is lower than 80 r/min, the feed ratio is 1:1, the drop rate is less than 1 drop/s, or the addition of oxidising agent H₂O₂ repairs the corroded bumps on the InSb chips.

4.2. IC Chips

With regard to the corrosion of IC chips, Fu et al. ^[23] pointed out that it is often related to the ambient humidity and temperature as well as the chlorine and copper plasma in the air. Therefore, the protection of IC chips should start from these points:

(1): Adjusting the reflow soldering oven temperature profile to appropriately increase the initial pre-treatment time and temperature and reduce the amplitude of temperature change on the components;
(2): Strengthening the sealing effect on the chip to prevent electrochemical corrosion of airborne ions with the chip ^[24].

Although there are differences in the causes of corrosion between InSb chips and IC chips, the reasonableness of the above chip protection techniques can be seen in the protection measures for both.

4.3. Sn–Zn Solder Chips

Sn–Zn-based, Pb-free solders have poorer corrosion resistance than other Sn-based, Pb-free solders due to the extremely high chemical activity of Zn in Sn–Zn solders and the susceptibility of Sn–Pb alloys to oxidation and corrosion ^[18]. For Sn–Zn solders as a class of Pb-free solders, alloying is the most common means of improving the corrosion resistance of Sn–Zn solder chips. The results of Zhao et al. ^[25] showed that the addition of trace amounts of Ag to Sn–Zn solders can generate Ag–Zn IMC, which inhibits Zn chemical activity and, thus, improves its corrosion resistance. In addition, once corrosion products are generated on the surface of Sn–Zn solder chips, the pores, pits, and cracks on the surface will lead to further contact with the corrosive medium, thus accelerating corrosion. The addition of trace amounts of Ti can slow down electron transfer and stabilize the surface area of the solder by means of a uniform, dense passivation film formed on the surface of the alloy, thereby enhancing its corrosion resistance ^[26]. It is worth noting that, when too much Ti is added, exceeding 0.1% of the alloy mass fraction in the Sn–Zn solder, the continuous arrangement of corrosion products will be broken due to the generation of Sn3Ti2 and Sn5Ti instead, expanding the contact surface area and leading to accelerated corrosion ^[27].

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Update Date: 07 Sep 2023

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