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
[53][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.
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3.2. Chemical Electrochemical Protection
Chemical electrochemical protection mainly uses the coating of protective coatings to increase the corrosion resistance
[31][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
[54][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
[37][18].
4.1. InSb Chips
Considering PCB failure analysis techniques, Zhou et al.
[55][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
[17][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
[56][21]. Bouslama et al
[57][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 H
2O
2 repairs the corroded bumps on the InSb chips.
4.2. IC Chips
With regard to the corrosion of IC chips, Fu et al.
[13][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)
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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;
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- (2)
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Strengthening the sealing effect on the chip to prevent electrochemical corrosion of airborne ions with the chip
[58][24].
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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
[37][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.
[59][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
[41][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
[60][27].