With the all-round development and continuous upgrading of electronic information industry, the application of electronic components has gradually penetrated into all walks of life. However, the problem of welding end oxidation of electronic components has been puzzling colleagues in the industry. Starting with the mechanism of solder joint oxidation of electronic components, this paper analyzes the causes of solder joint oxidation, and gradually traces back the solderability solution of solder joint oxidation according to its causes. And try to explore the solderability standard of welding end oxidation. Keywords: oxidation solderability of electronic components Text: With the wide application of SMT technology in computer, network communication, consumer electronics, automobile electronics and other products, the SMT industry is more and more clearly indicating that it will usher in a golden age in its development history. At present, the patch rate of electronic components in China has exceeded 60%, but there is still a certain gap compared with 90% of electronic products in the world. It can be said that there is still a good room for development in China's patch industry. The healthy development of SMT industry is inseparable from the common prosperity of upstream and downstream links of the industry. SMT production mainly uses a screen printer to print solder paste on the circuit board, then uses a mounter to attach electronic components to the corresponding positions of the circuit board, and then uses a reflow oven to complete the soldering of PCB chip components. In this process, due to various reasons such as poor screen printing, inaccurate installation and improper furnace temperature, welding defects such as virtual welding, offset, solder ball, short circuit and bridge may be caused. In this paper, only from the difficult problem of solder joint oxidation of electronic components, a shallow exploration is made, hoping to find an effective method to solve the solder joint oxidation of electronic components, so as to realize its solderability. Oxidation, as the name implies, means that the welding end of electronic components reacts with oxygen in the air, producing some metal oxides attached to the surface of the pad, which affects the full contact between solder, PCB and the component body and forms unreliable welding. At present, the welding ends of electronic components in the market are generally made of copper and aluminum, and then plated with Sn/Bi, Sn/Ag, Sn/Cu, etc. Almost all electronic components contain copper. When the external environment meets the conditions for chemical reaction of metallic copper, an oxidation reaction occurs at the welding end of electronic components, resulting in reddish-brown cuprous oxide (Cu2O equation: 4Cu+O2= 2Cu2O). This is why we often see that the welding end is reddish brown, but sometimes it is grayish black. This is because cuprous oxide is further oxidized to produce black copper oxide (CuO equation is: 2 Cu2O +O2= 4CuO), and sometimes it is found that a green film appears at the welding end, which is a more serious oxidation reaction. Copper reacts with oxygen (O2), water (H2O) and carbon dioxide (CO2) in the air to produce basic copper carbonate (Cu2(OH)2CO3, also known as copper rust, the equation is 2Cu+O2+CO2+H2O= Cu2(OH)2CO3). Sometimes we also call cuprous oxide "red copper oxide", and sometimes it is also called copper oxide when it is not strict, which can be considered as a generalized copper oxide. This is the basic phenomenon of welding end oxidation of electronic components that we usually see. Of course, we can clearly see the oxidation phenomenon at the welding end from the color, but some oxidation phenomena are not so obvious that we can't analyze them from the color, but it is indeed oxidation that leads to poor welding. What method can be used to prove its oxidation phenomenon at this time? Below we will list several methods to prove oxidation: 1, wipe the welding end with rubber before welding to see if it can be tinned; 2. Grind the solderable pad with sandpaper to see if its color changes; 3. Wipe the welding end with alcohol, then add flux and adjust the furnace temperature or soldering iron to see if the welding effect is improved; 4. Replace the electronic components with the same material and different batches, and weld them in the furnace or electric soldering iron with the same process conditions, and compare the effects of the two welding methods to draw a conclusion; 5. Observe carefully with a microscope to see if there are any subtle changes in its color; 6. Measure the solderability of electronic components with a solderability tester; 7. Semi-automatic biochemical analyzer is used to determine the content of copper ions, mostly in the laboratory. The above methods can sometimes draw a conclusion, but sometimes the oxidation phenomenon is not obvious, and several methods need to be used comprehensively, and repeated attempts can be made to draw a correct conclusion. So, what causes the oxidation of electronic components? It is necessary to find the root of the problem from the mechanism of oxidation. The essence of oxidation reaction is that the valence increases and electrons are lost, and copper is oxidized as a reducing agent to produce oxidation products. This reaction must meet appropriate conditions (air; Oxidant or chemical reagents). Specific to electronic components, mainly refers to the lack of effective isolation measures, oxygen or some high-priced metal oxides, high-priced metal salts, nitric acid, nitrosulfate, nitroso, peroxy acid and other chemicals react with exposed electronic components, resulting in the oxidation of the welding end of electronic components, which can not be effectively welded. Generally speaking, this has a lot to do with our material management and environmental condition control. So what are the storage conditions of electronic components and the environmental control during operation? The storage of general electronic components is related to temperature and humidity, and there is also a shelf life limit. Most require a temperature of 22+/-5 degrees, a humidity of less than 70% and a physical period of one year. Most electronic products need to be operated and stored under dry conditions. According to statistics, more than 1/4 industrial manufacturing defects are related to the harm of humidity every year in the world. For the electronics industry, the harm of humidity has become one of the main factors affecting product quality. The harm of moisture to semiconductor industry is mainly manifested in: moisture can penetrate ic plastic package and invade IC from gaps such as pins, resulting in IC moisture absorption. SMT forms water vapor during heating, which leads to cracking of IC resin package and oxidation of metal inside IC devices, leading to product failure. In addition, in the process of PCB welding, the release of water vapor pressure will also lead to virtual welding. Other electronic devices, such as capacitors, ceramic devices, connectors, switches, solder, PCB, crystals, silicon wafers, synchronous oscillators, SMT adhesives, electrode material adhesives, electronic pastes, high-brightness devices, etc. , will be hurt by moisture; And electronic equipment in the process of operation, such as: between the semi-finished product in packaging and the next process; Power on PCB before and after packaging; IC, BGA, PCB and so on. Unpacked but not used up; Devices waiting to be welded in the tin furnace; Equipment that needs preheating after baking; Unpackaged finished products, etc. , will also be hurt by moisture. In addition, the finished electronic machine will still be harmed by humidity during storage and transportation. Ideally, the humidity of the storage environment of electronic components should be below 40%, and some varieties require lower humidity. Under realistic conditions, how do we manage the storage environment of electronic products by modern means? Let's analyze the whole production process of electronic products first. Our focus is mainly on the temperature and humidity of raw material warehouses, production workshops, finished product warehouses and transport vehicles. The traditional management method is that storekeepers or managers will check and record the humidity values of warehouses and workshops from time to time, and use humidification or dehumidification equipment to control the humidity of warehouses and workshops when abnormal conditions are found. This management method is time-consuming and laborious, and the recorded data will not be very objective because of human factors, which does not meet the requirements of modern enterprise management; In terms of logistics, there is basically no way for enterprises to manage the temperature and humidity changes on transport vehicles. So what methods can be used to make enterprise management both scientific and standardized? The automatic temperature and humidity recorder on the market now is an effective solution. This kind of equipment generally consists of measuring part, instrument body and PC interface. Its functional characteristics are: it saves us the trouble of manually recording temperature and humidity, and makes the work of viewing temperature and humidity data very simple. The recording interval can be adjusted from 3 seconds to 24 hours according to our own specific situation. We can also set the upper and lower limits of temperature and humidity alarm on the software, and the software also has the function of data analysis. The information recorded by the temperature and humidity recorder includes date, time, temperature and humidity data, which can be divided into tabular data and curve data, and can also realize real-time alarm function as needed, thus realizing effective storage and strong control of electronic components. We have done a good job in the storage and custody of electronic components, which does not mean that the phenomenon of welding end oxidation will not happen again. After all, the range that we can control artificially is limited. The ideal non-oxidation situation has not been completely solved from theory to reality. In particular, we are in a special stage of transition from lead-free welding. There are no standards for lead-free materials, printed boards, components, tests, etc., and even reliability testing methods. We are very worried about reliability. At present, the lead-free process, especially in China, is in a chaotic stage. Due to the mixing of lead and lead, especially when lead solder and lead-free process are used for components of lead-free solder terminals, serious reliability problems will occur. These problems are not only the problems that should be paid attention to in lead-free welding in the current transitional stage, but also the problems that should be paid attention to in lead-free welding in the transitional stage. There is no standard for the weldability of oxidation at the welding end, but we must try our best to find a solution to this problem. When the soldering terminals and pins of components, the pads of printed circuit boards are oxidized or polluted, or the printed circuit boards are wetted, there will be soldering defects such as poor wetting, virtual soldering, solder balls and cavities during reflow soldering. These defects are caused by oxidation. In the past, we found these defects and generally repaired them directly. We thought that the repaired solder joints were firmer and more perfect, and the overall quality of electronic components was improved. In fact, this traditional concept is incorrect. Because the repair work is destructive, it will shorten the product life. If the repair method is not correct, the damage to components and printed circuit boards will be aggravated, and even PCB will be scrapped. Therefore, we must be careful when solving the solderability of welding end oxidation, otherwise we may fall into a new misunderstanding. In order to avoid falling into a misunderstanding, the first thing to do is to avoid oxidation, do a good job in material storage, environmental temperature and humidity control, equipment maintenance and research on new materials, and carry out anti-oxidation treatment on electronic components. Of course, oxidation is everywhere, all the time, it happens quickly and has strong destructive power, and the most terrible thing is that it is almost inevitable. So what should we do with the oxidized electronic components? Simply scrapping electronic components is obviously not the most feasible way. After all, we still have the link of cost control. In an appropriate controllable range, the oxidized electronic components are treated to ensure their solderability. Here are some common solutions: 1. According to IPC-M 190 J-STD-033 standard, SMD components exposed to high humidity air environment must be placed in a drying oven with humidity lower than 10%RH, and the exposure time is 10 times to restore the "workshop life" of components. 2. For mild oxidation, because the oxide layer is thin and powdery, you can gently wipe off the oxide layer on the surface of the pin with a drawing eraser. In addition, you can also use a dust-free cloth to soak in washing water for scrubbing, and generally you can also remove oxidizing substances. 3. For those with severe oxidation, tin is generally used, and the specific steps are as follows: ① Rosin can be dissolved in alcohol with flux, and the higher the concentration, the better, so as to ensure that it can be well attached to the pins of the device; (2) The tin-lining solder can be made of the same alloy as the solder paste, the temperature of the small tin furnace is set at 350℃-400℃, and the tin-lining time is 3-5 seconds; (3) After tin lining is completed, there may be individual pins with tin tips or short circuits, which can be cleaned by soldering iron; (4) Check that the tinned pins can generally meet the requirements of welding to ensure the final welding quality. The above method is mainly aimed at pin spacing above 0.5mm, not at devices and BGA packages below 0.5 mm. For this kind of devices, rosin flux can be coated on pins or solder balls before soldering, and then heated at 1 10℃- 130℃ for 40-60 seconds, or the oxide layer can be removed. 4. Scrape off the oxide layer on the surface of the metal wire with a small blade to expose the metallic luster of the wire, and then coat it with a layer of rosin alcohol solution to avoid re-oxidation. 5. The use of anti-rust and anti-static two-in-one anti-rust bag can not only prevent static electricity, but also prevent corrosion and oxidation, making up for the shortcomings of traditional anti-static bags. 6. Fully realize painting, electroplating, oiling and vacuum packaging, and further shorten the contact with the outside world before electronic components are put into processing. 7. Standardize the order of production site and strengthen the management of front-line employees. All personnel who come into direct or indirect contact with electronic components must be equipped with antistatic rubber finger covers and foot covers (antistatic work shoes). On the one hand, effective electrostatic protection is carried out, on the other hand, the oxidation problem caused by stains and sweat stains is avoided. 8, weldability test, verify the degree of oxidation of electronic components, and take corresponding measures according to its situation. This method is generally used in scientific research units and the trial-production stage before mass production. At present, the domestic standards of "weldability test" are:

Test method of precious metal paste for thick film microelectronics technology-Solderability and solderability test

GB/T 2423.32- 1985 Basic environmental test procedures for electrical and electronic products-Wet weighing method weldability test method

GB/T 2424.2 1- 1985 basic environmental test procedures for electrical and electronic products-guidelines for wet weighing solderability test.

Test method for bare wires (GB/T 4909. 12- 1985) weldability test tin ball electroplating.

QJ 2028- 1990 Coating weldability test Method.

SJ/T 10669- 1995 Solderability test of surface mounted components solution. At present, there is no unified standard in China, but this problem that has been bothering us for a long time must be solved. After all, the consequences of oxidation are not only the invisible expansion of our costs, but also the reliability and stability of our products, which will affect the healthy development of our entire industrial chain. With the continuous development of the electronic industry, I believe that colleagues in the industry will also have their own research, opinions and achievements on the oxidation of electronic components. When we are looking for the solderability solution of welding end oxidation, we must not leave the source of solving the problem-researching new materials and producing anti-oxidation electronic components by new technology. As long as the possibility of oxidation is cut off from the root, coupled with strict control and management of external conditions, it is not necessary to analyze the weldability of welding end oxidation. However, we still have a certain distance from this ideal state, but I believe we won't wait long.