What are the main components and characteristics of SMT solder paste?

BROADLY SPEAKING, THE COMPOSITION OF SOLDER PASTE CAN BE DIVIDED INTO TWO MAIN PARTS, NAMELY FLUX & SOLDER POWDER.

(1) The main components of flux and its function: A. Activation: This component is mainly used to remove oxides on the surface of PCB copper film pads and parts welding parts, and has the effect of reducing the surface tension of tin and lead; B. THIXOTROPIC: its main function is to adjust the viscosity and printing performance of solder paste, and prevent tailing and adhesion in the printing process; C. Resin (RESINS): The main function of this component is to enhance the adhesion of solder paste, protect the PCB after soldering, and prevent it from oxidizing again, which is very important for the fixation of parts; D. Solvent: This ingredient is the solvent of the flux component, which plays a role in adjusting the uniformity during the stirring process of the solder paste, and has a certain impact on the service life of the solder paste.

(2) Solder powder: Solder powder, also known as tin powder, is mainly composed of tin-lead alloy, the general ratio is 63/37, and when there are special requirements, a certain amount of silver, bismuth and other metals will be added to the tin-lead alloy to make tin powder. Generally speaking, the relevant characteristics and quality requirements of tin powder are as follows: A. The particle form of tin powder has a great influence on the working performance of solder paste: the important point is that the particle size of tin powder should be evenly distributed, which involves the problem of the particle size distribution ratio of tin powder. In domestic solder powder or solder paste manufacturers, the uniformity of solder powder is often measured by the distribution ratio. Taking 25 - 45 μm tin powder as an example, it is usually required that the index ratio of particles about 35 μm is about 60%, and the part below 35 μm and above accounts for about 20% each; In addition, the shape of the tin powder particles is also required. According to the relevant provisions of the "General Specification for Tin-Lead Paste Solder" (SJ/T 11186 - 1998) of the Electronic Industry Standard of the People's Republic of China: "The shape of the alloy powder shall be spherical, but the maximum ratio of the long axis to the minor axis is 1.5 is allowed. If the user agrees with the manufacturer, it can also be used for other shapes of alloy powder. "In actual work, it is usually required that the ratio of the length and short axis of the solder powder particles is generally less than 1.2, and the requirements cannot meet the basic requirements, and in the use of solder paste, it is likely to affect the printing, dispensing and soldering effect of solder paste. B. The ratio of solder powder to flux in different solder pastes is also different. When selecting solder paste, different solder pastes should be selected according to the products produced, production processes, the precision of soldering components and the requirements for soldering effects: according to the relevant provisions of the "People's Republic of China Electronic Industry Standard "General Specification for Solder-Lead Paste Solder" (SJ/T 11186 - 1998)", "the percentage (mass) content of alloy powder in solder paste should be 65% - 96%, and the measured value of the percentage (mass) content of alloy powder shall not deviate from the predetermined value of the order order of ±1%". Usually in actual use, the solder powder content of the selected solder paste is about 90%, that is, the ratio of solder powder to flux is roughly 90:10; Most of the common printing processes use solder paste with a tin powder content of 89 - 91.5%; When using the needle spot process, solder paste with a solder powder content of 84 - 87% is mostly used; Reflow soldering requires that the pin of the device is soldered firmly, the solder joint is full and smooth, and there is a solder climb of 1/3 to 2/3 height in the direction of the height of the end of the device (resistor vessel), and the content of metal alloy in the solder paste has a certain impact on the thickness of the solder (that is, the fullness of the solder joint) after reflow soldering. In order to confirm the existence of this problem, relevant experts have done relevant experiments, and the final experimental results are now displayed

As the metal content decreases, the thickness of the solder after reflow soldering decreases, and in order to meet the requirements for the amount of solder in the solder joint, a solder paste with an 85% to 92% content is usually used. C. The "low oxidation degree" of tin powder is also a very important quality requirement, which is also a problem that needs to be paid attention to in the production or storage process of tin powder. If you don't pay attention to this problem, the solder paste made with solder powder with a high degree of oxidation will seriously affect the soldering quality during the soldering process.

Classification and selection criteria of solder paste In general, the general category of solder paste is selected first, and then selected according to the alloy composition, granularity, viscosity and other indicators.

(1) Classification:

A. ORDINARY ROSIN CLEANING TYPE [DIVIDED INTO RA (ROSIN ACTIVATED) AND RMA (ROSIN MILDLYACTIVATED)]: THIS TYPE OF SOLDER PASTE SHOWS A GOOD "TINNING SPEED" IN THE SOLDERING PROCESS AND CAN ENSURE A GOOD "SOLDERING EFFECT". After the soldering work is completed, there will be more rosin residue on the surface of the PCB, which can be cleaned with appropriate cleaning agent, and the cleaned board surface is smooth and clean without residue, which ensures that the cleaned board surface has good insulation impedance, and can pass the technical testing of various electrical properties;

B. NC (NO CLEAN)): After the soldering of this solder paste is completed, the PCB board surface is relatively smooth and clean, with less residue, which can be tested by various electrical performance technologies and does not need to be cleaned again, which shortens the production process and accelerates the production progress while ensuring the quality of soldering;

C. WATER-SOLUBLE SOLDER PASTE [WMA (WATER SOLUBLE PASTES)]: DUE TO TECHNICAL REASONS, THE SOLDER PASTE PRODUCED IN THE EARLY STAGE GENERALLY HAS TOO MUCH RESIDUE ON THE PCB BOARD SURFACE, AND THE ELECTRICAL PERFORMANCE IS NOT IDEAL, WHICH SERIOUSLY AFFECTS THE PRODUCT QUALITY. At that time, CFC cleaning agents were mostly used for cleaning, and many countries have banned CFC because it is not good for environmental protection. In order to meet the market demand, water-soluble solder paste was born, and after the soldering work is completed, the residue can be cleaned with water, which not only reduces the production cost of customers, but also meets the requirements of environmental protection.

(2) Selection criteria:

1. Alloy components: In general, the selection of Sn63/Pb37 solder alloy components can meet the welding requirements; For the soldering of devices with silver (Ag) or palladium (Pd) coating, solder paste with an alloy composition of Sn62/Pb36/Ag2 is generally selected; For PCB soldering with devices that are not resistant to thermal shock, select a solder powder containing Bi.

2. Viscosity of solder paste: In the workflow of SMT, there is a process of moving, placing or handling the PCB from printing (or spotting) the solder paste and pasting the components to the reflow heating process. In this process, in order to ensure that the printed (or pointed) solder paste is not deformed and the components that have been attached to the PCB solder paste are not displaced, it is required that the solder paste should have good adhesion and retention time before the PCB enters the reflow soldering heat. A. For the viscosity index (i.e., viscosity) of solder paste, "Pa· S" is the unit. Among them, 200 - 600Pa· Solder paste is more suitable for needle dispensing or production process equipment with a high degree of automation; The printing process requires a relatively high viscosity of solder paste, so the viscosity of solder paste used in the printing process is generally 600 - 1200 Pa· S or so, suitable for manual or mechanical printing; B. High viscosity solder paste has the characteristics of good solder joint pile forming effect, and is more suitable for fine pitch printing; The low-viscosity solder paste has the characteristics of faster falling, no cleaning and brushing, and time-saving during printing; C. Another characteristic of the viscosity of solder paste is that its viscosity will change with the stirring of solder paste, and the viscosity will decrease when stirring; When stirring is stopped and left to sit slightly, its viscosity returns to its original shape. This is extremely important for the selection of solder pastes with different viscosities. In addition, the viscosity of solder paste has a lot to do with temperature, and in general, its viscosity gradually decreases as the temperature increases.

3. MESH (MESH): MOST DOMESTIC SOLDER PASTE MANUFACTURERS USE THE "GRANULARITY" OF SOLDER POWDER TO CLASSIFY DIFFERENT SOLDER PASTES, WHILE MANY FOREIGN MANUFACTURERS OR IMPORTED SOLDER PASTES USE THE CONCEPT OF "MESH (MESH)" TO CLASSIFY DIFFERENT SOLDER PASTES. The basic concept of mesh (MESH) refers to the number of mesh holes per square inch area of the screen. In the actual tin powder production process, most of the screens with several layers of different meshes are used to collect tin powder, because the mesh size of each layer of screen is different, so the particle size of the tin powder through each layer of mesh is not the same, and the particle size of the tin powder particles collected finally is also a regional value. A. From the above concept, the larger the mesh index of solder paste, the smaller the particle diameter of the solder powder in the solder paste; The smaller the mesh, the larger the particles of solder powder in the solder paste. Refer to the following table for comparison:

B. If the manufacturer of solder paste selects solder paste according to the mesh index of solder paste, it should be determined according to the spacing between the solder joints with the smallest distance on the PCB: if the solder joint spacing is large, you can choose the solder paste with a smaller mesh; On the contrary, when the spacing between each solder joint is small, a solder paste with a large mesh number should be selected; Generally, the particle size diameter is about 1/5 of the template opening.

Attention should be paid to the use of solder paste

(1) Storage requirements for solder paste: Solder paste should be sealed and stored in a freezer with constant temperature and humidity, and the storage temperature should be 0 °C - 10 °C. If the temperature is too high, the alloy powder and flux in the solder paste will undergo a chemical reaction, resulting in a decrease in viscosity and activity, affecting its properties; If the temperature is too low, the resin in the flux will crystallize and the solder paste will deteriorate. In the process of storage, it is more important to maintain a "constant temperature", if in a short period of time, the solder paste continues to repeatedly change different temperatures in various environments, which will also change the performance of the flux in the solder paste, thereby affecting the soldering quality of the solder paste.

(2) Requirements before use: When the solder paste is taken out of the freezer (or refrigerator), it should be in a sealed state and wait for it to return to room temperature before opening, which takes about 2-3 hours. If it is opened as soon as it is taken out of the freezer, the temperature difference will cause the solder paste to condense and condense into moisture, which will lead to the formation of solder beads during reflow soldering; However, it is not possible to return the solder paste to room temperature by heating, and the rapid heating will make the performance of the flux in the solder paste worse, thus affecting the soldering effect. This is also a problem that solder paste manufacturers need to pay attention to in the process of use.

(3) Precautions when using: 1. Scraper pressure: to ensure that the edge of the printed solder joint is clear, the surface is smooth, and the thickness is appropriate; 2. Scraper speed: to ensure that the solder paste is rolling rather than sliding relative to the scraper, under normal circumstances, 10 - 20mm/s is appropriate; 3. Printing method: contact printing is appropriate; In addition, when in use, the solder paste should be fully stirred, and then added to the printing screen according to the printing set amount. In the case of long-term printing, due to the volatilization of the solvent in the solder paste, it will affect the demoulding performance of the solder paste during printing, so the container for storing the solder paste can not be reused (can only be used once), the remaining solder paste on the stencil after printing should be stored in other clean containers, and the next time it is used, it should be checked whether there is agglomeration or solidification in the remaining solder paste, if it is too dry, the solder paste diluent provided by the supplier should be added to dilute before use. When the operator is working, care should be taken to avoid direct contact between the solder paste and the skin. In addition, the printed substrate should be welded on a daily basis.

(4) Working environment requirements: The best condition of the solder paste workplace is: temperature 20 - 25 °C, relative humidity 50 - 70%, clean, dust-free, anti-static.

Adjustment of the reflux curve

The purpose of reflow soldering: to make surface-mount electronic components (SMDs) and PCBs solder together correctly and reliably; Process principle: When the temperature of the solder, the component and the PCB reaches above the melting point temperature of the solder, the solder melts, fills the gap between the component and the PCB, and then cools and solidifies the solder to form a solder joint;

Process:

1. The first heating zone (preheating zone) The purpose of heating up: raising the temperature of solder paste, PCB and components from room temperature to the predetermined preheating temperature, and the preheating temperature is lower than the melting point of the solder. An important parameter in the warming section is the "warming rate", which should generally be valued at 1 - 2.0 °C/S. Due to the different heat absorption rates of PCBs and components, the heating rates of each component will also be different, resulting in a gradient in the temperature distribution on the PCB surface. Since the temperature of all the points in this section is below the melting point of the solder, the presence of a "temperature gradient" is not a big deal. At the end of the first warming zone, the temperature is about 100 degrees - 110 degrees; The time is about 30 - 90 seconds, and about 60 seconds is appropriate.

 2. Thermal insulation area (also known as dry penetration area) The purpose of "thermal insulation" is to allow the flux in the solder paste to have enough time to clean the solder joints and remove the oxide film of the solder joints, and at the same time make the PCB and components have enough time to reach temperature equilibrium and eliminate the "temperature gradient"; This phase should be set at 60 - 120 seconds; At the end of the holding section, the temperature is 140 - 150 degrees.

 3. The temperature of the second heating zone rises from about 150 degrees to 183 degrees, this temperature zone is the activation period of the activator, and it is the area where the temperature of the PCB board is uniform and consistent, the general time is 30 - 45 seconds, and the time should not be too long, otherwise it will affect the soldering effect.

4. Soldering area: The solder is melted in the soldering area and the purpose of good brazing of the PCB and component pins is achieved. When the temperature in the soldering area begins to rise rapidly, the components will still absorb heat at different rates, resulting in a temperature difference again, so it is necessary to control the temperature and eliminate this temperature difference. Generally speaking, the maximum temperature of this section should be more than 30 - 40 degrees higher than the melting point of the solder (183 degrees), and the time should be about 30 - 60 seconds, but the time above 225 degrees should be controlled within 10 seconds, and the time above 215 degrees should be controlled within 20 seconds; If the temperature is too high, the components will be damaged, and if the temperature is too low, it will cause wetting of some solder joints and poor soldering. In order to avoid and overcome the above defects, the forced hot air reflow soldering effect is better.

 5. Cooling zone Purpose: to solidify the solder, form a welded joint, and eliminate the internal stress of the solder joint as much as possible; The cooling rate should be less than 4 degrees/second, and the cooling to 75 degrees is sufficient. In short, the principle of the establishment of the reflow temperature curve is that the temperature rise rate of the welding area should be as small as possible, after entering the second half of the welding area, the heating rate should be increased rapidly, and the time control of the maximum temperature of the soldering area should be short, so that the PCB and SMD are less subject to thermal shock, and it must take a long time to adjust the temperature curve before production, and the reflow soldering equipment with several temperature zones should be selected according to the product characteristics and batch.

In the process of using solder paste, from the printing of solder paste, the placement of SMD to reflow soldering, we often encounter a variety of problems, which often plague the users of solder paste, and how to analyze and solve these problems has also become a problem for our solder paste manufacturers. Therefore, it is very necessary for solder paste manufacturers to continuously improve the professional quality and business level of marketing personnel, and assist users to deal with these problems properly and timely after the product is delivered to users, which can also reflect the service strength of suppliers. Here, I will only briefly introduce several common problems and cause analysis, which are also common problems encountered when serving customers in the past, for the reference of readers and users:

(1) When double-sided chip welding, the falling off of components Double-sided welding is becoming more and more common in the SMT surface mount process, under normal circumstances, the user will first print, mount the components and solder on the first side, and then process the other side, in this process, the problem of component falling off is not common; In order to save the process and save the cost, some customers omit the first side of the first side of the welding, but the welding of both sides at the same time, the result is that the component falls off during the welding becomes a new problem. This phenomenon is due to the insufficient vertical fixing force of the solder on the component after the solder paste is melted, and the main reasons are: 1. The component is too heavy; 2. The weldability of the welding leg of the component is poor; 3. Poor wettability and solderability of solder paste; If the second and third reasons are improved, this phenomenon still exists, we will suggest that customers should first use red glue to fix these falling components, and then carry out reflow and wave soldering, and the problem can be basically solved.

(2) Solder beads on the PCB surface after soldering: This is a common problem in the SMT soldering process, especially in the early stage of using a new supplier's products, or when the production process is unstable. After cooperating with the user customers and through a large number of experiments, we finally analyzed that the causes of solder beads may be as follows:

 1. The PCB board is not fully preheated during reflow soldering;

 2. The reflow soldering temperature curve is set unreasonably, and there is a large gap between the temperature of the plate surface and the temperature of the welding area before entering the welding area;

 3. The solder paste fails to fully recover to room temperature when it is taken out of the cold storage;

 4. Exposure to air for too long after the solder paste is opened;

 5. There is tin powder splashed on the PCB board surface during the patch;

 6. During printing or handling, there are oil stains or moisture sticking to the PCB board;

7. The flux itself in the solder paste is unreasonable, and there are non-volatile solvents or liquid additives or activators; The first and second reasons above can also explain why the newly replaced solder paste is prone to such problems, and the main reason is that the current temperature curve does not match the solder paste used, which requires customers to obtain the temperature profile that their solder paste can adapt to when changing suppliers; The third, fourth and sixth reasons may be caused by improper operation by the user; The fifth reason may be that the solder paste is not properly stored or the solder paste is beyond the shelf life, resulting in the non-stickiness of the solder paste or the viscosity is too low, which causes the splashing of solder powder during mounting; The seventh reason is the production technology of the solder paste supplier itself.

(3) After the welding is completed, there are many uncleared residues on the plate surface. Customers generally report that there are many residues on the PCB surface after soldering, which not only affects the smoothness of the board surface, but also has a certain impact on the electrical performance of the PCB. The main causes of excessive residue can be analyzed from the following aspects:

 1. In the process of promoting solder paste, if the product selection is improper due to failure to fully understand the customer's plate condition and specific needs, or other factors; For example, the customer clearly stated that he needed to use solder paste that was no-clean and residue-free, but the solder paste manufacturer provided rosin resin-based solder paste, resulting in a large amount of post-solder residue after use. In such cases, solder paste manufacturers need to pay special attention to product promotion to ensure that they accurately grasp customer needs and avoid similar problems.

 2. The content of rosin resin in solder paste is high or its quality is poor; This usually reflects a lack of technology on the part of solder paste producers. (4) The following problems may occur in the printing process: smearing, paper adhesion, blurry images, etc. This problem is relatively common in the printing process, and after in-depth analysis, we have summarized that the main reasons include the following aspects:

 1. The viscosity of solder paste is insufficient, which is difficult to meet the requirements of the printing process; This issue may stem from improper selection of solder paste, or if the solder paste is past its recommended expiration date. It is advisable to communicate and coordinate with the supplier to find a solution.

 2. Printing quality problems may stem from improper machine settings or non-standard operation by operators. For example, if the speed and pressure of the doctor blade are not set properly, it will directly affect the printing quality. In addition, the proficiency of the operator, including the mastery of printing speed, pressure control and number of prints, also has a significant impact on the final printing result.

 3. The gap between the network board and the substrate is too wide;

 4. Poor fluidity of solder paste;

5. Before using the solder paste, it is not stirred thoroughly, resulting in uneven mixing of the solder paste.

 6. During the screen printing operation, it was found that there was an uneven coating of the latex mask on the screen screen.

7. The metal content in the solder paste is insufficient, which is caused by the high proportion of flux components.

(5) The amount of tin in the solder joint is insufficient or uneven: The reasons for the lack of tin on the solder joint mainly include the following points:

1. The activity of the flux in the solder paste is insufficient, resulting in the oxide layer of the PCB pad or SMD soldering position not being completely removed.

 2. The wetting effect of the flux in the solder paste is not good.

3. Obvious oxidation and corrosion in the PCB pad or SMD soldering area are detected.

 4. If the preheating time is too long or the preheating temperature is too high during the overflow soldering process, it will lead to the loss of flux activity in the solder paste. 5. If it is found that the tin layer is not full in some solder joints, it may be due to the fact that the solder paste is not fully stirred before use, resulting in the flux and solder powder not being fully mixed evenly.

6. The temperature of the reflow soldering area is low;

7. The amount of solder paste applied in the solder joint area is insufficient.

(6) Solder joints are not smooth or shiny: In the field of SMT soldering technology, customers generally have certain expectations for the brightness of solder joints. Although it is true that this is a common problem in daily work, many times this request is more of a subjective feeling of the customer. In fact, there is no uniform evaluation standard for the brightness of solder joints. In short, the main causes of solder joints are as follows:

 1. There is obviously a certain difference between the products soldered without silver solder paste and the products soldered with silver solder paste. Therefore, it is important for customers to detail their specific requirements for solder joint performance to their suppliers when selecting solder paste.

 2. The tin powder in the solder paste has an oxidation reaction.

 3. The flux in the solder paste contains specific additives, which can produce a matting effect.

4. After the welding is completed, there are often rosin or resin residues on the surface of the solder joints, which is more common in actual operation. Especially in the case of rosin solder paste, although rosin flux can make the solder joints appear brighter than no-clean flux, the presence of residue tends to reduce this effect, especially at larger solder joints or integrated circuit (IC) pins. If you can clean the solder joints after soldering, it is believed that the gloss of the solder joints will be significantly improved. 5. In the reflow soldering process, if the preheating temperature is set too low, it may lead to the residue of non-volatile substances on the surface of the solder joint.

(7) Component displacement operation: "Component displacement" is a hidden danger that may cause other problems in the soldering process, and if this problem is not discovered before entering reflow soldering, it may cause more serious problems. The main reasons for component displacement can be analyzed from the following aspects:

 1. The viscosity of solder paste is insufficient, resulting in the phenomenon of no parts shifting in the process of handling and oscillation.

 2. The solder paste has exceeded the recommended service life, and the flux in it has deteriorated.

 3. During the placement process, if the air pressure of the suction nozzle is not adjusted correctly, resulting in insufficient pressure, or there is a mechanical failure of the placement machine, this may lead to inaccurate placement of components.

 4. After the completion of printing and placement operations, if vibration is encountered in the handling process or improper handling methods are taken;

 5. The proportion of flux in the solder paste is too high, and the fluidity of the flux causes the components to shift during the reflow soldering process. (8) Vertical placement of components after welding: Compared with other welding methods, "upright components after welding" is a unique problem in the surface mount technology (SMT) welding process, and this phenomenon is relatively common.

After in-depth analysis, we believe that the main causes of this problem can be summarized as follows:

 1. There is an unreasonable setting of the reflow soldering temperature curve, which leads to the failure of the drying and penetration steps to be fully carried out before the soldering area enters, resulting in an obvious "temperature gradient" on the PCB board. This phenomenon is manifested in the soldering area as the unevenness of the solder paste melting time on each solder joint, which leads to a significant difference in stress between the two ends of the component, and finally leads to the occurrence of "erection" defects.

2. During the reflow soldering process, the temperature setting in the preheating stage is too low.

3. The solder paste is not fully stirred before use, resulting in the uneven distribution of the flux in the solder paste.

4. Before entering the reflow soldering area, some components have a position shift.

5. When the solderability of SMD components is not good, it may also cause such problems.

In the use of solder paste, in addition to the issues mentioned above, there are some points that need to be paid attention to. For example, different brands of solder paste may differ in performance. According to market research studies, some well-known brands of solder pastes are more stringent in terms of flux composition ratio and quality control, which makes them more stable in terms of soldering results. For example, the activator activity of brand A's solder paste is stable over a wide temperature range, which reduces the risk of soldering failure due to ambient temperature changes. This is because the brand uses advanced chemical synthesis technology in the R&D and production of activators, which makes the molecular structure of its activators more stable, thereby improving the performance under various working conditions.

In addition, with the development of electronic products to miniaturization and high density, the demand for solder paste is also increasing. Judging from the current industry trend, fine pitch printing and micro welding technology have gradually become the mainstream. This requires solder paste to have higher standards in terms of particle size, shape and flux properties. For example, for fine-pitch solder joints below 0.3 mm, the solder powder particle size of the solder paste needs to be more uniform, and the deviation of the particle diameter needs to be controlled within a smaller range. Taking a high-end electronic product manufacturing enterprise as an example, when they produce a new generation of smartphone motherboards, they require the solder powder particle size of solder paste to be between 20 - 30μm, and the particle index ratio of about 30μm should reach more than 70%, which is much higher than the standard of ordinary solder paste. This is because at such a small solder joint spacing, uneven solder powder particles can lead to problems such as short circuits or virtual soldering.

At the same time, in today's increasingly stringent environmental protection requirements, the environmental performance of solder paste has also become an important consideration. Traditional leaded solder pastes have been restricted in many applications due to the toxicity of lead. Lead-free solder paste came into being, but there are certain differences between lead-free solder paste and lead-containing solder paste in terms of soldering performance. Lead-free solder pastes typically have a higher melting point than leaded solder pastes, which requires adjustment in the setting of the reflow curve. For example, the maximum temperature in the solder zone may need to be increased to around 240 - 250 degrees Celsius, and the holding time needs to be extended to ensure that the solder paste can be sufficiently melted and a good solder joint is formed. However, increasing the temperature and extending the time may cause damage to some heat-sensitive components, which requires a balance between product design and process optimization. For example, for some temperature-sensitive chips, local heat dissipation or optimized circuit board layout can be used to reduce thermal shock.

In addition, the automated application of solder paste in large-scale production processes presents some challenges. In automated printing and placement processes, the stability of solder paste supply, consistency of viscosity, and compatibility with automated equipment all need to be carefully considered. If the supply of solder paste is uneven, it may result in under- or over-printing, which can affect the quality of the solder joints. Inconsistent viscosity may cause distortion or blurring of printed graphics. For example, in high-speed automated printing equipment, the viscosity of solder paste is required to be stable over a long period of time to ensure that the solder paste can be accurately transferred to the printing template during the high-speed printing process. This requires the optimization of the solder paste formulation and the strict control of factors such as temperature and humidity of the production environment during the production process.

In short, solder paste plays a vital role in modern electronic manufacturing, from its composition, classification, precautions for use to possible problems and development under new technology and environmental protection requirements, we need to continue to study and explore in depth to improve the soldering quality and reliability of electronic products.