Posts Tagged ‘Solder paste’

What is solder paste? What is its function?

Thursday, August 29th, 2024

What is the role of solder paste? Electronic devices have been deeply integrated into our daily lives. Whether it is mobile phones, tablets or household appliances, they are inseparable from electronic components. How are these components accurately soldered to the circuit board? The answer lies in surface mount technology (SMT) and the important material it uses – solder paste.

In the process of SMT patch processing, solder paste is an indispensable and important material. The quality and use method of solder paste directly affect the welding effect and the performance of the final product.

What is the composition of solder paste?

Solder paste is a complex mixture of multiple components, and its main components include metal powder, flux and solvent.

What is solder paste? What is its function?

The metal powder in solder paste is usually composed of metal alloys such as tin, silver and copper. The particle size and distribution of metal powder have a direct impact on the welding effect. The smaller the particle size, the more uniform the distribution, and the better the welding effect.

At the same time, the composition of the metal alloy also determines the mechanical strength and electrical properties of the solder joint.

Flux is another important component in solder paste. Its main function is to remove oxides on the welding surface and improve the wettability and reliability of welding.

The type and formula of flux directly affect the melting state and solder joint quality during the welding process. Common fluxes include rosin-based flux, organic acid flux and halogen-free flux.

Solvents are used to adjust the viscosity and printing performance of solder paste. Appropriate viscosity can ensure that the solder paste is evenly distributed during the printing process without problems such as drawing and collapse. The evaporation rate of the solvent will also affect the drying time and welding performance of the solder paste.

What is the role of solder paste in SMT patches?

In the SMT (surface mount technology) patch processing process, solder paste plays a vital role. It is not only used to bond components, but also the key to ensure the quality of electrical connections and mechanical strength.

1. Bonding components

One of the main functions of solder paste is to bond components. After the solder paste is accurately printed on the pads of the PCB (printed circuit board), the pins or contact points of the electronic components will be placed on the solder paste. The solder paste melts during the reflow soldering process to form a strong bond, ensuring that the components are stably attached to the PCB.

2. Provide electrical connection

Solder paste melts during the reflow soldering process and forms metal solder joints, which not only bond components but also provide electrical connections. Good electrical connections ensure the effective transmission of electrical signals on the PCB, which is the basis for ensuring the normal operation of electronic equipment.

The solder joints formed by the metal components (such as tin, silver, and copper) in the solder paste after melting have excellent conductivity, ensuring the reliability and stability of electrical connections.

3. Ensure mechanical strength

The mechanical strength of the solder joints is the key to ensuring the stable operation of electronic components in various environments. The solder joints formed by the solder paste after reflow soldering have sufficient mechanical strength to resist external stresses such as vibration, impact, and thermal expansion and contraction. This not only protects the components and PCB, but also improves the reliability and service life of the entire electronic equipment.

Is solder paste the same as flux?

Solder paste and flux are not the same. ‌

Although both solder paste and flux are materials used in the welding process, their functions and uses are different.

Solder paste is a paste-like viscous body, the main components of which include metal powder, rosin, organic acid, thixotropic agent, and activator, and is used for welding in SMT automatic mounting process.

Flux is a liquid, a mixture with rosin as the main component, which is used to remove oxides on the surface of solder and the base material to be welded, so that the metal surface reaches the necessary cleanliness, prevents the surface from re-oxidation during welding, reduces the surface tension of the solder, and improves welding performance.

In general, although both solder paste and flux are indispensable materials in the welding process, they have obvious differences in form, function, and usage.‌

What is the storage method of solder paste?

The correct storage method can extend the service life of the solder paste and ensure its stable performance.

1. Temperature control

Solder paste should be stored in a low temperature environment, usually 0-10℃. Excessive temperature will cause the solvent in the solder paste to volatilize, affecting its viscosity and printing performance. Avoid direct sunlight and high temperature environment during storage to prevent the solder paste from deteriorating.

2. Humidity control

Humidity has a great impact on solder paste. Excessive humidity will cause the solder paste to absorb moisture, affecting its printing performance and welding quality. The relative humidity of the storage environment should be controlled below 50% to ensure the stability of the solder paste.

3. Sealed storage

The solder paste should be stored in a sealed container to prevent oxygen and moisture from entering the air. The solder paste after opening should be used up as soon as possible, and the unused solder paste should be resealed and stored in a low temperature environment.

How to use solder paste correctly?

1. Reheating treatment

The solder paste stored in a low temperature environment should be reheated before use. The reheating time is usually 4-8 hours. During the reheating process, it should be avoided to be directly exposed to a high temperature environment to prevent the solvent in the solder paste from volatilizing. The solder paste after reheating should be fully stirred to ensure that the metal powder and flux are evenly distributed.

2. Printing process

Solder paste printing is a key process in SMT patch processing. During the printing process, the scraper pressure, printing speed and template opening size should be controlled to ensure that the solder paste is evenly distributed on the pad. The printed solder paste should have a good shape and should not have problems such as drawing and collapse.

3. Solder paste reflow

The solder paste reflow process is the process of melting the solder paste and forming a firm solder joint with the pad and component pin. The temperature curve should be controlled during the reflow soldering process to ensure that the solder paste melts at an appropriate temperature and fully wets the pad and pin. Too high or too low reflow temperature will affect the welding quality.

4. Solder joint detection

The quality of the solder joint is an important indicator for evaluating the welding effect. After the welding is completed, the solder joint detection should be carried out to check the shape, size and wettability of the solder joint. Qualified solder joints should have a smooth and complete surface without defects such as solder balls and cold solder joints.

Conclusion:

Solder paste plays a vital role in SMT patch processing. Its composition, selection, storage and use methods directly affect the welding quality and the performance of the final product. By understanding and mastering the relevant knowledge of solder paste, the quality of SMT patch processing can be effectively improved, and defects and rework rates can be reduced.

BEST Technology has rich experience and strict control standards in the selection and use of solder paste, and can provide customers with high-quality SMT patch processing services. If you have any questions about our products or services, please feel free to contact us. Choose BEST Technology , choose quality assurance.

Types of Flux

Rosin Flux

This is one of the most commonly used fluxes in soldering. It includes activated rosin flux (RMA), which contains additional chemicals for enhanced cleaning of oxides, and non-activated rosin flux (RA), which offers basic cleaning for general purposes. Rosin flux is effective at preventing oxidation and improving solder flow, making it suitable for a wide range of electronic soldering applications.

Water-Soluble Flux

This type of flux uses water-soluble chemicals to provide strong cleaning action. It is easily removed with water, making it ideal for applications where thorough residue removal is necessary. Water-soluble flux is often used in automated soldering processes where post-soldering cleanup is a key concern.

No-Clean Flux

Designed to leave minimal, non-corrosive residue, no-clean flux does not require cleaning after soldering. This type of flux is beneficial in situations where cleaning is difficult or impractical, as it reduces post-soldering processing time while ensuring that the residue does not affect the performance of the PCB.

Organic Acid Flux

Contains organic acids like citric or formic acid, providing effective cleaning and fluxing. While it offers strong fluxing action, it is more corrosive compared to rosin fluxes. Organic acid flux is used in applications requiring robust cleaning, with careful consideration of the corrosion risk.

Solder Paste Flux

This flux is a combination of flux and solder powder, used in reflow soldering processes. It is commonly employed in surface-mount technology (SMT), where the paste is applied to PCB pads before component placement and reflow. Solder paste flux streamlines the soldering process by integrating fluxing and soldering into one step.

Is it Bad to Leave Flux on PCB?

There is obvious that leaving flux residue on a PCB surface can lead to several issues. Flux residues can attract moisture, resulting in corrosion of metal traces and component leads, which can compromise the integrity of the PCB over time. Some flux residues are conductive, potentially causing short circuits and affecting signal integrity, especially in high-frequency applications. Even no-clean flux can leave residues that impact sensitive components. Cleaning flux off the PCB can make sure the optimal performance and reliability of the overall product.

How to Remove Flux After Soldering?

We know leaving the flux on the PCBA surface is not a good thing, so how to remove it? Here we listing some common methods that manufacturers will used after soldering. Hope this information is helpful for you!

Isopropyl Alcohol (IPA)

Use high-purity IPA (90% or higher). Apply it to the flux residue with a brush or cotton swab, gently scrubbing the area to dissolve the flux. IPA evaporates quickly and is effective for most flux types.

Water Washing

Water washing is a common and straightforward cleaning method. It uses pure or deionized water to remove flux residues. This technique is simple, cost-effective, and easy to implement. However, water washing can potentially harm some PCBs and components if moisture accumulates on pads and pins, leading to short circuits or corrosion.

Solvent Cleaning

Solvent cleaning is an efficient method that dissolves flux residues using chemical solvents. The solvent is then rinsed or sprayed off to clear the flux. While this method provides rapid and effective cleaning, solvents can be costly and require careful handling due to their chemical properties and safety considerations.

Ion Cleaning

Ion cleaning is a high-tech approach that uses ion beams to clean the surface of PCBs. The high-energy and high-speed ion beams effectively remove contaminants and flux residues without damaging the PCB or components. However, ion cleaning equipment is expensive and requires specialized technology and support.

Oxidation Cleaning

Oxidation cleaning is a physical cleaning method where oxidizing agents convert flux residues into easily removable substances. This technique is suitable for PCBs and components that are not compatible with water or solvent cleaning. The cost of oxidizing agents can be high, and safety precautions are necessary due to their reactive nature.

Dry Ice Cleaning

Dry ice cleaning uses CO2 dry ice pellets as the cleaning medium. This method is efficient, environmentally friendly, and does not produce secondary pollution. During cleaning, high-speed CO2 dry ice pellets impact the flux residues on the PCB surface. The extremely low temperature of the dry ice causes the flux residues to become brittle, allowing them to be easily removed without damaging the PCB. This method offers a thorough cleaning solution while preserving the integrity of the circuit board.

FAQs

1. Can I use vinegar to clean flux off a PCB?

Vinegar can be used to clean certain types of flux, but it’s not as effective as IPA or specialized flux removers. It’s best to use a solvent designed for flux removal.

2. How often should I clean my PCB?

Clean your PCB after every soldering session to prevent residue buildup and ensure optimal performance.

3. Is it safe to use a hairdryer to dry a PCB after cleaning?

Yes, but use the lowest heat setting to avoid damaging sensitive components. Ensure the PCB is completely dry before powering it on.

4. Can I use a toothbrush for cleaning flux?

A toothbrush can be used, but a brush with anti-static properties is recommended to prevent static damage to the PCB.

5. Is no-clean flux really safe to leave on a PCB?

While designed to be left on, no-clean flux can still leave residues that may affect sensitive components. It’s best to clean it off for maximum reliability.

All in all, cleaning flux off your PCB is a crucial step to keep the reliability of your product. Remember, a clean PCB is a reliable PCB. Choose the right solvent, follow proper cleaning techniques, and your electronics will thank you with years of flawless performance.

For high-quality PCB & PCBA solutions and expert advice, choose Best Technology. We have more than 18 years in this field. Our commitment to excellence ensures your projects are in good hands. Contact us today to learn more about our products and services.

What is Meant by Dry Soldering?

Dry soldering refers to a poor solder joint that lacks proper electrical connectivity on a PCB assembly product. This issue occurs when the solder does not properly melt and bond to the components, leading to weak connections. These joints are often brittle and prone to failure, which can result in intermittent or complete loss of electrical connectivity.

Dry Soldering: How to Prevent and Fix Dry Solder Joint?

Why Dry Solder Joint Causes?

Dry solder joints occur due to several reasons, each impacting the quality of the solder connection. First of all, the solder paste reflow process is only a small area, which is easier to harden than the solder paste in the solder paste can. At this time, the solder paste will not melt, and the flux cannot cover the solder joint, resulting in poor welding of the solder joint. Meanwhile, the solder paste is easier to heat transfer, and the high temperature actually makes the solder paste not easy to melt, so we can slightly adjust the reflow welding temperature curve to solve the problem, or welding in a nitrogen environment is basically a good way to solve this problem.

Secondly, the solder paste does not melt because its own composition contains a very volatile flux, which is also the reason why the solder paste is easy to harden. Among them, the flux with the largest content of solder paste is rosin, rosin contains a lot of rosin acid, rosin acid is easy to lose activity at too high temperature. Therefore, the temperature of the welding process should be controlled to ensure that the temperature is about 200 ° C, which is not suitable for too high or too low. At the same time, the quality of thixotropic agent will also lead to the solder paste is easy to dry, the quality of thixotropic agent is not good will affect the viscosity of the solder paste, the viscosity of the solder paste is easy to dry. Therefore, the choice of high-quality solder paste can fundamentally solve the problem that the solder paste is easy to harden.

In addition, the use of solder paste scene, humidity, temperature and other external factors will also affect the solder paste in the use of hard non-melting phenomenon. So these external factors should be paid attention to. I hope these solutions can solve your problems.

How Do You Fix Dry Solder?

Solder paste is one of the very important materials in the electronics industry, and it has an important impact on the production quality of the entire component. Here are some tips that can help to fix the dry solder paste.

1.Add flux

Usually, if the solder paste is too dry, you can try to add some water to the right amount of flux, stir well and add it to the solder paste. This can play a certain role in alleviating drying and improve the fluidity of the solder paste.

2. Take some measurements during management

a. Keep the ambient temperature moderate during storage;

b. Stir well before use;

c. Cover the solder paste in time after welding to avoid exposure to the air.

3. Replace it with new one

If the solder paste becomes too dry, adding flux is difficult to restore its original properties, it is recommended to replace the solder paste to avoid affecting the quality of the components.

Therefore, we need to regularly maintain and manage the solder paste to ensure that its quality meets the standard requirements.

What Does a Dry Solder Look Like?

Recognizing a dry solder joint is crucial for proper diagnosis and repair. Unlike a good solder joint, which is shiny and smooth, a dry joint looks matte and rough. The joint might have visible cracks or look brittle. It might not be fully bonded to the component lead or the PCB pad. Identifying these visual cues can help in quickly addressing the issue.

How Do You Prevent Dry Solder?

Preventing dry solder joints is key to maintaining the reliability of your electronic projects. You can try to use these tips to prevent your solder paste become dry.

Proper heating
Clean surfaces
Use quality solder
Steady hand
Maintain equipment
Fast usage and storage

If you want to know more about solutions of dry solder paste, you can read our another post, How to Solve Dry Solder Paste.

How to Tell If Solder is Bad?

Bad solder can lead to dry joints and other issues. So, how can we identify if my solder paste is bad? May you can follow these points. If everything matches up, there’s no doubt that your solder paste is broken.

Appearance of solder joints

Bad solder joints often appear dull or matte instead of shiny and smooth. They may also show cracks or a brittle texture, indicating poor bonding or excessive heating. These visual signs suggest that the solder did not properly melt or flow.

Solder flow and coverage

If the solder does not adequately cover the component leads or PCB pads, or if it spreads unevenly, it is likely bad. Proper soldering should result in a well-formed, consistent fillet around the leads, ensuring reliable electrical connections.

Difficulty in melting

Solder that requires unusually high temperatures or takes a long time to melt may be old or contaminated. Proper solder should melt easily at the recommended temperature and flow smoothly to create a solid joint.

Contamination indicators

Oxidized or tarnished solder indicates contamination and can affect its performance. Excessive residue or debris also points to poor quality, affecting how well the solder adheres and flows.

Best Technology is a one-stop PCB manufacture and PCBA service provider, our SMT factory is equipped with more than 6 assembly lines. Meanwhile, we have automatic SPI machine and solder paste printing machine, with good management system, we can ensure the good quality of solder paste. In addition, there are many advanced equipment in our workshop, including online dual AOI, X-ray, Nitrogen reflow oven, dry-ice cleaning machine, and so on.

Trust us, we are the one of most reliable PCBA manufacturer in China and Vietnam. Contact us for more.

Part 1: What is Solder Mask?

If you had ever seen a printed circuit board, you may see there is a layer of green ink cover on the PCB surface while some orange-yellow areas didn’t cover by ink. In PCB industry, the green ink we called Solder Mask, or abbreviated as S/M, and exposed area is copper, they were leave as GND plane or soldering pads to mount electronic components.

Solder mask is a liquid acrylic oligomer, which has variety of colors such as red, blue, green, white, black. Green is commonly used in the process of PCB manufacturing, so some professional engineers call it as green oil.

Solder mask applied on the PCB designed as a protection layer to avoid oxidation, corrosion and other environmental impacts when they leave production line. In addition, solder mask between solder pads also can help to prevent forming to solder bridge when assembly.

Below are some other functions of coating a layer solder mask:

Prevent physical line breaking of copper trace
Only weld in the area that must be soldered to avoid waste of soldering
Reduce copper pollution to soldering groove
Prevent insulation deterioration and corrosion caused by dust, moisture and other external environmental factors
With high insulation, so that the high-density circuit is possible

Part 2: What is Solder Paste?

Solder Paste also known as “Solder cream”, is a most important soldering material used in surface mount technology (SMT) process. Mainly function for soldering resistors, capacitors, ICs and other electronic components onto the PCB surface to form a permanent connection.

The solder particles are a mixture of solder formed by mixing solder powder, flux and other surfactants and thixotropic. Traditionally this used to be tin and lead, but with the legislation has been introduced around the world, to only use lead free solders. These may be made from a variety of mixtures, Best Technology commonly used is SAC305 which includes 96.5% tin, 0.5% copper and 3.0% silver, some manufacturers also use 99.7% tin and 0.3% copper, whereas there are other mixtures that include other metals including tin.

Due to the role of solder paste in assembly, solder paste storage is extremely important. However, solder paste got into drying during storing became a common problem faced by most PCBA manufacturers, so How to solve solder paste dry problem is premier.

Part 3: The Difference Between Solder Mask and Solder Paste

Solder mask is a formal part of PCB, but solder paste ONLY for PCB assembly.
Solder mask is not allowed on the solder pads while solder paste can be printed on the solder pads openings.
Solder mask is used for applying solder mask ink, but solder paste is used for applying paste.
Solder mask has many available colors, but paste mask visually gray.
Solder mask is coating during PCB fabrication, but solder paste is printing when PCB assembly.

With over 16 years in PCB industry, Best Technology is one of the most reliable PCB and PCBA supplier in Asia, we commit to provide high quality products with excellent service before and after sales, to take care our customers wholeheartedly, and to treat customers’ business as ours. At the same time, we keep learning and continually to improve ourselves so that we can catch up the latest technology trend and provide better and better service for our customers.

Posts Tagged ‘Solder paste’

What is the composition of solder paste?

What is the role of solder paste in SMT patches?

Is solder paste the same as flux?

What is the storage method of solder paste?

How to use solder paste correctly?

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Types of Flux

Is it Bad to Leave Flux on PCB?

How to Remove Flux After Soldering?

FAQs

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What is Meant by Dry Soldering?

Why Dry Solder Joint Causes?

How Do You Fix Dry Solder?

What Does a Dry Solder Look Like?

How Do You Prevent Dry Solder?

How to Tell If Solder is Bad?

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Part 1: What is Solder Mask?

Part 2: What is Solder Paste?

Part 3: The Difference Between Solder Mask and Solder Paste

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