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SMT solder paste – a new soldering material with the advent of SMT in PCBA


As the demand for PCB in electronic products continues to expand, the PCBA industry is gradually developing. As one of the most important parts of this process, SMT consists of many steps and materials such as solder mask, SMT solder paste, PCB flux, components, reflow and so on. In this article we will introduce one of the substances used to connect components to the board pads – SMT solder paste.

What is solder paste used for?

What-is-solder-paste-used-forSMT solder Paste is a mixture of different chemicals which is widely used to join metals together. It’s also used for joining metal parts that are not compatible with each other, such as dissimilar metals. It is a metal alloy that has been processed to create a thin layer of metal between two surfaces. Solder paste can be used to make joints that have high current carrying capacity and low thermal resistance, which means they will not be damaged by heat.

The SMT solder paste is used in electronics and other applications where soldering is necessary. PCB soldering is a process of joining two different metals using heat and pressure. The solder must melt and flow into the joint to create an electrical connection. It can be used to repair broken electrical connections or as a joint between two pieces of metal that are too far apart to allow for a good solder connection.

What are the ingredients of SMT solder paste?

What-are-the-ingredients-of-solder-pasteSMT solder paste is a mixture of flux, metals, and other chemicals that is used to join metal parts together. The ingredients of SMT solder paste depend on what you’re doing with it, but typically include zinc or tin powder, flux (sometimes called rosin), and Boric acid or silver nitrate as an activator.

What are the types of solder paste?

There are three types of SMT solder paste used in different materials.

Type 3 is a tin-lead alloy. It is a very common type and had many applications. Type 3 is widely used for joining the metals together in soldering boards such as PCBs. This is because of the higher melting they possess. They also have a property of withstanding high temperature pressures and won’t even melt.

Type 4 is an alloy that contains silver, zinc, and tin. It melts at a lower temperature than T3 solder paste, so it can be used to repair smaller components on electronics.

Type 5 is a tin-lead alloy with a higher melting point than either T3 or T4. It is also more flexible and easier to work with as compared to other types of SMT solder paste.

Which solder paste is used in SMT?

Which-solder-paste-is-used-in-SMTAll of the mention types mentioned above are used in SMT or Surface Mount Technology as it is a process to mount the electronic components onto the PCB surface. The SMT solder paste utilized by SMT is an amalgam of different materials such as solder, tin and flux paste. It is applied to the soldering surface using a dispenser and then melted into the joint.

How does solder paste affect the quality of SMT?

Solder paste is a very important part of the Surface Mounting Technology. It is used to bond the components together, and if it is not properly applied, the quality of your product will suffer.

You have to apply the SMT solder paste between each part you need to solder in the printed circuit board. Do this carefully or the solder won’t bond together. The paste also functions as a barrier so that no foreign materials can get into the connection point and cause any damage. If you do not apply enough heat during the soldering process or if you do not apply enough pressure, then you will not get a strong enough bond between your components.

How do you test solder paste?

Pressing the solder solution through apertures with a tiny surface area of less than 0.66 while pausing it at intervals that get longer is a test to determine this. The volume of the SMT solder paste is measured, and variations in the average volume and average deviation are assessed after each interval.

About time of SMT solder paste


How long can solder paste sit before reflowing?

The time that SMT solder paste can sit before reflowing varies. It depends on the temperature and humidity where the paste is being used. Also, how much hot the SMT solder paste gets when it’s placed in somewhere hotter. However, on average it can be left on your PCB for a maximum of 2 hours after reflowing. After that, it needs to be removed from the PCB and replaced with a new one.

If you’re using a paste that contains tin, however, the temperature actually matters less than how long you leave it out: once you’ve applied your iron to cold solder joints and pressed firmly down for a few seconds, leaving them in contact with each other for too long can result in their oxidizing and becoming brittle.

How long does solder paste last?

SMT solder paste may last about 6 months if you’ve refrigerated it properly beforehand, although the amount of time it lasts is dependent on the kind of solder paste being used.

The shelf life of SMT solder paste is dependent on a number of factors, including the ingredients used in its manufacture and how it’s stored.

In general, particularly if you’re using tin/lead solder, you should avoid leaving your soldering iron on for long periods at a time: while this will cause no problems when you’re soldering one component to another, over time it can lead to overheating and damage to components.

FAQ about SMT solder paste


Are solder paste and flux the same?

No, these both are not the same. While they serve the same purpose, they are not interchangeable. SMT solder paste is a paste that you apply to a surface to help it connect with an item under heat. PCB Flux has an application while you’re soldering some circuit board. When you apply it after some time the solder paste melts and flows into spaces and get them stick together. PCB Flux is a paste-like material that’s brushed onto the joint after the part has been prepared with PCB solder paste.

How to store SMT solder paste?

Solder paste should be kept at a temperature somewhere between 4°C – 10°C. Storing above the freezing point will shorten shelf life and violate the warranty.

How to remove solder paste?

You can use your soldering iron to melt the solder paste in order to disconnect any electrical joint although to remove the flux, the most popular solvent for cleaning flux is isopropyl alcohol, but some branded companies have developed their own that can work more quickly and cheaply.


We know that PCB assembly is a complex process and also, applying the solder paste to the PCB is also a vital step. SMT solder paste helps electronic components like IC, capacitors and resistors to be soldered firmly to the PCB, which can completes the PCB assembly process and ensures the electrical functionality of the PCB.



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