Is Solder Paste The Same As Flux

Is Solder Paste The Same As Flux? ( Your Burning Question Answered)

Both solder flux and solder paste are used for gluing metal bodies together. A solder paste is a combination of ingredients and a product that can be used to glue and join the metal alloys and their different parts together. Solder flux is different from solder paste. The flux is usually added to a metal surface before a soldering process is initiated. However, the flux may also be added during the soldering paste. The role of flux in the soldering process is to clean the metal services that are being joined together. A clean surface will provide for a better action of the solder paste and will improve the quality of the joint.

If you are a soldering enthusiastic or if you work in industries including plumbing, metallurgy, and electric circuit boards among others, you need to know more about the soldering process and the ingredients, You should be aware of the nature of important components of soldering including the soldering flux and the soldering paste. You may want a detailed answer to your question “Is solder paste the same as flux?”, the guide below will provide you with more information in this regard and will make you more skilled, knowledgeable, and expert in the task of soldering.

Solder Paste

Solder paste is also called solder cream. The mixture is used for bonding and joining metal parts to one another. Solder paste is an important requirement of the soldering process and is used in a variety of projects including the manufacturing of electric circuit boards, metallurgy, and many others. The term soldering signifies combining metal parts. During the process, the solder is heated and gets melted. In that melted state, it acts as a glue through which the different metal surfaces are conjoined with each other. The solder joint is that point of conjoining where the solder paste applied to the process holds the two different metal surfaces together.

The solder paste is an evolution over the old glue and is more effective at connecting the mechanical and electrical metal parts. Unlike glue, the molten solder paste will also provide for the transmission of electric signals. Therefore, the use of soldering paste and soldering ensure that the wires and other kinds of metal objects can be joined together while also continuing to transmit the electricity without any interruption.

The Ingredients of a Solder Paste

The main ingredient of a solder paste is powdered metal. These tiny metal pieces are melted during the soldering process. When melted, the metals form a bed that acts as glue. It is the place where different metal parts and objects combine.

The solder paste also has a thick consistency and is sticky and tacky. Because the solder paste is made of metal, it connects the electrical parts of a circuit board and provides for the flow of electricity. Electric circuit boards are used for connecting electric circuits and therefore the flow of electricity should be continued and maintained. Solder paste is therefore a pre-requisite and an important gluing material for the soldering process.

The Pre-Requisite Properties of Solder Paste

A soldering paste can be chosen based on certain properties and attributes that are together referred to as “rheological properties”. The rheological properties depict the state of flow of a paste when it is in a liquid and soft state.

Slump: the term refers to how a certain substance will spread over a surface once it is applied. A paste and a substance that has a high degree of slump cannot be managed easily as it may spread beyond the required level. Therefore, a soldering paste should have a low degree of slump so that it does not flow into the undesired areas and bridges.

Tack: a soldering paste should be tacky and should retain its thickness for long durations. It will ensure that the base can hold together the metal parts for longer periods, and is also effective irrespective of the duration.

Viscosity: viscosity refers to the degree of fluidity or “how little” or” how much” the paste can float. The soldering pastes available in the market may have different kinds of viscosities and therefore it needs a careful choice.

RTP (Response-to-Pause): the RTP variable and attribute for a solder paste relates to the time taken by the paste to dry itself. It impacts the duration of the soldering process.

Working Life: these attributes relate to the duration for which a solder paste can be used on the intended location or the stencil before it gets diverted and is spilled over.

Using the Solder Paste

Before using a solder paste has to be mixed with the appropriate ingredients. The temperature of the paste at the time of melting is also important. The soldering paste should be melted to the appropriate temperature before it is used. This temperature may vary depending on the type of solder paste chosen or the brand. If you are using a pre-manufactured solder paste, you should check for its melting point and temperature before you use the paste.

A solder paste is applied to a circuit board by using a stencil, a printing syringe, or Jet printing. Automatic soldering machines are also available that can be used for more meticulous manual soldering. A soldering iron is often used for melting the soldering paste. When applied the soldering paste will hold the metal parts together for some time. However, for a permanent bond, these electrical parts and pieces should also be heated at the requisite temperature. For that to happen, the board is heated at the appropriate temperature.

Soldering Iron/Solder Iron

The handheld device that is used for soldering and applying a soldering paste to the metal surfaces and bed is called solder iron. The rod has got metal plating around it so that the interiors are protected. This interior is made of copper alloy, which also acts as a thermal conductor. Copper alloys and their variations are used in soldering iron as they have good thermal conductivity.

The soldering iron rod has a tip made of metal. The tip is used for applying the soldering paste. This iron may be plugged into a soldering machine or a wall outlet. The iron draws electricity and gets heated up. The handle of the soldering iron is insulated. The tip of the soldering iron is heated and the solder paste is melted through it. The iron’s tip can also be used for arranging the solder paste at the desired location.

Solder Flux

A solder Flux is also applied to the surface on which soldering is carried out. It provides for a clean soldering surface that also has better adhesiveness. Solder flux is applied usually before the soldering process. However, the flux can also be applied during the process.

The Ingredients of Solder Flux

There are different kinds of solder flux available and they carry different ingredients. These ingredients may include hydrochloric acid, rosin, or zinc chloride among others. The texture of solder flux resembles putti and it has a grey color.

The Need of Solder Flux

The application of the solder flux improves the quality of the bond between the metal parts and provides for their better strength. The application of flux also ensures that the soldering process is smooth and hassle-free. When flux is applied to the soldering surface, all the oxide layers on the surfaces are dissolved. Therefore, the solder can better prepare and “wet” a surface for gluing and adhesion if flux is applied. Because the surfaces are wet after the application of the solder flux, adhesion is stronger. The application of flux has a positive impact on the surface tension of the molten solder as well. It further improves adhesion and provides for quality bonding.

Application of flux ensures that the metal surfaces do not re oxidizing once the soldering process is over. Therefore, the bonds remain good for a longer period. The application of flux prevents oxidation and the surfaces do not corrode. Corrosion may cause the breakage of the solder joints.

Types of Soldering Flux

Soldering flux comes with different consistencies, which include a paste, liquid, or solid consistency and texture.

Rosin flux: the flux can be cleaned rather easily and is made from natural ingredients that are obtained from the pine trees. Rosen is the safest option available for the circuit board soldering process

Water-soluble flux: the soldering projects carried out in the plumbing industry usually use water soluble fluxes. The flux dissolves in water and is used for joining the copper and copper alloy pipes. However, a water-soluble flux can also be used in the water sprinkler, heating, and air conditioning systems that involve copper.

No Clean Flux: A no-clean flux can only be applied to surfaces that have been cleaned thoroughly before the soldering process. These fluxes do not require any cleaning after the solder paste is melted.


Solder paste should never be applied to the metal and alloy surfaces without the application of flux. Application of flux ensures that there is good adhesion on the surface, oxidation is removed, and the surfaces are cleaned thoroughly before the soldering is done. The solder joints thus obtained can last longer and are of good quality.

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