Solder Paste and Its Application in Surface Mount Technology

Solder paste is one of the important material used in the manufacture of Printed Circuit Boards. (PCBs). It is a powder metal solder suspended in a thick fluid medium, which is called flux. The solder paste is used to connect surface mount components to pads on the board. To change the composition for specialized applications, additional metals can also be added to the solder paste. Solder paste is used in surface mount technology to join Surface Mount Devices (SMDs) on to the printed circuit board. This post discusses about solder paste and its application in Surface Mount Technologies (SMT).

Some Important Properties of Solder Paste

Here are some properties of solder paste, which make it highly useful in diverse circuit assemblies:

  • Viscosity: Viscosity is the property, which determines a material’s resistance against the tendency to flow. With increase in the metal content the viscosity increases to the point where the paste can no longer be printed on the board. Also, viscosity is temperature dependent and it decreases with rising temperature.
  • Rheology: Rheology determines the flow and deformation of the solder paste for a given condition such as temperature and pressure. This affects the way in which the paste is deposited. Also, rheology is critical to the print quality of solder paste.
  • Slump: Slump refers to the spreading of a material after application. Slump depends mainly on temperature, height of paste deposited and viscosity of the plate. The presence of slump may create the risk of forming solder bridges or unequal deposit of paste between the two successive lands causing short circuiting.

Applications of Solder Paste in SMT

The beneficial features and properties of solder paste, make it ideal for use in several applications, some of which are as follows:

  • Solder Joints: Solder paste is a homogenous mixture of solder alloy, flux and vehicles. The paste is capable of forming metallurgical bond with the given soldering conditions, thus aiding in the creation of reliable solder joints.
  • Stencil Printing: Solder paste is typically used in stencil printing, wherein the paste is deposited over the stainless steel or polyester mask in order to create the desired pattern on the printed circuit board. This is done either by pin transfer or jet printing through the nozzles.
  • Lead components: Solder pastes are used to build Surface Mount Technologies (SMT) assemblies having leaded components. This helps in simplifying the design, improving the component density, lowering the manufacturing cost and increasing the reliability of the project.
  • Reflow Soldering Process: Solder pastes are used in the reflow soldering of Surface Mount Assemblies (SMA). It helps establish connection between the leads or termination of surface mount components.

Solder paste is used in various surface mount devices. If you plan to purchase solder paste for your printed circuit board applications, then you should approach an expert. Accelerated Assemblies is one of the reputed PCB manufacturers and suppliers in the USA, with a proficiency in solder chemistry.