What is Solder Paste?

Soldering PCB Basics 
1 Answer
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Raghav - ERF

Sep 11, 2020

Solder Paste is a form of solder than can be easily applied on a Printed Circuit Board. It has a viscous state and is grey in color. The paste consists of a combination of tiny balls of solder and flux mixed together to form a paste. It is applied to the pads on a PCB where electronic components need to be placed. When heated this paste melts to form a connection between the pads and the leads of electronic components placed on the PCB.

Solder paste is used during the PCB assembly process. The paste is applied on the PCB Board using a solder paste printer, in a process similar to screen printing i.e a stencil is placed over the PCB and then the solder is applied over the board using a solder paste printer. The components are then placed on the board. The viscosity of the paste helps keeps the components in place as the board is moved around or as the board is passed from the component placement section to the reflow oven using a conveyor belt. Once in the reflow oven, based on the thermal provide of the solder paste it melts and when cooled resulted in a soldered connection between the pads on the PCB and the leads of the electronic component.

Solder Paste is usually used for soldering Surface Mount Components on a PCB, however, this can also be used to solder thru-hole components by applying this paste using a brush or via an injection.

Solder Paste Storage

Solder paste should be stored in an airtight container to prevent oxidation and should be stored at low temperatures (but should not lower than freezing temperature) to prevent the flux degradation.

Composition of solder paste:

Solder paste is the mixture of tiny solder balls and solder flux. Depending upon the application, the solder ball's composition will vary. The Solder paste is mixed using solder paste mixers

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