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Solder Paste and Its Application in SMT

Solder Paste and Application in SMT – Learn What is Solder Paste & How to Use it to Solder SMD Electronic Components to PCB.

Here we will learn about Solder Paste and its Application in SMT. What is Solder Paste & How to Use?

What is Solder Paste?

Solder paste is simply a suspension of fine solder particles in a flux vehicle. In electronic industry, solder paste is used in Surface Mount Technology (SMT) to solder SMD Electronic Components on to the Printed Circuit Board.

The composition of the particles can be tailored to produce a paste of the desired melting range. Additional metals can be added to change paste compositions for specialized applications. Particle size and shape, metal content and flux type can be varied to produce pastes to varying viscosity.

Solder Paste

Lead-Free Solder Paste

With the implementation of RoHS (Restriction of Hazardous Substances) in the Electronics Industry by the European Union and Many other countries, most electronic companies are shifting to Lead Free. Lead Free Solder Wire and Solder Paste are manufactured using different composition and ratio. But the most popular and widely used composition and ratio is SAC (Tin Silver Copper) in the Ratio 96.5% Tin + 3.0% Silver and 0.5% Copper.

Lead-free solder has higher melting point than the conventional 63/37 or 60/40 Tin-Lead Solder. Also the solder joints are not as shiny as tin-lead solder.

Lead Free Solder

Screen Printer Machine

Some of the major features to consider when selecting screen printer for solder cream are the maximum size of the SMT Printed Circuit Board that can be handled, controls of accurate screen alignment and repeatability of print, and the board hold-down mechanism.

Considerable progress has been made for paste dispenser, screening and stenciling for pastes on substrates. Each method of dispensing solder cream has its own pros and cons but the most widely used method is stenciling for both rework and large scale production. Vastex is a well known manufacturer and supplier of screen printing equipment.

Solder Paste Screen Printer Machine

Screen Printer Machine

Stencils for Solder Paste Application

There are three main ways of making stencils:

  1. Chemical etching
  2. Laser cutting
  3. Electroforming

Chemical etching is the oldest, most widely used, and least expensive option. Laser cutting and electroforming, especially the latter, find appeal in applications where precision is paramount. In addition to the type of stencil, the type of squeegee blade is very important. Metal blade squeegees are widely used because they require less maintenance than rubber squeegees.

Solder Paste Application Process

Availability of Solder Paste

Solder paste is available in both leaded (with lead) and lead-free (with no lead) forms. It can be no-clean or water soluble. With no-clean pastes, there is not need to clean the board after soldering. Water soluble solder pastes are easily soluble in water with no harm.

Alpha Cookson is a Leading Manufacturer and Supplier of all Types of Soldering Material including, Wire, Paste and Bar.

How to Get the Best Solder Joints

In order to achieve good printing results, a combination of the right soldering material, the right tools and the right process are necessary.

Although suppliers like PCBA Tools are essentially responsible for providing the desired solder paste and screens or stencils and the squeegee blades, the user must control process and equipment variables to achieve good print quality. Even the best solder paste, SMT Equipment, and application methods are not sufficient by themselves to ensure acceptable results.

FAQs: Solder Paste in SMT

Solder paste consists of three primary components: solder powder (usually a mix of tin and lead or other alloys), flux, and a rheology modifier. The flux helps clean surfaces, prevent oxidation, and facilitate solder wetting. The rheology modifier maintains the paste's consistency during application.

Solder paste is applied using a stencil that's aligned over the PCB. The paste is pushed through the openings in the stencil using a squeegee, depositing controlled amounts onto the solder pads. This method ensures precise placement of the paste.

Reflow soldering is the process of melting the solder paste to create a solid connection between components and PCB pads. The PCB, with components and applied paste, is placed in a reflow oven. The oven's temperature profile is carefully controlled, heating the assembly to melt the solder, and then gradually cooling it to solidify the joints.

Solder paste and SMT can present challenges like tombstoning (components standing on end), insufficient solder paste, solder bridging (excess solder causing connections between adjacent pads), and voids in solder joints. These issues often arise from incorrect paste application, improper oven settings, or component design/layout problems. Careful process control and design considerations help mitigate these challenges.

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Santosh Das

Santosh, founder of this Electronics Tutorial Website, is an Electronics Geek, Blogger and Young Entrepreneur. He possesses vast experience in the field of electronics, electronic components, PCB, Soldering, SMT, Telecommunication, ESD Safety, and PCB Assembly Tools, Equipment and Consumables. Keep visiting for daily dose of Tips and Tutorials.

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38 Responses

  1. July 8, 2013

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  8. November 25, 2013

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  9. November 26, 2013

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  10. November 26, 2013

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  11. November 27, 2013

    […] from soldering tools and solder wire, you may also need few other consumables like solder flux, solder paste, braid etc. Chemtronics is a worldwide leader in manufacturer and supply of PCB rework […]

  12. November 28, 2013

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  13. November 28, 2013

    […] Solder Paste and Its Application in SMT […]

  14. April 18, 2014

    […] fresh solder paste on the track and place the NEW […]

  15. May 3, 2014

    […] Solder Paste. […]

  16. July 24, 2014

    […] solder pastes are used in the assembly of printed circuit boards (PCBs) for a wide variety of applications, […]

  17. August 29, 2014

    […] Solder Paste and Its Application in SMT […]

  18. July 6, 2015

    […] control temperature. Hot air flow through nozzle attached to the handle. This hot air helps to melt solder paste beneath the IC. An SMD Rework Station is also used as BGA Rework Station using some additional […]

  19. February 28, 2019

    […] Ch. 9. Solder Paste and Its Application […]

  20. March 5, 2019

    […] Solder Paste Printing Systems are available in three configurations: manual, semi-automatic and fully automatic. The machine can be table mounted, stand-alone, or in-line. Many semi-automatic printers offer manual vision alignment capability, while fully automatic printers offer automatic vision alignment. […]

  21. March 5, 2019

    […] Soldering: A soldering process that uses a specially formulated solder paste that does not require the residues to be cleaned after solder […]

  22. March 5, 2019

    […] Solder Paste and Its Application in SMT […]

  23. March 5, 2019

    […] Solder Paste and Its Application in SMT […]

  24. March 11, 2019

    […] or surface mount technology. Soldering material may include solder in the form of solder wire, solder paste, solder balls for BGA (Ball Grid Array) and soldering […]

  25. March 17, 2019

    […] using a hot air blower while soldering can be done using a soldering iron and solder wire or using solder paste or solder balls (BGA) and SMD Hot Air Blower / rework […]

  26. March 18, 2019

    […] be used with most flux chemistry. Again, however, these alloys vary greatly, and compatibility with solder paste, cored solder wire, and liquid flux chemistry is dependent upon the melting point and composition […]

  27. March 20, 2019

    […] solder called solder paste consisting of very fine solder and flux is dispensed on solder pads. Solder paste can be dispensed […]

  28. April 24, 2019

    […] the PCB assembly process, all kinds of Solder wire, solder bar, solder paste (Leaded or Lead-Free Solder), Different Types of Flux and SMT Glue or Adhesive are used. All these […]

  29. May 5, 2019

    […] Desoldering wire and soldering iron, remove all the extra solder paste from the PCB […]

  30. August 9, 2019

    […] Paste) for PCB assembly and rework / repairing. They also used No-Clean Liquid Flux and No-Clean Solder Paste. They did not bother to clean the PCB and the flux residue after assembly. These boards were later […]

  31. August 13, 2019

    […] SMT Baking Oven / Curing Oven: In electronics, an oven is required for both adhesive curing and solder paste baking operations. The same or different ovens may be used for adhesive curing and baking of solder paste. […]

  32. August 29, 2019

    […] soak zone: This is the high temperature zone where the temperature is high enough to melt solder paste so that the component leads get soldered to the pads on the circuit […]

  33. November 19, 2019

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  34. December 5, 2019

    […] Solder Paste smearing on underside of stencil. […]

  35. December 27, 2019

    […] Soldering with Solder Paste or Solder Preforms and Hot […]

  36. December 27, 2019

    […] Solder Paste – Used for SMD Soldering. […]

  37. February 4, 2020

    […] Paste Screen Printer Machine is needed to screen print solder paste onto the Printed Circuit Board (PCB) before placement of Surface Mount Components (SMD) for Reflow […]

  38. March 2, 2020

    […] solder pastes are used in the assembly of printed circuit boards (PCBs) for a wide variety of applications, […]

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