SMT Soldering Process & Assembly Techniques
SMT Soldering Process – SMD Soldering & SMT Assembly Techniques.
SMT Soldering Process and techniques is little different from through hole technology.
SMD soldering or Surface Mount Technology assembly needs different SMT Equipment and greater experience and expertise. SMT PCB has flat tin-lead or gold-plated copper pads without any hole. These traces are called “solder pads“.
Table of Contents:
SMT Soldering Process
- Semi-solid solder called solder paste consisting of very fine solder and flux is dispensed on solder pads. Solder paste can be dispensed using stencil with screen printing process with a SMT screen printer.
- Once the solder paste is dispensed, the circuit board is moved to a conveyor belt of a pick-and-place machine. SMD components are picked up by the pick-and-place machine and placed on the PCB.
- Once all the electronic components are placed on the SMT circuit board, it is then conveyed into the reflow soldering oven. The SMT reflow oven has different chambers. The first chamber or zone is called pre-heat zone, where the temperature of the board and all the components is gradually and uniformly raised to prevent any crack to the PCB due to thermal shock.
- The next zone is 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 board. The surface tension of the molten solder keeps the components in place. Surface tension also automatically aligns the components on their pads.
SMT Soldering Techniques
Reflow soldering can be done using different techniques:
- Infrared reflow;
- Hot gas convection; or
- Vapor phase reflow
Each method having its own advantages and disadvantages.
With double-sided PCBs, the reflow soldering process is repeated using either solder paste or glue to hold the components in place. If glue is used then the parts must be soldered later using wave soldering process.
After SMT Soldering Process is Over
Once the soldering process is over, the PCA or the PCB Assembly (PCBA) need to be washed to remove flux residues and any stray solder balls that could short out closely spaced component leads. This can be done with SMT solvent cleaning machine. Rosin flux can be cleaned with fluorocarbon solvents, high flash point hydrocarbon solvents, or low flash. Water soluble fluxes are removed with deionized water and detergent, followed by an air blast to quickly remove residual water. No-Clean fluxes don’t need any cleaning.
Inspection
Lastly, the Printed Circuit Assembly is visually inspected for any missing or misaligned components or solder bridging. This can be done using SMT Inspection Machine. If any fault is found during inspection, the board is sent for rework. Finally the board is sent for testing to verify that it is working correctly.
PCB Assembly Process Flow Chart (PCBA Process)
Video: Reflow Soldering SMT PCB Assembly Process
FAQs: Surface Mount Soldering Process
What is the difference between reflow soldering and wave soldering?
Reflow soldering involves heating the entire PCB to melt solder paste, which then forms connections between SMD components and the board. Wave soldering, on the other hand, involves passing the bottom side of the PCB over a "wave" of molten solder, which creates connections on the board's underside.
What is solder paste, and how is it used in SMT soldering?
Solder paste is a mixture of solder alloy particles and flux. It is applied to the PCB's solder pads using a stencil. The components are then placed on the paste. During reflow soldering, the paste melts, forming solder joints that attach the components to the board.
What are some common challenges in SMT soldering?
Common challenges in SMT soldering include solder bridging (excess solder connecting adjacent pads), tombstoning (component lifting on one end), insufficient solder (resulting in weak connections), and overheating sensitive components. Proper stencil design, temperature profiles, and equipment maintenance can help mitigate these issues.
How can I ensure the reliability of SMT solder joints?
To ensure solder joint reliability, consider factors like appropriate stencil design, accurate component placement, using quality solder paste, optimizing reflow profiles, and inspecting the final joints for defects. Regularly calibrating and maintaining soldering equipment also contributes to consistent and reliable solder joints.
Related Posts:
- Surface Mount Soldering Guide – SMD Soldering
- BGA (Ball Grid Array): Repairing and Soldering BGA
- SMT Vs Through Hole Technology – Advantages and Disadvantages
- SMT Manufacturing Line and Assembly Process
- Types of Surface Mounting in SMT
- How to Solder – Hand Soldering Tutorial
- Printed Circuit Board: Design, Diagram and Assembly
- Electronic Components, Parts and Their Function
- Top Electronic Companies in the World
- SMD Rework Station in India
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