In SMT processes, How to increase solder paste or solder volume locally?

With the miniaturization and increasing precision of electronic products, SMT used in electronics manufacturing widely. In SMT processes, the amount of solder paste affects the quality and reliability of solder joints directly. In certain cases, it is necessary to increase the amount of solder paste or solder locally to meet specific welding requirements.

1. Necessity of Increasing Solder Paste or Solder Volume Locally 

In some situations, increasing solder paste or solder volume locally is essential. Common reasons include:

Heat Dissipation: For components with high heat generation, increasing solder volume improves thermal conductivity.

Mechanical Strength: In areas subjected to mechanical stress, more solder can form stronger joints.

Compensating for Dimensional Tolerances: Due to variations in component leads and PCB pad sizes, additional solder may be needed to ensure reliable connections.

2. Methods to Increase Solder Paste or Solder Volume Locally 

Here are some methods to achieve this in SMT processes:

a. Adjusting Stencil Aperture Design

By adjusting the stencil aperture size, the amount of deposited solder paste can be controlled directly.

Enlarging Apertures: Increase the size of stencil openings for pads requiring more solder.

Special-Shaped Apertures: Use trapezoidal or elongated apertures to deposit more solder at pad edges.

Advantages: Simple, cost-effective, and requires no process changes.

Disadvantages: Improper adjustments may affect print quality, limited by stencil feature size constraints.

b. Multiple Printing

Perform multiple solder paste printings on the same PCB to increase solder deposition.

Advantages: Control over solder volume precisely, suitable for specific high-solder areas.

Disadvantages: Increases production time and cost, misalignment risks may affect print quality.

c. Using Solder Preforms

Place preformed solder pieces on PCB pads before reflow soldering.

Advantages: Control solder volume precisely, is suitable for high-solder applications.

Disadvantages: Manual placement is time-consuming, automation may require additional steps.

d. Dip Soldering or Wave Soldering

For through-hole components or specific pads, dip or wave soldering can add extra solder.

Advantages: Fast and effective for bulk solder addition, useful for post-reflow adjustments.

Disadvantages: Not applicable to all SMT applications; risk of solder bridging if uncontrolled.

e. Adjusting Solder Paste Composition

Use solder paste with higher metal content or adjusted rheology to increase post-reflow solder volume.

Advantages: Applicable to entire boards or selective areas; no stencil redesign needed.

Disadvantages: May impact reflow profile and process, requires specialized pastes, increasing cost.

Conclusion

The decision to increase solder paste or solder volume locally in SMT processes should be carefully evaluated, balancing benefits and potential drawbacks. Each method has its ideal use case, and often a combination of techniques is needed. Engineers must assess assembly requirements, component characteristics, and production efficiency to determine the optimal approach.