How do you design a PCB for reliable wave soldering?

Today's Discussion
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Wave soldering is commonly used for through-hole and hybrid PCB assemblies, but getting consistent solder coverage depends on more than the soldering equipment. PCB layout, component orientation, exposed metal area, and the interaction between through-hole and surface-mount components can all affect soldering quality.

Some layout decisions that seem minor can contribute to defects such as bridging, solder skips, and incomplete hole fill. I wanted to start a discussion on the PCB design practices you use to make boards easier to wave solder.

Illustration of wave soldering of a PCB
Illustration of wave soldering of a PCB957×423 25.4 KB

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A few design considerations that can make a difference:

  • Component orientation matters. Through-hole components should be oriented appropriately relative to the solder wave to reduce the chance of bridging.
  • Component placement can create shadowing. Larger components can prevent the solder wave from reaching smaller components positioned behind them.
  • Pad and lead geometry matters. Large pads and long leads can collect excess solder during wave separation.
  • Solder thieves can help control bridging when proper component alignment alone isn’t sufficient.
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Hybrid assemblies introduce additional challenges because the solder wave interacts differently with through-hole and surface-mount components.

SMD component bodies can affect solder flow and prevent the wave from reaching leads on the trailing side. Component placement and orientation therefore become even more important when through-hole and SMD components share the same assembly.

For assemblies using selective soldering pallets, clearance around through-hole components and the size and shape of pallet openings also need to be considered during layout.

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Wave soldering parameters also need to be considered alongside the PCB layout. Factors such as solder wave contact, thermal profile, conveyor speed, wetting, and exposed metal area can influence the final solder quality.

Of course, the best approach depends on your board design, component mix, and assembly process, so align with your assembly partner early. For a deeper look at wave soldering principles, common defects, and design considerations, check out this article: Making Sense of Wave Soldering.