Wave Soldering

Wave soldering forms multiple through-hole solder joints in one pass by flowing a molten solder “wave” across the underside of populated PCBs, ideal for volume assembly.

Overview

Wave soldering is an automated PCB assembly process where the underside of a board is passed over a controlled wave of molten solder. Fluxing, preheating, and a solder wave create consistent fillets on exposed through-hole leads and selected bottom-side surface-mount pads. It is optimized for repeatable, production-scale joining rather than individual joint control.

Use wave soldering when you have medium to high volumes of through-hole or mixed-technology boards with components accessible from the bottom side. It delivers strong, reliable joints with good process repeatability and low cost per joint once tooling is in place. Tradeoffs include limited suitability for very fine-pitch parts, thermal risk to heat-sensitive components, and the need for careful board and fixture design to avoid solder bridges and shadowing. Setup and tooling costs make it less attractive for very low volumes or highly customized boards.

Common Materials

  • FR-4 PCB laminate
  • Polyimide PCB laminate
  • Tin-lead solder
  • Lead-free SAC305 solder
  • Copper pads and traces

Tolerances

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Applications

  • Through-hole connector soldering on PCBs
  • Power supply and inverter boards
  • Automotive ECU and body-control PCBs
  • Industrial control and PLC boards
  • Consumer electronics mainboards
  • Telecom and networking backplanes

When to Choose Wave Soldering

Choose wave soldering for medium to high production volumes of through-hole or mixed-technology PCBs where most joints are accessible from the bottom side. It fits designs with standard-pitch leads, robust components, and layouts that can be optimized for solder flow and minimal bridging. It is especially effective when you need low cost per joint and repeatable quality across thousands of boards.

vs Torch Brazing

Pick wave soldering instead of torch brazing when you are joining electronic components on PCBs rather than structural metal parts. Wave soldering gives controlled thermal profiles, fluxing, and solder flow tuned for delicate components and fine features that open-flame torch brazing cannot handle without damage or inconsistency.

vs Furnace Brazing

Choose wave soldering over furnace brazing when you need fast, inline assembly of electronic circuit boards rather than batch joining of metal assemblies. Wave soldering targets copper pads and component leads with lower-temperature solders, avoiding the high temperatures and long cycles of furnace brazing that would destroy typical PCB materials and components.

vs Reflow Soldering

Favor wave soldering when the design is dominated by through-hole parts and only modest bottom-side SMT is present. Reflow is better for dense SMT on both sides, but wave is often faster and cheaper for large numbers of pins on connectors, transformers, and other through-hole components in higher volumes.

vs Hand Soldering

Use wave soldering instead of hand soldering when you have repeat builds and enough volume to justify fixtures and setup. It sharply reduces labor per joint, improves consistency, and minimizes operator variability, whereas hand soldering is better reserved for prototypes, rework, or very low volumes.

vs Selective Soldering

Choose wave soldering over selective soldering when most bottom-side through-hole joints can be soldered in one common pass without complex keep-out patterns. Selective soldering suits dense mixed-technology boards with many localized no-go areas, while wave is more economical and faster when the layout is wave-friendly.

Design Considerations

  • Keep the majority of through-hole parts and wave-soldered SMT components on the bottom side, and place heat- or wave-sensitive parts on the top side
  • Size plated through-holes and lead diameters to allow proper capillary action; avoid overly tight holes that block solder flow or excessively loose fits that promote voids
  • Orient connectors and multi-leaded components so their long edges run parallel to the direction of travel to minimize shadowing and solder bridging
  • Use solder mask dams and proper pad spacing on the wave side to reduce bridging, especially between fine-pitch leads and adjacent copper
  • Add thermal reliefs on large copper pours connected to pins that will be wave soldered to ensure full wetting and avoid cold joints
  • Plan panelization, tooling holes, and keep-out zones for pallets and wave fingers so the board can be fixtured securely without blocking solder access