Wave Soldering vs Reflow: Differences & How to Choose

Wave soldering and reflow soldering are the two mainstream ways to solder a PCB assembly. Reflow melts solder paste that was printed onto the pads and is the standard process for surface-mount (SMT) components. Wave soldering passes the underside of the board over a pumped wave of molten solder and is used mainly for through-hole (THT) components. Many real-world boards need both, so the real question is usually not "which is better" but "which process fits my board, volume and budget."

Quick answer

• SMT-only board: use reflow soldering.
• Through-hole parts in high volume: use wave soldering.
• Mixed SMT + through-hole board: reflow the SMT side first, then solder the through-hole parts with wave or selective wave soldering.

Table of Contents

• Wave Soldering vs Reflow Soldering: Side-by-Side Comparison
• What Is Reflow Soldering?
• What Is Wave Soldering?
• Can You Wave Solder SMD Components?
• Selective Soldering vs Wave Soldering
• How to Choose: Wave, Reflow or Selective Soldering
• FAQ: Wave Soldering vs Reflow Soldering

Wave Soldering vs Reflow Soldering: Side-by-Side Comparison

What Is Reflow Soldering?

Reflow soldering joins SMT components by melting solder paste that has been printed on the PCB pads. After the components are placed on the paste, the whole board travels through a multi-zone oven. The paste melts, wets the pads and component terminations, and solidifies into joints as the board cools. No mechanical pressure is needed. The temperature profile does the work.

Reflow is the default for SMT because it handles tiny parts and dense layouts that a wave cannot reach. Through-hole parts are normally added afterwards with wave or selective soldering. For a deeper definition, see our reflow soldering glossary entry.

Reflow Soldering Process: 4 Stages

1. Preheat. The board is brought up gradually (typically about 1–3 °C per second) to limit thermal shock and start driving off solvents in the paste.
2. Thermal soak. A plateau (often around 150–200 °C for 60–120 seconds) activates the flux, removes oxides and equalizes temperature between large and small components. Poor soak control is a common cause of tombstoning and uneven wetting.
3. Reflow. The temperature rises above the solder's melting point to a peak, and the paste melts and wets the pads. Too low and the joints are cold or incomplete; too high and you risk damaging components or the laminate. Time above liquidus is typically about 60–90 seconds for lead-free paste.
4. Cooling. Controlled cooling solidifies the joints and limits excessive intermetallic growth, which improves joint reliability.

For BGA and QFN packages the joints are hidden under the body, so watch for voids and head-in-pillow defects and verify with X-ray inspection.

Reflow quality also depends on paste deposition. Stencil thickness and aperture design directly affect bridging and insufficient solder, which is why fine-pitch boards need a well-specified SMT stencil.

What Is Wave Soldering?

Wave soldering is a bulk soldering process for through-hole components. The leads are inserted from the top, and the board's underside is passed over a standing wave of molten solder that fills the plated holes and forms all the joints in a single pass. It uses no solder paste; the solder comes directly from the molten bath. In some regions, especially in Japan, wave soldering is also called "flow soldering," so "flow soldering vs reflow soldering" is the same comparison.

Wave Soldering Process: 4 Stages

1. Flux application. Spray or foam flux removes oxides and lowers surface tension so solder can wet the leads and barrels. The flux must be compatible with the board, the solder alloy and your cleaning process. See our guide to solder flux.

   

2. Preheat. The board rides a conveyor through a preheat zone that activates the flux, evaporates solvents and reduces thermal shock to the laminate and components.

   

3. Solder wave. The bottom side contacts the wave for roughly 2–5 seconds. Many machines use a turbulent "chip wave" first, followed by a smooth laminar wave that drains excess solder and reduces bridging.

   

4. Cooling. The board cools on the conveyor so the joints solidify undisturbed. Movement during solidification can cause disturbed joints.

We keep this section short on purpose. For parameters, machine types and troubleshooting, read our full wave soldering process guide.

Advantages of Wave Soldering

• High throughput on through-hole boards. Hundreds of joints are soldered in one pass.
• Strong through-hole joints. Solder fills the plated barrel, which suits connectors and parts that see mechanical stress.

  

• Low per-board cost at volume. Once pallets and profiles are set up, the process is fast and repeatable.
• Mature, well-understood process. Defects are well documented and can be controlled with good design and profiling.

Its limits: it solders the bottom side only, it cannot handle fine-pitch or bottom-terminated packages, and it exposes the board to more thermal stress than selective methods.

Can You Wave Solder SMD Components?

Yes, but only in limited cases. Small SMD parts (chip resistors and capacitors, some SOT and SOIC packages) can be glued to the bottom side with an adhesive dot, cured, and then carried over the wave together with the through-hole leads. This was common in older mixed-technology designs.

Be careful with these constraints:

• Shadowing: tall components can block solder from reaching neighbors, so spacing and orientation rules apply.
• Not suitable for BGA, QFN, LGA or fine-pitch leaded packages.
• Extra steps: gluing and curing add process time and cost.

For most modern designs, the better approach is to reflow all SMD parts and solder the through-hole parts with selective soldering, or use pin-in-paste (paste printed into the holes so suitable through-hole parts go through the reflow oven).

Wave Soldering vs Reflow Soldering: Key Differences

1. Component compatibility

Reflow works for nearly every SMT package, including BGA, QFN and 01005 parts. Wave works for through-hole leads and a narrow set of glued SMD parts. Many connectors and electrolytic capacitors cannot tolerate a full pass through the reflow oven, which is why through-hole parts are usually soldered as a separate step.

2. Cost and setup

Neither process is cheaper in every case. SMT-only boards are naturally reflowed because paste printing and placement are needed anyway. For through-hole-heavy boards in volume, wave soldering lowers the cost per joint. For small batches, the pallets, fixtures and machine setup can outweigh that benefit, and selective or hand soldering may cost less overall.

3. Speed and throughput

A wave line is continuous and very fast for through-hole joints. Reflow throughput depends on the whole sequence of printing, placement and oven time, and it is the most efficient route for dense SMT designs.

4. Thermal stress and design constraints

Reflow heats the entire assembly with a controlled profile. Wave soldering hits the bottom side with molten solder, so bottom-side parts and the laminate see a sharper thermal event. Pad shape, spacing and component orientation matter more for wave than for reflow.

5. Defects and reliability

Neither method is inherently more reliable. Typical reflow risks are tombstoning, voids and head-in-pillow; typical wave risks are bridging, solder skips and icicles. Good profiles, design-for-manufacturing review and AOI/X-ray inspection reduce both.

Selective Soldering vs Wave Soldering

Selective soldering uses a programmable mini-nozzle to solder individual through-hole joints or small groups of joints instead of flooding the whole bottom side. It is the usual answer for mixed boards where a full wave would damage nearby SMT parts or heat-sensitive components.

• Choose wave soldering for simple, through-hole-dominant boards in high volume where speed matters most.
• Choose selective soldering for dense boards with SMT parts on the bottom, tight keep-out areas, thermal constraints, or high-mix and lower volumes.
• Trade-off: selective is slower per board but gives more control and less thermal stress; it also requires keep-out zones around the joints so the nozzle can reach them.

How to Choose: Wave, Reflow or Selective Soldering

Not sure which process your board needs?

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Design tips that make either process easier

• Keep all SMT parts on the top side where possible so the bottom side can go over a wave or be selectively soldered.
• Size plated through-holes roughly 0.2–0.4 mm larger than the lead so solder can flow up the barrel.
• Leave keep-out zones around through-hole joints for selective nozzles and pallet openings.
• Follow the pad, spacing and orientation rules for any SMD part that will be on the wave side, and avoid fine-pitch parts there.
• Plan for inspection: BGAs and QFNs need X-ray, and all boards benefit from AOI.

Common Soldering Defects

For fine-pitch SMD pads, a solder mask bridge between neighboring pads helps reduce solder bridging during reflow, provided the PCB manufacturer can hold the minimum bridge width.

Mixed-Technology Assemblies: The Usual Sequence

1. Print solder paste, place SMT components and reflow (repeat for the second side if needed).
2. Insert the through-hole components.
3. Solder them by wave or selective soldering, depending on layout, volume and thermal limits.
4. Inspect with AOI, X-ray where hidden joints exist, and test.

For the bigger picture of how these steps fit into the full build, see our PCB assembly guide and the overview of what SMT is.

Reflow, Wave and Selective Soldering at NextPCB

NextPCB handles the full range in-house: SMT assembly through automated reflow soldering, through-hole assembly through wave or selective soldering, and mixed-technology boards on the same order. X-ray inspection is applied to BGA and QFN boards to verify joints hidden under the package, and there is no minimum order quantity, so the same process control applies from a single prototype.

Before anything is built, our free DFM/DFA review flags issues that would cause soldering defects, so you can fix them at the design stage rather than after assembly.

Get an Instant Assembly Quote or view our full assembly capabilities.

Related resources

• PCB assembly services
• Wave soldering process: full guide
• Reflow soldering glossary
• SMD component types and how to identify them
• PCB manufacturing overview
• SMT stencil quote

FAQ: Wave Soldering vs Reflow Soldering

Which is better, wave soldering or reflow soldering?

Neither is better in general. Reflow is better for SMT, and wave is better for high-volume through-hole soldering. Mixed boards often use both.

Is wave soldering cheaper than reflow soldering?

It depends on the board. Wave lowers the cost per joint on through-hole-heavy boards in volume, while reflow is the most economical route for SMT. For small batches, setup and fixtures can make selective or hand soldering cheaper than wave.

Can a PCB go through both reflow and wave soldering?

Yes. In mixed-technology assemblies, SMT parts are reflowed first and the through-hole parts are then soldered by wave or selective soldering.

What is flow soldering?

"Flow soldering" is another name for wave soldering used in some regions. It refers to the same process of passing the board over flowing molten solder.

What is the difference between selective soldering and wave soldering?

Wave soldering floods the whole bottom side with solder, while selective soldering uses a small programmable nozzle to solder chosen joints only. Selective is better for dense or heat-sensitive mixed boards.

Can you wave solder SMD components?

Only small SMD parts glued to the bottom side. BGA, QFN and fine-pitch parts should be reflowed instead.

Conclusion

Use reflow soldering for SMT, wave soldering for high-volume through-hole, and selective soldering when a mixed board has tight keep-outs or heat-sensitive parts. Decide based on component types, board density, volume and inspection needs, and check your layout with a DFM review before production.

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About the Author

Lolly Zheng- Sales Account Manager at NextPCB.com

Four years of proven sales experience across electronic components and PCBA industries, with strong expertise in key account acquisition, customer relationship management, and contract negotiations. Focused on driving revenue growth through strategic client development and solution-based selling. Experienced in expanding high-value accounts, securing long-term partnerships, and consistently exceeding sales targets in competitive markets.

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