Soldering is one of the most important processes in PCB assembly because it creates the electrical and mechanical connection between electronic components and the printed circuit board.
Two of the most widely used soldering methods are wave soldering and reflow soldering.
Although both processes use solder to connect components to a PCB, they are designed for different assembly technologies.
In simple terms:
Reflow soldering is mainly used for SMT components.
Wave soldering is mainly used for through-hole or THT components.
However, modern PCB assemblies often contain both SMT and THT components, which means a complete PCBA production line may use both soldering processes.
So, wave soldering vs reflow soldering: what’s the difference?
The main differences involve:
- Component mounting method
- Solder application
- Equipment
- Process temperature profile
- Production sequence
- PCB design
- Throughput
- Typical applications
Wave Soldering vs Reflow Soldering: What’s the Difference?
This guide explains how both processes work and how PCB assembly factories can determine which soldering method is suitable for their products.
What Is Reflow Soldering?
Reflow soldering is the primary soldering method used in Surface Mount Technology, or SMT, assembly.
In an SMT line, solder paste is first printed onto PCB pads.
Surface-mount components are then placed on top of the solder paste by pick and place machines.
The PCB passes through a reflow oven, where the solder paste is heated according to a controlled thermal profile.
The solder melts and forms joints between the component terminals and PCB pads.
After cooling, the solder solidifies and creates the electrical connections.
A typical SMT production flow is:
PCB Loader → Solder Paste Printer → SPI → SMT Pick and Place → Reflow Oven → AOI → PCB Unloader
Reflow soldering is therefore a central process in modern high-density PCB assembly.
How Does Reflow Soldering Work?
A typical reflow process includes several thermal stages.
The exact profile depends on:
- Solder paste
- PCB design
- Component types
- Board thickness
- Thermal mass
- Production requirements
The main stages generally include the following.
Solder Paste Printing
Before reflow begins, solder paste is applied to the PCB pads using a stencil and solder paste printer.
The printing process must control:
- Solder paste volume
- Alignment
- Aperture transfer
- Print pressure
- Separation speed
Poor printing can create defects that cannot be corrected simply by changing the reflow profile.
Component Placement
SMT pick and place machines position components onto the printed solder paste.
Typical components include:
- Chip resistors
- Chip capacitors
- ICs
- QFPs
- QFNs
- BGAs
- Diodes
- Transistors
Accurate placement helps ensure proper solder joint formation during reflow.
Preheating
The PCB temperature rises gradually as the board enters the reflow oven.
The preheat stage helps prepare the PCB, solder paste, and components for higher temperatures.
Soak or Thermal Equalization
Depending on the profile strategy and solder paste specification, the board may pass through a region that helps reduce temperature differences across the assembly and supports flux activity.
Reflow
The solder paste reaches a sufficient temperature to melt.
During this stage, solder wets the PCB pads and component terminations and forms the joint.
Cooling
The PCB is cooled so that the molten solder solidifies.
Cooling conditions should also be controlled as part of the complete thermal process.
What Is Wave Soldering?
Wave soldering is commonly used for through-hole PCB assembly, also referred to as THT or, in many factories, DIP assembly.
In this process, through-hole components are inserted into holes in the PCB.
The PCB then travels over a controlled wave of molten solder.
The solder contacts exposed pads and component leads on the underside of the PCB and forms multiple joints during one continuous pass.
A typical wave soldering process is:
THT Component Insertion → Inspection → Fluxing → Preheating → Solder Wave → Cooling → Inspection
Wave soldering is widely used for components such as:
- Connectors
- Terminal blocks
- Relays
- Transformers
- Switches
- Large capacitors
- Pin headers
- Selected power components
How Does Wave Soldering Work?
Wave soldering involves several process stages.
THT Component Insertion
Component leads are inserted through the PCB holes.
Insertion can be:
- Manual
- Semi-automatic
- Automatic
The correct approach depends on component type, production volume, and automation level.
Flux Application
Flux is applied to the underside of the PCB.
It supports solder wetting by preparing the metal surfaces.
Important parameters include:
- Flux chemistry
- Application quantity
- Spray pattern
- Coverage
Preheating
The PCB passes through a preheat section.
The required profile depends on:
- PCB thickness
- Copper distribution
- Flux chemistry
- Solder alloy
- Component thermal mass
Solder Wave Contact
The PCB passes over the molten solder wave.
Important variables include:
- Solder temperature
- Conveyor speed
- Wave height
- Contact time
- PCB angle
- Board orientation
Cooling
After leaving the solder wave, the assembly is cooled before inspection and downstream processing.
Wave Soldering vs Reflow Soldering: Key Differences
The two technologies are complementary rather than direct substitutes in many factories.
Reflow Soldering Is Mainly Used for SMT
Modern SMT assembly relies heavily on reflow soldering.
The process allows large numbers of small components to be placed and soldered efficiently.
A typical SMT line may process:
- 0201 or other chip components
- Resistors
- Capacitors
- LEDs
- ICs
- QFP
- QFN
- BGA
- Other surface-mount packages
Because these components sit directly on the PCB surface, a molten solder wave is generally not the primary soldering method used for their main assembly process.
Instead, solder paste is printed onto the PCB before placement and then reflowed in the oven.
Wave Soldering Is Mainly Used for THT
Wave soldering is commonly used when components have leads passing through the PCB.
This can provide an efficient way to solder many through-hole joints in one process.
Typical applications include:
- Industrial control boards
- Power supply boards
- Automotive electronics
- Home appliance control boards
- Energy equipment
- Communication products
- Factory automation systems
Wave soldering is especially attractive when the PCB contains many suitable THT joints.
Which Process Has Higher Throughput?
Both processes can provide high throughput when used for the applications they are designed for.
Reflow Soldering Throughput
In an SMT line, throughput is typically influenced by:
- Pick and place capacity
- Printer cycle time
- Reflow oven conveyor speed
- Product changeover
- PCB dimensions
For many SMT lines, pick and place equipment is a major capacity factor.
The reflow oven should be sized so that it does not become the bottleneck.
Wave Soldering Throughput
Wave soldering throughput depends on:
- Conveyor speed
- PCB spacing
- PCB length
- Required preheat
- Soldering contact requirements
- Upstream THT insertion capacity
In many DIP/THT lines, manual component insertion can become the bottleneck rather than the wave soldering machine itself.
Reflow Soldering Equipment
The main machine used for reflow soldering is the reflow oven.
A modern SMT reflow oven can include:
- Multiple heating zones
- Cooling zones
- Conveyor system
- Temperature control
- Process recipe management
- Monitoring functions
The number of heating zones and machine configuration should be selected according to:
- PCB size
- Thermal mass
- Solder paste requirements
- Production capacity
- Product mix
A larger number of zones can provide more flexibility for developing and controlling thermal profiles, but the correct configuration depends on production needs.
Wave Soldering Equipment
A typical wave soldering machine can include:
- Flux spray system
- Preheating zones
- Conveyor
- Solder pot
- Wave system
- Cooling section
- Process controls
Supporting equipment may include:
- PCB loaders
- DIP insertion conveyors
- Inspection conveyors
- PCB unloaders
- Fume extraction
- Testing stations
The machine should be selected according to the complete THT production process rather than only solder pot size or maximum conveyor speed.
Which Process Requires Solder Paste?
Reflow soldering normally uses solder paste.
The solder paste contains:
- Solder alloy particles
- Flux system
- Other formulation components
It is printed onto PCB pads before component placement.
Wave soldering normally uses molten solder from the machine’s solder pot rather than printed solder paste for the through-hole joints being processed.
Flux is separately applied before the PCB contacts the solder wave.
Reflow Temperature vs Wave Soldering Temperature
These processes should not be compared using one simple temperature number.
In reflow soldering, the entire PCB passes through a controlled thermal profile with multiple temperature stages.
Wave soldering also includes preheating, but the solder side of the board ultimately contacts a molten solder wave.
The correct temperatures depend on factors including:
- Solder alloy
- Flux or solder paste
- PCB design
- Component limits
- Board thickness
- Process specification
There is no universal temperature setting suitable for every PCB.
Which Process Is Better for Small SMT Components?
Reflow soldering is generally the standard choice for modern surface-mount components.
It supports:
- High component density
- Precise placement
- Fine-pitch devices
- Automated production
This makes it suitable for compact electronics containing large numbers of SMT components.
Which Process Is Better for Large Through-Hole Components?
Wave soldering can be more suitable for products containing many through-hole components such as:
- Large connectors
- Relays
- Transformers
- Terminal blocks
- Large capacitors
However, selective soldering may be preferable for some complex mixed-technology PCBs.
What About Selective Soldering?
Selective soldering is another important THT soldering process.
Unlike wave soldering, which exposes a broader underside area to molten solder, selective soldering applies solder only to programmed joints or areas.
Selective soldering can be useful when:
- The PCB contains only a few THT joints
- Bottom-side SMT components restrict wave soldering
- Certain PCB areas must avoid solder contact
- Localized process control is required
So for THT production, the actual choice may be:
Wave Soldering vs Selective Soldering
rather than simply wave soldering vs reflow soldering.
Can Reflow and Wave Soldering Be Used on the Same PCB?
Yes.
This is very common in mixed SMT and THT assembly.
A typical process can be:
Solder Paste Printing → SPI → SMT Placement → Reflow → AOI → THT Insertion → Wave Soldering → Inspection → Testing
The SMT components are soldered first using reflow.
The THT components are then inserted and soldered using wave or selective soldering.
This allows one PCB to combine:
- High-density SMT components
- Larger THT components
- Connectors
- Relays
- Transformers
- Terminals
Why Is Reflow Usually Done Before Wave Soldering?
In a typical mixed-technology assembly, SMT components are assembled and reflowed before THT insertion.
This sequence makes it easier to:
- Print solder paste
- Place SMT components automatically
- Reflow the SMT side
- Inspect SMT solder joints
- Insert larger THT components afterward
Large through-hole parts could interfere with stencil printing, SMT placement, or reflow handling if installed too early.
However, the final manufacturing sequence should always be confirmed according to actual PCB design and process requirements.
Common Reflow Soldering Defects
Potential reflow defects can include:
- Solder bridging
- Tombstoning
- Insufficient solder
- Non-wetting
- Solder balls
- Component displacement
- Open joints
Possible causes can involve:
- Solder paste printing
- Stencil design
- Placement
- PCB pad design
- Component condition
- Reflow profile
Troubleshooting should therefore consider the complete SMT process.
Common Wave Soldering Defects
Typical wave soldering problems can include:
- Solder bridges
- Insufficient solder
- Poor wetting
- Incomplete hole fill
- Icicles
- Excessive solder
- Solder balls
Potential causes can include:
- Flux application
- Preheat conditions
- Solder temperature
- Conveyor speed
- Wave stability
- PCB orientation
- Component solderability
- PCB design
Again, the process should be analyzed as a system rather than adjusting one setting only.
Which Process Is More Automated?
SMT reflow production is generally associated with a highly automated line.
A typical line includes:
Automatic Loader → Solder Paste Printer → SPI → Pick and Place → Reflow → AOI → Unloader
DIP/THT production can also be automated, but component variety often makes insertion more challenging.
A THT line may use:
PCB Loader → Automatic/Manual THT Insertion → Inspection → Wave Soldering → Cooling → Inspection → Testing → Unloader
Therefore, the automation level of a complete PCBA factory depends on both product design and equipment configuration.
Wave Soldering vs Reflow Soldering Cost
There is no universal answer to which process costs less.
They serve different manufacturing purposes.
Cost factors for reflow soldering can include:
- Solder paste
- Stencils
- Reflow oven
- Energy
- Nitrogen where used
- Maintenance
- Profile development
Wave soldering cost factors can include:
- Solder alloy
- Flux
- Solder pot operation
- Electricity
- Nitrogen where used
- Pallets or tooling
- Maintenance
The relevant comparison should be based on the total PCBA manufacturing process rather than treating the two machines as direct substitutes.
How to Choose Between Wave and Reflow Soldering
The most important question is:
What type of components are being assembled?
Choose Reflow Soldering When:
- Components are mainly SMT
- High-density PCB assembly is required
- Automatic pick and place is used
- Fine-pitch devices are present
- Solder paste printing is part of the process
Choose Wave Soldering When:
- The PCB contains many THT components
- Through-hole leads need soldering
- PCB design supports wave contact
- High THT throughput is required
Consider Both When:
- The PCB contains SMT and THT components
- A complete mixed-technology PCBA process is required
How to Configure a Complete SMT + THT Production Line
A mixed production line may include:
SMT Section
PCB Loader → Automatic Solder Paste Printer → SPI → Pick and Place Machines → Reflow Oven → AOI → PCB Unloader/Buffer
THT Section
THT Component Preparation → DIP/THT Insertion → Inspection → Wave or Selective Soldering → Cooling → Inspection → Testing
The two sections should be balanced according to:
- PCB volume
- SMT component count
- THT component count
- Placement speed
- Manual insertion time
- Soldering throughput
- Inspection
- Testing capacity
A fast SMT line does not automatically result in high factory output if THT insertion or testing becomes the bottleneck.
What Information Is Needed Before Selecting Soldering Equipment?
Before choosing a reflow oven or wave soldering machine, manufacturers should prepare:
- PCB dimensions
- PCB thickness
- Panel design
- BOM
- SMT component list
- THT component list
- Component density
- Maximum component height
- Solder alloy
- Target production capacity
- Product mix
- Changeover frequency
- Existing equipment
- Factory layout
- Inspection requirements
- Testing requirements
- Automation level
- Budget
This information helps determine the correct production process and machine configuration.
SMT, THT and PCBA Production Line Solutions from Fuliu Electronics
Established in 2014, Fuliu Electronics is dedicated to providing customers with high-quality PCBA intelligent manufacturing solutions and services.
With extensive experience in the SMT industry, we specialize in dependable equipment, professional technical support, and complete SMT and PCBA production line solutions.
Our product portfolio includes SMT pick and place machines from Fuji, Panasonic, ASM, Yamaha, JUKI, and Hanwha, together with ERSA reflow ovens from Germany, MagicRay SPI/AOI inspection systems, automatic solder paste printers, supporting PCBA equipment, pre-owned SMT equipment, SMT spare parts, machine leasing, and maintenance services.
For customers planning a new SMT, DIP/THT, or mixed PCBA production line, Fuliu Electronics can help evaluate:
- PCB dimensions
- BOM
- SMT and THT component mix
- Production capacity
- Product variety
- Reflow requirements
- Wave or selective soldering requirements
- Inspection and testing
- Factory layout
- Existing equipment
- Automation level
- Investment budget
Rather than evaluating a reflow oven or wave soldering machine in isolation, manufacturers can plan the complete production process from solder paste printing and placement through soldering, inspection, and testing.
As part of our global growth strategy, Fuliu Electronics is actively expanding into international markets, with key focus areas including India, Vietnam, the Philippines, Indonesia, the Middle East, South Africa, and Europe.
Conclusion
So, wave soldering vs reflow soldering: what’s the difference?
The simplest answer is:
Reflow soldering is mainly used for SMT assembly.
Wave soldering is mainly used for THT/DIP assembly.
Reflow soldering uses solder paste, SMT placement, and a controlled reflow oven profile to solder surface-mount components.
Wave soldering uses fluxing, preheating, and a molten solder wave to solder through-hole component leads.
For many modern electronics products, the correct manufacturing solution is not choosing between the two.
It is using both processes in the correct sequence:
SMT Printing → SPI → Placement → Reflow → AOI → THT Insertion → Wave/Selective Soldering → Inspection → Testing
The right production configuration should be based on PCB design, BOM, component technology, target capacity, product mix, soldering requirements, inspection, testing, factory layout, and automation level.
If you are planning a new SMT production line, selecting a reflow oven, upgrading a wave soldering line, or building a complete SMT + THT PCBA factory, Fuliu Electronics can help evaluate your PCB dimensions, BOM, component mix, target capacity, existing equipment, factory layout, automation requirements, and budget to develop a suitable production solution.
Frequently Asked Questions
Reflow soldering is mainly used for SMT components and melts solder paste previously printed onto PCB pads. Wave soldering is mainly used for through-hole components and solders their leads by passing the PCB over molten solder.
Wave soldering can be involved in certain specialized PCB assembly processes, but modern SMT production is primarily associated with reflow soldering.
Standard THT production is more commonly associated with wave, selective, or manual soldering. Some specialized processes can differ, but reflow is primarily used for SMT assembly.
Yes.
Mixed SMT/THT boards commonly go through reflow first for SMT components and then wave or selective soldering for THT components.
A reflow oven is used to heat the PCB according to a controlled thermal profile and melt the solder paste.
A wave soldering machine typically integrates fluxing, preheating, a solder pot and wave system, conveyor transport, and cooling.