Why Wave Soldering is the Best Choice for THM Components

Wave soldering is a widely used process for attaching electronic components to printed circuit boards (PCBs) by soldering their leads or terminals. It involves passing the underside of the circuit board over a wave or fountain of molten solder. The solder wets the exposed metallic areas on the board, creating reliable mechanical and electrical connections.

THM (Through Hole Mounting) components are electronic parts with wire leads that are inserted into holes in the PCB and soldered to pads on the opposite side. The leads pass through the board entirely. Common THM components include resistors, capacitors, connectors, integrated circuits, transistors, and diodes.

Wave soldering is highly effective for soldering THM components due to its ability to form reliable joints on the leads protruding through the board. It provides an efficient and cost-effective process for high volume PCB production. This article examines why wave soldering is the preferred method for soldering THM components to printed circuit boards.

Benefits of Wave Soldering for THM

Wave soldering offers several key benefits that make it an ideal process for soldering Through-Hole Mount (THM) components.

High Production Speed

The high production speed of wave soldering is one of its biggest advantages. The conveyorized system can process boards at a rate of up to 150 inches per minute. This allows assemblers to solder high volumes of boards in a short timeframe. The speed and efficiency of wave soldering minimizes production bottlenecks.

Cost Effectiveness

Wave soldering is a very cost effective process compared to hand soldering or other techniques. The automated system requires less labor involvement. Additionally, the high throughput minimizes the cost per board. The equipment cost for a wave soldering system is relatively affordable compared to other soldering methods. This makes wave soldering scalable and economically feasible for all production volumes.


The repeatability of the automated wave soldering process also contributes to its reliability. It provides consistent heat profiles and solder joints. The even flow of solder over all connections reliably forms quality solder joints. This consistency delivers high first pass yields and minimizes rework. Reliable solder joints prevent field failures and keep manufacturing defects low. The dependability of wave soldering results in a robust soldering solution.

High Production Speed

Wave soldering offers extremely high production speeds compared to other soldering methods. The process time is very fast, allowing hundreds of boards to be soldered per hour.

Large circuit boards with dozens or hundreds of components can be soldered in just seconds as they pass over the solder wave. This is much faster than manual soldering or reflow soldering which must heat and cool each connection individually.

With a typical wave soldering system, conveyor speeds can reach 150 inches per minute. Multiply this by the width of the conveyor and you get an extremely high hourly production rate. It’s not uncommon for wave soldering to achieve between 400 to 800 boards per hour depending on the size.

The quick process time is ideal for high volume manufacturing. Companies can maximize throughput and meet tight deadlines when wave soldering THM components. The speed advantage over alternative soldering methods is a major reason wave soldering is the top choice.

Cost Effectiveness

Wave soldering is one of the most cost-effective methods for attaching electronic components to circuit boards in high volume. It requires a significantly lower equipment investment than alternative soldering techniques. The basic wave soldering system consists of a solder pot and pump, preheaters, and a conveyor. The equipment has minimal maintenance requirements and rarely needs replacement.

The consumable costs of wave soldering are also low compared to other techniques. Since the solder is contained in the pot, there is very little waste. Only small amounts of solder paste or flux are needed to prepare the boards. Nitrogen gas is used in some systems for an inert soldering environment, but the consumption is minimal. The solder pot does require periodic replenishment as solder is absorbed into the boards over time. However overall, the consumable costs per board are extremely low.

By keeping both equipment and consumable costs down, wave soldering provides very high production efficiency and maximum cost effectiveness. The economies of scale make it advantageous for high volume soldering applications. When throughput and costs are critical considerations, wave soldering is an optimal choice.


Wave soldering can deliver excellent reliability for THM components due to its ability to evenly coat all solderable surfaces. The conveyorized nature of the process ensures precise process control, leading to uniform solder coverage across the entire board. This even solder distribution helps minimize defects like solder voids, spikes, icicles, and bridges that can cause field failures.

In comparison to selective soldering and hand soldering methods, automated wave soldering has proven to result in substantially lower failure rates when used appropriately. The repeatable process conditions reduce inconsistencies between boards to near zero when the right settings and parameters are dialed in. This consistency translates into boards that function reliably over long service lifetimes without premature failures related to solder joint integrity.

Overall, wave soldering offers a level of process control and capability that makes it highly reliable for production runs of THM laden boards. The even wetting and uniform thermal profile applied to each board leads to robust solder joints that stand the test of time and use. With discipline and expertise, wave soldering can help achieve near zero defects and extremely high reliability demanded by modern electronics.

Ideal for THM Components

Wave soldering is particularly well-suited for through-hole mount (THM) components due to its ability to uniformly and reliably solder delicate parts.

The wave itself provides a gentle, even application of solder to all exposed THM leads simultaneously. This ensures every joint receives the proper amount of solder with no skips or bridges. The laminar flow of the wave prevents turbulent solder flow that could otherwise damage fragile component leads and small-pitch parts.

Additionally, the preheat stage gently brings the assembly up to soldering temperature to prevent thermal shock. Some THM components like electrolytic capacitors or MELF resistors require a controlled ramp-up to prevent internal damage. The staged heating in wave soldering provides this protection.

For populated boards with mixed surface mount and THM parts, wave soldering only applies solder to the underside THM leads. This selective soldering leaves SMT parts untouched, avoiding any risk of re-flow or solder splatter on sensitive SMT components.

With its ability to uniformly and safely solder all THM leads in a single pass, wave soldering is the ideal production soldering solution for boards using these universal and cost-effective components.

Best Practices

To achieve optimal results with wave soldering THMs, adhering to best practices is essential. This includes proper board design and precision process controls.

Proper Board Design

When designing boards destined for wave soldering, there are some important considerations:

  • Use a low standoff height between components and board. This allows the underside of the board to heat quickly and evenly.
  • Avoid high density component placement on the underside. This can lead to shadowing and uneven heating.
  • Include thermal reliefs around pads. This prevents solder wicking up pads and causing shorts.
  • Use solder masks defined openings. This confines solder flow to only desired areas.
  • Incorporate solder thieves to avoid bridging between closely spaced component leads.
  • Include peasant tops around through-hole leads to improve capillary flow.
  • Minimize the use of vias, which can lead to voids during soldering.

By optimizing board designs for the wave soldering process, it ensures THMs can be soldered effectively.

Precision Process Controls

In addition to design considerations, maintaining tight process controls is vital:

  • Use a well-calibrated profiling system to ensure the board reaches the ideal temperature curve through the preheat stages. This prevents thermal shock.
  • Closely monitor wave shape and temperature. Adjust as needed to achieve a smooth laminar wavefront with even contact.
  • Keep the solder pot composition consistent through regular testing and additions of fresh solder. This provides an ideal melting point and fluidity.
  • Use solder palletizers to remove dross and keep the solder surface clean.
  • Implement frequent maintenance schedules for pumps, heaters, and nozzles. This maintains solder quality and ideal fluid dynamics.

With precise process controls for parameters like temperature and wave quality, repeatable production of high-quality solder joints is possible. This reliability is key for THM assembly.

By following these best practices for both board design and process control, manufactures can fully realize the benefits of wave soldering for THM components. It enables maximizing throughput while achieving consistent joints and minimal defects.

Latest Innovations

Wave soldering technology continues to rapidly advance in ways that improve efficiency, quality, and flexibility. Some of the latest improvements include:

Improved Flux Application

  • New spray nozzle designs provide more precise control over flux deposition. This allows the ideal amount of flux to be applied in the optimal location.
  • Closed loop flux control systems actively monitor and adjust flux flow rates. This maintains consistency and minimizes flux usage.
  • Some systems use multiple spray nozzles or enclosed spray chambers. These innovations improve coverage and cut down on overspray.

3D Wave Technology

  • Standard wave soldering uses a planar wave. 3D wave systems create a complex wave pattern that includes peaks, valleys and wraparounds.
  • This exposes the underside of assemblies to precise amounts of contact time. The result is improved wetting and fillet formation.
  • 3D waves allow more consistent soldering of densely populated boards since their geometry can adapt to component spacing.
  • These systems provide high transfer efficiency while minimizing turbulent solder flow that can displace components.


In summary, wave soldering is an ideal choice for attaching THM (through-hole mounted) components to printed circuit boards. Wave soldering offers high production speeds, cost-effectiveness, and reliability when working with THM components.

The high-velocity turbulent wave of molten solder provides excellent wetting and ensures strong, reliable solder joints with THM leads inserted through holes in the PCB. Automated conveyor systems transport PCBs over the solder wave quickly and efficiently. This process is much faster than manual soldering and allows for high-volume manufacturing.

Additionally, wave soldering is more affordable compared to other soldering methods. The equipment has high throughput, lowering the cost per board. Nozzles, pumps, and other consumable parts are inexpensive and easily replaced, minimizing downtime.

When best practices are followed, wave soldered connections have excellent mechanical strength and low defect rates. Adjusting parameters like preheat, conveyor speed, and solder pot temperature optimizes the process for THM components. Nitrogen blanketing and solder pot maintenance reduces dross and oxidation.

With continual innovation in flux chemistry, alloys, and conveyor design, wave soldering machines have steadily improved. Modern systems have closed-loop feedback and excellent process control, producing extremely reliable solder joints. For high-volume production of boards with THM components, wave soldering is the proven, cost-effective choice.

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