{"id":56554,"date":"2026-08-20T16:24:12","date_gmt":"2026-08-20T14:24:12","guid":{"rendered":"https:\/\/smans.com\/?post_type=knowledgeportal&p=56554"},"modified":"2026-08-20T16:28:57","modified_gmt":"2026-08-20T14:28:57","slug":"optimising-selective-soldering-speed-height-and-nozzle-selection","status":"publish","type":"knowledgeportal","link":"https:\/\/smans.com\/en\/knowledgebase\/optimising-selective-soldering-speed-height-and-nozzle-selection\/","title":{"rendered":"Optimising selective soldering: speed, height and nozzle selection"},"content":{"rendered":"

Selective soldering allows the soldering process to be configured very precisely. This is a major advantage: different components on the same PCB can each receive a treatment adapted to their specific requirements.<\/p>\n

However, this flexibility does not mean that every parameter can be optimised independently. Soldering speed, soldering height, nozzle selection and heat transfer all influence each other.<\/strong> A change that improves cycle time, for example, may affect hole fill or increase the risk of bridging.<\/p>\n

The right settings are therefore not found by maximising a single parameter, but by considering them as part of the same process.<\/p>\n

Start with the right nozzle<\/h2>\n

Nozzle selection is often determined by the available space around the component to be soldered. But the nozzle also has an important thermal function.<\/p>\n

A larger nozzle brings more molten solder into contact with the soldering area. This means more thermal energy is available to heat the component lead, the plated through-hole and the surrounding PCB.<\/p>\n

A practical starting point is therefore:<\/p>\n

Use the largest possible nozzle that the available space around the component allows.<\/strong><\/p>\n

This does not mean that the largest available nozzle is always the best choice.<\/p>\n

When components are positioned close together, a smaller nozzle may be required to reach only the intended soldering area. The PCB layout therefore also determines how much room there is to optimise heat transfer through nozzle selection.<\/p>\n

Take protruding lead length into account<\/h2>\n

The nozzle diameter is not the only important factor. The position of the PCB in relation to the molten solder also requires attention.<\/p>\n

Through-hole components can have different protruding lead lengths. If a lead extends far below the PCB, sufficient clearance must remain between the lead and the nozzle.<\/p>\n

If the lead touches the nozzle, it can interfere with the process.<\/p>\n

At the same time, the molten solder needs to reach a sufficient height to make proper contact with the underside of the PCB and form the solder joint.<\/p>\n

Soldering height and lead length therefore need to be considered together.<\/strong><\/p>\n

Stable mechanical positioning is essential. Small variations in the distance to the solder wave can affect the contact conditions and therefore the repeatability of the process.<\/p>\n

How does soldering speed affect the process?<\/h2>\n

Soldering speed determines how long a particular area remains in contact with the molten solder.<\/p>\n

A lower speed generally means a longer contact time. This allows more time for heat to be transferred to the joint.<\/p>\n

This may be necessary for assemblies with a high thermal mass, such as a heavy connector or a PCB with a large amount of copper.<\/p>\n

A higher speed reduces contact time and can shorten cycle time. However, sufficient thermal energy must still be available to form the joint correctly within that shorter period.<\/p>\n

As a practical process range, speeds of approximately 5 to 10 mm\/s<\/strong> are often considered. Higher speeds may be possible when the thermal conditions, flux and solder alloy allow it.<\/p>\n

This should not be regarded as a universal setting.<\/p>\n

The fastest setting does not necessarily result in the best process.<\/strong> The correct speed is the one that provides sufficient heat transfer and a reliable solder joint without unnecessarily extending the contact time.<\/p>\n

More contact time is not always the best solution<\/h2>\n

When hole fill is insufficient, reducing the soldering speed may seem like a logical solution.<\/p>\n

Moving more slowly does provide more time for heat transfer. But if the underlying problem is insufficient preheating, a nozzle that is too small or unsuitable flux application, this approach mainly treats the symptom.<\/p>\n

A longer contact time also means that the PCB and component are exposed to molten solder and high temperatures for longer.<\/p>\n

When optimising the process, it is therefore better to first ask:<\/p>\n

Why does this joint need more time?<\/strong><\/p>\n

It may be possible to solder the same joint faster and more reliably by improving heat transfer in another way.<\/p>\n

Soldering height determines contact with the solder wave<\/h2>\n

The height of the solder wave relative to the PCB also affects the process.<\/p>\n

The molten solder needs to make sufficient contact with the required area. If the soldering height is too low, contact may be insufficient. If it is too high, there is a greater risk of solder reaching areas that should remain untouched.<\/p>\n

The geometry around the soldering point also needs to be considered, including protruding leads, neighbouring components and the available space around the nozzle.<\/p>\n

There is therefore no single ideal soldering height. The objective is to achieve stable and repeatable contact between the solder and the PCB<\/strong>, without unnecessary interaction with surrounding areas.<\/p>\n

The movement at the end of the soldering process also matters<\/h2>\n

What happens during contact with the solder wave is important, but so is the way the joint leaves the molten solder.<\/p>\n

This is particularly relevant when drag soldering connectors with multiple leads.<\/p>\n

As the joint leaves the solder wave, the molten solder forms a meniscus. The way this meniscus is broken can influence the amount of solder left behind and the formation of solder bridges between adjacent leads.<\/p>\n

A controlled end to the soldering movement is therefore important.<\/p>\n

One possible method is to lower the solder wave in a controlled manner at the end of the soldering path. This allows the meniscus to break gradually while the PCB remains in position.<\/p>\n

This can help reduce bridging between adjacent solder joints.<\/p>\n

Bridging is not always solved by changing one setting<\/h2>\n

When two adjacent solder joints are connected by excess solder, it can be tempting to identify a single machine parameter as the cause.<\/p>\n

In practice, bridging can have several causes.<\/p>\n

These include the movement as the PCB leaves the solder wave, soldering height, component geometry, nozzle selection and the properties of the flux and solder alloy.<\/p>\n

It is therefore important not to change settings at random.<\/p>\n

First determine at which point in the process the bridge is formed<\/strong>. Only then can you identify which parameter needs to be adjusted.<\/p>\n

Optimisation means looking at parameters together<\/h2>\n

Suppose you want to shorten cycle time by increasing the soldering speed.<\/p>\n

This is only possible if the joint still receives sufficient thermal energy during the shorter contact time.<\/p>\n

You can therefore investigate whether:<\/p>\n

    \n
  • a larger nozzle can be used;<\/li>\n
  • preheating can be optimised;<\/li>\n
  • the soldering height is set correctly;<\/li>\n
  • sufficient flux is applied in the right location;<\/li>\n
  • the solder alloy is suitable for the required process conditions.<\/li>\n<\/ul>\n

    This is precisely why selective soldering cannot be reduced to a table of standard settings.<\/p>\n

    Changing one parameter can have consequences for several other parts of the process.<\/p>\n

    From machine settings to a stable process<\/h2>\n

    The strength of selective soldering lies in the ability to precisely adapt the process to the PCB and component.<\/p>\n

    But having more adjustment options does not mean that more individual settings automatically result in a better process.<\/p>\n

    A robust process starts with understanding the function of each parameter:<\/p>\n

    nozzle selection influences heat transfer \u2192 soldering height determines contact \u2192 soldering speed determines contact time \u2192 movement out of the solder wave influences the final joint.<\/strong><\/p>\n

    Only by considering these factors as a whole can you optimise both solder quality and cycle time.<\/p>\n

    One important part of the process still remains: the chemistry. The flux and solder alloy also influence the size of the process window and which settings are achievable.<\/strong><\/p>\n","protected":false},"featured_media":56552,"template":"","class_list":["post-56554","knowledgeportal","type-knowledgeportal","status-publish","has-post-thumbnail","hentry"],"acf":[],"yoast_head":"\nOptimising selective soldering: speed, height and nozzle selection - Smans<\/title>\n<meta name=\"description\" content=\"How do soldering speed, soldering height and nozzle selection affect selective soldering? 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