In electronics, the reliability of soldered connections is crucial, especially in high vibration environments such as railroad technology, mining or construction vehicles.
Especially in critical or safety-relevant applications such as in railroad technology, where electronic components are exposed to very high mechanical loads over a very long period of time, stable soldered connections ensure reliable function. Here, the targeted use of high-quality, process-safe solder alloys and fluxes in assembly and connection technology plays a key role in preventing voids. These impair the electrical and mechanical connection and can lead to failures or loss of performance. Possible causes of voids include organic inclusions in the surface metallization, flux components or oxides dissolved in the solder. The formation is an interaction between the printed circuit board, component metallization and process control. The causes of void formation can therefore be many and varied.
Causes of void formation
These voids can destabilize the solder joints due to vibrations or temperature differences, which can ultimately lead to a break in the connection between the substrate and the component. To avoid this, in addition to an optimized soldering process, it is also necessary to select the right solder alloys and the right flux. It is generally agreed that SAC solders tend to form more pores than SnPb solders. There are various reasons for this: Firstly, the higher surface tension of SAC alloys makes it more difficult for gases trapped in the solder to outgas. Secondly, the higher process temperatures lead to the increased formation of potential gases from the flux, the circuit board and the components. Thirdly, the wetting properties of SAC solders are poorer due to the small difference between process temperature and melting point.
However, the surface tension between the liquid solder, the flux and the PCB also influences the degree of wetting and therefore the formation of voids. The better a flux is, the higher the degree of wetting, which leads to a lower formation of voids. Fluxes therefore have a special function, as they ensure that oxides are removed from the solder pads, for example, and a clean, oxide-free surface is created. This enables perfect wetting of the solder without inclusions and contamination and ensures a long-lasting connection. Emil Otto's fluxes, which have been specially developed for demanding requirements, have proven themselves over decades in the manufacture of electronic assemblies for the most demanding applications. Their composition has been continuously optimized over the years so that they not only create stable soldered connections, but also guarantee the long-term stability of the assemblies.
Factors influencing void density in soldered joints
Furthermore, there are additional parameters that also have an influence on the void density in solder joints. Among other things, the void ratio and the void size depend on the following factors:
- Surface and hole of the printed circuit board (oxide layer promotes void formation)
- Alloy and layout of the printed circuit board
- Storage of printed circuit boards and components
- Component metallization and oxide adhesion to the component (oxide layer promotes void formation)
- Preheating temperature and duration as well as dwell time of the THT component in the solder
- Nitrogen atmosphere for selective soldering (adjust if necessary)
Ultimately, the combination of a high-quality solder and flux and the resulting oxide-free solder pads and void-free solder joints can have a positive influence on the creation of long-lasting solder joints. This is a decisive factor for the safe transportation of goods by rail, the timely implementation of construction projects or the safe extraction of natural resources. Companies and individuals who rely on these technologies benefit from Emil Otto's reliably functioning products.