Soldering, a technique that originated in ancient Egypt, is indispensable in electronics production today. Despite all the progress made, defects can still occur, which can lead to unreliable solder connections and thus to malfunctions or even failure of the end product. It is therefore important to know the causes of soldering defects so that preventive action can be taken. With our expertise in soldering technology, we have been supporting our customers for over 30 years with all questions and problems in the field of reflow soldering and provide an overview of some of the causes of misaligned and missing components below.
Soldering has a long history dating back to ancient Egypt. Today, it plays an indispensable role in the manufacture of electronics, among other things. Despite numerous developments in soldering technology, soldering defects can still occur, resulting in electronic components not being reliably connected.
Such a faulty solder connection means that the circuit is not reliably closed, which can lead to malfunctions and even failure of the end product. In addition, defective connections can result in high electrical resistance and thus increased heat generation, which can damage the components or cause fires.
Unreliable end products and safety issues: they damage a company’s reputation and customer confidence in the brand. Manufacturers therefore endeavour to identify soldering defects during the production process and to sort out or repair faulty PCBs, although this is associated with significantly higher costs.
In addition, the probability of soldering defects can also be reduced before and during the soldering process: some causes of misaligned and missing components are shown below.
Misaligned Components
In the past, electronic assemblies floating in lead-containing solder were able to correct a slight displacement during the soldering process (self-alignment). As assemblies sink deeper into lead-free solders due to the lower wetting power as well as lower density and consequently a weaker buoyancy force, this phenomenon is less pronounced here (see Bell et al. 2021: 81f.): nevertheless, in the area of lead-free solders, the occurrence of component offset can also be reduced by selecting a solder paste with a high wetting force (see Neathway et al. 2008: 7ff.).
Attention must also be paid to the size of the pads: “In the case of large pads, there`s always the danger of subjecting the component to a torque force when only one paste deposits is melted initially. […] [W]etting dynamics are not sufficient in order to align the component when the second paste deposit is melted” (Bell et al. 2021: 84).
If the curtains at the inlet of the oven are too long, touching them can cause the assemblies to fall over or shift. The poor condition of the conveyor chains can also result in a shaking, which can cause larger, heavier components to move on the PCBs (see Bell et al. 2021: 88f.).
When soldering the second side of the circuit board, there is also a risk that soldered connections on the other side will be separated again and components will become partially or completely detached. To counteract this, the holding force of the molten solder must exceed the weight force of the various assemblies by at least the factor of two, with an ideal ratio of four. However, it should be noted that the holding force also depends on external conditions, such as shakings, as well as the changing surface tension of the solder depending on the temperature (see Bell et al. 2021: 89-92).
Missing Components
If a component can no longer be found in the desired position on the PCB after soldering, this is referred to as “blown away”. However, convection currents are not responsible for this, as is often assumed. Instead, moisture trapped in nearby components, such as tantalum capacitors, during the soldering process is blown out as gas, which can result in the displacement of other smaller elements. To counteract this, PCB components should be stored dry or dried before the soldering process (see Bell et al. 2021: 92f.).
Curious?
The technology manuals from Rehm Thermal Systems deal with many other exciting topics relating to reflow soldering: take a closer look at the reliability of soft solder joints and other soldering defects or immerse yourself in the technology and engineering of soft soldering. Find out what effects reflow profiles have on the soldering process and the soldering result, and what about bottom termination components and migration. You can order the volumes by e-mail: sales@rehm-group.com
Do you have questions on a specific topic?
We advise our customers and interested parties on all technological issues and provide support in selecting the right production process and associated parameters. Our employees in the Technology Centre will be happy to help you: applikation@rehm-group.com
References
Bell, H., Grossmann, G. & Wohlrabe, H. (2021). Reflow Technology. Fundamentals of Reflow Soldering. Part 3: Reliability and Failure Management (3rd ed.). Rehm Thermal Systems GmbH.
Neathway, P., Butterfield, A., Chu, Q., Tokotch, N., Haddick, R., Peallat, J.-M., Shea, C. & Chouta, P. (2008). A Study of 0201’s and Tombstoning in Lead-Free Systems, Phase II Comparison of Final Finishes and Solder Paste Formulations. Proceedings APEX 2008. www.ipc.org/system/files/technical_resource/E9%26S07_02.pdf [06.02.2025].
About Rehm Thermal Systems
Rehm Thermal Systems specialises in thermal system solutions and produces first-class reflow soldering systems for convection, condensation and contact soldering, coating and drying systems as well as cold and hot function test systems. We know from our many years of experience: individual requirements need customised solutions. That is why we offer a wide range of system configuration options for all systems. We will find the right system for the individual challenges of your manufacturing or production – while maximising quality and process reliability!
