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
Rehm Thermal Systems is a specialist in the field of thermal system solutions for the electronics and photovoltaic industries and is recognized as a leader in technology and innovation for the modern and cost-effective manufacturing of electronic assemblies. As a global manufacturer, we offer a wide range of products, including convection, condensation, or vacuum reflow soldering systems, drying and coating equipment, functional testing systems, equipment for the metallization of solar cells, and numerous custom solutions. With over 30 years of industry experience, we operate in all significant growth markets and provide innovative manufacturing solutions that set industry standards.
Contact
Rehm Thermal Systems
Carmen Hilsenbeck
Leinenstraße 7
89143 Blaubeuren
Phone: 07344 9606 535
Fax: 07344 9606 525
E-Mail: 
Url: http://www.rehm-group.com
Die Bildrechte liegen bei dem Verfasser der Mitteilung.