PCB + ASSEMBLY Soldering
PCB + ASSEMBLY Soldering field study A comparison was made here between these two soldering methods and different template apertures to evaluate the respective influencing variables. The stencils were also varied in material thickness and manufacturing method. A template with a 120 μm thickness was produced without any additional “refinement steps”. Its counterpart was built with a plasma-coated and electropolished surface and a template thickness of 110 μm. The test boards ran equally divided in numeric terms with both template variants. Histogram of surface soldering without vacuum in relation to the void content. Source: Rehm Thermal Systems Interaction of the solder paste with the soldering processes. In an extreme comparison of soldering at ambient pressure, compared with vacuum at 10 mbar, there were clear differences shown between vacuum application and standard reflow system. Throughput with reduced vacuum at 100 mbar verifies the result and shows that even with less effort, a result below 2 % voiding is achieved for the component combination. This has a significant influence on the cycle time, since during unthrottled vacuum pump operation, the necessary process times from 1000 mbar to 100 mbar are the same as from 100 mbar to 10 mbar (or 10 mbar to 1 mbar). This means that it is necessary to always work with only as much “pressure” as needed. Source: Voidexpert The influence of the selected aperture geometries only shows significant differences without the use of vacuum, mainly in the number of gas bubbles formed and partly on the total void ratio. The subjective impression is that the plasma template tends to result in a little less voiding, which can be attributed to the better release of the paste and the associated more stable printing process. A stable and constant paste pressure supports the soldering process here. Standard deviation of process Finally, a consideration of the process stability during soldering: the target figures for voiding are always absolute figures, such as
PRODUCT UPDATES PCB + ASSEMBLY Thermal gap fillers for various applications Source: Electrolube Electrolube launched thermal gap fillers that provide heat transfer solution. The GF300 and GF400 are two part, liquid silicone-based fillers, which provide thermal performance of The GF400 thermal interface material is a two-part liquid silicone-based filler that can be cured at room temperature or accelerated with heat. 3.0 W/m.K (GF300) and 4.0 W/m.K (GF400). They reduce the risk of air pockets forming by filling the entire heatsink, which is ideal for applications where the gap is non-uniform. Using a simple 1:1 mix ratio in either 50 ml or 400 ml cartridges, GF300 and GF400 are applied in a soft flexible ‚putty‘ that can be moulded around different shaped housings with low stress on components. They can be cured at room temperature or accelerated with heat. Both provide an operating temperature range between -50 to + 200 °C and have low viscosity. After curing, they form a low modulus elastomer, ensuring minimal degradation of heat dissipation. They are also UL approved with the UL94 V-0 flame retardancy rating and are RoHS compliant. Typically, thermal gap fillers are widely used in touch screen and mobile applications, but these interface materials are meeting the demands for various applications. This includes consumer electronics, PCB assembly, housing electronic components discretely, telecoms applications such as data centre Source: Electrolube servers and fiber optic equipment, lighting and LEDs applications, power electronics, and ECU’s and HEV/ NEV batteries. However, the company has seen demand surge for specific application requirements, including engine and transmission control modules, memory modules, power conversion equipment and more. www.electrolube.com The recently launched range of thermal gap fillers provide great thermal performance while reduce the risk of air pockets forming. The alternative to conventional fluxes Flux manufacturers have already reported a shortage of alcohol-based fluxes used in electronics manufacturing. Interrupted supply chains and an increasing demand for alcohol as a basis for disinfectants has resulted in massive price increases. Seho offers a solvent-free alternative – the PlasmaFluxer. In a plasma process, flux powder is deposited at the solder joints with great adherence and long-term stability. Product quality can also be improved. The PlasmaFluxer uses cold-active plasma to melt micrometer sized powder of pure adipic acid and is placed on the PCB surface. A liquid carrier material is not needed, and the gas that is used to create the plasma flame is Nitrogen. When processing assemblies, an aerosol formed out of meltable flux particles and Nitrogen is led into the plasma flame and directed to the PCB. Once the aerosols touch the surface, the particles solidify and form a stable coating. The plasma process substitutes the conventional wet-chemical flux activation with a dry process. Soldering results achieved with this process are comparable to standard liquid fluxes. An additional advantage is the cleanliness of the PCB surface after the soldering process. Therefore, an additional cleaning process can be avoided. Additionally, the degree of contamination of the fluxer work area and the soldering system is smaller, as there is no evaporation of solvents from the flux. Consequently, maintenance requirements are remarkably reduced while availability of the process equipment is increased. Solvent-based fluxes are declared as hazardous material and special measures are necessary in terms of storage, handling and waste management. In comparison, the handling and storage of powder is much easier, resulting in a reduction in manufacturing costs, and additional benefits emerge from the environment friendly concept of the plasma fluxing process. The selective flux application method leads to a reduction of the flux amount needed, and with the elimination of liquid, savings are achieved in the material costs. A particular benefit of the plasma fluxing method is its ability to “revive” overaged PCBs that show perfect wetting results. www.seho.de The PlasmaFluxer uses cold-active plasma to melt micrometer sized powder of pure adipic acid. Source: Seho Systems EPP EUROPE April 2020 37
