As reliability requirements are on the rise, microelectronic devices' solder joints are getting smaller, which enables them to endure more mechanical, electrical, and thermal strain. Electronic equipment could completely break down if even one solder joint fails- ensuring solder junction quality is crucial for contemporary electronic products. Electrical and rigid mechanical connections between various materials must be implemented through solder joints in electronic packaging technology such as SMT (Surface Mount Technology), CSP (Chip-Scale Package), and BGA (Ball Grid Array) technology for connection quality and reliability to establish the functionality and dependability of electronic products.
Traditional SnPb solder comprises Pb (lead), which, together with the chemical component lead, is so hazardous that its long-term use will cause severe harm to people's lives and the environment. Due to its advantages in protecting the environment, lead-free solder has been steadily replacing lead solder up to this point. However, due to altered specifications, the PCBA (Printed Circuit Board Assembly) method is where lead-free production differs from lead manufacturing. As a soldering technician, you must know the J-Std-001 standard that sets guidelines for soldering interconnections. WiththeJ-std-001 training kit, you can practice in better understanding the working and production of PCBA.
Comprehensive Concerns Regarding Lead-Free Manufacturing
The most obvious distinction between lead-free and lead-filled solder is the high tin content (>95%Wt). As a result, first-hand attention should be given to the following problems.
Tin Whisker Growth
● Tin whiskers, which take the form of columnar or cylindrical filaments, develop from a weak area of the tin oxide layer.
● Shortcuts between adjacent pins may result, among other issues.
● High-frequency features could be subject to negative effects.
The tin soldering layer contains pressure tension, which is thought to be the primary cause of tin whisker formation. Tin whiskers will be produced in the high tin alloy, which works well with pure tin. Excessive amounts of metal alloys like Pb or Bi can prevent or impede the growth of tin whiskers. For instance, when large quantities of irregular Cu6Sn5 metallic alloy are produced, many flaws are created, such as pressure stress accumulation on the tin layer, component pin deformation, and CTE mismatches, all leading to the development of tin whiskers. Tin whiskers may result in shortcuts while manufacturing fine-line components, such as QFP.
Metal Dendrite Growth
Tin whiskers and metal dendrites have different growth processes. In electrochemistry, the former is a product of ionic electromigration. Metal dendrite will result in shortcuts that worsen the failure of the circuit.
Development of CAF
Another electrochemical reaction-related failure type is conductive anodic filament (CAF). Copper-containing anode conductive filament that grows from the anode to the cathode of the PCB board causes CAF.
When the anode and cathode are coupled, CAF increases to a certain level, and short circuits eventually form between two poles, typically resulting in a catastrophic incident. High-density PCB assemblies can suffer from CAF, and lead-free solder used at higher temperatures makes this problem more likely.
Tin pest is a phase shift caused by pure tin spontaneous polymorphism. Pure tin will transform white tin, which derives from a central square structure and has a density of 7.30g/cm3, into gray tin, which derives from a central cubic structure and has a density of 5.77g/cm3. Tin pests might theoretically result in a reliability issue. However, this is rarely seen because tin is typically combined with impurities.
When lead-free solder is used, the problems mentioned above could become flaws. But they can be avoided if cutting-edge soldering methods are used during the PCBA process.
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