SZFitech

  The extreme operating environments of military electronics (e.g., high temperatures, high humidity, strong vibrations, huge temperature differences) place almost exacting demands on the materials used in their assembly - especially solder paste alloys. The core of their selection is always centred around the three principles of reliability, durability and resistance to extreme conditions. I. In-depth analysis of mainstream alloy system According to different application scenarios, a clear spectrum of alloys has been formed in the military field. 1. Gold-tin alloy (Au80Sn20): the ultimate solution in the field of high reliability. As the "king of performance" in the military field, gold-tin eutectic alloys take on the most critical tasks with their unique characteristics. Ultimate performance: its high melting point of 280°C makes it the only choice for high-temperature environments such as aircraft engine compartments and missile guidance heads. At th...

  Definition ： Lead-free solder paste has developed rapidly as an alternative to leaded solder paste. EU’s RoHS ISO9453 and Japan's JEIDA stipulate that solder alloys with Pb content less than 0.1wt% (1000ppm) can be defined as lead-free solder alloys. 1. Why Develop Lead-Free Solder Pastes ？ In the past, electronic product packaging adopted leaded solders. Widely-used Tin-lead eutectic solders have a series of advantages such as low melting point, good wettability, and bright solder joints. However, lead is a toxic substance with multi-affinity. Lead can damage the human nervous, hematopoietic, and digestive systems. Additionally, lead poisoning may induce serious diseases such as leukemia, kidney disease, heart disease, and mental disorders, causing great harm to people's health. Metal Lead severely pollutes water, soil, and air. Once the environment is polluted, it will be difficult to recover. Lead pollution management is complex, and the recovery cycle ...

  By optimising the thermal conductivity of the material, strengthening the metallurgical connection structure and adapting the alloy design to different application scenarios, solder paste achieves efficient heat dissipation of the chip, and its cooling mechanism can be analysed from the following three levels: I. Material innovation: high thermal conductivity alloy to build heat dissipation channel The traditional silver adhesive relies on epoxy resin bonding, the thermal conductivity of silver powder filling is only 5-15W/m-K, and silver migration is likely to occur at high temperatures, resulting in an increase in resistivity. And solid crystal solder paste using high-purity tin-based alloys (such as SnAgCu, SnSb), its thermal conductivity of up to 60-70W/m-K, more than 5 times that of silver glue. For example, a power module manufacturers in the IGBT package after the use of solid crystal solder paste, the chip junction temperature from 125 ℃ to 105 ℃, a redu...

 Gold embrittlement is a soldering defect that refers to solder joints that contain too much intermetallic compound (IMC), resulting in increased brittleness and reduced reliability. Gold embrittlement mainly occurs in two locations of BGA solder joints, namely between the BGA body and the solder ball and between the solder paste and the immersion plate pads. The BGA solder joint gold embrittlement can be subdivided into two categories, one is the gold embrittlement caused by insufficient heat, and the other is the gold embrittlement caused by excessive gold content. Gold embrittlement caused by insufficient heat Insufficient heat in the PCBA soldering process, the metal of the PCB immersion layer will enter the liquid solder, forming AuSn4 build-up in the vicinity of the intermetallic compounds (IMC) of the solder joints, resulting in gold embrittlement of the solder joints. This gold embrittlement problem can be improved by adjusting the PCBA soldering process co...

 Grape ball effect refers to the SMT reflow process, the paste can not be completely melted and wet pads, and the formation of a small ball similar to grapes, affecting the reliability and appearance of the solder joints. The causes of the grape ball effect is mainly related to the quality of the solder paste, printing process, reflow profile and other factors. In this paper, we will focus on analysing the effective life of the solder paste after printing on the impact of the grape ball effect. Solder paste printing effective life The effective life after printing of solder paste refers to the time after the printing of solder paste on the PCB, at room temperature can maintain a good printing shape and performance. Reasonable management of the effective life is critical to the control of the grapevine effect, as the solder paste may oxidise, dry out and collapse after exceeding the effective life, leading to a reduction in print quality and increased soldering risk....