How to solder？
The system in package process is based on electronic packaging technology, which serves to protect and connect semiconductor devices. In this process, solder joint play a critical role, as the most significant points of potential failure, directly affecting the overall solder reliability. Failures in solder joints can result from various factors, including temperature variations, inadequate cleaning, improper solder flux , and inconsistent reflow process soldering. These issues can decide electrical resistance and conductance, jointing technologies and mechanical properties. Therefore, careful control of soldering conditions, flux selection, and cleaning procedures is essential to ensure high-quality and durable solder joints in electronics packaging. After that proper surface preparation through laser etching, precision pattern printing of solder paste, and cutting boards used during substrate and lead-frame fabrication all contribute to accurate joint formation and interconnect consistency. In addition, metal and coating on substrates are widely applied to pads, connectors. Gold plated materals are typically. In this paper, how to solder and soldering tips will be analysis to better understand solder electric.
cleaning soldering iron tip
Clean soldering iron tip is necessary. When process soldering iron for electronics without clean may cause solder resist problem. Since conductive or prone to corrosion in moist conditions. Cleaning plates through holes and component leads. The purpose of this step is to remove oxide layer on substrate surface layer . For PCBs with sizable ventilation holes, avoid excessive flux remover spray, since it can reach the topside during wave soldering. Masking the holes beforehand can help.
What is flux in soldering?
Flux solder is a soldering tool to protect surface to reform oxidation during soldering and maintenance moist of solder balls and substrate surface on solder pad. Electronic solder flux tackiness keeps the flip chip bonding during die placement and reflow. The amount of solder joints is a key issue. Too much flux soldering will dirty substrate surface. Thus, flux dispensing should be taken to replace conventional methods. Which precise control over both the quantity and placement of the electric flux for soldering.
Mechanical Strength and Its Sensitivity to Solder Temperature Stress
In addition to process control, the long-term durability of a solder joint is largely governed by two fundamental mechanical properties: strength of materials and interfacial bond strength.material strength reflects the inherent robustness of the solder alloy, whereas bond strength represents the metallurgical adhesion between the solder and the solder pad.These strengths not only determine the initial mechanical integrity but also define how the joint will respond to environmental stress. Since both material strength and bond strength[1] degrade under temperature-related stresses such as aging, thermal shock, and thermal cycling, understanding these properties is essential before analyzing how temperature influences solder joint reliability.
Temperature-Induced Degradation in Solder Joints Reliability
When the current crowding, causing uniform current distribution. The soldering temp appear on the whole integrated circuit chip. Typically, In a flip-chip solder connection, the soldering temperature on the chip side is noticeably higher than that on the substrate side. To be specific, thermal diffusion happens while increasing current density. Thermal diffusion usually exist in solar panels and integrate circuit technology. At its core, soret effect represents a cross-effect in which a temperature gradient alters the chemical potential landscape, thereby driving atomic diffusion[2]. This coupled behavior is quantitatively formulated in none quilibrium thermodynamic through the constitutive relations linking heated flow and mass flow rate under thermal and potential chemical gradients.
Aging, thermal shock and thermal cycling are main factors to ensure solder joint reliability influenced by temperature.
Aging
When solder touch substrate, forming intermetallic (IMC) compound. at the edge of solder and base materials. With the time passing by, solder joint and interface will growth continually, promoting brittle and cracked solder joint . At the same time, With prolonged aging, the interfacial reaction layer within the solder joints continues to thicken due to ongoing intermetallic compound growth. This progressive coarsening weakens the mechanical integrity of the joint, resulting in a steady decline in joint strength and a deteriorating pronounce in overall reliability.
How to prevent aging?
According to research addictive element Ni could form a layer called (Cu1-xNix)6Sn5. To constrain the growth of IMC in the aging phrase, therefore, increasing the solder joint reliability. Ni plating are more likely to decrease the diffusion rate of particular element Cu and Sn atoms. In addition, Golding plating also can be applied in oxidation and corrosion.
Thermal cycling
The cyclical variation in ambient temperature, imposes alternating high- and low-temperature cycles on the solder joint. The thermal expansion react on materials and substrates. However, heat diffusion cause the solder joint undergoes repeated cycles of stress and thermal deformation. So that a considerable number of cracks emerge. It is predicted that the resilience of solder joint become weak affected by continuous thermal cycling[3].
How to stop thermal cycling?
To solve this problem, interrupted thermal cycling can be taken. Continuous thermal cycling resulted in joints characterized by poor recovery and extensive recrystallization process, whereas interrupted thermal cycling facilitated the development of a well-recovered and structurally stable microstructure.
thermal shock
A phenomenon happens in switching of low temperature and high temperature in the solder joints part. However, caused by high- and low-temperature cycling, withstand certain thermal shocks, the solder joints will fail. Thermal shock induces transient tensile stress—especially at the ceramic surface during cold shock—that lead to surface crack initiation, with the highest fracture risk occurring when the thermal SIF reaches its transient peak[4].
How to deal with thermal shock?
To overcome thermal shock problem, heating conditions, specimen geometry, and the material’s own thermo-mechanical properties need to be concerned. It is obvious that resistance to thermal shock decided by how these factors interact under real operating conditions , instead of a single factor.
Conclusion
Solder-joint reliability depends on both process quality and the mechanical integrity of the solder and its interface. Proper cleaning, controlled soldering flux use, and stable soldering conditions ensure good initial joint formation. Meanwhile, material strength and bond strength determine how the joint endures service stresses. Because these properties degrade under aging, thermal shock, and thermal cycling, understanding temperature effects is essential for ensuring long-term reliability in electronic package management system.
