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 Solder paste is used in most cases in SMT and BGA operations to connect chips and substrates. After reflow soldering is completed, the solder pastes solidify into solid solder joints with excellent electrical conductivity. The properties of solder joints determine whether the properties, such as mechanical strength, can meet the requirements. Diffusion at the solid-liquid interface is one mechanism that occurs during reflow. Copper pad atoms dissolve into the solder and form specific intermetallic compounds (IMCs). The evolution of IMCs at the solder joint interface has a geometric size effect during aging. The size effect of interfacial diffusion mainly focuses on the influence of solder joint volume and pad metallization layer thickness on interfacial diffusion. To gain insight into the effect of solder joint height on solid-liquid diffusion. Li et al. tested the influence of different heights of SAC305 solder joints on the solid-liquid interface diffusion. Figure ...

 Solder paste is used in most cases in SMT and BGA operations to connect chips and substrates. After reflow soldering is completed, the solder pastes solidify into solid solder joints with excellent electrical conductivity. The properties of solder joints determine whether the properties, such as mechanical strength, can meet the requirements. Diffusion at the solid-liquid interface is one mechanism that occurs during reflow. Copper pad atoms dissolve into the solder and form specific intermetallic compounds (IMCs). The evolution of IMCs at the solder joint interface has a geometric size effect during aging. The size effect of interfacial diffusion mainly focuses on the influence of solder joint volume and pad metallization layer thickness on interfacial diffusion. To gain insight into the effect of solder joint height on solid-liquid diffusion. Li et al. tested the influence of different heights of SAC305 solder joints on the solid-liquid interface diffusion. Figure ...

 Double-sided mounting process can improve the actual utilisation of PCB, reduce manufacturing costs, and meet the demand for miniaturisation and high integration of end products. However, the use of double-sided mounting, double-sided reflow process will bring the following problems. First, the second reflow, the bottom of the larger or heavier components may fall due to gravity or vibration, and the second is the bottom of the solder joints will affect the reliability of the solder joints because of the melting again. The following methods are generally used to solve the problem of component dropouts: 1. Choose a solder paste with higher viscosity. For most components, the second reflow, the surface tension of the solder joints molten solder paste can maintain the components on the bottom of the viscous force, so that the components are firmly fixed on the substrate? Obviously, there is a component quality and pin (pad) tension of the proportionality of the relati...

 The electronics industry has an increasing demand for lighter, smaller, and more flexible products. In order to realize the miniaturization of chips, the pad pitch becomes smaller and smaller. In addition, in order to make full use of chip space, more and more manufacturers adopt flip-chip packaging technology, which can produce more I/O interfaces, better electrical performance, and smaller package size. The researchers found that the use of electroplated solder paste to make bumps can meet the requirements of flip-chip packaging. The electroplating solder paste process can solve cost and mass production problems and meet fine-pitch requirements. Eutectic tin-bismuth solder paste is suitable for producing micro-bumps with low melting points and good mechanical properties. The flip chip requires placing a metal layer under the bumps. Solder paste is then deposited on the pads and reflowed to form solder joints. The eutectic Sn-Bi solder paste can be electroplated ont...

 For mobile devices such as mobile phones, area array packages such as BGAs, CSPs or POPs are prone to drop failures and need to be reinforced when they are assembled onto printed circuit boards. While underfill is an alternative solution, it increases manufacturing costs and reduces temperature cycling reliability due to the additional curing steps involved. As a result, an epoxy flux method is preferred, which eliminates the need for a curing step. The epoxy flux is used as a flux when encapsulating the reflowed array onto the printed circuit board and then self-cures after reflow, providing the required reinforcement without the need for an additional curing step. Since pad collapse is a major failure mode in many portable devices, epoxy fluxes have become the preferred choice for cost-effective and reliable SMT assembly among all polymer-based reinforcement solutions.                           ...

 A hybrid integrated circuit (HIC) is a high assembly density circuit formed by directly fixing the bare chip onto the substrate and realizing interconnection with the substrate. HIC can be two or more components packaged together to form microelectronic circuits, such as an integrated circuit and a passive electronic component packaged together and then installed on a PCB. Producing HICs is a relatively simple procedure. The general steps include assembling IC and passive components on the same substrate and then packaging them with plastic and other materials. Assembling components on the same substrate can reduce the number of solder joints and the spacing between components and the current path. Figure 1. Hybrid integrated circuit. The HIC can be divided into two categories of thin-film hybrid integrated circuits and thick-film hybrid integrated circuits. The substrate material of thin film HIC can be glass or ceramic, which can bring better heat dissipation ...

 The jetting process is an emerging non-contact solder paste deposition technology that utilizes a high-speed jetting valve to spray tiny solder paste droplets onto the pads of printed circuit boards (PCBs) to achieve on-demand, precise deposition of solder paste. The principle of the jetting process is similar to that of an inkjet printer. By controlling the movement of the nozzle and the frequency of the jetting, it is possible to achieve high-speed, high-precision and highly flexible solder paste deposition. Figure 1. Solder paste jetting process There are two main types of traditional solder paste application processes: stencil printing and syringe dispensing. Stencil printing requires the use of stencil templates, and the printing process time is long, low flexibility, and is only suitable for mass production; while syringe dispensing requires the use of air pressure control, low efficiency, the amount of solder paste is not easy to control, and high cost. Compar...

 Warpage is the phenomenon of bending or warpage of materials or components during the manufacturing or soldering process, usually in the fabrication and assembly of electronic components. This buckling usually occurs in board or film-like materials such as printed circuit boards (PCBs), chips, electronic packages, plastic parts, etc. Warpage can cause a component to fail to meet specifications and, in extreme cases, can even damage the component or cause performance problems in electronic equipment. Figure 1. Warpage due to mismatched coefficients of thermal expansion Effect of Solid-Liquid Coexistence Zone on Warpage The solid-liquid co-existence zone is the region of the solder where both solid and liquid phases are present in the solder during solidification. The width of this zone is influenced by the composition and temperature of the solder. In general, the wider the solid-liquid co-existence zone, the greater the likelihood of warpage, as this means that...

The void formation is a common problem in lead-free soldering. Gaps between lead-free solder paste particles can cause voids. Additionally, due to the inconsistent diffusion rate of metal elements, vacancies are usually left in the intermetallic compound layers, which will grow into voids after continuous aggregation. The appearance of voids affects the conductivity and thermal properties. Moreover, solder joints will have significant void growth after thermal aging, which increases the risk of failure. So how to quantify the effect of voids on the performance of solder joints?   The melting point temperature of SAC lead-free solder paste is about 217 ℃, so it is considered to be a more suitable connection material for flip chip LED. Liu et al. (2014) adopted SAC305 lead-free solder paste to conduct the packaging of DA3547 LED. Liu et al. analyzed how the volume of solder paste affected the formation of voids in LED chip packaging and explained the influences of the void ratio on t...