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 Desoldering refers to the reflow soldering process where one or more pins of a component cannot make normal contact with the pad, resulting in an incomplete or missing solder joint. Desoldering not only affects the performance and reliability of the circuit, but also increases the cost and difficulty of maintenance. The causes of desoldering can be divided into the following categories: Component pin deformation: components in the production, transportation or storage process, may be subject to mechanical shock or vibration, resulting in pin deformation or fracture, thereby affecting the alignment and contact with the pad. In addition, the component's pin material, shape and size will also affect its thermal expansion coefficient and stress distribution with the pad, which in turn affects the formation and stability of the solder joint. PCB pad coplanarity is poor: PCB is the carrier of components, the flatness and finish of its surface directly affects the components...

 Double-sided mounting process can improve the actual utilization of PCB, reduce manufacturing costs, to meet the demand for miniaturization and high integration of end products. However, the use of double-sided mounting, double-sided reflow process will bring the following problems. One is the second reflow, the bottom of the larger or heavier components may fall because of 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. In order to solve the problem of component dropping, there are generally the following methods: Translated with DeepL.com (free version) 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 pi...

 In PCB design, via is a common connection that connects different layers of wiring or provides a place for components to be soldered. There are various types of via, one of which is via in pad (via in pad), that is, the via is punched on the SMD or BGA pad, and then the hole is plugged with resin and plated with a layer of copper on the surface, so that the hole is not visible on the pad. Advantages and Disadvantages of Vid in Pad Vid in Pad (Vid in Pad) is the basic structure of HDI (High Density Interconnect) boards, and its advantages are obvious: reduce the distance between boards and signal transmission distance, which is beneficial to reduce signal interference and loss; plating filled with copper solid holes can effectively reduce the parasitic signals in the holes and parasitic inductance, which is conducive to the transmission of high-frequency signals; effectively reduce the thickness of the finished board, and increase the density of the wiring per unit are...

 Grape ball effect refers to the SMT reflow process, solder paste can not be completely melted and wet pad, 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 analyzing the effective life of the solder paste after printing on the impact of the grape ball effect. Translated with DeepL.com (free version) Effective Life after Solder Paste Printing Post-printing effective life of solder paste refers to the time that the solder paste can maintain good printing shape and performance at room temperature after it is printed on the PCB. Reasonable management of the effective life is critical to the control of the grapevine effect, as solder paste may oxidize, dry out, and collapse after exceeding the effective life, resulting in lower print qu...

 Solder paste is a mixture used to connect electronic components to printed circuit boards (PCBs) and is mainly composed of tin powder and flux. There are mainly the following solder heating methods for solder paste: Reflow soldering Reflow soldering is a soldering technique that uses heat such as hot air or infrared rays to heat the solder paste printed or dotted on the printed circuit board until it melts, forming a metallurgical connection with the components and pads. The tool for reflow soldering is usually a reflow oven consisting of a heating element and a fan. The reflow oven can be controlled according to different temperature profiles to accommodate different solder paste and component characteristics. The advantage of reflow soldering is that it can achieve large-area, high-density and high-precision soldering, which is suitable for soldering surface-mounted components (SMC/SMD) in SMT. Figure 1. Reflow oven appearance Laser Soldering Laser soldering is a ...

 Non-wetting and de-wetting phenomenon is a common defect in the welding process, they are respectively manifested as incomplete contact between solder and base metal and retreat after partial wetting. Non-wetting Non-wetting refers to the formation of a discontinuous film of solder on the surface of the base metal after welding. In the case of non-wetting, the solder is not in full contact with the base metal, so that the uncovered base metal surface can be clearly observed. This phenomenon can be caused by the following reasons: 1. the base metal does not have good solderability characteristics. 2. the flux used may be inactive or the flux may have deteriorated. 3. the presence of oil or grease on the surface prevents the flux and solder from making effective contact with the base metal. De-wetting Backwetting occurs when the solder first wets the surface of the base metal, but due to poor wetting, the solder shrinks, forming a thin film and forming separate balls of sol...

 Void is the presence of air bubble in a solder joint, which affects the mechanical strength, thermal conductivity and electrical properties of the solder joint. Under the same PCB and device conditions, some soldering materials are prone to void formation, while some solder pastes exhibit excellent properties for controlling solder joint void. Flux changes during the soldering process is a very complex process involving a variety of physical and chemical changes, the flux formula determines the soldering effect and characteristics. During the welding process, the flux removes metal oxides from the weld end surface to generate water and gasification to form void; the organic acids in the flux esterify to generate water and gasification to form void; and the organic matter in the flux cracks to form void. Basic reaction principle (a) welding process flux to remove the weld end face metal oxide layer, generating metal salts and water. 2RCOOH+SnO=(RCOO)2Sn+H2O^ 2HBr+CuO=CuB...

 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 cond...

 Metal segregation is a common phenomenon in the welding process, which refers to the inhomogeneous chemical composition distribution in the metal alloy. Some scholars have studied the influence of interface microstructure in crack growth, pointed out that the growth rate of fatigue cracks along the solder interface is related to the stress released with the aging time. In a long period of high-temperature aging, such as aging at 140 ° C 7 ~ 30 days, due to the Sn in the solder near the interface with the base metal Cu metallurgical reaction to form CuSn intermetallic compounds in the process of consuming Sn, and thus in the immediate vicinity of the interface of the IMC to form a continuous Pb-rich phase region and cause Pb segregation, as shown in Figure. Figure 1. Pb segregation Sequestration affects the reliability and performance of solder joints in the following ways. Impact on solder joint mechanical properties Metal segregation results in inhomogeneity of chemic...

 Water-soluble flux is a kind of flux widely used in the electronic soldering process, it can improve the wettability of the solder, prevent oxidation, and clean the residue with water after soldering. The biggest feature of water-soluble flux is that the flux component is highly soluble and active in water with good fluxing performance, and the residue after soldering is easily soluble in water, so water can be directly used as the cleaning solvent. No consumption of ODS and VOC, reducing environmental pollution and safety risks. According to the different active substances used, water-soluble can be divided into: Inorganic System Water-Soluble Flux Zinc chloride, tin chloride and ammonium chloride are often used as active substances, which have good soldering flux, high temperature resistance and easy cleaning. However, the corrosiveness of its post-soldering residue, so it is prohibited to use in the assembly of electronic products welding. Organic Water-Soluble Flux...

  Solder paste is a mixture of tin powder particles and flux paste. The flux in the solder paste has four static properties and four dynamic properties. The four dynamic properties of the industry is often referred to as "flux" - to remove the oxide layer, prevent re-oxidation, reduce the surface tension of liquid solder, to assist in the transfer of heat; the four static properties include the protection of powdered tin from oxidation, temporary fixation of components (adhesion), to maintain the shape of the paste after printing (anti-sagging), a certain degree of mobility (printability).   There are two popular solutions in the solder paste powder making industry today: centrifugal powder spraying and ultrasonic powder spraying. The processes of sieving, storage, transport and paste mixing after spraying can lead to oxidation of the tin powder. The smaller the tin powder particles, the larger the surface area of tin powder per unit weight, the higher the chance of oxidation...

 Mini LED is a new type of display technology that uses 50-200 micron LED chips as backlight or pixel units, achieving excellent display effects such as high brightness, high contrast and high colour gamut, etc. The chip package process of Mini LED mainly adopts flip-flop package, whereby the LED chip is inverted on a carrier board and solidified and electrically connected by solder paste or solder adhesive. This process not only eliminates the step of gold wire bonding, but also improves the heat dissipation performance and reliability of the chip. Due to the small size of Mini LED chips, the requirements for solder paste solder are higher, including particle size, melting point, wettability, void rate and residue. Currently on the market commonly used Mini LED packaging solder paste solder is mainly divided into two types: medium temperature solder and low temperature solder. Medium temperature solder refers to the melting point between 200-250 degrees Celsius lead-free alloy sol...