SZFitech

 The PCB surface treatment composite process - Immersion Gold + OSP is a process combination commonly used in the manufacture of high-end electronics. This combination process combines a sinker plate with an OSP (Organic Solderability Preservatives) process to achieve a better overall result. The intermetallic compound (IMC) in the solder joint of the sinker plate grows on the nickel layer, while the mechanical strength of the nickel-tin intergranules is slightly weaker than that of the copper-tin intergranules. The problem of insoluble black discs with high phosphorus content processes can arise in the immersed gold process, which is a difficult problem to solve. However, the sunken gold process still offers many advantages, such as a flat pad surface, the oxidation resistance and low resistivity properties of gold, and a wide process window. Application of composite processes In order to combine mechanical strength with other advantages, the smartphone manufacturin...

 There is a misconception about incomplete lead phase dispersion in the BGA mix and match process. With the global popularity of lead-free processes, most BGA devices have been soldered using lead-free processes, but some companies still use leaded processes for soldering due to special requirements. For products that do not involve BGA devices, the process can be operated exactly as a leaded process. Only the leaded process with lead-free BGAs is a true mixed assembly process. There are different views in the industry on this. Viewpoint 1: The replacement solder ball school (SJ school) This view is that solder balls must be replaced when Pb-free BGAs are used in a Pb-containing process, i.e. the original Pb-free solder balls are removed and replaced with Pb-containing solder balls, which are properly cleaned before use. The advantage of this view is that it allows for a complete implementation of leaded processes, but there are disadvantages: 1) Removing the lead-free ...

 In the process of lead-free reflow soldering, many companies are concerned about one question, that is, whether the oxygen concentration in the reflow oven will rise? What circumstances need to use N2 to protect the soldering method to reduce the oxygen concentration in the reflow oven? In fact, for consumer electronics products, taking into account the factors of product design and service life, it is best to avoid the use of N2 shielded reflow soldering methods that increase production costs. However, if the reliability of the product is very high, then the use of N2 shielded soldering should be considered. Due to the high melting point of lead-free solder, it is easy to cause oxidation problems during the soldering process, which affects the quality and reliability of soldering. In order to solve this problem, an effective method is to fill the reflow oven with N2 to form a low-oxygen environment, blocking the entry of air and reducing the occurrence of oxidation...

 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 o...

 Solder paste has 5 active lives: cold storage life in the fridge - generally 6 months; unopened paste return life - generally 2 hours ~ 2 weeks; active life after opening - generally 7 days; active scratch life on the stencil - generally 8 hours or 12 hours; active retention life after printing ~ before oven - generally 2 hours ~ 4 hours. Whichever life exceeds the control period, the activity of the solder paste will be affected. Loss of solder paste activity can lead to the appearance of solder beads, cold soldering, dummy soldering, short circuits and other defects. Factors that reduce the activity of solder paste Solder paste activity is generally reduced due to two factors: heat and flux loss. Heat means that the solder paste is artificially heated, artificially heated during delivery, or improperly protected during delivery so that the paste is heated. Flux depletion, i.e. the use of recycled solder paste, prolonged use of the paste on the stencil, long reside...

 Intermetallic compounds are a class of substances formed by chemical bonding of metallic elements in specific atomic proportions. In order to obtain a good welding result, a metallurgical reaction must take place between the solder component and the base metal component that creates a strong bond, i.e., an appropriate alloy layer (intermetallic compound, or IMC) at the interface. Therefore, in the welded joint interface, the formation of IMC or the formation of good or bad quality, the mechanical, chemical, electrical and other properties of the welded joint has a critical impact. Intermetallic compound formation conditions Solder joints serve two key purposes when joining two materials: good electrical conductivity and long-lasting mechanical joint strength. Sn-Pb solder, for example, when the two are connected to the base metal are Cu, to achieve a durable and strong mechanical connection, it must be heated to the solder joint temperature above the melting point of ...

 SAC305, as a widely used lead-free solder, has excellent mechanical strength, conductivity, and thermal conductivity. The copper substrate is one of the most common substrate materials, so the soldering effect of SAC305-type solder on the copper substrate is of great concern. For lead-free solder joints, the interface reaction between the solder and substrate is the key factor affecting soldering reliability. Usually, SAC305 solder paste reacts with Cu substrate during heating to generate Cu6Sn5 IMC. To achieve excellent solder joints, some process treatments can be carried out on the Cu substrate to control IMC growth. This article will discuss the soldering effect of SAC305 on different Cu substrates. Experimental processes Li et al. selected two Cu substrate treatment methods, including heating the Cu pad under atmosphere protection at 1000°C (H-Cu) and coating the Cu substrate with graphene (G-Cu). Subsequently, they melted SAC305 and SAC305-0.3Ni into 1.6mm diam...

  In the surface assembly process of electronic products, especially in the high-volume reflow soldering process, the tombstone effect of passive chip components to the PCBA assembly soldering adds a lot of trouble. With the SMC / CMD micro-miniaturisation, reflow soldering of these chip components will appear "upright", this phenomenon is also known as the "Manhattan" effect.   This phenomenon occurs mainly in small chip components, they are soldered on the opposite poles of the surface mount pads, in the soldering process, the components stand up vertically, as shown in the figure. Sometimes it is partially upright, and sometimes the component is completely upright on a pad, like a tombstone in a cemetery.     In the early SMT manufacturing process, usually "tombstone" and gas-phase reflow soldering (condensation soldering) associated with one of the reasons is related to the rapid rise in temperature heating. With the development of gas-phase reflow pro...

 With the BGA, CSP package devices to dense pitch, miniaturisation of the direction of development, the widespread application of lead-free processes to the electronic assembly process has brought new challenges. Pillow-head effect defects are BGA, CSP device reflow soldering is unique to a defective form. As shown in the figure, the solder ball and the solder between the solder is not completely fused, but like a pillow on a nest or a pile. This defect often occurs in the reflow soldering of BGA and CSP devices, and is more obvious in lead-free processes. This defect is not easily detected because there is often a partial connection between the solder ball and the solder. So the circuit may be able to pass functional testing, optical inspection and ICT testing. However, since the solder is not really fused and mixed with each other, the solder joints are not strong and may lead to failures in subsequent processes or in use. For example, after the soldering process, P...

 PCBA is a process of SMD assembly and through-hole component insertion on PCBs. PCBA is almost everywhere in the microelectronics and semiconductor industries. The high reliability of PCBA requires that every assembly step meets the requirements. However, there are often some unpredictable factors that will cause component failure. For example, residual corrosive substances on PCB are easy to cause chemical corrosion. Chemical corrosion can be divided into the following categories in principle. 1) Electrochemical migration: Electrochemical corrosion refers to the migration of conductive particles in a certain environment, which eventually leads to short circuits or electric leakage between conductors. When there is a certain degree of humidity and salts in the PCBs, electrochemical migration is easy to occur in the presence of voltage difference. 2) Chemical corrosion: Chemical substances such as inorganic acid, organic acid, and organic salt in solder paste flux wi...

 Factor two: Solder paste Solder paste is a stable mixture consisting of a solder alloy powder, viscous flux, and some additives, with a certain viscosity and good thixotropy. It has a certain viscosity at room temperature, which can mount the components initially. When heated to a certain temperature, the flux and other substances are volatilized, and the alloy powder melts into a liquid form. By the effects of surface tension and wettability, the solder paste fills pads to connect the pads and components, forming firm solder joints. The solder paste is printed onto the PCBs through the stencil apertures by a squeegee utilizing the thixotropy property of the solder paste. When the solder paste is under a certain temperature and shear force, the viscosity drops rapidly, allowing the solder paste to pass through the apertures. After the shear force is removed, the solder paste viscosity returns to normal. Solder paste is a shear-thinning material. When shear stress is present, the v...