SZFitech

 There are significant differences between solid crystal solder paste and regular solder paste in several ways.The following is a detailed comparison of the two: 1. Composition and particle size Solid crystal solder paste: Tin powder selection: solid crystal solder paste usually choose No. 6 powder, No. 7 powder or even No. 8 powder, these powder particles are very small. Alloy composition: solid crystal solder paste is mainly tin silver copper and other metal alloys as a substrate, high thermal conductivity, to meet environmental requirements (such as RoHS and halogen-free, etc.). Ordinary solder paste: Tin Powder Selection: Ordinary SMT solder paste generally uses No. 3, No. 4 powder or No. 5 powder, with relatively large particles. Alloy composition: The alloy composition and application range of ordinary solder paste is wide, may contain a variety of metal elements. 2. packaging and storage Solid crystal solder paste: Packaging: solid crystal solder paste is usua...

 Sn-Bi eutectic solder paste has low soldering temperature requirements and can be soldered at low temperatures. This solder paste is important in the solder market due to its advantages, such as low-temperature soldering and high tensile strength. However, Bi is a brittle metal and prone to segregation in the solder during the heating process. The localized Bi phase segregation and coarsening causing solder joint brittleness affect the application of Sn-Bi eutectic solder paste. Fortunately, adding some particles to Sn-Bi eutectic solder can enhance the solder strength. Experimental Design The most widely used low-temperature solder paste is made based on SnBiAg and SnBiAgIn alloys. This solder paste is added with a small amount of Ag and In on the basis of Sn42Bi58 eutectic solder paste to improve the physical properties. Hu et al. prepared a series of low-temperature solder alloys and verified their mechanical strength. Table 1. Experimental solder alloys. Results M...

 SAC series solder paste is a common medium-temperature solder in semiconductor packaging. This type of solder paste can be used for soldering work at relatively high temperatures, and the strength after soldering is considerable. However, as the thermal stress on the solder joint accumulates, there is a certain degree of deformation between the solder joint and the chip due to the difference in thermal expansion coefficient, and the fracture mode of the solder joint will change over time, leading to a decrease in strength and failure of the solder joint. Therefore, it is necessary to study how to improve the strength of the solder joint. To achieve higher solder joint strength, it is possible to add trace metals to the solder paste to enhance it. Steenmann, Richter, and Licht made tensile test samples from solder with micro-additives, where the solder was heated in the cavity of the copper substrate. The substrate cavity is ground and coated with TiCN to prevent cop...

 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. Figure 1. Epoxy Flux Spray and Dip Processes. Epoxy fluxes are self-assembling and self-correctin...

 One of the causes of thermomigration is the inconsistent internal temperature of the alloy. When heat treating a uniform binary alloy, due to the temperature difference between one end and the other end of the alloy, metal atoms will migrate, and the alloy will become uneven. Not only does thermal conduction cause thermomigration, but atomic diffusion within the alloy is also the cause of thermomigration. There are still some uses of binary alloy solder paste in semiconductor applications, such as SnAg, SnCu, SnPb solder paste, etc. The alloy elements such as Ag and Cu in these lead-free solder pastes diffuse in the gaps of Sn. Rapid interstitial diffusion will enhance the flux of thermomigration. Thermomigration of Cu atoms The interstitial diffusion of Cu in the Sn matrix is fast, especially driven by large thermal gradients. Figures 1 (a) and (b) show SnAg solder joints before electromigration and thermomigration tests. It can be found that Cu6Sn5 bonded well with...

 General guidance it is well known that 60-70% of all solder defects can be traced back to the printing defects such as solder bridging, cold slump and Uneven Solder Paste Deposit while fine tuning the reflow profile do benefit and avoid some soldering defects Tombstoning Tombstoning defects can be attributed to unbalanced wetting forces, generally found when assembling passive components (see Figure 1). To reduce tombstoning, minimizing the thermal gradient between pads prior to reflow is crucial, this can be accomplished by slowing the ramp rate from ambient to peak, allowing the PWB assembly to gradually/evenly rise in temperature. Fig.1 Solder balling/beading Solder beading Solder beading is big solder ball, it occurs when isolated solder paste aggregates are formed under low stand-off components. At reflow, the aggregate melts and emerges from the underside of the component, separate from the solder mass/joint. Fig.2 Solder balling occurs if the solder paste spa...