Solder balling of lead-free solder pastes

Abstract

Solder balling in Sn/Ag/Cu solder pastes was studied in this work. Three different solder pastes, several different reflow profiles and conditions, and two stencil thicknesses were used in the investigation. During the first phase, called the verification phase, the solder pastes were checked to ensure they met the minimum requirements. In the process-screening phase, the reflow profile was varied. Results show that besides flux chemistry, reflow atmosphere plays the major role in solder balling. The average number of solder balls with the best paste was one fifth of that with the worst paste. Furthermore, with all the pastes, the number of solder balls dropped close to zero when nitrogen atmosphere was used. Another finding during the reflow process screening was the influence of the stencil thickness on the solderballing result. With a thinner stencil, two of the pastes exhibited significant solder balling. This is assumed to be caused by the different ability of fluxes to withstand oxidation during the preheating in the reflow process. In the last phase, the effect of the solder-paste particle size on solder balling was studied more closely. The flux chemistry was kept unchanged, and the solder particle size was varied between type 3 and type 4. The results show that, with type 4 paste, significantly more solder balls are formed compared to type 3 paste. It was also confirmed that, regarding the reflow profile, the ramp-up rate from 150°C to 217°C and the reflow atmosphere were the most significant factors that determine the solder-ball formation for both types of paste.

Effect of Reflow Time on Wetting Behavior, Microstructure Evolution, and Joint Strength of Sn-2.5Ag-0.5Cu Solder on Bare and Nickel-Coated Copper Substrates

“…4. Sn-2.5Ag-0.5Cu solder alloy reflowed on Cu substrate for various reflow times showed Similarly, the Sn-2.5Ag-0.5Cu/Ni/Cu system showed (Cu,Ni) 6 Sn 5 intermetallic at the interface; its thickness increased up to 300 s, followed by a decrease thereafter. The samples reflowed for 500 s showed spalling, resulting in decreased joint strength.…”

“…At low levels, such compounds have a strengthening effect on the joint, but at higher levels, they tend to make solder joints more brittle. 6 Hence, it is vital to understand the sequence of IMC formation and growth during soldering, as the thickness and morphology of the IMC layer impact on solder joint strength. 7 Copper is the substrate most widely used in microelectronic devices due to its high corrosion resistance, good wettability, good solderability, and high thermal conductivity.…”

Encapsulation of lead-free Sn/Zn/Bi solder alloy particles by coating with wax powder for improving oxidation resistance

“…The soldering properties of wax-coated Sn/Zn/Bi alloy particles were evaluated through both the wettability test and the solder balling test. 18 The applicability of the treatment method to the improvement of characteristics of lead-free solder powder has been verified and the effects of wax coating on the soldering and storage properties have been discussed based on the experimental results.…”

A grey-ANN approach for optimizing the QFN component assembly process for smart phone application

“…Little solder particles encompassed in the flux residue locate around the solder joint (Figure 3). The solder-balling phenomenon is relatively complex, affected by many process and material parameters (Arra et al , 2002). In general, there are two forms of solder-balling, splattering and squeezing.…”