Papers about solder joint
by Dr. Ronald C. Lasky
It is likely that a modern mobile phone has more computing power than all of the computers that NASA used to send men to the moon in the late 1960s. This idea is especially interesting when one considers that the electronics of that era had almost no integrated circuits (ICs) and that many computer circuits were individual transistors, resistors, and capacitors. Today's PC microprocessors have the equivalent of hundreds of millions of these components, all electrically connected in the IC. Such miniaturization has enabled the electronics revolution.
PCB assembly, electronics assembly, solder joint, solder paste
[Permanent Link to this Paper ]
Posted on 4 Mar 2010
by Dr. Ning-Cheng Lee
In general,
new lead-free solder alloys with the following characteristics are desired in order to enable the continuation of miniaturization trend: (1) alloy with a reduced melting temperature, (2) alloy with a better solder spread, (3) alloy with a slower wetting speed at melting temperature, (4) a softer alloy, or alloy with a reduced voiding tendency or greater ductility, (5) alloy with a refined grain size, (6) alloy with low tendency to form large IMC plate, (7) alloy with a higher resistance toward corrosion and electrochemical migration, (8) alloy with a greater oxidation resistance. On the other hand, no-clean fluxes with the following features are needed: (1) reduced volatile, (2) halide-free, (3) greater fluxing
capacity, (4) higher residue resistivity, (5) more resistant to oxidation and charring, (6) more efficient oxidation barrier, (7) lower activation temperature, (8) slower wetting speed when solder begins to melt, (9) less spattering, (10) higher probe penetratability, (11) capability of inducing nucleation of solder upon cooling, and (12) greater resistance against slump.
SAC, solder joint, soldering, flux, solder alloy, lead-free
[Permanent Link to this Paper ]
Posted on 4 Mar 2010
by Dr. Ning-Cheng Lee , HongWen Zhang
Although lead-free soldering has been the main stream of industry since 2006, with the replacement of eutectic SnPb system by SnAgCu system, the development of drop-in lead-free alternatives for high melting high lead solder alloys is still far from mature. BiAg alloy exhibits acceptable bulk strength but very poor ductility and wetting, therefore it is not acceptable as an option. In current work, a mixed powder BiAgX solder paste system has been developed as a viable alternative, high temperature lead free solder. The metal powder in the paste is composed of a high melting first alloy powder as majority and the additive powder as minority. The additive contains a reactive element to react with various metallization surface finishes. The additive will melt and react on the parts before or together with the melting of the majority solder. The reactive element in the additive is designed to be converted completely into IMCs during the reflow process, hence resulting in a high melting solder joint. In the mixed powder paste system, a melting temperature above 260°C was verified by both DSC and TMA data. The mixed powder solders show a significantly improved wetting comparing to Bi11Ag. The voiding and TCT performance are comparable with high lead solders. The IMC layer thickness of the mixed powder system is insensitive toward thermal aging at 175°C, while the high lead ones do show a considerable increase.
BiAg, voiding, wetting, mixed alloy, solder joint, solder paste, solder, lead-free, high temperature
[Permanent Link to this Paper ]
Posted on 20 Oct 2011
by Wanda B. Hance, Dr. Ning-Cheng Lee
The mechanisms for void formation are investigated for applications involving solder paste in SMT. Generally the voids are caused by the outgassing of entrapped flux in the sandwiched solder during reflow. The voiding is mainly dictated by the solderability of metallization, and increases with decreasing solderability of metallization, decreasing flux activity, increasing metal load of powder, and increasing coverage area under the lead of the joint. Decrease in the solder powder particle size shows only a slightly negative effect toward voiding. The data indicate that voiding is also a function of the timing between the coalescing of solder powder and the elimination of immobile metallization oxide. The sooner the paste coalescing occurs, the worse the voiding will be. Increase in voiding usually is accompanied by an increasing fraction of large voids, suggesting factors causing voiding will have an even greater impact on the joint reliability than what shown by the total-void-volume analysis results. Preliminary data show that certain predry treatment and flux solvent with higher boiling point appear to cause increased voiding.
lead-free, pb-free, solderability, reflow, solder joint, SMT, voiding, void, flux, solder paste, soldering, solder
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
