Advances in the printed wire board industry toward miniaturization,finer traces and HDI technology,smaller through-holes and microvias have placed higher demands on board design,manufacturability and quality. One primary aspect in the overall board function is the acid copper plating process. The present process utilizes titanium anode baskets with soluble copper-phosphorus balls or anode slabs. Limitations associated with this standard anode technology is seen in low current density plating requirements,over-plating of copper to meet minimum plated board specifications and nodule defects plated into the boards due to copper-phosphorus impurities entering the bath,to name a few. Today there is an alternative,the mixed metal oxide (MMO) insoluble anodes,that is provided to the PWB industry. The company which produces custom fabricated Dimensionally Stable MMO anodes,provided a PWB manufacturer an insoluble anode package including a fully automated feedback controlled copper oxide feeder unit. The all-titanium mesh anodes are designed to provide long-life,superior plating uniformity across all board surfaces and with improved MMO anode throwing power producing a near 1:1 through-hole to surface plating ratio. The MMO anodes are supplied with a patented coating formulation addressing specific requirements of PWB acid copper bath chemistries. The company anodes are qualified in all commercial acid copper plating bath chemistries,demonstrating superior organic additives stability,with equal or better than copper-phosphorus soluble anode balls or slabs organic consumption requirements. The value added commercial PWB manufacturer,with the incorporation of the company’s MMO plating system demonstrated beneficial enhancements to their quality and technology driven,engineered commercial board packages. Dimensionally stable all-titanium MMO anodes create a safer,reliable,reproducible and higher producing plating operation for the PWB manufacturer. MMO anodes allow for the elimination of required maintenance for copper-phosphorus replenishment and copper generated sludge/passivation,providing greater operator safety. Immediate improvements in total rack and individual PWB copper uniformity and throwing power are observed on every engineered product,most importantly high technology designs (near 1:1 ratios hole to surface),especially fine traces and through-holes. Compared to soluble anodes,the company MMO plating system offers fewer impurities resulting in the elimination of nodules and provides better tensile/elongation (IPC Class 3A) and copper purity performance. The fully automatic controlled copper oxide replenishment system allows the PWB manufacturer to achieve 100% copper addition utilization and provides tighter control of copper plating bath concentration,resulting in the elimination of dummy plating and greater process control. The PWB manufacturers’ use of the company insoluble anode plating system yields a quality driven and world class manufacturing solution to meet the advancing technology demands for present and future PWB development and fabrication. Overall Copper plating distributions with the installed insoluble anode system were reduced by more than 50%.

The introduction of lead-free solders resulted in a selection of different chemistries for solder pastes. The higher melting points of lead-free alloys required thermal heat resistant rosin systems and activators that are active at elevated temperatures. As a result,more frequent maintenance of the filtration systems is required and machine downtime is increased. Last year a different method of cleaning reflow ovens was introduced. Instead of cooling down the process gasses to condensate the residues,a catalyst was used to maintain the clean oven. Catalytic thermal oxidation of residues in the nitrogen atmosphere resulted in cleaner heating zones. The residues were transformed into carbon dioxide. This remaining small amount of char was collected in the catalyst. In air ovens the catalyst was not seen as a beneficial option because the air extracted out of the oven was immediately exhausted into the environment. When a catalyst is used in an air environment there is not only the carbon dioxide residues,but also water. When a catalyst is used in an air reflow oven the question is where the water is going to. Will it condensate in the process part of the oven or is the gas temperature high enough to keep it out of the process area? A major benefit of using a catalyst to clean the air before it is exhausted into the environment is that the air pollution is reduced dramatically. This will make environmental engineers happy and result in less pollution of our nature. Apart from this,the exhaust tubes remain clean which reduces the maintenance of air ovens. This paper will give more detailed information of catalyst systems during development and performance in production lines.

Pockets of gas,or voids,trapped in the solder interface between discrete power management devices and circuit assemblies are,unfortunately,excellent insulators,or barriers to thermal conductivity. This resistance to heat flow reduces the electrical efficiency of these devices,reducing battery life and expected functional life time of electronic assemblies. There is also a corresponding increase in current density (as the area for current conduction is reduced) that generates additional heat,further leading to performance degradation. This paper will describe the results of a series of experiments performed in an in-line convection reflow oven,using a typical lead free reflow profile,with three types of bottom terminated components commonly used in power management applications. A solder paste flux and alloy with a known high level of voiding was used as the control. This solder alloy is of unique interest,despite its voiding in ambient reflow conditions,as it has shown superior resistance to failure under automotive thermal cycling conditions (-40C to +125C) and vibration. The experimental design was comprised of two levels of vacuum (5 and 20 torr) applied at two levels of time (30 seconds and 60 seconds) while the test assemblies were at or above the liquidus temperature of the lead free solder alloy. Each 2 x 2 factorial was performed on identical printed circuit boards with four (4) different substrate surface finishes,including Immersion silver,Immersion tin,ENIG (Electroless nickel,Immersion gold) and an Organic Solder Preservative (OSP) finish used. Each condition was repeated three times and three controls with no vacuum were also processed for each surface finish. Therefore,a total of 60 component/substrate samples were processed and subsequently examined for voiding using X-ray analysis. The results of this study indicate that the vacuum pressure,time under vacuum and the surface finish have little effect on the results when vacuum reflow is utilized. The use of a low pressure vacuum when the solder alloy is in liquidus conclusively results in a significant reduction of observable voids in each combination of surface finish and reflow process condition.

It is well known that during service the layer of Cu6Sn5 intermetallic at the interface between the solder and a Cu substrate grows but the usual concern has been that if this layer gets too thick it will be the brittleness of this intermetallic that will compromise the reliability of the joint,particularly in impact loading. There is another level of concern when the Cu-rich Cu3Sn phase starts to develop at the Cu6Sn5/Cu interface and an imbalance in the diffusion of atomic species,Sn and Cu,across that interface results in the formation at the Cu3Sn/Cu interface of Kirkendall voids,which can also compromise reliability in impact loading. However,when,as is the case in some microelectronics,the copper substrate is thin in relation to the volume of solder in the joint an overriding concern is that all of the Cu will be consumed by reaction with Sn to form these intermetallics. This paper reports an investigation into the kinetics of the growth of the interfacial intermetallic,and the consequent reduction in the thickness of the Cu substrate in solder joints made with three alloys,Sn-3.0Ag-0.5Cu,Sn-0.7Cu-0.05Ni and Sn-1.5Bi-0.7Cu-0.05Ni. A simple model developed for the reduction of the Cu thickness as a result of the diffusion controlled reaction with Sn to form Cu6Sn5 was found to fit the experimental data well. The results reported in this paper provide an example of the way in which microstructural features that can affect joint reliability are affected by small alloying additions.

Voiding is a key concern for components with thermal planes because interruptions in Z-axis continuity of the solder joint will hinder thermal transfer. When assembling components with solder paste,there is a high propensity for voiding due to the confined nature of the solder paste deposits under the component. Once reflowed,many factors contribute to the amount of voiding in a solder joint such as the reflow profile,designs of the component,board and stencil,and material factors. This study will focus on the solder paste alloy and flux combination as well as profile and board surface finishes. Several alloys have been developed in the last decade to boost performance in high-temperature environments and reliability in thermal cycling tests. These alloys typically consist of SnAgCu with additional elements such as Sb and Bi to modify performance. One of the key barriers to adoption of these alloys has been higher levels of voiding. Previous papers have explored the effect of process and stencil modifications with one or more of these alloys1. The solder pastes include several alloys within the range of compositions suggested for automotive applications in combination with different paste fluxes. The results will compare voiding with various alloys and common board surface finishes.

Solder paste has been used in the surface mount technology for many years. However,a complete understanding of the effect of key powder characteristics on the paste properties is still not achieved. This understanding becomes much more important when new solder pastes with finer powder size are developed for advanced applications. In addition,the effect of other parameters such as time,humidity and temperature may also influence the performance of pastes made with fine and ultra-fine powders. In this work,the influence of key powder characteristics on the reflow property of paste made with powders produced with a proprietary atomizing technology,particularly effective in producing solder powder ranging from 1 to 25 µm,is presented and discussed. Powder characteristics considered are particle size distribution and oxygen content. SAC305 powder were aged at various humidity/temperature conditions. The reflow performance of the pastes made with aged powder was evaluated. Moreover,the oxide layer formed at the powder surface was characterized using Auger Electron Spectroscopy and Transmission Electron Microscopy. The influence of external parameters such as humidity and temperature on the powder is discussed.