Leadless semiconductor plastic packages (QFN) is a growing package category in terms of market share and diversity. This is also valid for low pin count semiconductors (e.g.: transistors and diodes). Several semiconductor companies offer a wide variety of leadless packages for such products. For small,low pin count products,these leadless packages are known as DFN (Discrete Flat No leads) packages. The diversity of DFN packages is still growing. There are several advantages of DFN packages compared to conventional leaded (SO) packages. A disadvantage is that the quality of the AOI inspection of the solder joint on the PCB is limited because the device terminals are only at the bottom of the products. The best way to inspect the soldering quality on PCB is x-ray inspection. However,especially automotive customers have requested suppliers to find a reliable alternative solution. In response to the requests to enable AOI (Automatic Optical Inspection) capability for leadless packages,side wettable flanks for DFN packages have been invented. With the help of side wettable flanks,a satisfactory wetting with solder during reflow soldering process at SMT can be guaranteed. The resulting solder fillet can be reliably inspected with AOI systems. An additional benefit is that the mechanical robustness on PCB could be improved (e.g.: higher device shear force). This paper describes the evolution from leaded to leadless semiconductor (DFN) low pin count packages. It will include a survey of standard semiconductor low pin count leaded and DFN packages. The realization and boundaries of side wettable flanks will be discussed. Focus is on side wettable flanks for 3 to 6 I/Os DFN packages. Alternatives for >6 I/Os packages are considered: e.g.: “dimple”,saw plate saw and immersion Sn plating. Verification of AOI capability as done together with a leading AOI system supplier complete this paper.

The increased demand for electronic devices in recent years has led to an extensive research in the field to meet the requirements of the industry. Electrolytic copper has been an important technology in the fabrication of PCBs and semiconductors. Aqueous sulfuric acid baths are explored for filling or building up with copper structures like blind micro vias (BMV),trenches,through holes (TH),and pillar bumps. As circuit miniaturization continues,developing a process that simultaneously fills vias and plates TH with various sizes and aspect ratios,while minimizing the surface copper thickness is critical. Filling BMV and plating TH at the same time,presents great difficulties for the PCB manufactures. The conventional copper plating processes that provide good via fill and leveling of the deposit tend to worsen the throwing power (TP) of the electroplating bath. TP is defined as the ratio of the deposit copper thickness in the center of the through hole to its thickness at the surface. In this paper an optimization of recently developed innovative,one step acid copper plating technology for filling vias with a minimal surface thickness and plating through holes is presented. The direct current (DC) process is studied in a wide variety of conditions to collect information on its capabilities. The plating conditions allowing improved micro-distribution for the plated TH are discussed. Boards with various thicknesses and TH aspect ratios are included in this study. The responses included TP min.,TP knee,via dimple and cavity formation. A strong interaction between brightener and leveler concentrations was found. The results obtained allow for enhancing through hole micro-distribution while filling a wide range of BMV sizes. The process is designed for a variety of equipment applications with insoluble anodes,including vertical continuous plating equipment. In addition,a modified formula for soluble anodes applications is described. Filling of through via holes in core layers of HDI and IC substrates in a one-step DC process is also demonstrated. Through vias filled with <5 microns or zero dimple and no voids or defects are shown. Mechanical properties,tensile strength => 42,000 psi,elongation > 20% as well as the thermal resistance of copper deposits met and exceeded the IPC standards thus satisfying the need of a highly reliable copper electroplating process.

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%.

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.