Cleanliness is a product of design,including component density,standoff height and the cleaning equipment’s ability to deliver the cleaning agent to the source of residue. The presence of manufacturing process soil,such as flux residue,incompletely activated flux,incompletely cured solder masks,debris from handling and processing fixtures,and incomplete removal of cleaning fluids can hinder the functional lifetime of the product. Contaminates trapped under a component are more problematic to failure. Advanced test methods are needed to obtain “objective evidence” for removing flux residues under leadless components. Cleaning process performance is a function of cleaning capacity and defined cleanliness. Cleaning performance can be influenced by the PCB design,cleaning material,cleaning machine,reflow conditions and a wide range of process parameters. This research project is designed to study visual flux residues trapped under the bottom termination of leadless components. This paper will research a non-destructive visual method that can be used to study the cleanability of solder pastes,cleaning material effectiveness for the soil,cleaning machine effectiveness and process parameters needed to render a clean part. The test vehicle for this research study will be an engineered glass ceramic test substrate. The test substrate is transparent,precise and can be used for repeated studies. The ceramic engineered components are mounted to the substrate in a series of columns and rows. The standoff gap is 60µm and gap between components is 300um. Flux vehicles from many industry specific no-clean solder pastes will be included in this study. The response variable of the percentage of flux cleaned under the ceramic dies will be collected using an AOI machine and from optical imaging. This study will report the potential for cleaning flux residues trapped under leadless components when processed in aqueous spray batch cleaning tools using a next generation cleaning agent.

The requirement to reconsider traditional soldering methods is becoming more relevant as the demand for bottom terminated components (QFN/BTC) increases. Thermal pads under said components are designed to enhance the thermal and electrical performance of the component and ultimately allow the component to run more efficiently. Additionally,low voiding is important in decreasing the current path of the circuit to maximize high speed and RF performances. The demand to develop smaller,more reliable,packages has seen voiding requirements decrease below 15 percent and in some instances,below 10 percent. Earlier work has demonstrated the use of micro-fluxed solder preforms as a mechanism to reduce voiding. The current work builds upon these results to focus on developing an engineered approach to void reduction in leadless components (QFN) through increasing understanding of how processing parameters and a use of custom designed micro-fluxed preforms interact. Leveraging the use of a micro-fluxed solder preform in conjunction with low voiding solder paste,stencil design,and application knowhow are critical factors in determining voiding in QFN packages. The study presented seeks to understand the vectors that can contribute to voiding such as PCB pad finish,reflow profile,reflow atmosphere,via configuration,and ultimately solder design. A collaboration between three companies consisting of solder materials supplier,a power semiconductor supplier,and an electronic assembly manufacturer worked together for an in-depth study into the effectiveness of solder preforms at reducing voiding under some of the most prevalent bottom terminated components packages. The effects of factors such as thermal pad size,finish on PCB,preform types,stencil design,reflow profile and atmosphere,have been evaluated using lead-free SAC305 low voiding solder paste and micro-fluxed preforms. Design and manufacturing rules developed from this work will be discussed.

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%.