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Traditionally microvias have been considered to be the most reliable interconnect structure within a printed wiring board (PWB). With the advent of lead free assembly the vulnerability of high density interconnects to fail has increased,due to the elevated temperatures experienced during surface mount assembly and rework. Throughout the past 18 months microvias have been found to fail during assembly and in their end use environment. This paper outlines a case study of microvia failure; reliability test methods,failure analysis,fabrication process considerations,and assembly process considerations for tin/lead and lead free application and problem resolution of microvia reliability issues.

The following report is fundamentally focused on how three popular lead-free alloys react in a wave solder application. The alloys were SAC305,SAC405 and a proprietary,low silver SAC alloy. In the process of attaining that goal,a flux selection methodology,and a study of top convection pre-heat were required. These three subjects are included in this report. Existing wave solder machines,materials,and methods were modified and tested over this study. The study used only Bellcore approved no-clean fluxes. Statistical analysis of the alloy study data was completed. The conclusions drawn suggest that except for one point,at least the defect of excess solder shows that there was no significant difference between those alloys. The main effect plots of the process defects used in the study would be very valuable in directing effective corrective action. In the flux selection methodology,a large test population was reduced to a few final candidates at low cost with little machine time or expensive test vehicles. A very detailed and extensive study on top-side convection pre-heat,by itself and used with infra-red panels,proved the system superior to alternatives. The minimal thermal stress and exceptional uniformity in the pre-heat of the machine have significant effect in providing uniform and efficient product preparation for solder. While not part of the study,a potential issue with minor flaws from bare board fabrication,or possibly a moisture sensitivity issue in the board was discovered. The issue causes large voids.

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As the global electronic industry marches toward the brave new world of environmentally conscious electronic manufacturing,lead free soldering has made some fundamental shifts in the processing approaches to print wired assembly (PWA). With the popular adoption of Tin Silver Copper (SAC) alloys,advancements have been made in packaging designs,soldering materials,processing equipment,and surface finishes. Historically,Hot Air Solder Leveling (HASL) has dominated the PWB market as the preferred choice for many applications. In recent years,Organic Solderability Preservative (OSP) and some precious metal finishes,namely immersion Silver and Immersion Tin,have regained momentum in Lead free electronic assemblies. Although OSP has been used in electronic assembly for over 25 years,the conversion of Lead free technologies has presented some unique challenges to manufacturability,testability,and reliability. The focus of this article is to explore the challenges posed by OSP in a high volume,Lead free production environment and how different techniques can be utilized to optimize and improve the process windows.

Due to the European legislations (RoHS and WEEE) consumer products need to be soldered with lead-free solders from the first of July 2006. Since several properties (physical,chemical,mechanical and most pronounced but less severe visual) of lead-free solders are thought to be degenerated compared to the lead-containing variants,thorough investigation of the solders and of the solder processes is necessary.
In this research,different types of PTH and SMD components are hand soldered with lead-free solder (Sn-Ag-Cu,shortened SAC) on PCB’s with four finishes (Ag,Ni/Au,Sn and OSP). The as-soldered boards are analyzed,but also some boards were first exposed to thermal cycling tests for either 168,336,772 or 1008 cycles before analysis. The results are compared to the results for tin lead soldered PCA. Analyses have been performed by means of tensile strength tests and metallographic research by optical microscopy.
Most properties of the solder joint of lead-free SAC are inferior compared to lead containing solders: wetting behavior,formation of cracks and voids are more often observed for lead-free soldered assemblies than for SnPb soldered assemblies. It is also observed that the lead-free solder joints exhibit poor fatigue properties compared to lead containing joints. After thermal cycling tests,cracks are observed more frequent and their character is more sever. This can be contributed to the less ductile behavior of the lead-free solder. Cracks propagate intra- as well as intergranular for both alloys. However,the formation of cracks is also thought to be stimulated by defects introduced during the hand soldering process.
The tensile tests show that the lead-free SAC solder gives a mechanically stronger connection compared to SnPb. In addition lead-free soldered components on a board with a Ni/Au or Ag finish give a stronger connection compared to components soldered on PCBs with an OSP or Sn finish.

In response to growing concerns about the effects of hazardous materials in the waste stream on the environment,the European Union (EU) passed a directive in 2002 entitled the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (RoHS). Even though RoHS is simple in scope and limits the use of only six substances,it nevertheless has created significant challenges for manufacturers trying to prepare for the day they must begin to comply with the directive on July 1,2006.
Legislation such as RoHS and its sister ruling,the EU’s Waste Electrical and Electronic Equipment (WEEE) directive,are forcing companies to examine not only how to ensure compliance but also how to manage information about the parts used in the manufacture of their electronic and electrical equipment. Until recently,most manufacturers didn’t have to worry about parts information management and compliance. A recent study by Aberdeen Group revealed that less than one third of companies surveyed had standardized their product compliance practices across the organization.1 In addition,at the time of the report,80 percent of the surveyed organizations said that they lacked a cohesive systems infrastructure to track,audit or manage product compliance,while 75 percent admitted to not having audited product content in the previous six months.2
RoHS and WEEE aren’t the only environmental regulations with which companies are required to comply. In the EU,the End of Life Vehicles (ELV) directive requires car producers to limit their use of hazardous substances in the manufacture of their cars while also increasing the amount of recycled components used in their products. It also makes car manufacturers responsible for the recycling of their products once they are no longer being used. Additionally,in the United States,environmental regulations are pending in a number of states. In California,the Electronic Waste Recycling Act of 2003,like RoHS and WEEE,seeks to establish a system for the reduction,collection and recycling of electronic product waste. The situation is similar in China,where the government has developed the Regulation for Pollution Control of Electronic Products (RPCEP). Unlike RoHS,however,RPCEP seeks to eliminate the six substances that the EU is trying to limit. Although legislation has not yet been enacted in Japan,the Japan Green Procurement Survey Standardization Initiative (JGPSSI) has collaborated with the Electronics Industry Alliance (EIA) to publish Joint Industry Guidelines for hazardous materials declaration.
As more countries continue to jump on the environmental bandwagon,it’s becoming increasingly important for component manufacturers and Original Equipment Manufacturers (OEMs) alike to put in place the necessary infrastructure that allows them to track and manage parts data. Doing so will not only allow them to ensure compliance with RoHS,but will also help them comply with the host of other similar regulations they will undoubtedly be facing in the near future.

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The widespread use of electrotechnical products has drawn increased attention to their impact on the environment. In many countries all over the world this has resulted in the adaptation of regulations affecting wastes,substances and en-ergy use of electrotechnical products. The use of certain substance like Lead (Pb),Mercury (Hg),Cadmium (Cd),Hexavalent Chromium (Cr VI),and some types of brominated flame retardants (like Polybrominated Biphenyls,PBB,Polybrominated Diphenyl Ethers,PBDE) in electrotechnical products is regulated in current and proposed legislation e.g. in the European Union (EU) directive on the “Reduction of certain Hazardous Substances in electrical and electronic equipment” (RoHS),in Chinese draft legislation and in the US (California) Electronic Waste Recycling Act of 2003. In-dustry is convinced of the importance of defining testing protocols for regulated substances of electrotechnical products that enter or are made available on markets,where legislation regulating the substance content of electrotechnical prod-uct is enacted. Certain test procedures to determine regulated material content already exist,but most are not appropriate for testing electrotechnical products and are not internationally recognized. Currently no procedures for compliance or enforcement of the substance restrictions have been agreed upon or mandated by countries regulating substances in elec-trotechnical products. Testing procedures,which are being discussed by industry associations and academia to determine presence and levels of these banned substances differ from each other. Until a common agreement between governments,industry and other stakeholders is reached on how regulated substances should be measured in electrotechnical products,industry has no legal certainty that products will be found compliant if tested by national enforcement authorities or by Non Governmental Organizations (NGOs) in different countries. The purpose of the work by the IEC (International Electrotechnical Commission) TC (Technical Committee) 111 “Environment” WG (Working Group) 3 is therefore to provide test procedures that will allow the electrotechnical industry to determine the levels of the regulated substances Pb,Hg,Cd,Cr VI,PBB,PBDE (EU RoHS,China,US,Japan,etc.) in electrotechnical products on a consistent global basis.