The change to lead-free solders in electronic assemblies created a need to replace tin-lead solderable termination finishes with materials such as pure tin or soft gold,on electronic components and substrates. Gold presented a risk of solder joint embrittlement,which could reduce the joint mechanical durability. Several case studies were run,because solder joint embrittlement prevention requires a clear understanding of the materials and mechanisms of embrittlement. We confirmed two known mechanisms and verified two other ways in which gold finishes can degrade solder joints. The known mechanisms are,1) A gold layer dissolves from one side of a surface mount joint and precipitates AuSn4 compound onto the opposing termination and 2) The gold fully dissolves from a surface mount termination,but it results in an excessive gold weight percentage in the joint. The other ways are,3) A manual soldering process temperature is high enough to dissolve some nickel along with the gold and 4) A slow dissolving,hard gold surface finish incompletely dissolves during plated-through-hole soldering and solid state diffusion forms an AuSn2 compound layer. Close-up and cross-sectional images with SEM/EDS compositional information are shown for each case. A table of solder and gold volumes,which produce 3.0 and 4.0 weight percent gold,is provided. The embrittlement problems and their reliability solutions are discussed (over twenty literature references). The data suggests how to improve gold plating requirements,for solder joint embrittlement prevention,in solder assembly industry standards.

There is considerable interest in finding and replacing lead based solder alloys in high power environments and for existing high temperature operating environments. The high power electronics market requires alloys that do not contain lead but perform equally as well. With the increasing temperature requirements for harsh electronics in automotive and drilling applications the temperature these products require are increasing from 150 C to 200 C and equally need to consider alternatives. This project compared solder joints consisting of existing lead-free and leaded solders produced with laser and robotic iron soldering on polyimide substrates. The soldering of through-hole connectors was used to examine the changes that take place during high temperature storage of different solder alloys. This part of the work was aimed at the existing high temperature organic level assembly market or those companies moving into that product environment. There currently is a dearth of published data in this area. The work reported here can be compared to sintered silver joining trials reported elsewhere. Flux residues were considered in this work,particularly those from cored wire,where spitting and solder balling can be an issue. Robotic and laser soldering can achieve rapid heating of the solder with undesirable spitting of the flux as the result. We looked at the various approaches to solving this problem.

Printed Circuit Boards (PCBs) and Printed Electronics (PE) both describe conductor/substrate combinations that makeconnections. Both PCB and PE technologies have been in use for a long time in one form or another with PCBs currently the standard for complex,high speed electronics and PE for user interface,complex form factor or other film based applications. New and innovative applications create the opportunity for promising structures. Taking advantage of the PCB shop’s capability as well as the material set can help create these structures and indeed PE materials can find use in more traditional PCBs. New materials and new uses of existing materials open up many possibilities in electronic interconnecting structures. PCB manufacturers have a complex manufacturing infrastructure,well suited for both additive and subtractive conductor processing. While built around rigid material processing (flex PCB being the exception),there are opportunities for PE substrate processing. As electronics devices are applied to more and more parts of our lives,we need to continually push for better solutions. Fit,function,manufacturability,and cost are all important considerations. Crossing the PCB/PE boundary is a way to meet the challenge.

This paper discusses a nano copper based paste for use in via filling. The company manufactures nano copper and disperses the coated nano copper into a paste in combination with micron copper. The resultant paste is injected or fills a via. The via is subsequently sintered by means of photonic sintering,or by heat in a reducing environment. The process will be accomplished in under an hour and results in filled solid copper vias.

This paper documents the experimental work performed to further understand the impact on mid-chip solder balling from both the manufacturing process and the flux chemistry. Mid-chip solder balling is a defect typically associated with solder paste exhibiting poor hot slump and/or insufficient wetting during the reflow soldering process,resulting in paste flowing under the component or onto the solder resist. Once molten,this solder is compressed and forced to the side of the component,causing mid-chip solder balling. To increase the understanding of what factors can impact mid-chip balling,a study was undertaken to examine the effects of process variants and flux chemistry. Stencil thickness,aperture size and aperture shape were all identified as potentially significant factors with regards to process influence. Testing also revealed that the volume of paste was not necessarily proportional to the number of mid-chip balls,but was more influenced by the position of the paste relative to the pad. Comparative testing of a range of flux chemistries indicated that this also had a substantial effect on mid-chip ball occurrence. The data suggested that mid-chip balling could be controlled by both process and flux design. New methods of quantifying the severity of mid-chip solder balling are currently being investigated.

A materials study of high reliability electronics cleaning is presented here. In Phase 1,mixed type substrates underwent a condensed contaminants application to view a worst-case scenario for unremoved flux with cleaning agent residue for parts in a silicone oil filled environment. In Phase 2,fluxes applied to copper coupons and to printed wiring boards underwent gentle cleaning then accelerated aging in air at 65% humidity and 30 OC. Both sets were aged for 4 weeks. Contaminants were no-clean (ORL0),water soluble (ORH1 liquid and ORH0 paste),and rosin (RMA; ROL0) fluxes. Defluxing agents were water,solvents,and engineered aqueous defluxers. In the first phase,coupons had flux applied and heated,then were placed in vials of oil with a small amount of cleaning agent and additional coupons. In the second phase,pairs of copper coupons and PWB were hand soldered by application of each flux,using tin-lead solder in a strip across the coupon or a set of test components on the PWB. One of each pair was cleaned in each cleaning agent,the first with a typical clean,and the second with a brief clean. Ionic contamination residue was measured before accelerated aging. After aging,substrates were removed and a visual record of coupon damage made,from which a subjective rank was applied for comparison between the various flux and defluxer combinations; more corrosion equated to higher rank. The ORH1 water soluble flux resulted in the highest ranking in both phases,the RMA flux the least. For the first phase,in which flux and defluxer remained on coupons,the aqueous defluxers led to worse corrosion. The vapor phase cleaning agents resulted in the highest ranking in the second phase,in which there was no physical cleaning. Further study of cleaning and rinsing parameters will be required.

Although reflow ovens may not have been dramatically changed during the last decade the reflow process changes step by step. With the introduction of lead-free soldering not only operation temperatures increased,but also the chemistry of the solder paste was modified to meet the higher thermal requirements. Miniaturization is a second factor that impacts the reflow process. The density on the assembly is increasing where solder paste deposit volumes decreases due to smaller pad and component dimensions. Pick and place machines can handle more components and to meet this high through put some SMD lines are equipped with dual lane conveyors,doubling solder paste consumption. With the introduction of pin in paste to solder through hole components contamination of the oven increased due to dripping of the paste. The iNemi Roadmap identified seven key metrics for the reflow process: 1. Temperature delta performance 2. Inerting capability 3. Cooling rates 4. Flux management 5. Cost of operation 6. Traceability 7. Change over time. The current flux collection systems need to focus on improvements to minimize maintenance downtimes. Flux management and cost of operation will benefit from an efficient oven cleaning method. The filter and condensation systems that were successful running in SnPb processes have to be reviewed and new technology is introduced to have a more efficient removal of solder paste,board and component gasses.

Proper assembly of components is critical in the manufacturing industry as it affects functionality and reliability. In a heat sink assembly,a detailed manual process is often utilized. However,an automated fixture is used whenever applicable. This paper will illustrate the use of strain gauge testing and Finite Element Analysis (FEA) as a simulation tool to evaluate and optimize the heat sink assembly process by manual and automated methods. Several PCBAs in the production line were subjected to the manual and automated assembly process. Strain gauge testing was performed and FEA models were built and run. Results were compared with the goal of improving the FEA model. The updated FEA model will be used in simulating different conditions in assembly. Proposed improvement solutions to some issues can also be verified through FEA.

Electrical overstress causes damage to sensitive components,including latent damage. A significant source of EOS is high-frequency noise in automated manufacturing equipment. This paper analyses sources of such noise,how it affects components and how to mitigate this problem.

Press-fit technology is a proven and widely used and accepted interconnection method for joining electronics assemblies. Printed Circuit Board Assembly Systems and typical functional subassemblies are connected through press-fit connectors. The Press-Fit Compliant Pin is a proven interconnect termination to reliably provide electrical and mechanical connections from a Printed Circuit Board to an Electrical Connector. Electrical Connectors are then interconnected together providing board to board electrical and mechanical inter-connection. Press-Fit Compliant Pins are housed within Connectors and used on Backplanes,Mid-planes and Daughter Card Printed Circuit Board Assemblies. High reliability OEM (Original Equipment Manufacturer) computer designs continue to use press-fit connections to overcome challenges associated with soldering,rework,thermal cycles,installation and repair. This paper investigates the technical roadmap for press fit technology,putting special attention to main characteristics such,placement and insertion,inspection,repair,pin design trends,challenges and solutions. Critical process control parameters within an assembly manufacturing are highlighted.