From the first time we heard of new thin,low Dk,flex laminate material from DuPont we were excited. The material is what is now known,and commercially available,as DuPont’s Pyralux TK®. Working with DuPont on the development we called the material by a code name that we used so often amongst ourselves that now it is difficult to refer to it by its commercial name: Pyralux TK®. For the benefit of the reader,however,I will indulge herein by using the term “TK”®. And in the process hope to explain why we remain very excited about the opportunities that his new material provides the flexible circuit manufacturer.
When first approached by DuPont in the summer of 2009 about beta testing TK® we were most concerned about how the material would react through our standard flex circuit fabrication process. We assumed that DuPont had developed the material thoroughly and that the electrical properties promoted where accurate. But,as veteran flex circuit techies we live in fear of the four-letter word “Teflon”® - and the history that follows that material in flex circuit circles. So,we set out to develop a DOE (design of experiment) that would not only test the material against our standard process,but also against other common flex circuit laminates.

Modern flexible printed circuits demand improved signal integrity due to increasing data rate requirements for interconnects. At the same time,form factors available to designers are becoming smaller. All polyimide flexible circuit materials have been used in high-reliability applications for decades. [1,2] There is a well-established infrastructure of fabricators skilled in manufacturing controlled impedance flexible circuits. Solutions to meet the challenge of thinner,higher speed controlled impedance circuits include improved materials,more disciplined manufacturing and more comprehensive,improved,electrical characterization data.
Historically,performance specifications for flexible circuits were driven by mechanical properties. Electrical considerations were secondary. Today,controlled impedance circuit tolerances are becoming tighter and higher frequency performance is an additional requirement. Since flexible circuit dielectrics are very thin,small differences in dielectric properties can have a large impact on impedance. These thinner dielectrics reduce form factor due to decreased volume,also thin layers can be folded into tighter bends than conventional printed wiring.
Designers and fabricators use software tools like Polar [3] to model circuit geometry to achieve the target impedance. Unfortunately,dielectric data available in typical data sheets is inadequate to successfully design and fabricate a controlled impedance flexible circuit. As a response to this reality,each fabrication shop and design house uses slightly different values for dielectric constant. This approach works OK if the impedance tolerance is relatively wide,but becomes unsustainable for tighter tolerances or higher frequencies.
This paper is divided into two parts:
Part 1 describes differential impedance test structures using adhesive/polyimide,all polyimide,and new high speed flexible circuit materials. Measured data is compared to Polar models with increasing degrees of complexity. The values of dielectric constant used will show agreement between measured and modeled results of 2.5% or better.
Part 2 summarizes the evaluation results of new high speed flexible circuit materials from the perspective of a leading flexible circuit fabricator. The ease and quality of processing will be compared to traditional adhesive/polyimide and all polyimide flex materials. Results will confirm that the high speed flexible circuit materials are fully compatible with standard flexible circuit processing without significant process modifications.

- Solar Module Assembly vs. PCBA
- Crystalline Silicon Module (c-Si) Construction
- Module Assembly Process (c-Si)
- PV Cells – String - Array - Module
- Tab & String Process
- Lamination Process
- Junction Box Attach
- Quality Verifications
- Cell – String Inspection Methods
- Cell and Module Flash Testing
- CPV Module
- IPC Solar PV Module Standards
- Solar Module Assembly: Key Considerations
- EMS Role in Solar Module Assembly

•A vision of a solar-powered world
•Importance of reliability to success of solar
•Working together to establish reliability
•R&D issues related to:
•Product Development
•Quality Assurance during Manufacturing
•Lifetime Predictions
•Current status
•Technology-specific R&D issues
–Selected highlights

•The 2011 iNEMI Solar PV roadmap
•Involvement of the electronics supply chain
•Example of an electronics opportunity – micro-inverters

• 2010 turned out to be an unexpectedly strong year: > 130% growth in both cell production and installations over 2009
• 24GWp cell production
• All leading suppliers are expanding production capacities at a high rate
• Differentiated,high-efficiency PV cell products are being introduced by all leading suppliers
• CIGS thin-film modules are progressing toward high-volume production,with efficiencies approaching that of c-Si modules
• Thin-film technologies were unable to gain further production share over 2009,due to greater difficulty in expanding manufacturing capacities
• Production is now clearly dominated by Asia,with Europe and Japan continuing to lose importance
• Module price reductions and new incentive programs are leading to greater geographic diversity in installations
• PV installation market is becoming more robust—no longer completely dependent on Germany

Consider defluxing at the design stage. This involves determining how product design may impact the assembly process. It also involves selecting the most effective,rugged defluxing option relative to the assembly design. The reward is reliable,competitive,and profitable electronics assembly. Selecting the right defluxing process must take into consideration not only performance requirements and costs but also miniaturization,component configuration,as well as local,national and international regulatory constraints. Changes in product design and the increase in highly-populated assemblies may impel modification of the defluxing process. Changes in the defluxing chemistry and in the defluxing process can benefit product quality and performance.

Because of the phase out of CFC’s and HCFC’s,standard solder pastes and fluxes evolved from RA and RMA fluxes,to No-Clean,to low residue No-Clean,to very low residue No-Clean. Many companies came out with their cleaning solu-tions,aqueous and semi-aqueous,with each product release being more innovative than the previous one. Unfortunately for most of the suppliers of cleaners,two other trends appeared; lead-free soldering and the progressive miniaturization of electronic devices.
Past chemicals like CFC’s,HCFC’s,brominated solvents,detergents and glycols cannot do a good cleaning job anymore because most flux formulations have changed. Also,assembly processes have been modified due to smaller components and more compact board assemblies. Thus,it is important to remember that the world is composed of two main things: organics and inorganics. Organics are made of resins and activators,whereas inorganics are made of salts,metallic salts and fillers.
Cleaning performance is affected by three main criteria. The first involves the Hansen Parameters which is a characterization of a contaminant to be dissolved and which can be simplified by the solvency power of a product also known as the Kauri Butanol Index (KB Index). The second is surface tension,expressed in mN/m. This parameter must be considered because when the cleaning product cannot make contact with the contaminants under or around components,the contaminants cannot be dissolved.
This second parameter drives us to the third point,which is physical parameters like temperature,mechanical activities,and the duration of the process.
The mastery to manage all of these parameters while facing high-tech miniaturization and environmental care,like ROHS,REACH,etc. brings innovation to cleaning in this electronic world.

Our insatiable desire for smaller,faster and highly functional electronic devices presents numerous challenges for package designers and manufacturers. Current day popular approaches include stacked components and boards,high I/O density,and short interconnection distances. Unfortunately,these solutions make flux residue removal from underneath components increasingly difficult. Adding to the challenges are the changing global environmental and safety regulations which make the cleaning task even more challenging. The objectives of this study are to 1) evaluate cleaning effectiveness of several currently available cleaning chemistries/processes in removing flux residues from underneath low standoff height components,2) determine differences in the effectiveness of these individual cleaning processes on Sn/Pb and Pb-free solder paste residues,and 3) evaluate inherent advantages or limitations for each type of cleaning chemistry and process.

The process cleaning rate theorem holds that the static rate (chemical forces) plus the dynamic cleaning rate (mechanical forces) equals the process cleaning rate. New lead-free flux residues result from more demanding soldering drivers created by high soldering temperature,surface tension effects,and
miniaturization. Lead-Free flux compositions require thermal stability,resistance against burn-off,oxidation resistance,oxygen barrier capability,low surface tension,high fluxing capacity,slow wetting,low moisture pickup,high hot viscosity,and halogen free. The static cleaning rate for lead-free flux residues is dramatically different from eutectic tin-lead flux residues. To clean lead-free soils,longer wash exposure time,high cleaning agent concentrations,and high levels of mechanical energy are needed. The purpose of this research paper is to measure the cleaning variability induced by lead-free flux residues and to compare the cleanability of lead-free flux residues to determine the viability of new cleaning agent designs.