LEADFREE KISS PROCESS KEEPITSIMPLESOLDERING SUPERIOR FLUX MFG CO

LEAD-FREE, KISS PROCESS (KEEP-IT-SIMPLE-SOLDERING) SUPERIOR FLUX & MFG. CO. 6615 Parkland Blvd. Cleveland, OH 44139

OBJECTIVE OF LEAD-FREE SOLDER WEEE/Ro. HS and Japanese regulations originally set July 1, 2006 as the date when electronics assembly be Lead. Free. n Primary Reason: Landfill Lead Leaching into Soil.

ELECTRONICS USE OF LEAD Electronics assembly represents 0. 30. 5% overall use of lead*. n With such a small use of lead, why is electronics targeted? Number of landfills led to this legislation; the high profile of electronics in ‘garbage dumps’; and the ‘wealth’ of the highly profitable electronics market. * Source: Alpha. Metals div. of Alpha/Fry Group.

ELECTRONIC PRODUCTS Electronics targeted for addressing European legislation removing lead from landfills. n A wide variety of Tin/Lead solders are used in televisions, cell phones, telephones, computers and monitors, and other consumer products. Adding electronic assemblies to Lead. Free list continues the removal of Lead from solder, that is now standard for plumbing solders.

WHO HAS CONDUCTED LEAD-FREE RESEARCH? Primary American research has taken place at the Department of Energy’s (DOE) Ames Laboratory at Iowa State University, under Dr. Iver Anderson, who has conducted research into Tin/Lead alternatives and arrived at a patent for the basis of the SAC alloys. The alloy that they have patented and recommend is a ternary alloy combination of: Sn: 93. 6% Ag: 4. 7% Cu: 1. 7% Eutectic Melt Point: 217ºC

ADDITIONAL LEAD-FREE ‘SAC’ ALLOYS While the previous terneray ‘SAC’ alloy is the patented solder, new ‘SAC’ alloy solders have been presented to the market by a number of different metals/solder companies: 1 2 3 Sn : 96. 5 95. 8 Ag: 3. 0 4. 0 3. 5 Cu: 0. 5 0. 7 Additional ‘SAC’ Alloy Solders are also available. These different alloy combinations all claim a ‘Eutectic’ of 217ºC.

BINARY EUTECTIC ALLOYS While the talk has been of ternary ‘SAC’ alloy Lead-Free solders, there are binary options: 1 2 Sn 96. 5 99. 3 Ag 3. 5 -Cu -0. 7 Eutectic 221ºC 227ºC

…AND STILL MORE Additional Lead-Free Alloys Exist n 42 Sn/58 Bi: 138ºC Eutectic n 95 Sn/5 Sb: Plastic range 232 -240ºC n n 96. 2 Sn/2. 5 Ag/0. 8 Cu/0. 5 Sb: 218ºC Eutectic (AIM Castin® Solder) 91 Tin/9 Zinc: and many more… 199ºC Eutectic

DEFINITION OF EUTECTIC Eutectic: Designating or of a mixture or alloy with a melting point lower than that of any other combination of the same components. * Most widely used metals in electronics solders and metal melt-points**: n n n n • • Tin (Sn): Lead (Pb): Silver (Ag): Copper Cu): Indium (In): Bismuth (Bi): Antimony (Sb): Melting Point Melting Point *Source: Webster’s New World Dictionary ** Source: Merck Index, Twelfth Edition 232ºC 327. 4ºC 960. 5ºC 1083ºC 155ºC 271ºC 630ºC

FACTORS IN LEAD-FREE SOLDER COMPOSITION The key factor in selecting a Lead-Free solder has been driven by price, cost, and temperature requirements. Tin price, which has increased more than 100% since 1/1/2003, rises from 63% of solder content to a minimum of 93. 6%. n This raises price, cost, and temperature of Lead-Free Solders. Other alloys, such as bismuth and indium, used in fusible alloys, have too low a melt-point for reliability and stability of finished products; are too weak as solder alloys and may yield unreliable field dependability; or too expensive due to limited global supply. Antimony, long used in industrial applications, has been kept from electronics applications for many years due to a high temperature requirement, and, if too much antimony is used, yield a weak joint that may peel over time and cause electric failure.

WITH SO MANY LEAD-FREE SOLDERS TO CHOOSE FROM, WHY IS IT SO DIFFICULT? The Eutectic melt-point of 63 Tin/37 Lead alloy is 183ºC. The lowest melt Eutectic Lead-Free alloys used primarily as fusible alloys, 48 Sn/52 In is 118ºC and 42 Sn/58 Bi is 138ºC, are too low for stable and dependable life-cycle reliance use in a vast majority of applications. 91 Sn/9 Zn is 199ºC, currently used in aluminum soldering applications, is closer to the 183ºC base-line melt-point of the current industry standard , but the alloy is too corrosive for electronics applications.

WHICH FOCUSES THE ALLOY BASE TO… This leads to the Tin-Based Alloys, which include: n n 100 Sn: Melt-point of 232ºC 99. 3 Sn/0. 7 Cu: Eutectic of 227ºC 96. 5 Sn/3. 5 Ag: Eutectic of 221ºC ‘SAC’ Alloys: claim Eutectic of 218ºC Actual plastic phase of 218 -220ºC n n AIM Castin® Alloy: Eutectic of 218ºC Kester SAF-A-LLOY: Plastic 219 -235ºC

TIN PROPERTIES All Lead-Free alloys, that meet the requirements for electronics applications, are high tin-content alloys. All melt-points with these alloys are, a minimum, of 34ºC above the Eutectic Tin/Lead Solder. Tin, by itself, is a corrosive metal that requires changes in the solder pots or lining of solder baths used for wave soldering or solder dip applications. Post-solder tin-based alloys must be watched for “Tin Whiskers” that occur over time as the alloy ‘settles’ and forces out tin spikes from a previously flat surface. Tin reacts with copper and creates tin/copper Intermetallics that can cause metal cracking or embrittle the alloy.

‘BACK TO THE FUTURE’ While legislation from Europe and the Far East is leading to the removal of Lead from the electronics assembly process: Lead-Free soldering is not new! When surface mount technology (SMT) reflow soldering was introduced, double- sided boards were reflowed in a two step process: n Step One: 96. 5 Sn/3. 5 Ag with 221ºC reflow was the first side. n Step Two: 63 Sn/37 Pb with 183ºC reflow was the second side. The dual alloy process was incorporated to create a 38 ºC temperature difference between the Eutectic Melt-points of the solders. This included stability in alloys that allowed the dual reflow process to take place that did not displace or cause any alterations to the first process step that incorporated the Sn/Ag alloy. At the time, metallurgical properties included an alloy that, today, can be used as a Lead-Free alloy with a proven track record. When US Mil Standards were used to establish which alloys were acceptable in SATCOM and Aerospace applications, the only Lead. Free alloy that was proven and, therefore, specified, was 96. 5 Sn/3. 5 Ag, meeting specification QQ-S-571.

KISS LEAD-FREE Given the variety of different Lead-Free Solders, Binary: 96. 5 Sn/3. 5 Ag, 99. 3 Sn/0. 7 Cu Ternary SAC Alloys: 93. 6 Sn/4. 7 Ag/1. 7 Cu, 96. 5 Sn/3. 0 Ag/0. 5 Cu, 95. 8 Sn/3. 5 Ag/0. 7 Cu, 95. 5 Sn/4. 0/Ag/0. 5 Cu, and others. Quad Alloys: 96. 2 Sn/2. 5 Ag/0. 8 Cu/0. 5 Sb Five or more alloy solders: Include Tin, Copper, Silver, Bismuth, Indium, and other combinations A number of critical factors must be considered, but all lead to: KEEP-IT-SIMPLE-SOLDERING!!!

ARE THE ALLOYS PROVEN FOR ELECTRONICS? The only alloy which meets military specifications and has been subjected to life tests that meet SATCOM requirements is 96. 5 Sn/3. 5 Ag binary Eutectic alloy of 221ºC. n The fewer metal elements in any solder alloy make for a more reliable, dependable solder and are similar to the 63 Sn/37 Pb in terms of binary formulation, solder stability, and Eutectic consistency. The IPC, to date, has not written any specifications under the ANSI-J-STD 004, 005, 006 Standards for Lead-Free alloys. Potential patent infringement has led to the variety of different ‘SAC’ Alloys all claiming to be Eutectic. This has led to a re-definition of Eutectic to include a plastic range of 218 -220ºC as ‘Eutectic’.

WHAT DOES LEAD-FREE SOLDER CONNECT WITH BEST? Silver Immersion is recommended for PCB coating over HAL, Gold, OSP and other PCB finishes. n The Lead-Free solders that are emerging as ‘the choice’ are generally a combination of alloys containing Silver. Having a like-to-a-like in the Silver Immersion PCBs and the Solders ensures a better fusion of solder to PCBs in assembly processes.

SHEAR STRENGTH VS. DUCTILITY In all tests conducted to prove a Lead-Free Solder can be used to replace Sn/Pb, the ‘strength’ of the solder, defined by Shear Strength, is the factor employed to determine how reliable a solder will be. Tin/Lead solder will always lose to the Lead-Free alloys, which have greater shear strength. n However, the ductility, or ability to be forgiving, is overlooked as the true strength for the Tin/Lead solders that have been the industry standard for more than 50 years. n The Lead-Free Alloys, with high tin-content are more prone to: Cracking than tin/lead, due to the tensile strength and lower ductility. Tin Whiskers in the event that the alloy-balance is altered by metals content and fluctuation over time. Tin/Copper Intermetallics developing between the tin and copper reaction.

PCB ASSEMBLY PROCESS SMT Reflow (Recommended alloys: 96. 5 Sn/3. 5 Ag, SAC Alloys) Higher temperature and longer time profiles are necessary to accommodate the higher melt-point of Lead-Free alloys. Components, sensitive to high temperatures, must be carefully monitored to ensure that over-heating does not affect reliability. Once established, thermal profiling must be strictly adhered to, to ensure consistent PCB output Wave Soldering (Recommended Alloy: 99. 3 Sn/0. 7 Cu*) Solder pots formulated for Tin/Lead solders must be replaced or retrofit with a special lining to ensure that the tin does not corrode, or ‘eat-away’, at the metal-lining of the pot and corrupt the solder. Solder temperature must be raised from 235 -250ºC to 260 -290ºC (or higher) to create similar flow action to the tin/lead solder onto, and up into, the PCB leads and joints. Higher solder temperatures create greater dross than the lower temperature of the Tin/Lead solders. The use of nitrogen on the solder bath can greatly improve flow and reduce dross content on the solders. *Ask Superior Flux about this alloy vs. SAC and other alloy recommendations.

SOLDER PASTES AND FLUXES SMT REFLOW Conventional solder paste mediums can, and should be used, for all Lead-Free solder alloys and provide: n n n No slumping. No tomb-stoning No white residues on PCBs Non-halide Activation system Consistent rheology, thixotropy, and viscosity. Clear, pin-testable residues with all No-Cleans. WAVE SOLDERING Fluxes n n When going Lead-Free, consider a VOC-Free/Lead-Free operation for workplace and environmental safety. No-Clean fluxes require more activity to meet the higher temperature requirements of the Lead-Free Solder process. Water-Soluble fluxes, with higher solids contents and activity levels, can be used as drop-in fluxes. VOC-Free and Alcohol-based fluxes all meet the process and performance requirements for Lead-Free applications in watersoluble and No-Clean formulations.

REFLOW OPTIONS Vapor Phase n Can use a fixed temperature of 230ºC with the Lead-Free Alloys, but must maintain consistent process time at temperature phases. Convection n Recommended temperature is 245250ºC and must maintain 45 -60 seconds at temperature.

LEAD-FREE REFLOW PROFILE 4ºC does not make a difference in Reflow Profiles for the Lead-Free alloys.

PRICE OF SOLDER AND COST OF OPERATIONS Question anyone who tells you that the Lead-Free conversion only costs ‘tenths of a penny per PCB joint’. Lead-Free alloys are more expensive than Tin/Lead and the costs of the joints add up. But this is not the sole cost added in the conversion: n Engineering costs and the time invested in establishing and developing a consistent process adds rapidly. n Higher melt point of solders require hotter ovens and solder pots, which increase capital equipment operations and maintenance costs. n Potential for using nitrogen, an additional consumable, increases in Lead-Free wave solder applications to reduce dross and extend solder life. n Capital equipment costs, such as hotter ovens for reflow and retrofitted or new solder baths for wave soldering add-up. n Rework and repair will likely increase at the outset of any operation/process change.

SUMMARY OF LEAD-FREE SOLDERING The new Lead-Free solders are meeting legislation, not metallurgical/scientific discovery. If Lead-Free soldering offers so many advantages, and Lead -Free solders have been used in many applications for many years, why was it not chosen as the base alloy until legislation forced it upon the electronics industry? All Lead-Free alloys will be more costly than the Tin/Lead solder, as will operation and process costs. All Lead-Free alloys that are being touted as the ‘best choice’ have a higher melt point than 63 Sn/37 Pb solder. Higher solder temperature will push the semiconductors and components to the edge of performance. Multiple alloys are developing as the standard for SMT and Wave Soldering, but the industry, as a whole, have not formulated a global standard for the solder alloys and performance characteristics.

CONCLUSION KEEP-IT-SIMPLE- SOLDERING SMT Reflow The sole long proven alloy that meets Lead-Free requirements is 96. 5 Sn/3. 5 Ag. It is a binary alloy with a true Eutectic of 221 ºC. If a SAC Alloy is the specification that must be met, the closest alloy to the Tin/Silver Eutectic is 96. 5 Sn/3. 0 Ag/0. 5 Cu. The melt point falls in the 218 -220ºC range and is not different, in terms of setting process guidelines, than the Tin/Silver. However, with copper as part of the solder, potential tin/copper Intermetallics and/or whiskers must be investigated. Wave Soldering A 99. 3 Sn/0. 7 Cu, due to cost and a wider process window available in this process, make this 227ºC Eutectic alloy the preferred choice. However, with copper as part of the solder, potential tin/copper Intermetallics and/or whiskers must be investigated. Again, if a SAC alloy is specified, the 96. 5 Sn/3. 0 Ag/0. 5 Cu is recommended to maintain consistency of boards used in Reflow and Wave soldering. With copper as part of the solder, potential tin/copper Intermetallics and/or whiskers must be investigated.

CONCLUSION KEEP-IT-SIMPLE- SOLDERING SMT Reflow and Wave applications actually show that there may be alloys that meet the specific Lead-Free soldering processes, while maintaining a simple process approach to the Lead-Free conversion. The assembly processes must be evaluated from a number of different angles, and the final process must bring these elements together. This includes: n Metallurgical n Chemical n Temperatures n Timing n Acceptable output levels n How to minimize rework and repair All PCBs must be given extended time, after initial process evaluations have been conducted, to ensure stability, longlife, and dependability of the PCBs that have been converted to the Lead-Free alloys.

LEAD-FREE, KISS PROCESS (KEEP-IT-SIMPLE-SOLDERING) SUPERIOR FLUX & MFG. Co. 6615 Parkland Blvd. Cleveland, OH 44139