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Lead-Free Solutions | Kester

Legislation, Regulation & Direction

Summary of Legislation, Regulations and Directions

USA Legislation

  • Lead has already been banned by law in paint, automobile fuel, food cans, automobile body solders, light bulbs and plumbing solder and fixtures.
  • Lead is permitted in solder for electronics: however, the American Industry was asked by the U.S. EPA to reduce the use of hazardous materials. Lead is currently on its list of hazardous materials.
  • Recycling of solder in electronic products is possible, but could become a large cost.
  • Pressure is mounting from offshore communities to eliminate lead use. NEMI Association has formed a Lead-Free Task Force to investigate alternatives to lead bearing alloys.
  • NCMS -found 3 possible replacements for lead-alloys out of 80 considered -No drop-in replacements
  • An alloy is considered to be lead-free if it contains < 0.2% (but no official definition exists)
  • NEMI at APEX ’00 has named Sn 95.5Ag3.9Cu0.6 (±0.2%) as its choice for a lead-free alloy candidate
  • Intends for North American companies to produce lead-free products by 2004
  • Total lead elimination by 2004 on a voluntary basis
  • Assist in modifying industry standards for Pb-free

Status of the Lead-Free Issue in a Number of States

  • California - Updated list yearly of toxic chemicals
  • Connecticut - General permit for collecting some recyclables (early 2000)
  • Florida - Pilot program of end-of-life for some electronics
  • New Jersey - Pilot program for electronic recycling (3 & 6 graders)
  • South Carolina - Bill introduced on state wide electronics recycling

Japan and Europe “International Lead-Free Soldering Roadmap Framework”

  • Launched at the 2nd Lead-free Summit meeting in November 2002.
  • Iinvolves Europe’s SOLDERTEC and Japan’s JEITA (Japan Electronics and Information Technology Industries Association).
  • Recommendations: – Manufacturers have a complete inventory of lead-free components by the end of 2004. – The recommendation that industry adopts the use of 0.1weight percentage as a maximum allowable percentage lead in “lead-free” products.
  • Agreement on the EU WEEE (Waste Electrical and Electronic Equipment) and RHS (Restriction of Hazardous Substances in Waste Electrical and the Electronic Equipment) Directives.
  • RHS ban on hazardous materials confirmed as July 1, 2006. This directive makes lead-free a requirement for products on sale to European Consumers after this date.
  • In addition to phasing out lead, the RHS mandates a phase out of: – Cadmium – Mercury – Hexavalent Chromium – Two types of brominated flame retardants.
  • Recommends the following schedule for manufacturers. The roadmap suggests that leading manufacturers are expected to conform to these time frames one year ahead of schedule while other manufacturers may reach them 2 years later.
  • Components – Some availability of lead-free components since the end of 2001. – Complete line-up of components with lead-free terminations by the end of 2003. – Complete line-up of lead-free components by the end of 2004.
  • Assemblies: – Manufacturing of lead-free soldered assemblies began by the end of 2002. – Complete lead elimination from products by the end of 2005.
  • The roadmap recommends a solder alloy composed of Sn-Ag-Cu for board assembly. The roadmap recommends that industry leaders develop a system for labeling.

Lead-Free Alloys

The NEMI consortium in USA recommends SnAg3.9Cu0.6 for surface mount reflow soldering and SnCu0.7 for wave soldering. The JEITA lead-free roadmap in Japan recommends SnAg3.0Cu0.5 for reflow soldering with SnAg and SnZnBi as secondary alternatives. JEITA also recommends SnAg3.0Cu0.5 for wave soldering with SnCu as a secondary alternative. The IDEALS consortium in Europe preferred SnAg3.8Cu0.7 for reflow soldering and SnAg3.8Cu0.7Sb0.25 for wave soldering. SOLDERTEC lead-free roadmap in Europe recommends alloy range SnAg(3.4-4.1)Cu(0.45-0.9) for reflow and wave soldering.The SnAgCu family is the alloy of choice for all regions of the world at present. The true eutectic composition has been argued to be within the range SnAg(3.5-3.8)Cu(0.7-1). NIST has defined the true eutectic composition as SnAg3.5Cu0.9 .In Japan 2/3 of companies use SnAgCu for reflow and wave soldering. For surface mount reflow SnAg, SnZnBi, SnAgCuBi and SnInAgBi are also used to a lesser degree. For wave soldering SnCu and SnAg are also used to a lesser degree. About 3/4 of companies use SnAgCu for hand soldering. The predominant SnAgCu alloy in use in Japan is SnAg3.0Cu0.5 and increasing trend elsewhere as well. Kester is a licensee of ISURF SnAgCu(Bi) patent 5,527,628, Senju-Matsushita SnAgCu(Bi) patent 3027441 and Oatey SnAgBiCu patent 4,879,096. Below is a reference listing of Pb-free alloys in order of melting point. It is not meant to be an exhaustive list and is not meant to preclude the potential use of other alloys.

Alloy Melting Point °C Remarks
SnSb5 232-240 Plumbing industry standard in USA; good shear strength and thermal fatigue resistance
SnCu2.0Sb0.8Ag0.2 219-235
Sn 232
SnCu0.7 227 Common low cost alternative for wave soldering
SnAg2.5Cu0.8Sb0.5 217-225 AIM patent
SnAg4.0Cu0.5 217-224 *
SnAg3.9Cu0.6 217-223 * NEMI alloy
SnAg3.5 221
SnAg2.5Bi1.0Cu0.5 214-221
SnAg3.0Cu0.5 217-220 * Predominant alloy in Japan
SnAg3.8Cu0.7 217-218 *
SnAg3.5Cu0.7 217-218 * Commonly used
SnAg2.0Bi3.0Cu0.75 207-218
SnAg3.5Cu0.9 217 * NIST determined to be the true eutectic
SnIn4.0Ag3.5Bi0.5 210-215 Mitsui Metal patent
SnAg3.4Bi4.8 201-215
SnBi7.5Ag2.0 191-216
SnIn8.0Ag3.5Bi0.5 197-208 Matsushita (Panasonic) patent
SnZn9 199 Prone to atmospheric corrosion and oxidation
SnZn8Bi3 191-198 Prone to atmospheric corrosion and oxidation
SnIn20Ag2.8 175-187
SnBi57Ag1 137-139 Motorola patent
SnBi58 138
SnIn52 118

*Note – it is generally agreed that all of these SnAgCu alloys melt at ˜217°C, but published melting range for each alloy varies; the indicated melting range is estimated from NIST phase diagram; in any case NIST determined there will be =0.1% solid material in any of these alloys at 220°C.

Alloy Material Cost vs Sn63Pb37*

Alloy Family Relative Cost Ratio: Sn63Pb37 = 1
SnInAg(Bi) 3.3-3.5
SnAgCu 2.9-3.3
SnAg 3.1
SnAgBi(Cu) 2.4-3.1
SnBiAg(Cu) 2.1-3.1
SnBi 1.7
SnCu 1.5
SnZn(Bi) 1.4

*Note – cost is based on metals market price.

Physical Properties of Lead-free Alloys

SnAgCu(Bi) Alloys

  • Higher melt point lead-free alternative. SnAgCu family is electronics industry standard which in most cases has shown equal or greater thermal cycle fatigue resistance than SnPb.
  • Higher surface tension and poorer wetting than SnPb.
  • Ag provides greater strength but less ductility than Pb.
  • Cu reduces the melting point of the solder. Cu improves thermal cycle fatigue resistance. Cu improves wettability. Cu retards the dissolution rate of copper from boards and components into the molten solder during soldering.
  • Bi reduces melting point of the solder. Bi improves wettability. In the presence of lead from HASL boards or components Bi can greatly reduce thermal cycle fatigue resistance due to the formation of Sn16Pb32Bi52 (MP=95C) which can diffuse along the grain boundaries.

SnBi58(Ag) Alloy

  • Low melt point lead-free alternative potentially suitable for some consumer electronics. Low melt point precludes its use for applications where operating temperature is close to 138C.
  • Large Bi proportion greatly reduces melting point of the solder, but alloy is more brittle. Bi improves wettability, but is somewhat offset by higher oxidation rate. In the presence of lead from HASL boards or components Bi can greatly reduce thermal cycle fatigue resistance due to the formation of Sn16Pb32Bi52 (MP=95C) which can diffuse along the grain boundaries.
  • Small amount of Ag can improve strength and thermal cycle fatigue resistance, assuming the absence of lead.

SnZn(Bi) Alloy

  • Moderate melt point lead-free alternative is only slightly higher than SnPb.
  • Zn lowers melting point. Zn exhibits high oxidation rate and is susceptible to atmospheric corrosion. High oxidation rate precludes it use for wave soldering. Stencil life or shelf life of solder paste may be reduced due to reactive nature of zinc.
  • Bi further lowers melting point. Bi improves wettability and slightly improves corrosion resistance. In the presence of lead from HASL boards or components Bi can greatly reduce thermal cycle fatigue resistance due to the formation of Sn16Pb32Bi52 (MP=95C) which can diffuse along the grain boundaries.

SnInAgBi Alloy

  • Moderate melt point lead-free alternative is lower than SnAgCu.
  • Ag provides strength.
  • Indium reduces melting point. Indium is a ductile material. In the presence of lead from HASL boards or components indium forms a ternary compound that has a phase change at 114C.
  • Bi further lowers melting point and improves wettability. In the presence of lead from HASL boards or components Bi can greatly reduce thermal cycle fatigue resistance due to the formation of Sn16Pb32Bi52 (MP=95C) which can diffuse along the grain boundaries.

Lead-Free Tech Papers

Lead-Free Reflow Profile Recommended reflow profile for Kester solder paste formulations containing the Sn96.5Ag3.5 and Sn96.5Ag3.0Cu0.5 alloys
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K100LD & K100 Case Studies Summary This PowerPoint pictorial examines a successful implementation of K100LD and K100 lead-free alloys at SMT Dynamics and Ayrshire Electronics.
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Standard Reflow Profile The recommended reflow profile for Kester solder pastes manufactured with standard tin/lead alloys.
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K100 Implementation at SMT Dynamics This paper shows results obtained at a contractor in successful builds using SAC305 for reflow soldering and K100 solder for wave assembly.
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Developing a Reliable Lead-free SMT Assembly Process This article offers valuable information to be used during the successful lead-free reflow process implementation.
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How do you create a RoHS Compliancy-Lead-free Roadmap? This article describes the various considerations in the transition to lead-free but also RoHS comnpliancy.
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How do you ready a solder pot for lead-free solder? This article in designed for those cleaning a leaded solder pot to convert it to lead-free solder. It insures the solder is not contaminated with lead during the switchover.
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Implementation of Reliable Lead-free Wave and SMT Processes This article describes the points to consider in transitioning to lead-free wave and reflow soldering.
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Lead-free Hand-soldering – Ending the Nightmares Hand-soldering with lead-free solders can be challenging but not if the points in this article are understood.
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Lead-free Reliability – Building it right the First Time This article describes the comparison done in reference to lead-free and leaded solder joints. The article also gives insight on the points to improve overall reliability with lead-free solders.
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Lead-free SMT Soldering Defects How to Prevent Them This paper shows how avoid soldering defects with lead-free solder pastes. Process control is emphasized to reduce defects.
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Lead-free Wave Soldering This article shows the impact to wave soldering with lead-free materials and how to create a reliable defect free process.
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Creating Solder Joint Reliability with SnCu Based Solders Tin-copper systems with lead-free wave and selective soldering are a growing option. This paper shows how to implement a reliable process using K100 or K100LD SnCu based solders.
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Tin-copper based solder options for lead-free assembly This article details the process changes associated with K100 or K100LD solder systems.
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Case Study on the Validation of SAC305 and SnCu Based Solders in SMT Wave and Hand-soldering This paper describes the work done at a contract assembler who implemented a successful process to build over 500,000 assemblies using both Kester K100 and SAC305 solders.
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