Environmental and health issues with lead
The Environmental Protection Agency (EPA) announced lead and its compounds as one of the 17 chemical poisons that threat human life and environment. When lead accumulates in the body for a long time, it will produce adverse health effects. The Environmental Protection Agency (EPA) announced lead and its compounds as one of the 17 chemical poisons that threat human life and environment. When lead accumulates in the body for a long time, it will produce adverse health effects because lead combines strongly to proteins in the body and prohibits normal functions of proteins in the human body, which causes disorder of nervous and reproductive system resulting in delaying neurological and physical development. Those effects are some of the adverse effects of lead on human health. When the level of lead in the blood exceeds 50 mg/dl of blood, lead poisoning is considerable enough to occur the adverse effects. Lead level even below the official threshold causes hazardous situation to humane neurological and physical development, especially for children.
Lead-free alloy selection
The descried issues forced one to perform examining and understanding of the implications for lead-free alternatives to tin-lead eutectic solder. The Department of Trade and Industry (DTI) developed a progressive report on the selection of lead-free solder. DTI first tasked the introducing a possible lead free solder alternatives. Once a material is selected, DTI manufactured a sample with the selected material on the same procedure of manufacturing lead-based alloys, and tested the sample to see the performance which should be equivalent to the lead-based alloys. The criteria of selecting lead-free alternatives to tin-lead eutectic solder are follows: The descried issues forced one to perform examining and understanding of the implications for lead-free alternatives to tin-lead eutectic solder. The Department of Trade and Industry (DTI) developed a progressive report on the selection of lead-free solder. DTI first tasked the introducing a possible lead free solder alternatives. Once a material is selected, DTI manufactured a sample with the selected material on the same procedure of manufacturing lead-based alloys, and tested the sample to see the performance which should be equivalent to the lead-based alloys. The criteria of selecting lead-free alternatives to tin-lead eutectic solder are follows:
1. The lead-free alloy stays with at most ternary alloys if possible. Quaternary alloys may make control difficult.
2. The lead-free alloy should be located in near the eutectic point. If it would be far away from the point, the solder have large pasty range during cool-down.
3. The lead-free alloy should have similar melting point comparing with tin-lead alloy in order to use existing manufacturing equipments.
4. The lead-free alloy should be equal or better characteristics than tin-lead alloy in reliability when it is used in electronics assembly.
5. The lead-free alloy should create equal or less cost comparing with tin-lead alloy.
6. If possible, the lead-free solder should be free from the existing patents.
7. The information of lead-free solder should be well known in the industry.
8. The lead free solder should be free from the health and environment issues.
Transient Liquid Phase Bonding (Cu/Sn/Cu structure)
Candidate alloy compositions
The second task to select the alternatives is to find a lead free solder that is free from patents of alloys because more than 30 companies have already achieved the patent about technologies and components related to lead-free alloy. Based on the criteria for selecting new lead-free alloys, the International Electronics Manufacturing Initiative evaluated more than 79 solder alloys, and then selected the solder alloy in the following:The second task to select the alternatives is to find a lead free solder that is free from patents of alloys because more than 30 companies have already achieved the patent about technologies and components related to lead-free alloy. Based on the criteria for selecting new lead-free alloys, the International Electronics Manufacturing Initiative evaluated more than 79 solder alloys, and then selected the solder alloy in the following:
1. Sn-Bi alloy
2. Sn-Zn (or Sn-Zn-Bi) alloy
3. Sn-Ag (or Sn-Ag-Bi) alloy
4. Sn-Ag-Cu alloy
5. Sn-Ag alloy
6. Sn-Cu alloy