At present, all the countries in the world have put forward the requirements of lead-free printed circuit board and its assembly. Why in the printed circuit board, a lead component is not allowed and the assembly process and product? There are two reasons: one is the lead is toxic, environmental impact; two is the lead in solder applicability is not enough, can not adapt to the new assembly technology. PCB industry should be positive and rapid development of lead-free.Tin lead solder coating on the surface of PCB will cause harm from three aspects:
(1) The processing process will be exposed to lead. The process to contact lead tin lead layer as anti corrosion in electrolytic tin lead pattern plating process, after removing the corrosion of tin lead solder process, hot air leveling (spray tin) process, some hot melt soldering process. Despite the ventilation protective measures in production, long-term exposure will inevitably suffer.
(2) Tin lead electroplating wastewater containing lead, and hot air leveling (HASL) leaded gas impact on the environment. Lead wastewater from electroplating cleaning water and drip or scrap tin lead solution, the water content is less often considered, water treatment and more difficult, so no treatment and into the pool to discharge.
(3) On the printed circuit board containing tin lead plating / coating, the printed board scrap or for use in electronic equipment scrap material which cannot lead recycling, if garbage buried underground after the underground water will Months and years pass by. containing lead, which has polluted the environment. In addition, the use of tin lead solder in the PCB assembly in the wave soldering, reflow soldering or manual welding operation in the presence of lead gas, affecting the human body and the environment, while leaving more lead content on the PCB.
Tin lead alloy solders are not suitable for the current high density interconnect products, which can be used as welding and oxidation resistant coatings. At present, such as printed circuit board coating layer on surface of the world although 60% is the use of HASL tin lead, but met SMT when installing some tiny components PCB welding disc surface is very smooth, and the element is connected with the PCB disk by wire bonding and non welding method, then hot air leveling Tin Lead layer is flat enough. Or not hard enough, or too large contact resistance and other factors, other coatings will adopt non tin lead.
Lead free industrial products in Europe, the first proposed in the world in 90s, the formation of the law to lead the march. Japan is now doing a good job, by 2002, the introduction of lead-free electronic products in general, in 2003 the new products are lead-free solder. Lead free electronic products in the world actively promote.
Full realization of lead free of printed circuit board. At present, in addition to surface coating of tin lead alloy, has been widely used in the organic protective coatings (OSP), electroplating or electroless nickel / gold, a tin plated or immersion tin, a silver plating or immersion silver, as well as the use of palladium, rhodium or platinum and other precious metals. In practical application, the general consumer electronic products using OSP surface finishing suitable performance meet and cheap prices; more durable industrial electronic products using nickel / gold coating, but the relative processing process is complex and the cost is high; the platinum noble metal coating only special requirements of high performance electronic products, the price is very good performance high. At present, it is a good choice to replace the Sn Pb alloy coating by chemical immersion tin or chemical immersion silver. The production process of chemical immersion tin or chemical leaching silver is simpler than chemical immersion nickel / gold, low cost, good weldability and surface smoothness, and high reliability when using lead-free solder.
Lead-free PCB assembly application of lead-free solder has also been realized. Lead free solder is still the main component of tin, tin content in general more than 90%, in addition to silver, copper, indium, zinc or bismuth and other metal components. These alloys have different compositions and different melting temperatures, which can be selected between 140 and 300 DEG C. From the point of view of adaptability and cost factors, the solder joints are different from those of wave soldering, reflow soldering and manual welding.