Definition and classification of welding quality issues: In SMT applications, the quality of the weld of the product can be described by the following definitions。 “A certain degree of mechanical and electrical performance can be maintained during the intended use environment, method and lifetime。”
Since July 1, 2006, the European WEEE (Electrical and Electronic Equipment Waste) Guide clearly stipulates that the import of lead-containing electronic products is prohibited, and the product with the highest lead content (by weight) not exceeding 1000 ppm is marked as “green”. Environmentally friendly products. The industry must develop the ideal solder and corresponding processing equipment to meet the current requirements of lead-free production.
Sn96.5Ag3Cu0.5 and Sn95.5Ag4Cu0.5 lead-free alloys are suitable for the replacement of Sn63 alloy. This Sn97Ag3 and Sn96Ag4 variant is used to stabilize/reduce the copper content, which requires the wavesolder bath to depend on the lead-free wave soldering process conditions. With all the alpha metal rod solder, Alpha's proprietary Vaculy® alloying process is used to remove impurities, especially certain oxides.
First, the reasons for the lead-free process, why should we change the lead-free wave soldering, lead-free reflow soldering equipment? Lead is a toxic heavy metal. Excessive absorption by the human body can cause poisoning. Ingestion of small amounts may affect human reproduction, nervous system and intelligence system. Now the global electronics industry consumes about 60,000 tons of solder per year, and this figure is still Increasingly, the resulting lead-salt industrial waste is seriously polluting the environment, and the world has called for a reduction in the use of lead. Many large companies in Europe and Japan, which are at the forefront, are vigorously developing lead-free replacement alloys, which have been realized in 2002. In the beginning of the year, the use of lead was gradually reduced in the assembly of electronic products. In 2004, the massive use of lead in industry was completely eliminated. (Currently in the electronics industry, the widely used lead is the traditional solder composition 63Sn/37Pb).
Lead-free wave soldering is increasingly popular with manufacturers because of its independence from the work space。 However, most of the lead-free wave soldering materials on the market are placed in the middle slot, which is not only unsightly and easy to damage, but also generates noise when pushing and pulling。
I believe that everyone knows about the lead-free wave soldering. Below I will collect the system and introduce a lead-free wave soldering for everyone. Including concepts - classification - advantages and uses.
Many people believe that the conversion of tin-lead (SnPb) to lead-free can be achieved by directly adding lead-free solder to an existing wave soldering machine. Others believe that it is necessary to use a new type of wave soldering machine in the lead-free process.
1. The European Union passed the Act in 1998. It has been clear that from January 1, 2004, lead-free solder should not be used in any electronic products. 2. Since 1997, the National Manufacturing Science Center (NCMS) lead-free soldering project, jointly conducted by 11 industrial groups and national laboratories in the United States, has completed a four-year plan to identify and evaluate tin/lead solder substitutes. The purpose of the project is to determine whether lead-containing solders in the manufacture of electronic products are safe, reliable, non-toxic and economical alternatives. 3. Japanese companies' self-defined lead-free targets and products for batch production
1。 The higher melting point sharply reduces the process window。 The melting point of lead-tin solder is 183 ° C, the temperature of complete liquefaction is 205 ° C - 215 ° C, and the limit temperature of printed circuit board is 230 ° C - 240 ° C, the existing process The balance is 15 °C-35 °C; the common lead-free solder has a melting point of 217 °C-220 °C, and its complete liquefaction temperature is 225 °C-235 °C。 Since the board temperature of the PCB does not change, the process margin is reduced to 5 ° C - 15 ° C, if the narrow process margin requires reflow ovens now have high repeatability, and a tight circuit board indicates temperature difference。
1. Alloys used in solder paste: 96, 5Sn/3, 5Ag Melting point is 221°C95, 5Sn/4, 0Ag/0, 5Cu Melting point is 217°C 2. Alloy solder used in wave soldering and hand soldering: 99, 3Sa/0, 7Cu melting point is 227 ° C (In terms of materials, several new solder pastes have been put on the market, but they cannot replace the existing lead-tin solders. They all need to be adjusted accordingly. The main difference between the new solder pastes and the traditional solder pastes is that the melting point is relatively high. High, commonly used lead-free solder paste melting point is usually 217 ° C -225 ° C)
1。 Price: Many manufacturers require that the price cannot be higher than 63Sn/37Pn, but at present, the finished products of lead-free substitutes are 35% higher than 63Sn/37Pb。
Lead is a toxic heavy metal. Excessive absorption of lead in the human body can cause poisoning. Low intake of lead may affect human intelligence, nervous system and reproductive system. The global electronic assembly industry consumes about 60,000 tons per year. Solder, and it is increasing year by year, the industrial residue containing lead salt is seriously polluting the environment, so reducing the use of lead has become the focus of attention around the world. Many large companies in Europe and Japan are accelerating the development of lead-free alternative alloys. And has planned to gradually reduce the use of lead in electronic product assembly in 2002. Completely eliminated by 2004. (Traditional solder composition 63Sn/37Pb, lead is widely used in the current electronic assembly industry)
>The pursuit of miniaturization of electronic products, the previously used perforated plug-in components have been unable to reduce the functionality of electronic products more complete, the integrated circuit (IC) used has no perforated components, especially large-scale, high-integration ICs, have to use surface patches element. >Product batching, production automation, the factory must produce high-quality products at low cost and high yield to meet customer needs and strengthen the development of market competitive electronic components; > The development of integrated circuits (ICs), the multi-application of semiconductor materials, the electronic technology revolution is imperative, chasing the international trend.
>High assembly density, small size and light weight of electronic products。 The size and weight of patch components are only about 1/10 of that of traditional plug-in components。 After SMT is generally used, the volume of electronic products is reduced by 40%~60%, and the weight is reduced by 60%。 ~80%。 >High reliability and strong anti-vibration ability。 The solder joint defect rate is low。 >High frequency characteristics are good。 Reduced electromagnetic and radio frequency interference。 > Easy to automate and increase productivity。 Reduce costs by 30% to 50%。 > Save materials, energy, equipment, manpower, time, etc。
SMT is the surface mount technology (short for Surface Mounted Technology) and is currently the most popular technology and process in the electronics assembly industry。