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). Second, some lead-free alternatives commonly used in the market: 1. Alloy solder used in wave soldering and reflow 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 wave solder paste melting point is usually 217 ° C -225 ° C) 2. Alloys used in solder paste: 96, 5Sn/3, 5Ag melting point is 221 ° C 95, 5 Sn / 4, 0 Ag / 0, 5 Cu melting point is 217 ° C Third, what kind of lead-free substitutes meet the requirements: 1, conductivity. 2, has good wettability. 3. Good thermal conductivity. 4. Smaller solid-liquid coexistence range: Most experts recommend that this temperature range be controlled within 10 °C to form a good solder joint. If the solidification range of the alloy is too wide, there is a possibility that cracking of the lead-free wave solder joint may occur, causing premature failure of the electronic product. 5. Supply capacity. 6. Repeatability of production, consistency of solder joints: Since the electronic assembly process is a high-volume manufacturing process, it is required to maintain a high level of repeatability and consistency, if some alloy components cannot be in high-volume conditions. Repeated manufacturing, or its melting point in the mass production, due to changes in composition, can not be considered. 7. Appearance of solder joints: The appearance of solder joints should be close to the appearance of tin/lead solder. 8. Compatibility with lead: Since it will not be fully transformed into a lead-free system in the short term, lead may still be used on the terminals of PCB pads and components. If solder is mixed, it may cause solder alloy. The melting point is very low and the strength is greatly reduced. 9, low toxicity: alloy components must be non-toxic. 10. Good physical properties (strength, tensile, fatigue): The alloy must be able to provide the strength and reliability that Sn63/Pb37 can achieve without protruding fillet welds through the device. 11. 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. 12. Melting point: Most manufacturers require a solid phase temperature of at least 150 ° C to meet the working requirements of electronic equipment. The liquidus temperature will depend on the specific application. Wave soldering electrode: For successful lead-free wave soldering, the liquidus temperature should be lower than 265 °C. Solder wire for manual soldering: The liquidus temperature should be lower than the soldering iron operating temperature of 345 °C. Solder paste: The liquidus temperature should be below 250 °C. Fourth, the temperature curve of reflow soldering: 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 reflow 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 board is not changed, 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. 2. The liquefaction time is longer: the liquefaction time of the traditional lead solder paste is 40s-60s; the liquefaction time of the lead-free reflow solder paste is generally 60s-90s. If the liquefaction time and the liquefaction temperature are guaranteed, there will inevitably be a very high peak temperature of about 260 ° C, which will inevitably cause thermal shock or even damage to the PCB board and components. Solution: 1 The same production capacity does not shorten the overall size of the heating zone to reduce oxidation; 2 The independent temperature is reduced, and the number of heating zones is increased to facilitate process adjustment; 3 Use more than 2 heating temperature zones to make the welding temperature zone; 4 The preheating temperature of the flux is unchanged before the tin melting; 5 Design a new type of intermediate support device to reduce the problem of large deviation due to the intermediate support device. 6 It is recommended to use a nitrogen protection process (not necessary);