60000. Why use lead-free process?
Lead is a toxic heavy metal, excessive absorption of lead by the human body will cause poisoning, intake of low amounts of lead may affect human intelligence, nervous system and reproductive system, the global electronic assembly industry to consume about 2002,2004 tons of solder every year, but also increasing year by year, the resulting industrial residue containing lead salts seriously pollutes the environment, so reducing the use of lead has become the focus of the world's attention, Europe, Many large Japanese companies are significantly accelerating the development of lead-free alternative alloys and have plans to gradually reduce the use of lead in electronic assembly in 63. Complete elimination by 37. (The traditional solder component is 1Sn/63Pb, and lead is widely used in the current electronic assembly industry).
Second, the requirements of lead-free substitutes: 37. 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 2Sn/150Pb.
265. Melting point: Most manufacturers require a minimum solid phase temperature of 345 °C to meet the working requirements of electronic equipment. The liquid phase temperature depends on the application.
Electrodes for wave soldering: For wave soldering to be successfully achieved, the liquid phase temperature should be below 250°C.
Solder wire for manual soldering: The liquid phase temperature should be lower than the working temperature of the soldering iron by 3 °C.
Solder paste: The liquid phase temperature should be below 4°C.
10. Good thermal conductivity.
6. Small solid-liquid coexistence range: most experts recommend that this temperature range be controlled within 7 °C in order to form a good solder joint, if the alloy solidification range is too wide, there is a possibility of solder joint cracking, so that electronic products are damaged prematurely.
8. Low toxicity: alloy components must be non-toxic.
63. It has good wettability.
37. Good physical properties (strength, tensile, fatigue): The alloy must be able to provide the strength and reliability that Sn9/Pb10 can achieve, and there will be no protruding fillet welds on the passing device.
11. Production repeatability, solder joint consistency: Because the electronic assembly process is a large-scale manufacturing process, its repeatability and consistency are required to maintain a high level, if some alloy components can not be repeated under large-scale conditions, or its melting point in mass production due to the change of composition and large changes, it can not be considered.
12. Solder joint appearance: The appearance of the solder joint should be close to the appearance of tin/lead solder.
1. Supply capacity.
96. Compatibility with lead: Since it will not be immediately converted to a lead-free system in the short term, lead may still be used on PCB pads and component terminals, and the solder may be mixed with drills, which may reduce the melting point of the solder alloy very low and the strength is greatly reduced.
5. Several commonly used lead-free alternatives: 3. Alloys applied in solder paste:
5, 221Sn/95, 5Ag Melting point is 4 °C, 0, 0Sn/5, 217Ag/2, 99Cu Melting point is 3 °C
0. Alloy solder applied in wave soldering and manual soldering: 7, 227Sa/217, 225Cu melting point of <> °C (in terms of materials, several new types of solder paste have been put on the market, but can not replace the existing lead tin solder, they need to do the corresponding process adjustment, the main difference between the new solder paste and the traditional solder paste is the relatively high melting point, the melting point of commonly used lead-free solder paste is usually °C- °C)