What is lead-free soldering? Technical difficulties of lead-free welding

Date：2022-04-07 15:29:12Views：877

What are lead-free electronic products? "Lead free" here refers to Wuxi welding line. Lead free tin wire is a product of welding wire. Tin wire can be divided into lead-free tin wire and lead-free tin wire, both of which are used for the welding of circuit board. Lead free solder wire is also called environmental protection tin wire. Lead free solder wire is also called environmental protection tin wire. Its main components are tin (SN), silver (Ag), copper (Cu), and the rest include trace lead (PB), mercury (Hg), cadmium (CD), polybrominated biphenyls (PBBs), etc. It is characterized by less rosin, less harmful gas, less volatile gas, no smell on the inner surface, and no smell. With ROHS logo, it has fully passed SGS detection and does not pollute the environment. So, what is lead-free soldering? What are the technical difficulties of lead-free welding?

Lead free welding requires high equipment, high welding temperature and expensive equipment and welding materials. The main advantages are non-toxic, pollution-free and environmental protection. Generally, products exported to developed countries and regions such as the European Union and the United States are required to be lead-free.

1. The melting point of lead-free solder should be low, as close as possible to the eutectic temperature of 63 / 37 tin lead alloy 183 ℃. If the eutectic temperature of new products is only a few degrees higher than 183 ℃, it should not be a big problem. However, there is no such lead-free solder that can be really popularized and meet the welding requirements at present; In addition, before developing lead-free solder with low eutectic temperature, the melting interval temperature difference of lead-free solder should be reduced as much as possible, that is, the temperature range between solidus and liquidus should be reduced as much as possible, and the minimum solidus temperature is 150 ℃, The liquidus temperature depends on the specific application (tin bar for wave soldering: below 265 ℃; tin wire: below 375 ℃; solder paste for SMT: below 250 ℃. Generally, the reflow temperature should be lower than 225 ~ 230 ℃).

2. Lead free solder should have good wettability; Generally, the time for the solder to stay above the liquidus during reflow soldering is 30 ~ 90 seconds, and the time for the solder pin and the base plate surface of the circuit board to contact with the tin wave peak during wave soldering is about 4 seconds. After using lead-free solder, it is necessary to ensure that the solder can show good wettability within the above time range to ensure high-quality welding effect;

3. The conductivity and thermal conductivity after welding should be close to that of 63 / 37 Sn Pb alloy solder;

4. The tensile strength, toughness, ductility and creep resistance of solder joints are not much different from those of tin lead alloy;

5. Reduce the cost as much as possible; At present, it can be controlled at 1.5 ~ 2 times of tin lead alloy, which is an ideal price;

6. The developed lead-free solder has good brazing performance with the copper base of the circuit board, the lead-free solder plated on the circuit board, the lead-free solder on the component pin or its surface and other metal coatings;

7. The newly developed lead-free solder should match all kinds of flux as much as possible, and the compatibility should be as strong as possible; It can not only work with the support of active rosin resin flux (RA), but also apply mild, weak active rosin flux (RMA) or non cleaning flux without rosin resin, which is the future development trend;

8. After welding, the inspection and repair of welding joints shall be easy;

9. The selected raw materials can meet the long-term sufficient supply;

10. It is compatible with the equipment and process currently used and can work without replacing the equipment.

Technical difficulties of lead-free welding

1. Increased manufacturing costs: PCB components, welding materials, flux, equipment, personnel, etc;

2. The difficulty of processing technology increases: the welding temperature of lead-free solder increases and the process window is narrow;

3. High requirements for production equipment: wave soldering, reflow soldering, visual inspection equipment, on-line test equipment, repair equipment, etc;

4. Increase of working pressure: designate the person in charge to complete the preparation work, determine the leader schedule, instrument and equipment value-added budget, etc;

5. Reduced production quality: lead content in incoming materials, reduced brightness of solder joints, increased residue, increased difficulty of on-line testing, increased surface insulation resistance, etc.

In conclusion, lead-free welding technology explores from the current research results that the melting point temperature of alternative alloys is higher than that of existing tin lead alloys. This article is introduced here. I hope it can be helpful to you. We will bring more wonderful content later. The company's testing services cover: electronic component testing and verification, IC authenticity identification, product design and material selection, failure analysis, function testing, factory incoming material inspection, tape braiding and other testing items. Welcome to call Chuangxin testing. We will serve you wholeheartedly.