What are the requirements for lead-free solder?

Date：2022-05-31 15:45:00Views：750

What is lead-free solder? Common lead-free solder component Zn can reduce the melting point of Sn. If Zn increases by more than 9%, the melting point will rise, and Bi will reduce Sn Zn, but with the increase of Bi, its brittleness will also increase. Zn can reduce the melting point of Sn. If Zn increases by more than 9%, the melting point will rise, and Bi will reduce Sn Zn, but with the increase of Bi, its brittleness will also increase. This kind of solder is the most commonly used lead-free solder at present. Its performance is relatively stable, and the characteristics of various welding parameters are close to those of lead solder. Although in can reduce the liquidus and solidus of Sn alloy, it has defects such as heat fatigue resistance, ductility, alloy brittleness and poor workability, so this formula is rarely used at present.

The characteristics of lead-free solder are high VSN Ag Cu melting point (217 ℃) and high temperature (260%26plusmn; 3 ℃). V lead free products are the pioneer of green environmental protection, beneficial to human physical and mental health, and non corrosive.After electronic products are scrapped, lead in PCB solder is easy to dissolve in oxygenated water. Polluting water sources and damaging the environment. Solubility makes it accumulate in the human body, damaging nerves, leading to dullness, hypertension, anemia, reproductive dysfunction and other diseases; Excessive concentration may cause cancer. Cherish life, the times require lead-free products.

Requirements for lead-free solder

1. The melting point of lead-free solder is low, which is as close as possible to 183 ℃ of the eutectic temperature of 63/37 Sn Pb alloy. If the eutectic temperature of the new product is only 183 ℃ higher, it should not be a big question, but no such lead-free solder can be actually implemented and meet the welding requirements. In addition, once the lead-free solder with low eutectic temperature is developed, the temperature difference in the melting zone of the lead-free solder should be reduced as much as possible, that is, the temperature range between the solidus and liquidus should be reduced as much as possible. The solidus temperature shall be at least 150 ℃, and the liquidus temperature depends on the specific application (wave soldering tin tape: lower than 265 ℃; tin wire: lower than 375 ℃; patch solder paste: lower than 250 ℃; the reflow soldering temperature is generally required to be lower than 225~230 ℃.

2. Lead free solder shall have prominent moisture; Under normal conditions, the time for the solder to remain above the liquidus during reflow soldering is 30-90 seconds, and the time for the solder pin and the surface of the circuit board substrate to contact the tin liquidus peak during wave soldering is about 4 seconds. In the future, when lead-free solder is used, it is necessary to ensure that the solder can show outstanding moisture function within the above time range to ensure high-quality welding effect.

3. The conductivity and thermal conductivity after welding shall be close to 63/37 tin lead alloy solder.

4. The tensile strength, resistance, ductility and creep resistance of solder joints are similar to those of tin lead alloys.

5. The developed lead-free solder has excellent soldering function with copper base of circuit board, lead-free solder plated on circuit board, lead-free solder plated on component pins or their surfaces.

6. The inspection and repair of welded joints after welding shall be simple.

7. The selected raw materials can be fully supplied for a long time.

8. It is compatible with current equipment technology and can work without replacing the equipment.

9. The newly developed lead-free solder shall match various fluxes as much as possible, and the compatibility shall be as strong as possible. The future development trend is not only to be able to operate with the support of active rosin resin flux (RA), but also suitable for mild weak active rosin flux (RMA) or non cleaning flux without rosin resin.

The above is the content related to lead-free welding compiled by the core detection team. I hope it can help you. Shenzhen Chuangxin Online Testing Technology Co., Ltd. is a well-known professional testing institution for electronic components in China, with 3 standardized laboratories covering an area of more than 1000 square meters. The scope of testing services covers: testing and verification of electronic components, IC authenticity identification, material selection for product design, failure analysis, function testing, factory incoming material inspection, X-ray testing of components and parts, tape braiding and other testing items.