In the complex transition from lead to lead-free, many challenges are involved, such as soldering materials (lead-free alloys, flux), printed boards (materials, plating), electronic components, lead-free processes, SMT processing Equipment, chip processing technology, welding reliability and cost, etc.

Some process defects are often encountered in lead-free soldering (as shown in the figure below), including: tombstones, solder balls, voids, electromigration, black disks, peeling, Kirkendall voids, etc. These defects directly affect the reliability of lead-free soldering. Therefore, specific problems should be analyzed for each type of defect.

Next, I will mainly introduce the reliability of lead-free soldering.

Compared with tin-lead processes, cold soldering, tin beading, bridging, electromigration, tombstones, voids, tin whiskers and insufficient strength of solder joints, embrittlement, etc., are defects with a higher incidence of lead-free processes. Due to the difference between the material properties of lead-free solder and lead-tin materials, many related reliability problems have been caused. The second is that the melting point of lead-free solder is higher. The melting point of SAC lead-free alloy is about 217°C, while the traditional 63/37 Sn/Pb eutectic solder joint is 183°C. Therefore, the peak temperature of the temperature curve is greatly increased. The increase of the curve will bring about problems such as easy oxidation of solder and rapid growth of intermetallic compounds. In addition, since the solder does not contain lead, the wettability of the solder is poor, which easily causes the self-alignment ability, tensile strength, and shear strength of the solder joints of the product to fail to meet the requirements.

In addition, due to the high lead-free soldering temperature, the growth rate of intermetallic compounds (MC) is relatively fast, and it is easy to cause cracks at the interface and cause failure.

Since lead-free has not been implemented for a long time, there are still many imperfections. At present, internationally, the reliability of lead-free products and lead-free solder joints (including test methods) is still in the initial research stage. There are still uncertain factors in the long-term reliability of lead-free solder joints. Therefore, the implementation of high-reliability products is not The lead process must carefully consider long-term reliability issues.