PCB News - PCB manufacturers, the main difficulties and corresponding strategies of lead-free soldering iron

PCB manufacturers, the main difficulties and corresponding strategies of lead-free soldering iron

The so-called lead-free soldering means that the solder used for soldering PCB is not allowed to contain Pb, and the content of Pb in the commonly used solder is as high as 40%. The key to achieving Pb-free soldering is to find a Pb-free solder that can replace the current lead solder. Leaded solder has been used for hundreds of years, because this solder has a series of superior properties, is cheap, and has sufficient reserves.

In the past 20 years, the electronics industry and related scientific and technological circles all over the world have devoted a lot of manpower and material resources to the research and development of Pb-free solder. However, due to the demanding requirements of this new electronic material, the progress is not ideal. At present, only relatively good Sn-Ag-Cu alloys can be used as temporary substitutes for Sn-Pb alloys.

Sn-Ag-Cu solder is currently the main variety used for Pb-free soldering. Sn-Ag-Cu series alloys are commonly used SAC305-Sn-3.OAg- 0.5Cu, SAC405-Sn-4.OAg- 0.5Cu.

Compared with the 63/37Sn-Pb solder, the fatal defects of SAC305 and SAC405 are as follows:

1. High melting point (SAC is about 220 degree Celsius, Sn-Pb is about 183 degree Celsius);

2. Poor wettability (the wettability of SAC is equivalent to about 70% of Sn-Pb).

The main problem caused by the increase in the melting point of lead-free solder is to reduce the process window. The variable range of welding operating temperature is significantly reduced. This not only brings difficulties to the process, but also easily jeopardizes the performance of the substrate and components due to over-temperature, coupled with the poor wettability of the error-free solder, which increases the difficulty of lead-free soldering.

In order to meet the needs of lead-free soldering iron, the current main countermeasures are as follows:

1. Carry out technical training for operators, first understand the characteristics of lead-free soldering in theory, and be fully prepared for consciousness.

2. PID temperature-controlled electric soldering iron is used to ensure the stable and correct temperature of the soldering iron.

3. Select the solder wire. Sn-Ag-Cu series solder wire is preferred, in which the Ag content can be 1%, not necessarily 3%~4%, the diameter of the solder wire can be thick or thick, and Sn-Ag-Cu-In-X series can be selected if necessary Solder wire.

4. Practice operational skills. When soldering, add solder to the base metal for a certain preheating time (generally no more than 3s). Pay attention and be cautious when operating.

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