We know that the SMT rework process requires the operator's skilled operation technology and good rework tools to work closely together. When rework, care must be taken to prevent overheating of the circuit board and components, otherwise it is very easy to cause plated through holes, components and components on the circuit board. Damage to the pad. The following Sanjing let everyone know about several common SMT component rework soldering techniques:

(1) Contact soldering: The characteristic of contact soldering is to use a heated electric soldering iron head or ring to directly contact the soldering medium. After a certain period of time, an acceptable solder joint is formed at a specific position. The soldering medium includes pads, solder wires, and flux. And other substances.

The welding head is used to heat a single welding point, and the welding ring is used to heat multiple welding points at the same time. Welding heads come in various forms such as single-head, double-head, or four-sided surround, and are mainly used for component removal. The shape design of the soldering ring is mainly used for the desoldering of multi-pin components of bilateral and peripheral pin packages, such as the desoldering of components such as integrated circuits.

Features of contact welding: ①The cost of soldering is relatively low; ②The pre-fixed components can be easily removed with a solder ring; ③The soldering iron ring must directly contact the soldering points and pins to get the corresponding heating efficiency; ④No Electric soldering tips or welding rings with limited welding temperature are susceptible to temperature shocks, which may damage ceramic components, especially multilayer capacitors.

(2) Heating gas (hot air) welding: Hot air welding uses a nozzle to guide heated air or inert gas (such as nitrogen) to the solder joints and pins to complete the soldering heating process.

Since the hot air system is uniformly heated, the local thermal stress that may occur in contact welding can be avoided. The adjustable temperature range of hot air is generally 300~400℃, and the time required to melt solder depends on the amount of hot air.

The structure design of the hot air nozzle of the hot air welding system is very important. Most of them have two parts: one is the vacuum nozzle, which is used for disassembly or welding to pick up and place the components; the other is the hot air diversion cavity, which is mainly used to remove the heat generated by the repair device. The airflow is directed to the disassembled or welded components, and the second function is to maintain local heat.

Compared with contact welding, hot air welding has the following advantages: as a heat transfer medium, hot air has low heat transfer efficiency, can effectively reduce the thermal shock caused by high heating rate, and can eliminate the physical damage that may be caused by the heat medium, and the temperature and temperature of the system The heating rate is controllable, repeatable, and predictable; the price of the equipment ranges from low to high, and the selection range is wide. However, the automatic hot-air welding system is more complicated and requires the operator to have a higher technical level.

The above is the introduction of the types and characteristics of SMT component rework soldering technology, I hope it can be helpful to everyone!