The difference between laser welding and reflow soldering in PCBA processing

As all types of electronic products begin to trend towards miniaturization, the application of traditional welding technology on various new electronic components faces certain challenges. In order to cater to such market demand, welding process technology can be said to be constantly improving, and welding methods are becoming more diversified. This article selects the traditional welding method reflow soldering and the innovative laser welding method for comparison, so that we can more clearly see the convenience brought to us by technological innovation.

Introduction to reflow soldering

The most obvious difference between reflow soldering and traditional wave soldering is that in traditional wave soldering, the lower part of the PCB is completely immersed in liquid solder, while in reflow soldering, only some specific areas are in contact with the solder. During the welding process, the position of the solder head is fixed, and the robot drives the PCB to move in all directions. Flux must also be pre-applied before soldering. Compared with wave soldering, flux is only applied to the lower part of the PCB to be soldered, rather than the entire PCB.

Reflow soldering adopts the mode of first applying flux, then preheating the circuit board/activating the flux, and then using a soldering nozzle for soldering. Traditional manual soldering iron welding requires point-to-point welding of each point of the circuit board, so there are many welding operators. Wave soldering adopts an assembly line industrial mass production model. Welding nozzles of different sizes can be used for batch welding. Usually, the welding efficiency can be improved dozens of times compared with manual welding (depending on the design of the specific circuit board). Due to the use of a programmable movable small tin cylinder and various flexible and diverse welding nozzles (the capacity of the tin cylinder is about 11 kg), certain fixing screws and reinforcements under the circuit board can be avoided through program settings during welding. Ribs and other parts to avoid damage caused by contact with high-temperature solder. This kind of welding mode does not require the use of customized welding trays, etc., and is very suitable for multi-variety, small-batch production.

Reflow soldering has the following obvious characteristics:

●Universal welding carrier

●Nitrogen closed loop control

●FTP (File Transfer Protocol) network connection

●Optional dual-station nozzle

●Flux

●Preheating

●Collaborative design of three welding modules (preheating module, welding module, circuit board transmission module)

●Flux spraying

●Crest height calibration tool

●GERBER (data input) file import

●Can be edited offline

In the soldering of through-hole component circuit boards, reflow soldering has the following advantages:

●High production efficiency in welding and the ability to achieve a high degree of automated welding

●Precise control of flux injection position and amount, microwave peak height, and welding position

●Able to protect the surface of microwave peaks with nitrogen; optimize the process parameters of each solder joint

●Quick replacement of nozzles of different sizes

●Technology that combines fixed-point welding of a single solder joint and sequential welding of through-hole connector pins in rows

●The "fat" or "thin" shape of the solder joint can be set according to the requirements.

●A variety of preheating modules (infrared, hot air) and preheating modules added above the board are optional

●Electromagnetic pump maintenance-free

●The selection of structural materials is fully suitable for the application of lead-free solder

●Modular structural design reduces maintenance time

Introduction to laser welding

The light source of green laser welding uses laser light-emitting diodes, which can be accurately focused on the solder joint through an optical system. The advantage of laser welding is that it can precisely control and optimize the energy required for welding. Its applicable occasions are selective reflow soldering process or connectors using tin wire. If it is an SMD component, you need to apply solder paste first and then solder it. The soldering process is divided into two steps: first, the solder paste needs to be heated, and the solder joints are also preheated. Afterwards, the solder paste used for soldering is completely melted, and the solder completely wets the pad, finally forming a solder. Using laser generator and optical focusing component for welding, it has high energy density and high heat transfer efficiency. It is non-contact welding. The solder can be solder paste or tin wire. It is especially suitable for welding solder joints or small solder joints in small spaces with low power and energy saving. .

Laser welding features:

●Multi-axis servo motor board control, high positioning accuracy

●The laser spot is small and has obvious welding advantages on small-sized pads and spacing devices.

●Non-contact welding, no mechanical stress or static electricity risk

●No tin slag, reducing flux waste and low production cost

●Rich types of weldable products

●Multiple solder options

Advantages of laser welding:

For ultra-miniaturized electronic substrates and multi-layered electrical components, "traditional processes" are no longer applicable, which has prompted rapid technological advancement. The processing of ultra-fine parts that are not suitable for traditional soldering iron methods is finally completed by laser welding. "Non-contact welding" is the biggest advantage of laser welding. There is no need to touch the substrate or electronic components at all, and soldering is provided only by laser irradiation without causing physical burden. Efficient heating with a blue laser beam is also a major advantage, allowing the irradiation of narrow areas that are inaccessible to the soldering iron tip and changing angles when there is no distance between adjacent components in dense assembly. The soldering iron tip needs to be replaced regularly, while laser welding requires very few replacement parts and has low maintenance costs.