Laser reflow soldering technology

Update:02-04-2018
Summary:

Perfect spot solder paste system, which can use a varie […]

Perfect spot solder paste system, which can use a variety of technical methods to complete the welding of solder joints according to the heating requirements of different products. Similar to other heating methods, misuse of laser energy can easily burn out parts. The laser heater takes full advantage of the transmission and absorption characteristics of the laser energy and creates a reflow environment based on the reflow characteristics of the solder paste. This can make very difficult welding tasks possible at a very high throughput rate.

Reflow testing with samples has been a mature method to determine if laser reflow is appropriate for the product and the process parameters that must be controlled in order to achieve the desired solder joint quality. Theoretical analysis of how lasers work is one thing, but practical application is another matter. If on a product, the reflow of the solder paste is determined using laser as a viable method, then it is possible to cooperate with the supplier of solder paste and laser equipment systems, and the best combination of product materials and equipment.

Carbon dioxide lasers are the strongest continuous wave lasers available today. Carbon dioxide lasers can produce infrared light with a wavelength of about 10,600 nm and 20% power. CO2 lasers are mostly used for metal cutting and welding. Carbon dioxide lasers are made from yttrium aluminum garnet doped yttrium metal and are commonly referred to as Nd:YAG lasers. The Nd:YAG laser can generate high energy with a wavelength of 1,064 nm in the infrared spectrum. Similar to the CO2 lasers, they are mainly used for cutting and welding metals, and also for marking metals and other materials. High-power diode lasers (HDL) rely mainly on GaAs semiconductor strips. It can provide wavelengths ranging from 790 to 980 nm and output power of 50 watts each. In the past few years, advances in diode cooling technologies that target diode temperature have significantly increased the power, life, and efficiency of diodes.

Some users choose to use laser heating because it is the best option in many ways; while others find that because of the limited available heating means, the laser will be the solution to the heating problems they face. The most direct reason for using laser heating is the desire for non-contact local heating. Although the motivations are different, the goal is the same: the return flow is limited to a certain position and does not spread to other areas, and is completed in a very short time, so as to effectively prevent the other parts of the product from being conducted more heat. .

Solder paste is spotted on all pads before the cable is placed. The laser heating is performed on a line immediately after the spot solder paste process, and the added heat just forms a solder joint. The solder is in the molten state for no more than 3 seconds. The amount of heat conducted to the surface of the glass substrate upon heating is small, preventing thermal expansion from bursting. The appearance of solder joints meets the consistency requirements. As in the previous process, solder paste is soldered at each pin location and each pin is individually heated with a laser. Due to thermal conduction, the first pin has a longer heating time than the fourth pin. The local heating temperature is sufficient and the total heat is safe for plastic parts.