CN117340378A

CN117340378A - Mini LED combined laser welding process

Info

Publication number: CN117340378A
Application number: CN202311565518.5A
Authority: CN
Inventors: 张军; 赵俊龙
Original assignee: Chengdu Hongrui Photoelectric Technology Co ltd
Current assignee: Chengdu Hongrui Photoelectric Technology Co ltd
Priority date: 2023-11-22
Filing date: 2023-11-22
Publication date: 2024-01-05

Abstract

The application provides a Mini LED combined laser welding process, and relates to the technical field of laser welding. A Mini LED combined laser welding process comprises the following steps: preheating: slowly heating the PCBA processed by the patch to volatilize a solvent in the soldering paste on the PCBA to obtain a preheated part; and (3) constant temperature treatment: conveying the preheating piece to a constant temperature treatment area through a conveying belt, and slowly heating to obtain a constant temperature piece; and (3) reflow soldering treatment: conveying the constant-temperature part to a reflow soldering area through a conveying belt, and heating by laser to obtain a soldering part; and (3) cooling treatment: and conveying the welding parts to a cooling area through a conveying belt, and cooling to room temperature to finish the welding treatment. The Mini LED direct display product welded by the process has high welding yield, high efficiency and long service life of the laser, and is also suitable for industrial automatic production.

Description

Mini LED combined laser welding process

Technical Field

The application relates to the technical field of laser welding, in particular to a Mini LED combined laser welding process.

Background

The nitrogen reflow soldering mainly fills nitrogen in the reflow soldering hearth, and the contact between the air in the reflow soldering hearth and the element is blocked as much as possible, so that the oxygen content in the hearth is very small, the contact between the element and the oxygen can be avoided during soldering, and the soldering quality is greatly enhanced. The nitrogen reflow soldering is mainly applied to precise electronic products such as aerospace, automobiles, medical treatment and the like, and has very high requirements on quality reliability and stability.

At present, a Mini LED (sub-millimeter light emitting diode) direct display product in the industry is welded by adopting traditional nitrogen reflow soldering, and as the melting points of two soldering tin in the lead-free PCBA (printed circuit board assembly) process and the secondary soldering are close, a welding process window is smaller, and cold soldering and chip falling occur. Since cold welding and chip dropping are not individual phenomena, the welding is completed by a large factor and cannot be repaired pertinently. Laser soldering is thus an effective way to address PCB (printed circuit board) cold soldering and chip dropping.

Laser welding is a highly efficient and precise welding method that uses a laser beam of high energy density as a heat source. The method is mainly used for welding thin-wall materials and low-speed welding, the welding process belongs to heat conduction, namely laser radiation is used for heating the surface of a workpiece, surface heat is diffused to the inside through heat conduction, and the workpiece is melted by controlling parameters such as the width, the energy, the peak power, the repetition frequency and the like of laser pulse, so that a specific molten pool is formed. Because of its unique advantages, it has been successfully applied to precision welding of micro and small parts.

But the current industry uses a low-power laser which can only correspond to a point scanning mode and has too low efficiency; the high-power laser device is required to be matched with operation, the high-power laser device is high in manufacturing cost, and the high-power laser device is rapid in ageing and short in service life, is not suitable for workshop automatic production, and cannot meet production requirements.

Therefore, a laser welding process which effectively improves the welding yield, has high efficiency and long service life of a laser and is suitable for industrial automatic production is urgently needed.

Disclosure of Invention

The purpose of the application is to provide a Mini LED combined laser welding process, which has the advantages of effectively improving the welding yield, being high in efficiency, being long in service life of a laser and being suitable for industrial automatic production.

In order to solve the problems, the invention adopts the technical method that:

the embodiment of the application provides a Mini LED combined laser welding process, which comprises the following steps:

preheating: slowly heating the PCBA processed by the patch to volatilize a solvent in the soldering paste on the PCBA to obtain a preheated part;

and (3) constant temperature treatment: conveying the preheating piece to a constant temperature treatment area through a conveying belt, and slowly heating to obtain a constant temperature piece;

and (3) reflow soldering treatment: conveying the constant-temperature part to a reflow soldering area through a conveying belt, and heating by laser to obtain a soldering part;

and (3) cooling treatment: and conveying the welding parts to a cooling area through a conveying belt, and cooling to room temperature to finish the welding treatment.

In some embodiments of the present application, the laser heating described above employs an area array light source.

In some embodiments of the present application, the PCBA is heated to 140-160 ℃ at a rate of 1-2 ℃/s.

In some embodiments of the present application, the preheating member is heated to 190-210 ℃.

In some embodiments of the present application, the thermostatic element is heated to 230-260 ℃ by a laser at a speed of 5 ℃/s, the power of the laser being less than 100W.

In some embodiments of the present application, the weld cooling rate is 3-5 ℃/s.

Compared with the prior art, the invention of the application has at least the following advantages or beneficial effects:

the Mini LED direct display product welded by the process has high welding yield, high efficiency and long service life of the laser, and is also suitable for industrial automatic production.

Specifically, the solvent in the soldering paste can be removed through preheating the PCBA in the preheating treatment step, so that the solvent volatilization process and the soldering process are prevented from overlapping in the subsequent soldering process, the formation of cavities is avoided, and the soldering quality is improved.

And then the temperature of the preheating piece is uniform in the constant temperature treatment step, the thermal stress impact entering the reflow area is reduced (the shock cooling and the heat shock can lead to the deformation of the bonding pad), the cell tearing caused by the thermal expansion and the cold contraction of soldering tin can be avoided, cold welding is formed, some welding defects (original tilting, cold welding of a large volume of original and the like) can be avoided, meanwhile, the soldering flux in the soldering paste can be subjected to active reaction, the wettability of the surface of the preheating piece is increased, the soldering paste can be well wetted on the surface of the preheating piece, the subsequent laser welding effect is guaranteed in the subsequent reflow welding process, the solvent in the soldering paste can be further removed, and the formation of a cavity is further guaranteed.

Then, in the reflow soldering step, the constant-temperature piece is subjected to laser heating soldering, at the moment, the soldering paste is melted and subjected to wetting reaction, an intermetallic compound layer is formed, and finally, the peak temperature is reached, so that the soldering of the constant-temperature piece is completed; the temperature of the laser heating welding spot is fast, the heat conduction speed of the PCB is slow, when the front surface is completely melted, the back surface is not melted, and the risk problem of component falling can be effectively solved (traditional nitrogen reflow soldering in the prior art, when soldering, the PCBA is heated by nitrogen hot air because the melting points of two soldering tin are close to each other in secondary soldering, and the PCBA is heated indiscriminately due to the characteristic of a hot air circulation mode, so that a soldering process window is smaller, and the chip falling occurs); and because of adopting preheating treatment and constant temperature treatment in advance, when welding, can use the area array laser of miniwatt (found after the research of this application inventor, weld in the same time, ordinary laser welding needs to rise to about 260 ℃ from the room temperature, around 230 ℃ of difference in temperature, and this application is through preheating the back, around 210 ℃ to 260 ℃ of rising to about 50 ℃ of difference in temperature, according to W=PT know, can reduce the laser power several times after preheating), can reduce welding cost, can also promote welding efficiency, and because the laser power is low, can improve the durability of laser, make the laser longe-lived, the reliability is high.

And finally, cooling the welding piece through an air cooler in the cooling treatment step, wherein the cooling treatment step and the welding step are not in the same cavity, so that the hot air and the cold air are not doped and fused, the welding speed is high, and the microstructure of the welding spot can be thinned due to the high cooling speed. The morphology and the distribution of intermetallic compounds are changed, the mechanical property of the solder alloy is improved, and the defects can be reduced and the reliability is improved by improving the cooling rate under the condition that the lead-free welding is not adversely affected.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered limiting the scope, and that other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a welding flow chart of a Mini LED combined laser welding process according to an embodiment of the present application;

FIG. 2 is a graph comparing the effect of conventional nitrogen reflow soldering and laser reflow soldering of the present application;

FIG. 3 is a product diagram of example 2;

fig. 4 is a product diagram of comparative example 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The present application will be described in detail with reference to specific examples.

The application embodiment provides a Mini LED combined laser welding process, referring to FIG. 1, comprising the following steps:

Then, in the reflow soldering step, the constant-temperature piece is subjected to laser heating soldering, at the moment, the soldering paste is melted and subjected to wetting reaction, an intermetallic compound layer is formed, and finally, the peak temperature is reached, so that the soldering of the constant-temperature piece is completed; the temperature of the laser heating welding spot is fast, the heat conduction speed of the PCB is slow, when the front surface is completely melted, the back surface is not melted yet, and the risk problem of component falling can be effectively solved (traditional nitrogen reflow soldering in the prior art, when soldering, the PCBA is heated by nitrogen hot air because the melting points of two soldering tin are close to each other in secondary soldering, and the PCBA is heated indiscriminately due to the characteristic of a hot air circulation mode, so that a welding process window is small, and the chip falling happens, referring to FIG. 2); and because of adopting preheating treatment and constant temperature treatment in advance, when welding, can use the area array laser of miniwatt (found after the research of this application inventor, weld in the same time, ordinary laser welding needs to rise to about 260 ℃ from the room temperature, around 230 ℃ of difference in temperature, and this application is through preheating the back, around 210 ℃ to 260 ℃ of rising to about 50 ℃ of difference in temperature, according to W=PT know, can reduce the laser power several times after preheating), can reduce welding cost, can also promote welding efficiency, and because the laser power is low, can improve the durability of laser, make the laser longe-lived, the reliability is high.

In some embodiments of the present application, the laser heating described above employs an area array light source. The area heated by the area array light source is larger than the heating area of the spot laser and the line laser, so that the efficiency is higher, the compatibility of position tolerance is strong, the alignment is not needed, the full irradiation of welding spots of the constant-temperature piece during welding can be ensured, the welding effect is further ensured, and the sealing performance and the precision of welding can be improved.

In some embodiments of the present application, the PCBA is heated to 140-160 ℃ at a rate of 1-2 ℃/s. The inventor of the application researches and discovers that the external organic solvent is volatilized rapidly to form a hard film caused by too fast temperature rise, and at the moment, the internal components of the hard film volatilize to form bubbles, so that the external hard film is burst, and the welding precision is affected; and too slow a temperature rise can also affect welding efficiency. Based on the above, the inventor of the application slowly heats the PCBA at the speed of 1-2 ℃/s, and can ensure the welding precision on the basis of ensuring the welding efficiency.

In some embodiments of the present application, the preheating member is heated to 190-210 ℃ at a rate of 1-2 ℃/s. The solder paste can be attached to the melting point of the solder paste after being heated to 190-210 ℃, but the solder paste cannot be melted, and the subsequent welding can be facilitated.

In some embodiments of the present application, the weld cooling rate is 3-5 ℃/s. The cooling at the speed can change the microstructure of the welding spot, thereby improving the welding effect, reducing the generation of defects, improving the welding reliability and avoiding the occurrence of the phenomenon of falling of chips.

In some embodiments of the present application, the solder paste is SAC305 solder paste.

The features and capabilities of the present application are described in further detail below in connection with the examples.

Example 1

A Mini LED combined laser welding process comprises the following steps:

preheating: heating the PCBA processed by the patch to 140 ℃ at a speed of 1 ℃/s to volatilize a solvent in soldering paste on the PCBA to obtain a preheated part;

and (3) constant temperature treatment: conveying the preheating piece to a constant temperature treatment area through a conveying belt, and slowly heating to 190 ℃ at a speed of 1 ℃/s to obtain a constant temperature piece;

and (3) reflow soldering treatment: conveying the constant-temperature part to a reflow soldering area through a conveying belt, and heating to 230 ℃ at a speed of 5 ℃/s through laser of a laser to obtain a soldering part;

and (3) cooling treatment: and conveying the welding piece to a cooling area through a conveying belt, and cooling to room temperature at a speed of 3 ℃/s to finish the welding treatment.

Example 2

A Mini LED combined laser welding process comprises the following steps:

preheating: heating the PCBA processed by the patch to 150 ℃ at the speed of 1.5 ℃/s, and volatilizing the solvent in the soldering paste on the PCBA to obtain a preheated part;

and (3) constant temperature treatment: conveying the preheating piece to a constant temperature treatment area through a conveying belt, and slowly heating to 200 ℃ at a speed of 1.5 ℃/s to obtain a constant temperature piece;

and (3) reflow soldering treatment: conveying the constant-temperature part to a reflow soldering area through a conveying belt, and heating to 240 ℃ at a speed of 5 ℃/s through laser of a laser to obtain a soldering part;

and (3) cooling treatment: the weldment was transported to a cooling zone by a conveyor belt and cooled to room temperature at a rate of 4 c/s, completing the welding process, as shown in fig. 3.

Looking at fig. 3, it can be seen that the product of fig. 3 has a smooth surface, free of bubbles and cracks.

Example 3

A Mini LED combined laser welding process comprises the following steps:

preheating: heating the PCBA processed by the patch to 160 ℃ at the speed of 2 ℃/s, and volatilizing a solvent in the soldering paste on the PCBA to obtain a preheated part;

and (3) constant temperature treatment: conveying the preheating piece to a constant temperature treatment area through a conveying belt, and slowly heating to 210 ℃ at the speed of 2 ℃/s to obtain a constant temperature piece;

and (3) reflow soldering treatment: conveying the constant-temperature part to a reflow soldering area through a conveying belt, and heating to 260 ℃ at a speed of 5 ℃/s through laser of a laser to obtain a soldering part;

and (3) cooling treatment: and conveying the welding piece to a cooling area through a conveying belt, and cooling to room temperature at a speed of 4 ℃/s to finish the welding treatment.

Comparative example 1

This comparative example is substantially identical to example 2, except that: the PCBA was warmed up at a rate of 3 ℃/s.

The welded product is shown in fig. 4.

Comparing fig. 3-4, it can be seen that there are significant bubbles, particularly framed portions, on the surface of the product of fig. 4, due to the too high temperature, resulting in rapid volatilization of the external organic solvent to form the hard film, which in turn volatilizes the internal components of the hard film to form bubbles, resulting in burst of the external hard film.

In conclusion, the Mini LED direct display product welded by the process has high welding yield, high efficiency and long service life of the laser, and is also suitable for industrial automatic production.

The embodiments described above are some, but not all, of the embodiments of the present application. The detailed description of the embodiments of the present application is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.

Claims

1. The Mini LED combined laser welding process is characterized by comprising the following steps of:

2. The combined Mini LED laser welding process according to claim 1, wherein the laser heating uses an area array light source.

3. The Mini LED combination laser welding process of claim 1, wherein said PCBA is warmed to 140-160 ℃ at a rate of 1-2 ℃/s.

4. The Mini LED combination laser welding process of claim 1, wherein said pre-heat is heated to 190-210 ℃ at a rate of 1-2 ℃/s.

5. The Mini LED combination laser welding process of claim 1, wherein said thermostatic element is heated to 230-260 ℃ by laser light at a rate of 5 ℃/s, said laser light having a power of less than 100W.

6. The Mini LED combination laser welding process of claim 1, wherein the weld cooling rate is 3-5 ℃/s.