CN116944676A

CN116944676A - Laser welding process method for LED flip chip

Info

Publication number: CN116944676A
Application number: CN202311100811.4A
Authority: CN
Inventors: 李旸; 张国生
Original assignee: Beijing Institute of Graphic Communication
Current assignee: Beijing Institute of Graphic Communication
Priority date: 2023-08-30
Filing date: 2023-08-30
Publication date: 2023-10-27

Abstract

The invention discloses a laser welding process method of an LED flip chip, which comprises the following steps: the controller controls the X-Y motion control platform to move, so that the circuit board with the LED flip chip die bonding completed enters the center of the visual field of the machine vision device, and an image template of the LED flip chip and related circuits after die bonding is set; setting position parameters of the LED flip chip; adjusting the Z-direction height, XY position and pitching angle of the laser to enable the two laser sources to synchronously indicate light spots to symmetrically irradiate on a circuit outside the edge of the positive electrode pad and the negative electrode pad of the LED flip chip; the laser irradiates a circuit outside the edge of the positive electrode bonding pad and the negative electrode bonding pad of the LED flip chip according to set duration and power, and heat energy is transferred to the bonding pad position through the circuit to finish the welding of the LED flip chip; and automatically identifying the positions of the LED flip chips to be welded, and completing LED flip chip welding one by one. The method utilizes the laser beam and the optimized welding parameters to accurately control the welding position and energy, and realizes the high-precision and high-efficiency welding of the chip and the substrate.

Description

Laser welding process method for LED flip chip

Technical Field

The invention relates to the technical field of chip welding, in particular to a laser welding process method of an LED flip chip.

Background

Currently, conventional LED flip chips use solder paste or eutectic bonding, but among others, reflow soldering suffers from the following drawbacks:

the thermal resistance is high: in flip chips, the electrodes need to be connected to the metal substrate by solder paste. However, solder paste has relatively poor thermal conductivity, resulting in high thermal resistance. This may lead to higher temperatures of the LED chip during operation, affecting its performance and lifetime.

Thermal expansion mismatch: the LED chip and the metal substrate have different coefficients of thermal expansion. During operation, thermal expansion mismatch between the two may cause stress concentration of the solder joint due to temperature variations, resulting in cracking or failure of the solder joint.

The welding quality is unstable: manual operations and conventional solder paste soldering techniques may lead to instability in the solder quality. Artifacts or improper process parameter settings during the welding process may cause problems such as poor welding, missing welding, short circuits, etc.

Limiting heat dissipation design: because of the poor heat conduction performance of solder paste, the heat dissipation design of flip chips is limited to a certain extent. The difficulty in heat dissipation may cause the temperature of the LED chip to rise, thereby affecting its brightness and lifetime.

In addition, the eutectic furnace adopted in the prior eutectic welding has the defect that inert gas protection is needed in a vacuum state during welding, and a high-power fan or water cooling equipment is needed for ensuring that the cooling curve is rapidly reduced, so that the corresponding eutectic furnace equipment has high manufacturing cost. Meanwhile, the range of the practical weldable working area in the hearth of the eutectic furnace is smaller, the working efficiency is lower, and the industrial continuous batch on-line production is not facilitated.

Therefore, how to solve the defect of the conventional flip-chip bonding of the LED has prompted people to seek better flip-chip bonding technology to improve performance and reliability. Which is a problem to be solved by those skilled in the art.

Disclosure of Invention

In view of the above, the invention provides a laser welding process method for an LED flip chip, which can solve the problems of welding quality defect in solder paste welding and low production efficiency and high equipment complexity cost of eutectic furnace welding in the prior art.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

the invention provides a laser welding process method of an LED flip chip, which adopts laser welding equipment of the LED flip chip to realize the laser welding of the LED flip chip, and specifically comprises the following steps:

(1) The controller controls the X-Y motion control platform to move, so that a circuit board which is fixed on the fixed clamp and is subjected to LED flip chip die bonding enters the center of the visual field of the machine vision device, and an image template of the LED flip chip and related circuits which are not welded after die bonding is set through the machine vision device;

(2) Setting the position parameters of all the LED flip chips to be welded on the circuit board on a controller;

(3) Adjusting the Z-direction height, XY position and pitching angle of a first laser source and a second laser source in the laser, so that synchronous indication light spots of the two laser sources are symmetrically irradiated on a circuit outside the edge of a positive electrode pad and a negative electrode pad of the LED flip chip;

(4) Adjusting the laser to enable the diameter of the synchronous indication light spot of the laser to be matched with the width of the circuit;

(5) Setting the output power and irradiation time length of two laser sources on a controller;

(6) According to the set position parameters of the LED flip chip, synchronously starting two laser sources, emitting laser to irradiate on a circuit outside the edge of a positive electrode bonding pad and a negative electrode bonding pad of the LED flip chip, and transmitting heat energy to the bonding pad position through the circuit to finish the laser welding of the LED flip chip and the circuit;

(7) The controller controls the X-Y motion control console to automatically move in the X-Y direction, and laser welding of all the LED flip chips and the circuits is sequentially completed according to the image templates of the LED flip chips and related circuits and the position parameters of the LED flip chips on the circuit board; until the end.

Further, the step (2) includes:

setting chip spacing and arrangement path data at a controller end through a graphical interface according to the position requirement of the LED flip chip;

or the setting of the chip spacing and the arrangement path data is realized by inputting the setting file.

Further, in the step (6), the laser welding temperature is the temperature of the LED flip chip bonding pad, the temperature range is 180-450 ℃, and the laser soldering and the laser eutectic welding are realized.

Further, the laser welding apparatus of the LED flip chip includes: the device comprises a device body, wherein a machine vision device, a laser, a fixed clamp, an X-Y motion console and a controller are arranged on the device body;

the controller is respectively connected with the machine vision device, the laser and the X-Y motion console;

the fixed clamp is arranged on the X-Y motion console and is used for fixedly bearing a cylindrical circuit or a plane circuit; under the control of the controller on the X-Y motion console, the axial rotation, horizontal displacement or horizontal displacement of the plane circuit of the cylindrical circuit is realized;

the laser comprises two laser light sources, the working time length and the output power of the laser are set under the control of the controller, and the preset position of a synchronous indication facula of the laser on a cylindrical circuit or a plane circuit is set, so that the LED flip chip is welded on the cylindrical circuit or the plane circuit;

the machine vision device is arranged between the two laser light sources, captures real-time images of the cylindrical circuit or the plane circuit, is used for identifying and positioning the bonding pad and the chip, and sends the real-time images to the controller.

Further, the machine vision device is a CCD camera.

Further, the two laser sources are symmetrically arranged on two sides of the machine vision device, are movably connected with the cross rod on the same cross rod, and are adjustable in up-down, left-right direction and pitching angle.

Further, the fixing clamp is provided with a tensioning shaft structure and is used for clamping the cylindrical circuit.

Further, the fixing clamp is provided with a positioning structure and a negative pressure adsorption structure and is used for positioning and fixing the planar circuit.

Compared with the prior art, the invention discloses a laser welding process method for an LED flip chip, which comprises the following steps: the controller controls the X-Y motion control platform to move, so that the circuit board with the LED flip chip die bonding completed enters the center of the visual field of the machine vision device, and an image template of the LED flip chip and related circuits which are not welded after die bonding is set; setting position parameters of the LED flip chip; adjusting the Z-direction height, XY position and pitching angle of the laser to enable the two laser sources to synchronously indicate light spots to symmetrically irradiate on a circuit outside the edge of the positive electrode pad and the negative electrode pad of the LED flip chip; the laser irradiates a circuit outside the edge of a positive and negative bonding pad of the LED flip chip according to set duration and power, and transmits heat energy to the bonding pad position through the circuit to finish laser welding of the LED flip chip; and identifying positions of the LED flip chips to be welded, and completing LED flip chip welding one by one. The method utilizes the laser beam and the optimized welding parameters to precisely control the welding position and energy, and realizes the high-precision and high-efficiency welding of the chip and the substrate.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of a laser welding device for an LED flip chip according to the present invention.

Fig. 2 is a schematic diagram of a fixing clamp with a tensioning shaft structure.

Fig. 3 is a schematic diagram of a positioning structure and a negative pressure adsorption structure of a fixing clamp provided by the invention.

Fig. 4 is a flowchart of a laser welding process method of an LED flip chip provided by the present invention.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Because the bonding pad of the flip chip faces downwards, laser is difficult to irradiate the bonding pad, and therefore, related products and technologies for welding the LED flip chip by the laser do not exist at home and abroad. The embodiment of the invention discloses a laser welding process method of an LED flip chip, which considers that silver is adopted as a circuit on a substrate, has good heat conductivity, and can consider that laser is irradiated to the edge of the chip, namely the silver circuit, and the heat conduction of silver is utilized to be conducted under a bonding pad so as to realize the laser welding of the chip.

The welding mode comprises the following steps: laser solder paste welding (tin soldering) and laser eutectic welding. The difference is that the soldering is at about 180-300 degrees of laser temperature, and the eutectic soldering is at about 300-450 degrees of laser temperature. If the spot solder paste realizes laser soldering, a reflow soldering mode can be replaced; if the point scaling powder realizes eutectic laser welding, the vacuum heating eutectic welding mode of the eutectic furnace is replaced.

Example 1:

the invention adopts the laser welding equipment of the LED flip chip to realize the laser welding of the LED flip chip, wherein the laser welding equipment of the LED flip chip comprises the following components as shown in figure 1: the apparatus body 1, which is a main body of the entire apparatus, provides a position and support for the installation of each key component. The equipment body is provided with a machine vision device 11, a laser 12, a fixed clamp 13, an X-Y motion console 14 and a controller 15; the fixing clamp is shown in fig. 2, and is provided with a tensioning shaft structure and is used for clamping a cylindrical circuit and ensuring the stability of welding. In addition, the fixing clamp can also be provided with a positioning structure and a negative pressure adsorption structure as shown in fig. 3, and is used for accurately positioning and fixing the plane circuit.

Wherein the controller 15 is respectively connected with the machine vision device 11, the laser 12 and the X-Y motion console 14; the fixed clamp 13 is arranged on the X-Y motion console 14 and is used for fixing a cylindrical circuit or a planar circuit;

the X-Y motion console 14 provides multi-axis motion control so that the welding process can be precisely adjusted in multiple directions. Under the control of the controller 15 to the X-Y motion console, the axial rotation, horizontal displacement or horizontal displacement of the cylindrical circuit or the plane circuit is realized.

As shown in fig. 2, the tensioning shaft structure includes: rubber pad 21, inflatable shaft 22, inflatable shaft base 23, fastening nut 24, gear 25 and air tube 26;

wherein, a rubber pad 21 is installed at the outer circumference of the inflatable shaft 22 for increasing friction and providing buffering; ensuring that proper pressure is provided while clamping the cylinder circuit while protecting the cylinder circuit from damage. The inflatable shaft 22 is arranged on the inflatable shaft base 23, and one end of the inflatable shaft 22 is sequentially connected with the fastening nut 24 and the gear 25; one end of the air pipe 26 is connected with one end of the tensioning shaft through a through hole or a pipeline on the inflatable shaft base 23, and the other end is used for being connected with an air source.

And (2) base: the base is the base part of the tensioning shaft and is usually made of metal. It has mounting holes or slots for securing the tensioning shaft and there is usually a reserved securing location in the device. The base must be firmly installed in the apparatus to ensure stability of the tensioning shaft.

The gear of the tensioning shaft is a central component part for connecting all parts of the tensioning shaft, and the gear is generally cylindrical and is made of metal; the tension shaft has the functions of supporting and transmitting in the integral structure of the tension shaft.

The inflatable shaft is a core component of the tensioning shaft and is generally made of materials such as metal, rubber and the like. The shaft has a special structure, and the diameter can be adjusted by inflation or deflation so as to control the clamping force. When the inflatable shaft is inflated, the rubber pad is ejected out by an air bag in the inflatable shaft, and the diameter of the inflatable shaft is increased, so that a roller or a clamp of the inflatable shaft clamps a cylindrical circuit; when air leakage occurs, the rubber pad is contracted into the air inflation shaft, the diameter of the air inflation shaft is reduced, and the clamping of the column surface circuit is released.

The gear on the tensioning shaft is connected with the motor through a rubber belt, and the motor is controlled by the controller to drive the air expansion shaft to axially rotate, so that the air expansion shaft can rotate when needed. The air pipe is used for supplying air or exhausting air to the inflatable shaft, so that the inflatable shaft is inflated and deflated. The air pipe is connected to one end of the tensioning shaft and is connected with an air source through a through hole or a pipeline on the base.

The cylindrical circuit is clamped by adjusting the inflatable shaft, so that stable clamping effect is ensured in the circuit.

As shown in fig. 3, the fixing jig has a positioning structure and a negative pressure suction structure for precisely positioning and fixing the planar circuit. The fixing clamp is used for placing a planar circuit board, for example, the size of the adaptable maximum circuit board is 200mm by 300mm. The positioning structure of the fixing clamp is used for positioning the planar circuit board. The negative pressure adsorption structure has a negative pressure adsorption function, and can adsorb the glass or ceramic substrate circuit board on the surface of the tray, so that the displacement of the planar circuit board in the moving process is prevented.

In specific implementation, the positioning structure adopts female hole positioning: the fixture surface is provided with a convex female hole, and the corresponding position on the planar circuit board is provided with a corresponding groove, so that the planar circuit board can be accurately inserted into the fixture, and the planar circuit board is prevented from rotating or moving in the fixture.

Such as using a dowel pin: the fixture and the planar circuit board are provided with holes or grooves for positioning pins, and the planar circuit board can be accurately positioned by inserting the positioning pins into the corresponding holes or grooves.

As shown in fig. 3, for example, the longitudinal limit bars 31 and the transverse limit bars 32 are used for positioning: the two opposite side surfaces of the planar circuit board can be fixedly clamped, so that the accurate positioning of the planar circuit board can be ensured.

The negative pressure adsorption structure is characterized in that a sucker is arranged on the upper surface of a fixing clamp, and negative pressure is generated by connecting the sucker to a vacuum source, so that the sucker and the surface of a planar circuit board generate adsorption force, and the fixing is realized.

As shown in fig. 3, a series of small holes 33 are also provided on the surface of the fixing clamp, and by connecting to a vacuum source, a negative pressure is generated, so that an adsorption effect is formed between the planar circuit board and the orifice plate, thereby realizing fixation.

As shown in fig. 1, the laser 12 includes two laser light sources, and under the control of the controller 15, the working time and output power of the laser can be set through a graphic interface, and the preset position of the laser synchronous indication light spot on the cylindrical circuit or the planar circuit is set, so that the LED flip chip is welded on the cylindrical circuit or the planar circuit;

the machine vision device is arranged between the two laser light sources, captures real-time images of the cylindrical circuit or the plane circuit, is used for identifying and positioning the bonding pad and the chip, and sends the real-time images to the controller to realize accurate control of the welding process. In the implementation, a CCD camera can be used as a machine vision device, so that images with rich details can be captured. This is important for the identification and positioning of pads and chips, and can provide more accurate positional information.

In addition, the CCD camera has higher photosensitive performance, and can acquire clear images under different illumination conditions. During laser welding, light may be disturbed by the laser, but the CCD camera is able to adapt to light variations and maintain image quality. The CCD camera can provide accurate, clear and stable image data, and reliable visual feedback is provided for the welding process of equipment.

The two laser sources adopt two sets of optical fiber coupling laser systems with the wavelength of 455nm, the output power of 20W, and the cooling mode is air cooling and the working voltage is 24V (DC). The two laser sources are respectively and independently arranged on the cross rod, fine adjustment of the upper, lower, left, right and pitching angles can be carried out between the laser sources and the cross rod through software at the end of the controller, wherein the upper and lower (Z-axis direction) adjusting range is 10cm, the left and right adjusting range is 5cm, and the pitching angle adjusting range is 30-150 degrees.

In the embodiment, two laser sources are utilized to heat and weld the anode and cathode bonding pads of the LED circuit at the same time, so that the energy consumption and the welding time are reduced. Meanwhile, as laser energy is gathered, the problem of uneven heat distribution is solved, and the product yield is improved. And the laser is not used for directly irradiating the LED flip chip, but is used for transmitting heat energy to the bonding pad by irradiating a metal conductive circuit outside the edge of the LED flip chip, so that the laser welding of the LED flip chip is finished. Therefore, the problems of high power consumption, easiness in generating holes and low product yield caused by chip welding by heating at a constant temperature in a large area are solved.

The on-off time and the working time of the laser source are controlled by the software of the controller, and the software interface of the controller can synchronously display the pictures of the welding cameras when the laser source is welded.

The controller is a core control unit of the device, and can be, for example, an industrial personal computer, wherein the industrial personal computer has important computer properties and characteristics, such as a computer CPU, a hard disk, a memory, peripheral equipment and an interface, and has an operating system, a control network and protocol, a computing capability and a friendly man-machine interface. For example, the related control parameters of the machine vision device, the laser and the X-Y motion control console can be set on a built-in software interface, and feedback data of the components can be obtained and connected with the machine vision device, the laser and the X-Y motion control console. Is responsible for controlling the operation of the whole equipment and the accurate control of the welding process. Through the data interaction with the machine vision device and the motion control console, the welding parameters are set and monitored in real time.

The controller may also be a PLC controller, which is a programmable logic controller (Programmable Logic Controller, PLC), a digital electronic device with a microprocessor, for automated control. The PLC controller can load the control instructions of the machine vision device, the laser and the X-Y motion control console into the memory for storage and execution.

As shown in fig. 1, the laser welding apparatus for the LED flip chip further includes a fan 16 installed at a position above the laser welding point, the fan being used for exhausting waste gas generated during the laser welding process, protecting the laser lens, and reducing scattering and absorption during the laser transmission process. The fan should blow air towards the position of the laser welding point, and the specific installation position is based on the condition that the working of the laser is not hindered; but also for heat dissipation and protection of the soldered areas. It can effectively improve welding quality and stability.

In this embodiment, the laser welding equipment of this LED flip chip, equipment structure is simple, can realize the high accuracy, the continuous laser welding of high efficiency to post face circuit or plane circuit LED flip chip, and the bonding is stable, and the yields is high.

Example 2:

the invention provides a laser welding process method of an LED flip chip, which uses the laser welding equipment of the LED flip chip of the embodiment 1, and is shown by referring to FIG. 4, and specifically comprises the following steps:

(1) The controller controls the X-Y motion control platform to move, so that a circuit board which is fixed on the fixed clamp and is subjected to LED flip chip die bonding enters the center of the visual field of the machine vision device, and the machine vision device is used for setting an image template of the LED flip chip and related circuits after die bonding is finished;

in machine vision devices, a high resolution camera is used to acquire images of the LED flip chip. The adapted algorithm and template are designed to identify the location, orientation and associated circuitry of the LED flip chip. Through technologies such as image processing and pattern matching, automatic positioning and accurate image recognition of the LED flip chip are realized.

(2) Setting the position parameters of all the LED flip chips to be welded on the circuit board on a controller; and setting controller parameters such as chip spacing, arrangement mode and the like according to the position requirements of the actual LED flip chip. The flexibility and customization of parameter setting can be realized by means of a graphical interface or an input file.

according to the position parameters of the LED flip chip on the circuit board, the position and the angle of each laser source in the laser are accurately adjusted, so that the laser spots can be ensured to be accurately irradiated on the circuit outside the edge of the target bonding pad. And the automatic control is utilized to realize the precise control of the height adjustment, the XY position adjustment and the angle adjustment of the laser.

(4) Adjusting a lens of the laser to enable the diameter of the synchronous indication light spot of the laser to be matched with the width of the circuit;

and adjusting parameters of a laser lens according to the circuit width and welding requirements of the LED flip chip so as to control the diameter of the laser beam and ensure the matching with the circuit width. Through automatic adjustment, accurate adjustment and matching of laser lens parameters are realized. For example, in the implementation, the width of the chip and the circuit is 0.5mm, and the diameter of the two lasers which are symmetrical left and right is also set to be 0.5mm.

the output power of the two laser sources is set through the controller so as to meet the welding requirement. Experiments and optimizations may be performed to determine the optimal power setting according to the particular situation. Likewise, the duration of the laser irradiation is set to ensure that sufficient energy is transferred to the pad locations to complete the soldering of the LED flip chip.

and sequentially welding each chip according to the preset positions according to the position parameters and the welding sequence of the LED flip chip. And the two laser sources are synchronously started to ensure that the two laser sources are simultaneously irradiated to a circuit outside the edge of the positive electrode bonding pad and the negative electrode bonding pad of the LED flip chip, so that the heat energy is transferred to the bonding pad during welding.

Through reasonable movement path design, the X-Y motion control console can automatically move according to the set position sequence, and the welding of all LED flip chips is completed. In the moving process, the controller can monitor the progress and the state of welding in real time and ensure the accuracy and consistency of welding.

The method utilizes the laser beam to precisely control the welding position and energy, solves the problem of uneven heat distribution due to laser energy aggregation, and improves the product yield. And the laser does not directly irradiate the LED chip, but irradiates a metal conductive circuit outside the edge of the LED chip to transfer heat energy to the bonding pad, so that the LED flip chip is welded. Therefore, the invention solves the problems of high power consumption, easy generation of holes and lower product yield caused by chip welding by heating at constant temperature in a large area, and realizes high-precision and high-efficiency chip and substrate welding. The method can provide better heat dissipation performance and reliability, and simultaneously reduce maintenance cost.

In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The laser welding process method for the LED flip chip is characterized in that laser welding equipment of the LED flip chip is adopted to realize laser welding of the LED flip chip, and the method specifically comprises the following steps of:

2. The method of claim 1, wherein the step (2) includes:

3. The method of claim 1, wherein the laser welding temperature in the step (6) is the temperature of the LED flip chip bonding pad, and the temperature range is 180-450 ℃, so as to realize laser soldering and laser eutectic welding.

4. The laser welding process method of an LED flip chip according to claim 1, wherein the laser welding apparatus of an LED flip chip comprises: the device comprises a device body, wherein a machine vision device, a laser, a fixed clamp, an X-Y motion console and a controller are arranged on the device body;

5. The laser welding process of an LED flip chip of claim 2, wherein said machine vision device is a CCD camera.

6. The laser welding process method for the LED flip chip of claim 4, wherein the two laser sources are symmetrically arranged on two sides of the machine vision device, are movably connected with the cross rod on the same cross rod, and are adjustable in up-down, left-right direction and pitching angle.

7. The laser welding process of the LED flip chip according to claim 2, wherein the fixing clamp is provided with a tensioning shaft structure for clamping the cylindrical circuit.

8. The method of claim 2, wherein the fixture has a positioning structure and a negative pressure suction structure for positioning and fixing the planar circuit.