KR102377003B1 - Flow transfer type laser reflow method - Google Patents

Abstract

The present invention for achieving the above object is by irradiating a laser beam from above the bonding object while linearly transferring a rectangular substrate on which a plurality of electronic components, which is a bonding object, are disposed from one side to the other, to transfer the electronic component to the substrate. Bonding, but the shape, density, and displacement of the laser beam [Equation 1] P = kLl (Ls + Ld) Ef {In Equation 1, P is the output power of the laser beam (w), k is the thickness of the substrate ( The heat transfer coefficient according to t), Ll is the major axis length of the laser beam (cm), Ls is the minor axis length of the laser beam (cm), Ld is the distance traveled per unit time (second) (cm), Ef is the energy density of the laser beam (w/cm2)}.

Description

Linear transfer type laser reflow method {Flow transfer type laser reflow method}

The present invention relates to a laser reflow method of a linear transfer method, and more particularly, a substrate on which a plurality of electronic components, which are bonding objects, are disposed on the substrate while continuously flowing from one side to the other side and linearly transferred (flow transfer). It relates to a laser reflow method of a linear transfer method for continuously bonding an electronic component to a substrate between linear transfer of a bonding object by irradiating a laser beam to the electronic component.

In industrial laser processing, an application field with micron (㎛) precision is micro laser processing, which is widely used in the semiconductor industry, display industry, printed circuit board (PCB) industry, and smartphone industry. Memory chips used in all electronic devices have developed technologies to reduce the circuit spacing to a minimum to realize the degree of integration, performance, and ultra-high speed communication speed, but now, the required technology level has been achieved just by reducing the circuit line width and line width gap. It is difficult to do so, and it has reached the level of stacking memory chips in a vertical direction. The stacking technology up to 128 layers has already been developed by TSMC, and the stacking technology up to 72 layers is being applied to mass production by Samsung Electronics and SK Hynix.

In addition, technology development for mounting a memory chip, a microprocessor chip, a graphic processor chip, a wireless processor chip, a sensor processor chip, etc. in one package is intensely researched and developed, and a considerable level of technology has already been applied in practice.

However, in the process of developing the aforementioned technology, more and more electrons have to participate in the signal processing process inside the ultra-high-speed/ultra-high-capacity semiconductor chip, so the power consumption increases, and the issue of cooling treatment for heat has been raised. In addition, in order to achieve the requirements of ultra-high-speed signal processing and ultra-high-frequency signal processing for more signals, a technical issue that large amounts of electrical signals must be transmitted at high speed has been raised. In addition, since the number of signal lines has to be increased, it is no longer possible to process the signal interface lines to the outside of the semiconductor chip using a one-dimensional lead wire method, but a ball grid array (BGA) method (Fan-In BGA) that processes two-dimensionally at the bottom of the semiconductor chip. Or Fan-in Wafer-Level-Package (FIWLP)) and a signal layout redistribution layer under the ultra-fine BGA layer under the chip, and a second fine BGA layer is installed under it. The method (referred to as Fan-Out BGA or Fan-Out Wafer-Level-Package (FOWLP) or Fan-Out Panel-Level-Package) is being applied.

Recently, in the case of semiconductor chips, products with a thickness of 200 μm or less including an EMC (Epoxy-Mold Compound) layer have appeared. As such, in order to attach a micron-level ultra-thin semiconductor chip with a thickness of only several hundred microns to an ultra-thin PCB, the same mass reflow (SMT) standard process, Thermal Reflow Oven technology, is used. When the MR) process is applied, the semiconductor chip is exposed to an air temperature environment of 100 to 300 degrees (℃) for a period of several hundred seconds. - Various types of soldering bonding defects such as border warpage (PCB-Boundary Warpage) and Random-Bonding Failure by Thermal Shock may occur.

Accordingly, looking at the configuration of a laser reflow device that has recently been spotlighted, a laser head module presses a bonding object (semiconductor chip or integrated circuit IC) for a few seconds while irradiating a laser to bond the semiconductor chip or integrated circuit. (IC) Bonding is performed by irradiating a laser in the form of a surface light source corresponding to the size.

An example of such a laser reflow apparatus in the prior art is disclosed in Korean Patent No. 0662820 (hereinafter referred to as 'prior document 1'). Referring to Prior Document 1, a configuration of a flip-chip hot-pressing module for heating the flip-chip by irradiating a laser to the rear surface of the flip-chip and pressing the flip-chip to the carrier substrate is disclosed.

However, the laser reflow apparatus of the conventional pressurization method disclosed in Prior Document 1 includes a means for adsorbing a chip and moving it to a bonding position, heating the back surface of the chip through a laser and simultaneously pressing the chip to a carrier substrate. In the case of bonding a plurality of semiconductor chips such as a semiconductor strip, the operation time has to be increased because the operation of irradiating a laser while pressing one semiconductor chip must be repeatedly performed as many as the number of semiconductor chips.

On the other hand, referring to Korean Patent Application Laid-Open No. 2017-0077721 (hereinafter referred to as 'Prior Document 2'), the laser reflow device mentioned in Prior Document 2 is a laser head in a state in which the pressurization head simultaneously presses several flip chips. It is generally mentioned that bonding processing is possible by irradiating each flip chip with a laser one by one while transporting it in the horizontal direction, or by irradiating a laser to several flip chips by a single laser head at the same time.

However, since the conventional laser reflow method of the above-mentioned Prior Document 2 also performs bonding by a pressurization method using a single laser source, the laser beam is homogenized as the laser beam is incident at various angles on a plurality of flip chips disposed on the substrate. Many technical difficulties are expected to reflow a plurality of flip chips at once without irradiating the beam and without defects.

Accordingly, in the conventional laser reflow method disclosed in Prior Document 2, the total working time has to be increased by sequentially pressing and reflowing a single flip chip one by one, or depending on the size of various bonding objects for a plurality of processing. Even when a single laser beam is simultaneously irradiated to a plurality of horizontally arranged flip chips, it is virtually difficult to evenly transmit sufficient heat energy to each flip chip, so it still takes a lot of work time and it is difficult to improve the bonding defect rate. .

Accordingly, the present invention has been devised to solve the above problems, and while a substrate on which a plurality of electronic components as a bonding object are disposed continuously flows from one side to the other and is linearly transferred, electrons disposed on the substrate By irradiating at least one laser beam on the part, the bonding object is heated from room temperature to the preheating temperature and the solder is melted using only the thermal energy of the laser beam during the laser reflow process, which is this process, without preheating the bottom surface of the bonding object with a separate heater as in the prior art. Provides a linear transfer laser reflow method that rapidly heats to temperature and continuously and stably bonds the electronic component to the substrate between linear transfer of the bonding object without causing bonding defects such as overflow in the solder even in the rapid heating process aim to do

According to an embodiment, the present invention for achieving the above object is by irradiating a laser beam from above the bonding object while linearly transporting a rectangular substrate on which a plurality of electronic components, which is a bonding object, are disposed from one side to the other side. The electronic component is bonded to the substrate, and the shape, density, and displacement of the laser beam are [Equation 1] P = kLl (Ls + Ld) Ef {In Equation 1, P is the output power of the laser beam (w), k is the heat transfer coefficient according to the thickness (t) of the substrate, Ll is the long axis length of the laser beam (cm), Ls is the short axis length of the laser beam (cm), Ld is the movement distance per unit time (sec) (cm), Ef is It is controlled based on the energy density (w/cm2) of the laser beam.

Also, according to an embodiment, the laser beam is a rectangular laser beam having a long axis Ll perpendicular to the transport direction of the bonding object and a minor axis Ls parallel to the transport direction of the bonding object.

Also, according to an embodiment, the laser beam is irradiated from at least one or more provided laser head modules, and when two or more laser head modules are provided, the laser beams are simultaneously or sequentially irradiated from the laser head modules.

In addition, according to an embodiment, when the two or more laser head modules are provided, the laser beams irradiated from the laser head modules are always overlapped or intermittently overlapped and irradiated to a specific part.

Also, according to an embodiment, the substrate is a printed circuit board (PCB) in which a thin copper layer for electric wiring is formed on at least one side of the insulating layer around a resin-based insulating layer.

In addition, according to one embodiment, the thickness (t) of the substrate is formed within the range of 0.1mm to 1mm, the heat transfer coefficient (k) according to the thickness (t) of the substrate is in the range of 0.9 to 2.7 of the substrate increases in proportion to the thickness.

Also, according to an embodiment, the long axis length Ll of the laser beam is formed to be equal to or larger than the length in the width direction of the bonding object perpendicular to the transfer direction of the substrate.

Also, according to an embodiment, the movement distance Ld per unit time (second) has a value of at least 0.2 tsu.

Also, according to an embodiment, the output power P of the laser beam has a value of at least 400w.

Also, according to an embodiment, the energy density (Ef) of the laser beam is controlled within the range of 40w/cm2 to 60w/cm2.

In addition, according to an embodiment, the minor axis length (Ls) of the laser beam is fixed so that all other variables (k, Ll, Ld, Ef) other than the output power (P) of the laser beam do not change based on Equation 1 case increases proportionally as the output power P of the laser beam increases.

In addition, according to an embodiment, the minor axis length (Ls) of the laser beam does not change all other variables (P, k, Ll, Ef) other than the movement distance (Ld) per unit time (second) based on Equation 1 When it is fixed so that it is not fixed, it decreases in inverse proportion as the movement distance Ld per unit time (second) increases.

In addition, according to an embodiment, the rectangular substrate on which the plurality of electronic components, which is the bonding object, is disposed, is linearly transported along with the movement of the carrier in a state seated on the upper surface of the carrier, or the laser head module is in a stopped state. relatively moved.

In addition, according to an embodiment, as the carrier is mounted on the conveyor unit and the driving of the conveyor unit is controlled, the moving distance Ld per unit time (sec) is controlled.

In the present invention as described above, while a substrate on which a plurality of electronic components, which is a bonding object, is disposed, continuously flows from one side to the other side and is linearly transferred, at least one laser beam is applied to the electronic components disposed on the substrate. By continuously bonding the electronic components to the substrate between the irradiation and linear transfer, there is an effect of shortening the process time and greatly improving productivity by mass reflow processing.

In addition, by precisely controlling the irradiation of the laser beam by the laser head module according to the set conditions and reference values, a contact defect or overflow of some solder that may occur during mass reflow processing of a plurality of electronic components disposed on the substrate There is an effect of greatly improving various process defects that damage the substrate due to excessive laser beam applied to the substrate, such as bonding defects and yellowing.
In addition, the present invention provides bonding as in the prior art by irradiating at least one laser beam to the electronic components disposed on the substrate while a substrate on which a plurality of electronic components, which is a bonding object, are disposed continuously flows from one side to the other and is then linearly transferred. In the laser reflow process, which is this process, without preheating the bottom of the object with a separate heater, the bonding object is rapidly heated from room temperature through the preheating temperature to the melting temperature of the solder only with the thermal energy of the laser beam, and from the room temperature through the preheating temperature Even in the rapid heating process of rapidly increasing the temperature to the melting temperature of the solder, there is an effect that the solder is stably melted and bonded without any bonding defects such as overflow in the solder.

1 is a perspective view showing the entire laser reflow apparatus according to an embodiment of the present invention;
2 is a block diagram schematically showing the configuration of a laser head module according to an embodiment of the present invention;
3 is a conceptual diagram of a multi-laser head module according to another embodiment of the present invention;
4 to 7 are diagrams of a laser optical system applicable to a laser head module according to an embodiment of the present invention;
8 is a state diagram in which a single laser beam is irradiated along the width direction of a bonding object according to an embodiment of the present invention;
9 is a state diagram in which a multi-laser beam is partially overlapped and irradiated along the width direction of a bonding object according to another embodiment of the present invention;
10 is a state diagram in which a multi-laser beam is partially overlapped and intermittently irradiated along the width direction of a bonding object according to another embodiment of the present invention;

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as "comprise" or "have" to "include" are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the present specification exist, but one It should be understood that it does not preclude the possibility of the presence or addition of or more other features or numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise herein, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present specification. shouldn't

Hereinafter, a reflow apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying FIGS. 1 and 2 .

1 is a perspective view of a flow laser reflow apparatus according to an embodiment of the present invention as a whole, and FIG. 2 is a block diagram schematically showing a configuration of a laser head module according to an embodiment of the present invention.

First, a carrier 100 on which a substrate on which a plurality of electronic components and solders, which are bonding objects 11 are placed, is mounted is provided. According to one embodiment, the carrier 100 may be implemented as a rectangular metal plate that is linearly transported in a state in which the bonding object 11 is simply raised and placed. As the vacuum suction hole and flow path (not shown) of the vacuum suction hole and flow path (not shown) are further formed, it is possible to vacuum adsorb the bonding object 11 seated on the upper surface so that it can be fixed between linear transfers.

In addition, according to an embodiment, a heater 110 for preheating the bonding object 11 to a predetermined temperature may be further provided under the carrier 100 . The heater 110 preheats and maintains the surface temperature of the carrier 100 to less than 200° C. while the bonding object 11 is linearly transferred for the reflow process in a state in which it is seated on the carrier 100 .

At this time, as the heater 110 may be further provided inside the carrier 100 as described above, the substrate, the electronic component, and the solder, which are the bonding objects 11 , are continuously preheated to a predetermined temperature. For example, the preheating temperature is preferably set below the melting temperature of the solder, and is preferably maintained below 200°C, which is a temperature range in which thermal damage is not applied even when the substrate and electronic components are exposed for a predetermined time or longer.

If the bonding object 11 is not preheated as described above, the bonding object 11 must be rapidly heated from room temperature to the melting temperature of the solder only with the thermal energy of the laser beam during the laser reflow process, which is this process, in this case, rapid heating This may cause bonding defects such as overflow in the solder. Therefore, as the temperature is gradually increased from the preheating temperature to the melting temperature of the solder, the solder is stably melted and the bonding defect can be minimized. For example, the melting temperature of the solder may be different depending on the material of the solder, but may be 200° C. or higher, which is the melting temperature of a general solder paste.

In addition, as the carrier 100 is mounted on the conveyor unit 200 to be linearly transported from one side to the other, the transport speed of the carrier 100 is controlled by controlling the driving of the conveyor unit 200 .

On the other hand, a single laser for bonding the electronic component to the substrate by reflowing the solder by irradiating at least one laser beam to the bonding object 11 of the substrate, the electronic component, and the solder being linearly transferred above the conveyor unit 200 . A head module 300 is provided.

Referring to an embodiment of the accompanying drawings, a single laser head module 300 according to the present invention is a laser beam shape and area while the bonding object 11 is linearly transported while seated on the carrier 100 . By controlling , density and displacement, the solder is reflowed to bond electronic components to the substrate.

A detailed configuration of the laser head module 300 will be described in more detail with reference to FIGS. 3 to 7 to be described later.

In addition, referring to FIG. 1 according to an embodiment, one side of the laser head module 300 has an infrared (IR) camera 500 that measures the temperature of the laser beam irradiated on the bonding object 11 in a non-contact manner. And, a position measuring camera 600 for measuring the position of the bonding object 11 may be provided.

In addition, according to an embodiment, the laser head module 300 may control the shape, density, and intensity of the laser beam in conjunction with each temperature data measured by the infrared (IR) camera 500 .

In addition, according to one embodiment, when the position measuring camera 600 detects the bonding object 11 located below the laser head module 300, the conveyor unit 200 is suitable for the reflow process carrier 100 can change the movement speed of

For example, when the carrier 100 is in the initial preheating section, that is, after the bonding object 11 is loaded and seated on the carrier 100, until entering the reflow section where the laser beam is irradiated, the carrier ( 100), the process time of the entire laser reflow can be shortened by quickly controlling the feed rate.

After that, when the bonding target 11 enters the reflow section where the laser beam is irradiated in the preheating section, the transport speed of the carrier 100 is adjusted in accordance with the density and intensity of the laser beam in consideration of the melting point of the bonding target 11 . It can be paused or decelerated to feed more slowly.

3 is a conceptual diagram of a multi-laser head module according to another embodiment of the present invention.

Referring to FIG. 3 , a laser head module 300 irradiating a laser in the form of a surface light source to the bonding object 11 is a multi-laser head of the first, second and third laser head modules 310 , 320 , 330 . It can be composed of modules.

Each of the laser head modules (310, 320, 330) includes a laser oscillator (311, 321, 331) having a cooling device (316, 326, 336), a beam shaper (312, 322, 332), an optical lens module ( 313 , 323 , 333 ), driving devices 314 , 324 , 334 , control devices 315 , 325 , 335 , and power supply units 317 , 327 , 337 are included.

Each of the laser head modules 310 , 320 , 330 converts a laser generated by the laser oscillators 311 , 321 , 331 and transmitted through an optical fiber into a surface light source and irradiates the bonding object 11 .

Each of the laser head modules 310 , 320 , 330 includes beam shapers 312 , 322 , 332 that convert a spot type laser into a surface light source type, and is disposed below the beam shaper and includes a beam shaper 312 . An optical unit ( 4 to 7) may be implemented.

Each of the laser head modules 310 , 320 , 330 may rise or fall along the z-axis, move left or right along the x-axis, or move along the y-axis for alignment with the bonding object 11 .

Therefore, the laser reflow method of the present invention linear transport method linearly transports the bonding object 11 in a state seated on the carrier 100, and the bonding object 11 while the bonding object 11 is linearly transferred. By irradiating a laser beam from above to reflow the solder, the reflow process tact time of the bonding object 11 can be shortened by continuous processing of the laser reflow process, thereby realizing high-speed bonding operation. . In addition, when the laser beam is continuously irradiated to the bonding object 11 in a fixed state without being linearly transferred in the prior art as the laser beam is irradiated between linear transport of the bonding object 11, thermal damage that may be applied to the bonding object 11 (eg, distortion or warpage of the substrate, yellowing, etc.) can be minimized.

In addition, although not shown in the drawings, each laser head module 310 , 320 , 330 according to another embodiment of the present invention may be transported or rotated in up-down, left-right directions, for this purpose, the x-axis, the y-axis, or the z-axis It should be interpreted as including a configuration that is movable on the axis and supports each of the laser head modules 310 , 320 , 330 to be rotated.

In addition, each of the laser head modules 310 , 320 , 330 may include a linear encoder (not shown) as a height sensor, and through this, the height to calculate the irradiation distance of the laser beam to the bonding object 11 . It can provide technical data to confirm position values or to find more accurate values for the density and intensity of the laser beam.

Hereinafter, detailed configurations of the laser head modules 310 , 320 , and 330 will be described in detail.

Except where necessary, the first laser head module 310 among the laser head modules 310 , 320 , and 330 having the same configuration will be mainly described in order to avoid overlapping description.

The laser oscillator 311 generates a laser beam having a wavelength and output power in a predetermined range. The laser oscillator is, for example, a diode laser (Laser Diode, LD) having a wavelength of '750 nm to 1200 nm' or '1400 nm to 1600 nm' or '1800 nm to 2200 nm' or '2500 nm to 3200 nm' or a rare-earth medium fiber laser (Rare-Earth- It may be a Doped Fiber Laser) or a Rare-Earth-Doped Crystal Laser, and alternatively, a medium for emitting alexandrite laser light having a wavelength of 755 nm, or Nd Yag (Nd) having a wavelength of 1064 nm or 1320 nm :YAG) may be implemented including a medium for emitting laser light.

The beam shaper 312 converts a spot type laser generated from the laser oscillator 311 and transmitted through an optical fiber into an area beam type having a flat top. The beam shaper 312 may be implemented by including a square light pipe, a diffractive optical element (DOE), or a micro-lens array (MLA).

The optical lens module 313 adjusts the shape and size of the laser beam converted from the beam shaper 312 to the surface light source shape to irradiate the electronic component mounted on the PCB board or the irradiation area. The optical lens module 313 constitutes an optical system by combining a plurality of lenses, and the specific configuration of the optical system will be described later with reference to FIGS. 4 to 7 .

The driving device 314 moves the distance and position of the laser head module 310 with respect to the irradiated surface, and the controller 315 controls the driving 314 to shape the beam when the laser beam reaches the irradiated surface. , adjust the beam area size, beam sharpness and beam irradiation angle. The controller 315 may also integrally control the operation of each part of the laser head module 310 in addition to the driving device 314 .

On the other hand, the laser power adjustment unit 370 is each laser head module from the power supply unit 317, 327, 337 corresponding to each laser head module (310, 320, 330) according to a program received through the user interface or a preset program. Controls the amount of power supplied to The laser output adjustment unit 370 receives the reflow state information for each part, each area, or the entire reflow state on the irradiation surface from one or more camera modules 350 and controls each power supply unit 317 , 327 , 337 based on the received information. Contrary to this, the control information from the laser power adjusting unit 370 is transmitted to the control devices 315, 325, 335 of each laser head module 310, 320, 330, and in each of the control devices 315, 325, 335 It is also possible to provide a feedback signal for controlling each corresponding power supply 317 . In addition, unlike FIG. 3 , it is also possible to distribute power to each laser head module through one power supply unit. In this case, the laser output adjusting unit 370 needs to control the power supply unit.

When implementing the laser overlap mode, the laser power adjusting unit 370 is configured so that the laser beam from each laser head module 310 , 320 , 330 has a required beam shape, beam area size, beam sharpness and beam irradiation angle. Controls the module and the power supply (317, 327, 337). In the laser overlap mode, the first laser head module 310 is used to preheat the area around the bonding target position, and the second laser head module 320 is used to additionally heat a narrower reflow target area, as well as a preheating function. It also applies when controlling each laser head module to have a required temperature profile by properly distributing the additional heating function between the first, second, and third laser head modules 310, 320, and 330.

Meanwhile, when one laser light source is distributed and input to each laser head module, a function for simultaneously adjusting the output and the phase of each distributed laser beam may be provided in the laser power adjusting unit 370 . In this case, the beam flatness can be significantly improved by controlling the phase to induce destructive interference between the respective laser beams, which further increases the energy efficiency.

On the other hand, in the case of implementing a multi-position simultaneous processing mode, the laser power adjusting unit 370 sets the beam shape of each laser beam so that some or all of the laser beams from each laser head module 310, 320, 330 are different. Controls one or more of area size, beam sharpness, beam irradiation angle, and beam wavelength. Even at this time, when one laser light source is distributed and input to each laser head module, a function for simultaneously adjusting the output and the phase of each distributed laser beam may be provided in the laser power adjusting unit 370 .

Through this function, bonding between the electronic components and the substrate in the irradiation surface can be performed or bonding can be removed by adjusting the laser beam size and output. In particular, when a damaged electronic component is removed from the substrate, the laser beam heat applied to other adjacent or normal electronic components existing on the substrate can be minimized by minimizing the area of the laser beam to the corresponding electronic component area. Accordingly, it is possible to remove only the damaged electronic component to be removed.

On the other hand, when a plurality of laser head modules emit laser beams having different wavelengths, the laser head module has a plurality of material layers (eg, EMC layer, silicon layer, solder layer) included in the electronic component. It can consist of individual laser head modules with absorbing wavelengths.

Accordingly, the laser reflow device according to the present invention selectively increases the temperature of the electronic component and the temperature of the intermediate bonding material such as solder, which is a connecting material between the printed circuit board or the electrode of the electronic component, to optimize bonding (Attaching or Bonding) or separation (Detaching or Debonding) process may be performed.

Specifically, it penetrates both the EMC mold layer and the silicon layer of the electronic component so that all energy of each laser beam is absorbed by the solder layer, or the laser beam does not penetrate the EMC mold layer and heats the surface of the electronic component to lower the electronic component It is also possible to conduct heat to the bonding part of the

On the other hand, by utilizing the above function, a certain area of the bonding object including the reflow target electronic component area and its surroundings is preheated to a predetermined preheating temperature by at least one laser beam, and then ripple by at least another laser beam The temperature of the raw electronic component area is selectively heated up to the reflow temperature at which the melting of the solder occurs.

4 to 7 are diagrams of a laser optical system applicable to a laser head module according to an embodiment of the present invention.

4 is an optical system of the simplest structure applicable to the present invention. When the laser beam emitted from the beam transmission optical fiber 410 is focused through the convex lens 420 and is incident on the beam shaper 430, the beam shaper 430 ), converts the spot-shaped laser beam into a flat-top-shaped surface light source A1, and the square laser beam A1 output from the beam shaper 430 is the desired size through the concave lens 440. It is irradiated to the image-forming surface (S) with the expanded surface light source (A2).

5 is a block diagram of a laser optical system according to another embodiment of the present invention.

The surface light source B1 from the beam shaper 430 is enlarged to a predetermined size through the concave lens 440 to become the surface light source B2 irradiated to the first imaging surface S1. If the surface light source B2 is to be further enlarged and used, the boundary of the edge portion of the surface light source B2 may become more unclear according to the additional enlargement, so that the final irradiation surface is the second imaging surface S2 ), the edge is trimmed by installing the mask 450 on the first imaging surface S1 in order to obtain the irradiated light with a clear edge.

The surface light source passing through the mask 450 is reduced (or enlarged) to a desired size while passing through the zoom lens module 460 composed of a combination of one or more convex and concave lenses, and the second imaging surface on which electronic components are disposed. A rectangular irradiation light B3 is formed in (S2).

6 is a block diagram of a laser optical system according to another embodiment of the present invention.

After the square surface light source C1 from the beam shaper 430 is enlarged to a predetermined size through the concave lens 440, it passes through at least a pair of cylindrical lenses 470 and is enlarged (or reduced) in the x-axis direction, for example. (C2) and again passing through at least a pair of cylindrical lenses 480, for example, is reduced (or enlarged) in the y-axis direction and converted into a rectangular-shaped surface light source C3.

Here, the cylindrical lens is a shape in which a cylindrical shape is cut in the longitudinal direction, and functions to expand or reduce the laser beam according to the shape in which each lens is disposed in the vertical direction, and the lens on the surface on which the cylindrical lens is disposed is x, y The laser beam is adjusted in the x-axis or y-axis direction according to the shape arranged in the axial direction.

Then, the surface light source C3 is enlarged (or reduced) to a desired size while passing through the zoom lens module 460 composed of a combination of one or more convex and concave lenses, and the second imaging surface S2 on which electronic components are disposed. ) to form a rectangular irradiation light C4.

7 is a block diagram of a laser optical system according to another embodiment of the present invention.

The optical system of FIG. 7 has a configuration for trimming the edge of the laser beam by applying a mask to the optical system of FIG. 6, and it is understood that the final surface light source D5 having a sharper edge can be obtained compared to the case of FIG. will be able

Hereinafter, the laser reflow method of the present invention linear transfer method will be described in detail with reference to FIGS. 8 to 10 .

8 is a state diagram in which a single laser beam is irradiated along a width direction of a bonding object according to an embodiment of the present invention.

According to one embodiment of the present invention, the bonding object 11 while the rectangular substrate on which the plurality of electronic components are disposed is linearly transferred from one side to the other side while seated on the carrier 100. A single laser beam is irradiated from above to reflow the solder to bond the electronic component to the substrate.

At this time, the shape, density, and displacement of the laser beam irradiated from the laser head module 300 to the bonding object 11 for laser reflow while the bonding object 11 is linearly transferred is based on Equation 1 below. can be controlled.

[Formula 1]

P=kLl(Ls+Ld)Ef

In Equation 1, P is the output power of the laser beam (w), k is the heat transfer coefficient according to the thickness (t) of the substrate, Ll is the long axis length of the laser beam (cm), Ls is the short axis length of the laser beam (cm) , Ld is defined as the movement distance (cm) per unit time (second), and Ef is defined as the energy density (w/cm2) of the laser beam.

In the following embodiment for Equation 1, the laser beam irradiated from the laser head module 300 has a long axis (Ll) perpendicular to the transport direction of the bonding object and a minor axis (Ls) parallel to the transport direction of the bonding object. A laser beam having a rectangular shape was used.

On the other hand, the printed circuit board (PCB) used in this embodiment is a printed circuit board (PCB) in which a thin copper layer for electrical wiring is formed on at least one side of the insulating layer around the resin-based insulating layer, The ED (Electro Deposit) method of electroplating with a copper layer on both sides of the mid (PI) insulation layer of 1/3 OZ (12 μm) was used. . In addition, PSR (White) ink was additionally coated on the outer surface of the printed circuit board.

In addition, as the printed circuit board, products having various thicknesses (t) within the range of 0.1mm to 1mm were used, and the heat transfer coefficient (k) according to the thickness (t) of the board is increased in proportion to the thickness of the board, , the heat transfer coefficient (k) for the substrate thickness (t) 0.1 mm to 1 mm was derived as shown in Table 1 below within the range of 0.9 to 2.7.

Heat transfer coefficient (k) according to the thickness (t) of the PCB board k t k t 0.9 0.1mm 1.9 0.6mm One 0.15mm 2 0.65mm 1.1 0.2mm 2.1 0.7mm 1.2 0.25mm 2.2 0.75mm 1.3 0.3mm 2.3 0.8mm 1.4 0.35mm 2.4 0.85mm 1.5 0.4mm 2.5 0.9mm 1.6 0.45mm 2.6 0.95mm 1.7 0.5mm 2.7 1mm 1.8 0.55mm

In addition, preferably, the long axis length Ll of the laser beam is formed to be equal to or larger than the width direction length so as to cover all the lengths in the width direction of the bonding object perpendicular to the transfer direction of the substrate.

In addition, the energy density (Ef) of the laser beam may be variously controlled within the range of 40w/cm2 to 60w/cm2. Here, the minimum value of 40w/cm2 is a state in which the solder is normally reflowed according to the insufficient energy irradiation of the laser beam, so that the electronic component is not electrically bonded to the solder, that is, a soldering defect such as a cold soldering joint occurs. It is the lower limit of the possible energy density. In addition, the maximum value of 60w/cm2 is a phenomenon in which deformation due to discoloration or thermal damage of the printed circuit board occurs as an excessive laser beam is irradiated, that is, a phenomenon in which process defects such as yellowing may occur. is the upper limit. That is, the laser reflow method of the linear transfer method of the present invention is such that a laser beam having an appropriate energy density value is irradiated between the minimum energy density value, which is a lower limit to avoid soldering defects, and a maximum energy density value, which is an upper limit value, to avoid process defects. need to be controlled.

According to the control range of the energy density value, the output power (P) of the laser beam is variously controlled within the range of 400w to 2000w, and also per unit time (sec) for linear transport of the printed circuit board (PCB) The movement distance (Ld) was variously controlled within the range of 0.2 cm to 1.6 cm and changes were observed.

Table 2 below shows the results of calculating the energy density according to the movement distance per unit time (sec) of a printed circuit board having a thin thickness (t) of 0.15 mm based on Equation 1.

Energy density calculation result according to moving distance per unit time (sec) (t=0.15mm) turn long axis
(Ll,cm) shorten
(Ls, cm) area
(A1=Ll×Ls) Output power (W) Movement distance per unit time (second) (Ld,cm) One 20 0.2 4 420 0.2 2 20 0.2 4 610 0.4 3 20 0.2 4 770 0.6 4 20 0.2 4 970 0.8 5 20 0.2 4 1190 One 6 20 0.2 4 1410 1.2 7 20 0.2 4 1630 1.4 8 20 0.2 4 1850 1.6 turn Travel distance + shortened length (L2) area
(A2=Ll×L2) Energy density output
(kEf,w/cm2) Reference value: minimum energy density
(k×40w/cm2) Reference value: maximum energy density
(k×60w/cm2) One 0.4 8 52.5 40 60 2 0.6 12 50.833 40 60 3 0.8 16 48.125 40 60 4 One 20 48.5 40 60 5 1.2 24 49.583 40 60 6 1.4 28 50.357 40 60 7 1.6 32 50.938 40 60 8 1.8 36 51.389 40 60

In addition, Table 3 below is the result of calculating the energy density according to the movement distance per unit time (sec) of a printed circuit board having a thicker thickness (t) of 0.35 mm based on Equation 1.

Energy density calculation result according to moving distance per unit time (sec) (t=0.35mm) turn long axis
(Ll,cm) shorten
(Ls, cm) area
(A1=Ll×Ls) Output power (W) Movement distance per unit time (second) (Ld,cm) One 20 0.2 4 550 0.2 2 20 0.2 4 820 0.4 3 20 0.2 4 1080 0.6 4 20 0.2 4 1400 0.8 5 20 0.2 4 1710 One turn Travel distance + shortened length (L2) Area (A2=Ll×L2) Energy density output
(kEf,w/cm2) Reference value: minimum energy density
(k×40w/cm2) Reference value: maximum energy density
(k×60w/cm2) One 0.4 8 68.75 56 84 2 0.6 12 68.333 56 84 3 0.8 16 67.5 56 84 4 One 20 70 56 84 5 1.2 24 71.25 56 84

Through the energy density calculation results in Tables 2 and 3, the input conditions of individual variables applicable in the actual field, that is, the long axis length (Ll) of the laser beam = 20 cm, the short axis length (Ls) = 0.2 cm, the laser beam output Power (P) = 550 to 1850w, movement distance per unit time (second) (Ld) = 0.2 to 1.6 cm. Considering the input conditions, the calculated values of all energy densities are between the minimum energy density value and the maximum energy density value. It was confirmed that an appropriate energy density value was derived.

Accordingly, it is possible to variously set and control the laser reflow process conditions within the input condition range of all individual variables indicating the appropriate energy density value. More preferably, in order to reduce the tact time of the laser reflow process, setting and controlling the process conditions by setting the movement distance (Ld) per unit time (second) to the maximum value of 1.6 cm is the tact time It is the shortest, and it was judged to be the most advantageous in terms of process efficiency and productivity increase.

On the other hand, the minor axis length (Ls) of the laser beam is fixed so that all other variables (k, Ll, Ld, Ef) other than the output power (P) of the laser beam are not changed based on Equation 1 above. It can be inversely calculated that the minor axis length Ls of the laser beam is also proportionally increased as the output power P of is increased.

Similarly, the minor axis length (Ls) of the laser beam is a unit when all other variables (P, k, Ll, Ef) other than the movement distance (Ld) per unit time (second) are fixed so as not to change based on Equation 1 It can be inversely calculated that the movement distance Ld per time (second) is inversely proportional to the increase.

Accordingly, by appropriately setting the output power (P) of the laser beam and the movement distance (Ld) per unit time (second), the shape of the laser beam is reduced to a line type laser beam with a minimized short axis length (Ls). It is possible to design the process to be investigated.

At this time, as described above, the rectangular substrate on which a plurality of electronic components, which is the bonding object 11, are disposed, is linearly transferred along with the movement of the carrier 100 while seated on the upper surface of the carrier 100, The carrier 100 is mounted on the conveyor unit 200 and by controlling the driving of the conveyor unit 200, the movement distance Ld per unit time (sec) may be controlled.

9 is a diagram illustrating a state in which a multi-laser beam is partially overlapped and irradiated along a width direction of a bonding object according to another embodiment of the present invention.

According to another embodiment, the laser beam may be simultaneously or sequentially irradiated from the two or more multi-laser head modules 310 and 320 in a state in which two or more laser head modules are provided.

Referring to FIG. 9 , a state in which the laser beams LB1 and LB2 irradiated from the first laser head module 310 and the second laser head module 320 are completely overlapped and irradiated along the width direction of the bonding object is exemplified do.

At this time, the first laser beam LB1 irradiated from the first laser head module 310 and the second laser beam LB2 irradiated from the second laser head module 320 are simultaneously irradiated on the bonding object 11 . When the two laser beams LB1 and LB2 are completely overlapped. Here, the complete overlap means a state in which one laser beam completely belongs to the other laser beam.

Accordingly, it is predictable that the density, intensity, and temperature of the laser beams are higher than those of the first and second laser beams LB1 and LB2, respectively, in the overlapping area OA. That is, the first laser head module 310 irradiates the laser beam LB1 for pre-heating the bonding object 11, and the second laser head module 320 irradiates the laser beam LB2 for bonding. The density, intensity, and temperature conditions of the first and second laser beams LB1 and LB2 are the physical properties or bonding area of the bonding object 11 during the reflow process, and the movement distance (Ld) per unit time (second). In consideration of the above, each may be controlled complementary to each other.

In contrast to the case of irradiating a strong laser beam at once for actual bonding, the laser beam irradiation through overlap can reduce the temperature deviation with the pre-heated bonding object, and minimize thermal damage such as warping, warping, and yellowing. be able to

When irradiating a plurality of laser beams simultaneously or sequentially overlappingly irradiated in this way, the temperature deviation with the preheated bonding object can be reduced compared to the case of continuously irradiating a single strong laser beam at once for actual bonding, and It is possible to minimize thermal damage such as warping, warping, and yellowing.

Meanwhile, the shapes of the laser beams LB1 and LB2 irradiated from each of the laser head modules 310 and 320 are shown in a rectangular shape according to an embodiment, but are not limited thereto and are square, circular, dotted or line shapes. The two laser beams can be varied in the same or different form depending on the bonding object and the process conditions of the reflow process.

10 is a diagram illustrating a state in which multi-laser beams are always overlapped or intermittently overlapped along a width direction of a bonding object according to another embodiment of the present invention.

According to another embodiment, in the laser beam, the laser beam irradiated from the two or more multi-laser head modules 310, 320, 330 in a state in which two or more laser head modules are provided. there is.

Referring to FIG. 10 , the laser beams LB1 and LB2 irradiated from the first laser head module 310 and the second laser head module 320 are always overlapped and irradiated along the width direction of the bonding object, while the third A state in which the laser beam LB3 irradiated from the laser head module is intermittently further irradiated to the always overlapping area OA is exemplified.

At this time, the first laser beam LB1 irradiated from the first laser head module 310 and the second laser beam LB2 irradiated from the second laser head module 320 are simultaneously irradiated on the bonding object 11 . When the two laser beams LB1 and LB2 are completely overlapped or partially overlapped, the third laser beam LB2 may be irradiated by intermittently supplementing the portion requiring additional heating. Here, regular overlap means that two or more laser beams are always irradiated in an overlapping state, while intermittent overlap means that two or more laser beams do not always overlap and the laser beams are temporarily overlapped and irradiated according to some specific time or period. it means.

Accordingly, it is predictable that the density, intensity, and temperature of the laser beams are higher than those of the first and second laser beams LB1 and LB2, respectively, and the third laser beam LB3 intermittently occurs in the always overlapping area OA. The overlapped irradiated area may be partially formed to have a higher density, intensity, and temperature of the laser beam according to a specific time or period. That is, the first laser head module 310 irradiates the laser beam LB1 for pre-heating the bonding object 11, while the second and third laser head modules 320 and 330 are laser beams for bonding. By irradiating (LB2, LB3) to be superimposed on (LB2, LB3) constantly or intermittently, the density, intensity, temperature condition, and irradiation time of the first, second, and third laser beams (LB1, LB2, LB3), etc., are adjusted to the bonding object during the reflow process. In consideration of the physical properties of (11), the bonding area, and the movement distance (Ld) per unit time (second), each can be controlled complementary to each other.

In this way, when irradiating a plurality of laser beams to be superimposed or intermittently overlapped, the temperature deviation with the preheated bonding object can be reduced compared to the case of continuously irradiating a single strong laser beam at once for actual bonding, and the substrate It is possible to minimize the thermal damage such as distortion or warping of the product, and yellowing.

Meanwhile, the shapes of the laser beams LB1 , LB2 , LB3 irradiated from each of the laser head modules 310 , 320 , 330 are all shown in a rectangular shape according to an embodiment, but are not limited thereto. Square, circular, Depending on the bonding object such as a point or line shape and the process conditions of the reflow process, several laser beams may be variously changed to the same or different shape.

In addition, the present invention is not limited only by the above-described embodiment, and since it is possible to create the same effect even when changing the detailed configuration, number, and arrangement of the device, those of ordinary skill in the art will present the present invention It is specified that various additions, deletions, and modifications are possible within the scope of the technical idea of

11: bonding object 100: carrier
110: heater 200: conveyor unit
300: laser head module 310: first laser head module
320: second laser head module 410: beam transmission optical fiber
420: convex lens 430: beam shaper
500: infrared camera 600: position measurement camera
Ll: major axis length of laser beam Ls: minor axis length of laser beam
P: output power of the laser beam
Ld : Moving distance per unit time (sec) of bonding object
Ef: energy density of the laser beam

Claims (15)

Bonding the electronic component to the substrate by melting solder by irradiating a laser beam from above the bonding object while linearly transferring the rectangular substrate on which a plurality of electronic components, which are bonding objects, are disposed from one side to the other,
The shape, density, and displacement of the laser beam are controlled based on Equation 1 below,
[Formula 1]
P=kLl(Ls+Ld)Ef
{P is the output power of the laser beam (w), k is the heat transfer coefficient according to the thickness of the substrate (t), Ll is the long axis length of the laser beam (cm), Ls is the short axis length of the laser beam (cm), Ld is the substrate Distance traveled (cm) per unit time (sec), Ef is the energy density of the laser beam (w/cm2)}
The laser beam is irradiated from at least one laser head module, and the substrate is rapidly heated from room temperature through the preheating temperature to the melting temperature of the solder by the laser beam irradiated from the laser head module,
The substrate is a printed circuit board (PCB) in which a thin copper layer for electrical wiring is formed on at least one side of the insulating layer around a resin-based insulating layer,
The thickness (t) of the substrate is formed within the range of 0.1mm to 1mm,
The heat transfer coefficient (k) according to the thickness (t) of the substrate increases in proportion to the thickness of the substrate within the range of 0.9 to 2.7,
The moving distance (Ld) per unit time (second) has a value of at least 0.2 cm,
The output power (P) of the laser beam has a value of at least 400w,
The energy density (Ef) of the laser beam is characterized in that it is controlled within the range of 40w/cm2 to 60w/cm2,
Linear feed laser reflow method. The method of claim 1,
The laser beam is a rectangular laser beam having a long axis (Ll) perpendicular to the transport direction of the bonding object and a minor axis (Ls) parallel to the transport direction of the bonding object,
Linear feed laser reflow method. The method of claim 1,
The laser beam is irradiated simultaneously or sequentially from two or more laser head modules,
Linear feed laser reflow method. 4. The method of claim 3,
The laser beams irradiated from the two or more laser head modules are always overlapped or intermittently overlapped and irradiated to a specific part,
Linear feed laser reflow method. delete delete 3. The method of claim 2,
The long axis length (Ll) of the laser beam is equal to or greater than the width direction length of the bonding object perpendicular to the transfer direction of the substrate;
Linear feed laser reflow method. delete delete delete The method of claim 1,
The short-axis length (Ls) of the laser beam is the output power of the laser beam ( increased proportionally with increasing P),
Linear feed laser reflow method. The method of claim 1,
The short axis length (Ls) of the laser beam is fixed so that all other variables (P, k, Ll, Ef) other than the movement distance (Ld) per unit time (second) based on Equation 1 are fixed so that the unit time ( decreases in inverse proportion as the movement distance (Ld) per second) increases,
Linear feed laser reflow method. The method of claim 1,
The rectangular substrate on which the plurality of electronic components, which is the bonding object, is disposed, is linearly transported together according to the movement of the carrier in a state seated on the upper surface of the carrier, or the laser head module is relatively moved while the carrier is stopped,
Linear feed laser reflow method. 14. The method of claim 13,
The carrier is mounted on the conveyor unit and the movement distance (Ld) per unit time (sec) is controlled by controlling the driving of the conveyor unit,
Linear feed laser reflow method. The method of claim 1,
The preheating temperature is characterized in that less than 200 ℃, a temperature range in which thermal damage is not applied even when the substrate and electronic components are exposed for a certain period of time or more,
Linear feed laser reflow method.

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