JP2003060340A - Solder segregation controller and component reworking method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a temperature gradient generated in a solder flow process by process control and to suppress segragation. SOLUTION: A segragation controller is used for the solder flow process for soldering electronic components on the surface of a board by using the Pb free solder of a high melting point and soldering the different electronic components, by giving a solder jet from the rear face of the board. The solder segragation controller is provided with a heater 100 for heating an opposite side at the time of soldering by the solder jet and a controller 110 for controlling the heater 100 to be a prescribed temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder segregation control device and a component rework method used when mounting or separating and remounting electronic components on a printed circuit board.

[0002]

2. Description of the Related Art Eutectic solder is most often used as a connecting material for electronic parts on a printed circuit board. Since this eutectic solder contains Pb (lead), it is necessary to consider the environment, and a solder material not containing Pb has been developed. The solder mounting method includes reflow soldering in which a solder supplied in advance is heated and melted, and flow soldering in which a substrate is brought into contact with a molten solder jet to perform soldering.

The conventional flow soldering process will be described. FIG. 7 is an explanatory diagram showing a conventional flow soldering process. Here, when the large component (electronic component) 10 is mounted on the substrate 20, the large component 10
The terminals (component leads) 10a are electrically connected by the solder 30. In this joining, the large-sized component 10 is already connected to the opposite side, and the molten solder jet 40
It is performed by contacting.

As a reference technical document, Japanese Unexamined Patent Publication No. 2001
-36233, "Mounting structure using Pb-free solder" is disclosed. Here, in order to prevent the segregation of the constituent elements in the solder from occurring easily, a heat conductive material is provided between the component body and the substrate to suppress the generation of a large temperature gradient in the solder joint.

[0005]

However, in the conventional flow soldering process as shown above, large parts or the like already connected to the opposite side have a large heat capacity and the temperature does not rise immediately. Therefore, a temperature gradient is generated in the solder portion of the joint portion by heating from the back side of the substrate and heat transfer to the component side. That is, when performing flow soldering, if there is a component already joined by reflow soldering on the opposite surface of the substrate, the low melting point component eluted from the component electrode in the Pb-free solder causes segregation, and the reliability of the joint is improved. Will significantly reduce the sex.

It is considered that such segregation, that is, the phenomenon that the distribution of the constituent elements becomes non-uniform, results from the occurrence of a large temperature gradient in the solder joint. As a solution to this problem, as disclosed in Japanese Patent Application Laid-Open No. 2001-36233, it is known to provide a heat conductive material between the component and the substrate, but in this case, the number of components and the number of steps thereof increase. However, the cost will be increased.

The above phenomenon will be further described. Figure 8
FIG. 9 is an explanatory diagram showing a temperature gradient of a connection portion on the opposite surface during flow soldering, and FIG. 9 is an explanatory diagram showing a segregation state of low melting point components. For the terminal (component lead) 10a,
In some cases, a low melting point element such as Pb is used as the plating material. As shown in FIG. 8, when a temperature gradient occurs in the bonded solder portion, the low melting point component segregates during the solidification process. In particular, as shown in FIG. 9, Pb (lead), Bi (bismuth), etc. used for component electrode plating segregate.

The present invention has been made in view of the above, and it is a first object of the present invention to reduce a temperature gradient generated during a solder flow process by process control and suppress segregation.

A second object is to intentionally control the occurrence / non-occurrence of segregation to rework parts.

[0010]

In order to achieve the above object, in a solder segregation control device according to a first aspect of the present invention, an electronic component is soldered to the surface of a substrate using a high melting point Pb-free solder. After that, a solder segregation control device used in a solder flow process of soldering another electronic component by applying a solder jet from the backside of the board, and heating the opposite side when performing soldering by the solder jet And a control means for controlling the heating means to a predetermined temperature.

According to the present invention, by heating from the side opposite to the solder jet portion during the flow soldering process, it becomes possible to eliminate the temperature gradient in the solder joint portion on the opposite side of the substrate.

Further, in the solder segregation control device according to the second aspect, the heating means uses infrared rays.

According to the present invention, in claim 1, it is possible to suppress the temperature gradient on both sides of the substrate by heating the opposite side of the solder jet portion by a simple heating means utilizing infrared rays.

Further, in the solder segregation control device according to the third aspect, the heating means uses a laser beam.

According to the present invention, in claim 1, by using the heating means by the laser light, it is possible to suppress the generation of the temperature gradient due to the heating from one surface of the substrate, and at the same time, the minute area is formed by the laser light. It is possible to control heating and irradiation time.

Further, in the solder segregation control device according to claim 4, the heating means generates hot air.

According to the present invention, in claim 1, the opposite side of the solder jet portion is heated by generating hot air with a simple structure such as a heater and a fan,
It is possible to suppress the temperature gradient on both sides of the substrate.

Further, in the component reworking method according to the fifth aspect, a layer having a weak mechanical strength, which causes segregation of a trace element intentionally contained in the bonding solder and can separate the bonding portion by an external force. Heating / cooling is performed so as to form

According to the present invention, when a component rework for separating a component soldered to a substrate and mounting a new component is performed, a trace amount of a trace element intentionally contained in the solder joint at the solder joint is By heating / cooling so as to cause segregation and to form a layer with weak mechanical strength that can separate the bonded portion by an external force, a segregated portion with weak mechanical strength can be created, and separation at that portion Can be easily performed.

Further, in the component reworking method according to claim 6, the solder joint is heated and melted from one direction,
A temperature gradient is generated during solidification to segregate trace elements, and then external force is applied to separate the parts.

According to the present invention, in claim 5, when the component rework for separating the component soldered to the substrate and mounting a new component is performed, the solder joint is heated and melted from one direction to be solidified. By generating a temperature gradient in the case of, a segregation portion having weak mechanical strength can be formed, and separation at that portion can be easily performed.

In the component reworking method according to claim 7, the component side is heated to cause segregation at the interface between the component lead and the solder, and the solder is left on the substrate side.

According to the present invention, in the sixth aspect, when the component rework for separating the component soldered on the substrate and mounting a new component is performed, the component side is heated to form the component lead and the solder. By causing segregation at the interface, the solder residue can be left uniformly on one side.

In the component reworking method according to the eighth aspect, a new component is mounted on the solder portion left on the substrate side and rejoined.

According to the present invention, in claim 7, when the component reworked to separate the component soldered to the substrate and mount a new component, the component is left on the substrate after the component separation. It is possible to reconnect by using the solder as it is.

In the component reworking method according to the ninth aspect, only the flux is applied to the electrode of the new component to be mounted, then the electrode is mounted, and then heat melting is performed.

According to the present invention, in claim 8, only the flux is applied to the electrode of the new component to be mounted when the component soldered on the substrate is separated and the component rework for mounting a new component is performed. By mounting afterwards and heating and melting, misalignment of parts during mounting due to adhesiveness of flux is reduced.

Further, in the component reworking method according to the tenth aspect, the remelting at the time of joining is controlled so that the temperature of the joined portion becomes the same on the upper and lower surfaces.

According to the present invention, in claim 8, when the component rework for separating the component soldered to the board and mounting a new component is performed, the interface between the component lead and the solder is separated after the component is separated. It becomes possible to rejoin the segregated low melting point component element in the solder.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a solder segregation control device and a component rework method according to the present invention will be described in detail below with reference to the accompanying drawings. The present invention is not limited to this embodiment.

FIG. 1 is an explanatory diagram showing a schematic configuration of a solder segregation control device according to an embodiment of the present invention. In the figure, reference numeral 100 is a heating device which is provided on both sides of the substrate 10 and heats a solder joint surface at a predetermined temperature. Reference numeral 110 is provided with an operation unit, a display unit and the like with a microcomputer system as a center, and a temperature of the heating device 100. Is a control device for controlling the.

In FIG. 1, after using Pb-free solder having a high melting point to solder a large component (electronic component) 10, a solder jet is applied from the back surface of the large component (electronic component) 10 to connect another electronic component. When performing, the heating device 100 on the upper surface side of the substrate 20 is controlled by the control device 110. That is, in order to eliminate the temperature gradient of the solder joint portion on the opposite side of the substrate during the flow soldering process, the heating is also controlled from the opposite side of the solder jet portion. As a result, it is possible to suppress the segregation of the trace element elements in the solder due to the temperature gradient generated from the cooling due to the propagation of heat to the atmosphere on the component side and the heating due to the contact of the molten solder on the back surface of the substrate 20.

FIG. 2 is an explanatory view showing an example of heating means of the heating device in FIG. As the heating device 100, for example, a laser output device 10 for heating by laser irradiation
0a, an infrared output device 100b that heats by infrared irradiation, or a hot air output device 100c that heats by a heater and a fan may be selected and used in consideration of the state of the substrate.

That is, by applying infrared rays from the infrared output device 100b or the hot air output device 100c from the upper surface of the substrate 20, heating from one direction is possible. In addition, since the beam spot diameter is small by using the laser light from the laser output device 100a, it becomes possible to control the heating amount by local heating or time control for a minute portion.

By the way, if there is segregation of the low melting point component, the mechanical strength (bonding strength) of the segregated portion is lowered, and when an external force is applied to the component, a crack is generated due to the strength reduction, and the component is removed from the substrate. To separate. When parts are repaired and melted and separated, the solder is separated into electrodes on both sides, and remounting requires a process of removing solder and resupplying solder in a later step.

Therefore, by utilizing the ease of separation at the segregation portion, the low melting point component elements such as Pb and Bi intentionally contained are arbitrarily segregated, and the components mounted on the substrate by the external force are removed. By separating, the solder can be left on either the component side or the substrate 20 side. Hereinafter, examples of segregation / separation / remounting will be described with reference to FIGS.

In order to cause the segregation, heating and melting are performed from one side of the bonding portion, and a temperature gradient is generated in the vertical direction in the cooling process, so that the segregation is formed at the interface between the solder material and the electrode. That is, as shown in FIG. 3, by heating with the heating device 100 only from the component lead (terminal 10a) side and then cooling, a temperature gradient is generated, and Pb is generated at the interface between the component lead (terminal 10a) and the solder. Segregation 30a
Can be forced to wake up. That is, the low melting point component elements uniformly dispersed in the bonding solder are used for the component leads (terminal 1
0a) and solder are segregated at the interface.

Next, after the segregation generation step as described above, an external force is applied to the parts, whereby cracks are generated in the segregated portions having weak strength, and the parts are separated. As a result, as shown in FIG. 4, most of the solder remains on the substrate 20 side, and the formation of the solder leaves the mount shape of the component lead (terminal 10a) maintained.

Further, when the new component is remounted after the above-mentioned separation of the components, by mounting the new component on the remaining solder as shown in FIG. 5, it is not necessary to re-supply the solder. . That is, since the removed shape of the component lead is maintained, it is possible to stably remount a new component. In addition, by applying flux to the leads of the new component in advance by a method such as transfer, the yield of component mounting accuracy is improved by the adhesive force during mounting. Also, the yield of soldering is improved due to the effect of removing the oxide film during reheating and melting.

After remounting according to FIG. 5 above,
Further, the control device 110 heats the component from above and below, and controls the heating device 100 so that a temperature gradient is not generated, so that the component is solidified. That is, as shown in FIG. 6, when re-bonding, the low melting point component is uniformly dispersed by controlling heating and cooling so as not to create a temperature gradient. As a result, the elements segregated on the mount surface are dispersed in the solder, and good component connection is realized in terms of reliability without forming a portion with weak bonding strength.

[0041]

As described above, according to the solder segregation control device (claim 1) of the present invention, by heating from the opposite side of the solder jet portion during the flow soldering process, Since it is possible to eliminate the temperature gradient in the solder joint, it is possible to eliminate the occurrence of solder segregation during the current process and improve the reliability of the joint.

Further, according to the solder segregation control device (claim 2) of the present invention, in claim 1, since the opposite side of the solder jet portion is heated by a simple heating means utilizing infrared rays, both sides of the board are heated. It is possible to suppress the temperature gradient that tends to occur and to easily eliminate segregation.

According to the solder segregation control device (claim 3) of the present invention, the heating means by the laser beam in claim 1 suppresses the generation of the temperature gradient by heating from one surface of the substrate. It is possible to heat the micro area by laser light,
Since the irradiation time can be controlled, the occurrence of segregation can be suppressed more accurately.

Further, according to the solder segregation control device (claim 4) of the present invention, in claim 1, the opposite side of the solder jet part is heated by generating hot air with a simple structure such as a heater and a fan. Therefore, generation of a temperature gradient on both sides of the substrate is suppressed, and segregation can be easily eliminated.

Further, according to the component reworking method (claim 5) of the present invention, when the component reworking for separating the component soldered on the substrate and mounting a new component is performed, the solder joint is joined. Since the trace elements intentionally contained in the solder are segregated and heating / cooling is performed so as to form a layer with weak mechanical strength that can separate the joint part by external force, the segregated part with weak mechanical strength Can be formed arbitrarily, and separation at that part can be easily performed,
The efficiency of the parts rework process can be improved.

Further, according to the component reworking method (claim 6) of the present invention, when the component reworking for separating the component soldered on the substrate and mounting a new component is performed, the solder joint portion is removed. Since it is heated and melted from the direction and a temperature gradient is generated during solidification, a segregated portion having weak mechanical strength can be arbitrarily formed, and parts can be easily separated at that portion.

According to the component rework method (claim 7) of the present invention, in the component rework according to claim 6, when the component soldered to the substrate is separated and a new component is mounted, By heating the side where the component is soldered to cause segregation at the interface between the component lead and solder, it is possible to leave the remainder of the solder uniformly on one side, so when remounting the component A solder removing step for flattening the board surface is unnecessary.

Further, according to the component reworking method (claim 8) of the present invention, in the component reworking according to claim 7, when the component soldered to the board is separated and a new component is mounted, Since the solder left on the substrate after the separation of the components is used as it is for reconnection, the solder resupply process at the time of rework is not necessary.

According to the component reworking method (claim 9) of the present invention, in the component reworking according to claim 8, when the component soldered to the board is separated and a new component is mounted, By applying flux only to the electrodes of the new component to be mounted and then mounting and heating and melting, the misalignment of the component at the time of mounting due to the adhesiveness of the flux is reduced, so the yield in component mounting is improved and Oxidation of the solder surface is prevented during heating and the wettability of that portion is improved, so that stable reconnection can be performed.

According to the component reworking method (claim 10) of the present invention, in the component reworking according to claim 8, when the component soldered to the board is separated and a new component is mounted, Since the low melting point component element segregated at the interface between the component lead and the solder after the component is separated can be rejoined in the solder, rejoining with improved initial strength and reliability is realized.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a solder segregation control device according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing an example of heating means of the heating device in FIG.

FIG. 3 is an explanatory diagram showing a forced segregation forming process according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a separated state of components by segregation formation according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a remounting state after component separation according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a state of rejoining (heating) after remounting according to the exemplary embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a conventional flow soldering process.

FIG. 8 is an explanatory diagram showing a temperature gradient of a connection portion on the opposite surface during conventional flow soldering.

FIG. 9 is an explanatory diagram showing a conventional segregation state of low melting point component elements.

[Explanation of symbols]

10 Large parts 20 substrates 30 solder 100 heating device 100a laser output device 100b infrared output device 100c Hot air output device 110 control device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B23K 31/02 310 B23K 31/02 310F F term (reference) 4E080 AA01 5E319 AB01 BB01 CC24 CC44 CC45 CC46 CC49 CD21 CD57

Claims (10)

[Claims] 1. A solder segregation control used in a solder flow process in which an electronic component is soldered to a front surface of a substrate using a high melting point Pb-free solder and then a solder jet is applied from the rear surface of the substrate to solder another electronic component. An apparatus, comprising: a heating unit that heats the opposite side when performing soldering by the solder jet; and a control unit that controls the heating unit to a predetermined temperature. Solder segregation control device. 2. The solder segregation control device according to claim 1, wherein the heating means uses infrared rays. 3. The solder segregation control device according to claim 1, wherein the heating means uses a laser beam. 4. The solder segregation control device according to claim 1, wherein the heating means generates hot air. 5. The heating / cooling is performed so as to cause the segregation of a trace element intentionally contained in the bonding solder to occur, and to form a layer having weak mechanical strength in which the bonding portion can be separated by an external force. How to rework parts. 6. A component reworking method, wherein a solder joint is heated and melted from one direction, a temperature gradient is generated during solidification, segregation of trace elements, and then external force is applied to separate the components. 7. The component reworking method according to claim 6, wherein the component side is heated to cause segregation at the interface between the component lead and the solder, and the solder is left on the substrate side. 8. The component reworking method according to claim 7, wherein a new component is mounted on the solder portion left on the substrate side and rejoined. 9. The component reworking method according to claim 7, wherein only the flux is applied to the electrode of the new component to be mounted, the electrode is mounted, and then the heating and melting are performed. 10. The component reworking method according to claim 8, wherein the remelting at the time of joining is controlled such that the temperatures of the joined portions are the same on the upper and lower surfaces.