JP2004063508A - Method for soldering using lead-free solder and method of manufacturing mounting substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable mounting method by which the anxiety about the fracture of circuits can be eliminated even when the circuits are heated in a flow furnace at the time of mounting surface-mounted components and insertion-mounted components on a wiring board in a mixed state, by using a lead-free solder manufactured by paying attention to the environmental problem. <P>SOLUTION: In this method, the insertion-mounted components 9 are arranged on the wiring board 1 provided with a circuit wiring pattern, land sections 2 for connecting the surface-mounted components 5, and through hole sections 3 for connecting the insertion-mounted components 9 after the surface-mounted components 5 are arranged on the board 1 and electrically connected by using the lead-free solder 11. In this method, the mounting of the components 5 and 9 is performed by cooling a required portion of the wiring board 1 so that the temperatures of the soldered junctions of the surface-mounted components 5 may become ≤150°C in the soldering step of the insertion-mounted components 9. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of soldering an electronic component to a wiring board using lead-free solder and a method of manufacturing a mounting board, and more particularly to a method of mounting a surface mounting component and an insertion mounting component using lead-free solder. The present invention relates to a soldering method and a method of manufacturing a mounting board.
[0002]
[Prior art]
Conventional mounting of electronic components on a wiring board involves forming a circuit pattern made of a conductive material such as copper on the required location of the board made of paper phenolic resin, glass fiber reinforced epoxy resin, polyimide resin, etc. Active elements, passive elements such as capacitors and resistors are arranged at required positions of the pattern, and are electrically and mechanically connected and fixed by means such as soldering. Surface mounting and insertion mounting are performed as means for mounting these electronic components on a wiring board.
[0003]
In surface mounting, a circuit pattern and an electronic component connection terminal portion, a so-called land portion, are formed on the surface of the wiring board, and the electronic component is placed on the land portion, and the terminal portion and the land portion of the electronic component are mounted on the wiring board surface. The connection is made by soldering. Electronic components for such surface mounting include a quad flat package component called QFP, which leads terminals from a rectangular encapsulant in four directions, and a solder ball on the lower surface of a package called BGA. There is a component having terminals arranged therein, a component called an SOP having terminals derived from two sides of the package portion, or an electronic component such as a chip capacitor.
To perform the surface mounting, specifically, a solder paste is applied to a land portion of a wiring board on which a circuit wiring pattern is formed, an electronic component is mounted at a required position, and a terminal portion and a land portion of the electronic component are mounted. In the contact state, the entire substrate is heated in a reflow furnace such as an infrared heater heating method, a hot air heating method, or a combination method of the above two methods, and the solder paste is melted and solidified to be electrically and mechanically connected. It is fixed. FIG. 8 shows an example of this reflow furnace. In FIG. 8, reference numeral 62 denotes a reflow furnace main body, on which a wiring board 61 is conveyed along a rail 63 provided to extend inside the main body, and soldered by a heating device 64 such as an infrared heater. The portion to which the paste is supplied is heated to a temperature equal to or higher than the melting temperature of the solder paste, so that the solder paste is melted and then solidified to perform soldering.
[0004]
Also, insertion mounting means that a through hole that is a hole penetrating this wiring board is formed in the wiring board, a conductive material layer is formed on the inner surface of the through hole, and the lead wire of the electronic component is inserted into the through hole. Soldering and mounting. As electronic components for performing such insertion mounting, there are electronic components such as a resistor, a capacitor, and a DIP (Dual Inline Package).
In order to perform the insertion mounting, the electronic component is placed on a wiring board in which a through hole having a conductive layer is formed on an inner surface of a circuit wiring pattern and an electronic element connecting portion, and leads of the electronic component are inserted into the through hole, and a solder material is inserted. Is carried into a flow furnace equipped with a molten solder bath, the back surface of the wiring board is brought into contact, and the molten solder material is filled into the through-hole into which the lead wire of the electronic component is inserted by surface tension. The connection is fixed electrically and mechanically. One example of this flow furnace is shown in FIG. In FIG. 9, reference numeral 72 denotes a flow furnace main body. A rail 73 is disposed in the flow furnace so as to extend, and the wiring board 71 is conveyed along the rail 73. A heating device 74 such as an infrared heater is arranged near the entrance in the flow furnace, and the wiring board 71 is preheated to a predetermined temperature. A solder bath 75 containing molten solder 76 is arranged in a post-process area of the preheating area. The molten solder 76 is accommodated in the solder bath 75, and one or more nozzles 77 for injecting the molten solder 76 upward are arranged. At this ejection position, the lower surface of the wiring board 71 conveyed on the rail 73 comes into contact with the molten solder 76 so that soldering is performed.
[0005]
In recent electronic devices that are mounted in a complicated and high-density manner, a so-called mixed mounting method in which these surface-mounted elements and insertion-mounted elements are mixed has been widely adopted. In such mixed mounting, a process as shown in FIG. 10 is widely employed. That is, in step a, a wiring pattern is formed of a conductive material such as copper as a wiring board material, a land portion for surface mount components, and a through-hole portion are formed to manufacture a wiring substrate. Next, in a step b, a solder paste containing a fine powder of a solder material and a flux is applied to the land by a screen printing method. Next, in step c, the surface-mounted component is arranged at a predetermined position. Next, in step d, the wiring board on which the surface-mounted components are arranged is carried into a reflow furnace shown in FIG. 8, the solder paste is melted, and the surface-mounted components are connected and fixed to the wiring board. Next, in step e, the lead wire of the insertion mounting component is inserted into the through-hole portion and arranged on the wiring board. Next, this is carried into the flow furnace shown in FIG. 9, and the molten solder is brought into contact with the back surface of the wiring board, and in the through-hole portion, the through-hole of the wiring board and the lead wire of the inserted mounting component are connected and fixed. Complete the implementation of.
[0006]
By the way, conventionally, as a solder material for joining a wiring pattern and an electronic component in such mounting, tin-lead eutectic solder has been used in view of wettability to an electrode material, joining reliability, soldering temperature, and the like. It has been widely used because of its superiority. However, when this lead-containing solder material, which has been widely used in electrical equipment, is discarded, lead harmful to the human body elutes into the environment, causing heavy metal contamination. The use of free solder materials is rapidly advancing.
[0007]
As lead-free solder materials widely known at present, materials such as Sn-Ag-Cu, Sn-Ag-Bi-In, Sn-Zn-Bi, Sn-Cu, and Sn-Zn are known. These lead-free solder materials have a slightly higher melting point (183 ° C.) than the tin-lead solder material.
On the other hand, as a material of the terminal part of the electronic component, Cu, Fe, or a Fe-Ni alloy called 42 alloy is used, and the surface of the terminal part material improves the wettability during soldering. In order to do so, plating is applied. As the plating material, Sn-Pb plating is widely used.
[0008]
By the way, it has been found that, depending on the combination of a lead-free solder material generally used at present and a plating material on the surface of a lead, when mixed mounting is performed, frequent contact failures occur at a connection portion of the surface mounting. That is, after using a ferrous material as a lead wire and mounting the component by surface mounting a component whose surface is subjected to Sn-Pb plating using Sn-Ag-Cu solder material, mounting another component by insertion mounting In order to connect, when soldering by introducing into a flow furnace, the solder connection part of the already mounted surface mount components, that is, Sn-Ag-Cu as a solder material and Sn-Pb as a plating material are used. In the mixed region, a structure having a low melting point such as Sn-Ag-Pb is formed, and it is considered that the structure is caused by melting due to the heat of the flow furnace and breaking the joint.
[0009]
[Problems to be solved by the invention]
The present invention has been made in order to solve the above-described problems in mounting a wiring board formed by mixing and mounting a surface mounting component and an insertion mounting component, using a lead-free solder material in consideration of environmental issues, It is an object of the present invention to provide a highly reliable mounting method which does not cause a circuit breakage even when heated by a flow furnace when mounting a mixed wiring board.
[0010]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a wiring board including a circuit wiring pattern, a land portion for connecting a surface mounting component, and a through hole portion for connecting an insertion mounting component. After arranging the surface mount components on the wiring board and electrically connecting them using lead-free solder, arranging the insertion mounting components on the wiring board and electrically connecting them using lead-free solder In the method of soldering electronic parts,
In the step of soldering the insertion mounting component, a required portion of the wiring board is cooled so that a temperature of a solder joint of the surface mounting component is 150 ° C. or less. It is a method of attaching.
[0011]
In the first aspect of the present invention, the cooling of the wiring board is performed by a cooling block arranged around a surface mounting component, or a position where the wiring board and the molten solder come into contact in a soldering step of the insertion mounting component. In the above, the cooling medium may be sprayed onto the surface of the wiring substrate.
[0012]
According to a second aspect of the present invention, there is provided a wiring board having a circuit wiring pattern, a land portion for connecting a surface mounting component, and a through hole portion for connecting an insertion mounting component, wherein the surface mounting component is connected to the wiring board. Placed on top and electrically connected using lead-free solder, a mounting board is placed on the wiring board, a method of manufacturing a mounting board for soldering electronic components using lead-free solder,
A method of manufacturing a mounting board, comprising: cooling a required portion of a wiring board so that a temperature of a solder joint of the surface mounting component is 150 ° C. or less in the soldering step of the insertion mounting component. .
[0013]
In the second aspect of the invention, the cooling of the wiring board is performed by a cooling block disposed around a surface-mounted component, or the wiring board is cooled in a soldering step of the insertion-mounted component. This can be performed by injecting a cooling medium onto the surface of the wiring substrate at a position where the molten solder contacts the substrate.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment]
In the present embodiment, when heating in a flow furnace, a heat dissipation block is arranged around the surface of the surface-mounted component to suppress a rise in the temperature of the solder joint of the surface-mounted component.
A mounting method according to the present embodiment will be described in detail with reference to FIG. 1 which is a partially cutaway cross-sectional view of a wiring board on which mixed mounting is performed. In FIG. 1, reference numeral 1 denotes a wiring board on which a surface mounting component 5 and an insertion mounting component 9 are mixed, and a land for mounting the surface mounting component 5 and electrically and mechanically connecting and fixing the wiring substrate 1. It has a through hole 3 that is a through hole for inserting and electrically and mechanically connecting and fixing the lead 2 of the insertion mounting component 9 by inserting the lead 2 of the component 2. A conductive layer 4 such as copper is formed on the inner surface of the through hole 3.
[0015]
An electronic component 5 such as a QFP component is arranged near the land 2, and leads 6 of the electronic component 5 are connected to the land 2 by solder 8. The lead 6 is made of a metal such as copper or an iron alloy such as Fe-Ni called 42 alloy, and its surface contains lead in order to improve the wettability with the solder 8. Plating 7 is applied.
The insertion mounting component 9 includes a component main body and a lead 10 led out from the component main body. The lead 10 is inserted into the through hole 3, and the lead 10 and the inner surface of the through hole 3 are soldered by the solder 11. Is connected to the conductive layer 4 formed on the substrate.
[0016]
Hereinafter, a method of mounting the wiring board for performing the mixed mounting of FIG. 1 will be described with reference to FIGS.
A circuit wiring pattern is formed on the surface of a substrate material 1 such as a paper phenol resin, a glass-epoxy resin, or a polyimide resin, and is connected to a land portion 2 for connecting to a mounted surface mounting component and an insertion mounting component 6. Is formed and a conductive layer 4 on the inner surface of the through hole 3 is formed to manufacture a wiring board (step a).
[0017]
A solder paste 12 is applied to the surface of the land portion 2 by screen printing, and a surface mount component 5 having a lead-containing plating layer at a terminal portion is disposed near the land portion 2. Is arranged such that the lead wire 6 is in contact with the land portion 2 via the solder paste 12 (step b).
[0018]
Then, the surface of the wiring board 1 is heated from the surface side of the wiring board 1 to a temperature equal to or higher than the melting temperature of the solder paste 12 by using a reflow device (not shown), and the land portion 2 and the leads 6 are soldered. The connection is fixed electrically and mechanically (step c).
[0019]
The lead wire 14 of the insertion mounting component 6 is inserted into the through hole 3, and the heat radiation block 20 is disposed on the upper surface of the surface mounting component 5. It is arranged so as to be in contact with the lead wire 6 of the component 5 (step d).
[0020]
Next, the wiring board 1 is placed on a flow device (not shown) and transported to a flow furnace equipped with a solder bath containing molten solder as shown in FIG. In this flow furnace, the molten solder material flows as a jet in the direction of the wiring board passing above the solder bath, and the molten solder contacts the lower surface of the wiring board and is inserted into the lead 10 inserted into the through hole. And the conductive layer 4 on the inner surface of the through hole 3 are soldered (step e). At this time, when soldering the through-hole portion, the lead wire of the surface mount component is heated by the molten solder, but the heat is dissipated by the heat radiation block, so that the connection between the land portion 2 and the lead wire 6 is made. There is no accumulation in the department. Therefore, the temperature of the connecting portion does not rise to 150 ° C. or more, and as a result, the solder 8 connecting the land portion 2 and the lead wire 6 does not re-melt and does not break.
[0021]
In the above-described embodiment, the heat radiation block is arranged above the lead wire of the surface mount component. However, as seen in steps (d) and (e) of FIG. Around the lead wire so as to surround the lead wire. If such an arrangement is adopted, if the number of lead wire terminals is small and sufficient heat cannot be dissipated, or if the length of the lead wire terminals is short, or if the terminals are arranged below the surface-mounted components like a BGA, It can also be applied to components with structures that are not suitable for mounting blocks.
[0022]
In the present invention, a flat package shape such as QFP is suitable as a surface mount component on which the heat radiation block is mounted. The shape of the heat radiation block disposed in contact with such a surface mount component is as shown in FIG. 4 such that the heat radiation block is in contact with the lead wire of the flat package, or is surrounded by a hollow square pillar so as to surround the periphery of the lead wire. It is preferable to use a frame (FIG. 4 (a)) or a shape in which a part of the lower part of the columnar block is cut away to form a recess (FIG. 4 (b)). The material is preferably a material having excellent thermal conductivity, light weight, and poor solderability. The most suitable material is aluminum.
[0023]
[Second embodiment]
In the present embodiment, spot cooling is performed in order to prevent a temperature rise of a surface mount component, which is expected to rise in a flow soldering process. In other words, after mounting the surface-mounted components and soldering the surface-mounted components in a reflow furnace, disposing the insertion-mounted components in required places, carrying the components into the flow furnace, and soldering the through-holes. The surface of the wiring board is locally cooled to prevent the temperature of the lead wire joint of the surface mount component from rising to 150 ° C. or more.
[0024]
FIG. 5 shows a temperature curve of the wiring substrate in this flow furnace. In FIG. 5, the horizontal axis represents the elapsed time, and the vertical axis represents the surface temperature at an arbitrary point on the lower surface of the wiring board in contact with the solder bath. As shown in FIG. 5, the wiring board is preheated at the initial stage when it is carried into the flow furnace. Next, the lower surface of the wiring board contacts the molten solder twice, once and twice, at the molten solder jets provided at two locations in the solder bath, and at this time, the temperature of the wiring board reaches the maximum temperature. Then, the lead wire of the insertion mounting component is soldered. Then, when the wiring board separates from the region of the solder bath, the temperature gradually decreases, and the solder solidifies. In such a wiring board which is soldered through a temperature history, when the injection position of the solder bath at which the upper surface of the wiring board records the highest temperature, that is, the temperature of the region A in FIG. Since there is a great possibility that the solder joint between the mounted component and the land portion will peel off, it is important to control the temperature of this portion to 150 ° C. or less.
[0025]
On the other hand, cooling the entire area of the flow furnace not only reduces energy efficiency and is not economical, but also causes insufficient connection of the solder due to insufficient solder bonding. Therefore, it is practically necessary to cool only a specific area in the flow furnace, and it is preferable to cool the area A in FIG.
For this reason, it is preferable to dispose a cooling medium pressure feeding nozzle above the flow furnace and blow a cooling medium such as cooling air or cooling nitrogen onto the wiring board located above the molten solder injection nozzle.
[0026]
FIG. 6 is a cross-sectional view of a main part of a flow furnace that can be used in the present embodiment. In FIG. 6, reference numeral 52 denotes a solder bath, in which a molten solder 54 is accommodated. A rail 53 extends near the upper part of the solder bath 52, and the wiring board 51 is transported along the rail 53. In the solder bath 52, a nozzle 55 for injecting the molten solder 54 upward is arranged. At the position of the injected molten solder, the wiring board 51 and the molten solder 54 come into contact with each other, The molten solder is absorbed and filled in the through-hole portion, and soldering is performed. Above the injection position of the molten solder 54, a cooling medium injection nozzle 56 is arranged, and a cooling medium such as cooling air is blown to a required location on the surface of the wiring board 51 to perform spot cooling.
[0027]
In this flow furnace apparatus, the cooling medium supply nozzle 56 is provided with an on-off valve, and when the wiring board is approaching the jet position, the valve is released and the cooling medium is injected by cooling the wiring board to cool the wiring board. It is preferable that the on-off valve be shut off and the supply of the cooling medium is stopped when the jet position is desorbed.
Alternatively, it is preferable that the cooling medium supply nozzle is set to start and stop the supply of the cooling medium by a pump. In any case, the supply of the cooling medium is preferably stopped when the wiring board is not present at the jet position.
Further, the cooling medium supply nozzle may be a nozzle having one opening extending in the horizontal direction of the wiring board, or a plurality of openings may be arranged in one row in the horizontal direction of the wiring board. The shape may be a nozzle. Further, the plurality of nozzles may be controlled so as to be uniformly opened and closed by an on-off valve, or the individual nozzles may be individually controlled and partially opened and closed. Good. By using a device that can individually control the individual nozzles in this manner, it is possible to cool only a specific portion of the wiring board that requires specific cooling, and unnecessary cooling is not performed. improves.
[0028]
[Third Embodiment]
Generally, a large number of electronic components differing in heat resistance, terminal form, and the like are mounted on the mixed mounting substrate surface. When manufacturing such a wiring board on which a large number of electronic components are mounted, mounting the heat radiating block on top of all the surface mount components requires a manual operation since the mounting of the heat radiating block is performed manually. It is a factor that reduces the performance. Therefore, it is necessary to select a surface mount component on which the heat radiation block is mounted.
The present embodiment relates to a method for selecting a surface mount component on which a heat radiation block is mounted.
The point of selection in the present embodiment is that a surface mount component that satisfies all the two requirements that the material of the lead wire of the surface mount component is iron or an alloy thereof and that the plating material contains lead. Only the radiating block is placed on the radiating block. As a result, a decrease in productivity is suppressed to a minimum, and even in a subsequent flow soldering step, soldering with high reliability can be achieved without peeling off connection of the lead portion of the surface mount component.
[0029]
【Example】
Hereinafter, the present invention will be described with reference to examples.
Using a glass epoxy resin substrate, a substrate on which a wiring pattern, a land portion, and a through hole were formed was manufactured. A solder paste containing Sn-Ag-Cu-based solder was applied to the lands on the substrate. Next, a QFP type surface mount component in which Sn-Pb plating was applied to the surface of a terminal made of 42Alloy, which is an Fe-Ni-based alloy, was mounted so that the terminal portion was arranged on the land portion. This was reflowed at a peak temperature of 240 ° C. to perform soldering.
Next, an insertion mounting component is arranged in a through hole of the board, and a thermocouple is attached to a solder joint of a surface mounting board mounted on the wiring board. The substrate was carried into a flow furnace, and flow soldering was performed while changing the temperature of the solder joint of the surface-mounted component from 100 ° C. to 190 ° C. With respect to the mounting board thus obtained, the temperature of the solder joint of the surface mount component, the bonding strength of the surface mount component, and the remelting occurrence rate were measured for each of the five pins from the four sides of the QFP, and the 20 Was calculated. FIG. 7 shows the result.
As is clear from FIG. 7, when the lead wire temperature of the surface mount component was 150 ° C. or less, the bonding strength stably showed a value near 1350 gf, but at 160 ° C., the strength reached 800 gf. At a temperature of 180 ° C. or higher, the strength decreased to 420 gf. Similarly, the rate of remelting (the rate of occurrence of lead peeling at all lead wire joints) was 0% in the region of 150 ° C. or less, but 20% at 160 ° C. At a frequency of 180 ° C., and at 180 ° C., the rate of occurrence reached 60%.
[0030]
【The invention's effect】
According to the present invention, in mounting a wiring board in which surface mount components and insertion mount components are mixed, a highly reliable mounting method that does not cause peeling of solder joints while using lead-free solder in consideration of the environment. Can be provided.
[Brief description of the drawings]
FIG. 1 is a partially cutaway sectional view of a wiring board on which components of the present invention are mounted.
FIG. 2 is a mounting process diagram by a cross-sectional view in which a part of the wiring board of the present invention is cut away.
FIG. 3 is a mounting process diagram by a cross-sectional view in which a part of the wiring board of the present invention is cut away.
FIG. 4 is a perspective view of the cooling block of the present invention.
FIG. 5 is a graph showing a change in a wiring board surface temperature in a flow furnace.
FIG. 6 is a schematic sectional view showing a flow furnace of the present invention.
FIG. 7 is a graph showing an example of the present invention.
FIG. 8 is a schematic sectional view showing a conventional reflow furnace.
FIG. 9 is a schematic sectional view showing a conventional flow furnace.
FIG. 10 is a process diagram of mounting a wiring board on which conventional components are mixed.
[Explanation of symbols]
1, 51, 61, 71 Wiring board 2 Land 3 Through hole 4 Conductive layer 5 Surface mount component 6, 10 Lead wire 7 Plating layer 8, 11 Solder 9 Insert insertion component 20 ... heat dissipating blocks 52, 75 ... solder baths 53, 63, 73 ... rails 54, 76 ... molten solder 55, 77 ... molten solder injection nozzle 56 ... cooling medium injection nozzle 62 ... reflow furnaces 64, 74 ... heating device

Claims (6)

Place a surface mount component on the wiring board on a circuit board provided with a circuit wiring pattern, a land portion for connecting a surface mount component, and a through hole portion for connecting an insert mount component, and lead-free. After electrically connecting using solder, the insertion mounting component is arranged on the wiring board, and in a method for soldering electronic components that are electrically connected using lead-free solder,
In the step of soldering the insertion mounting component, a required portion of the wiring board is cooled so that a temperature of a solder joint of the surface mounting component is 150 ° C. or less. Attachment method. 2. The soldering method using lead-free solder according to claim 1, wherein the cooling of the wiring board is performed by a cooling block arranged around a surface mount component. The cooling of the wiring board is performed by injecting a cooling medium onto the surface of the wiring board at a position where the wiring board and the molten solder come into contact in the soldering step of the insertion mounting component. A soldering method using the described lead-free solder. Place a surface mount component on the wiring board on a circuit board provided with a circuit wiring pattern, a land portion for connecting a surface mount component, and a through hole portion for connecting an insert mount component, and lead-free. After electrically connecting using solder, a method of manufacturing a mounting board for soldering electronic components using lead-free solder, arranging an insertion mounting component on the wiring board,
A method for manufacturing a mounting board, comprising: cooling a required portion of a wiring board so that a temperature of a solder joint of the surface mounting component is 150 ° C. or less in the step of soldering the insertion mounting component. 5. The method according to claim 4, wherein the cooling of the wiring board is performed by a cooling block arranged around the surface mount component. The cooling of the wiring board is performed by injecting a cooling medium onto the surface of the wiring board at a position where the wiring board and the molten solder come into contact in the step of soldering the insertion mounting component. A manufacturing method of the mounting board described in the above.

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