JP2007150079A - Reflow device and soldering method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflow device capable of stably performing a soldering and of realizing a bonding state of high quality. <P>SOLUTION: The reflow device comprises a treatment for mounting an installing body and an installed material which are bonded by the soldering; a minute oscillation impresser for impressing a minute oscillation to the treatment portion; and a minute oscillation generator for generating the minute oscillation transmitted to the minute oscillation impresser, wherein the treatment portion and the minute oscillation impresser are united. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention mainly relates to a reflow apparatus for soldering a mounted object to a mounted material, and more particularly to a reflow apparatus for bonding an electronic component, which is a mounted object, to a substrate, which is a mounted material, using solder not containing lead.

  In recent years, portable electronic devices such as digital cameras and DVD players have become highly functional and miniaturized. Along with this, the substrates built into the devices are also downsized and are becoming thinner. In addition, in order to improve the degree of freedom when arranging the substrate in the housing, the use of a film substrate is also progressing.

  As the functionality of devices increases, the heat resistance of electronic components mounted on a substrate tends to decrease. For example, the heat resistance temperature of electronic components such as CCD modules and optical pickups is extremely low compared to the heat resistance temperature of conventional electronic components and is 150 ° C. or lower.

  Furthermore, the use of solder containing lead is being reconsidered due to increased awareness of environmental protection. For example, in Europe, the use of solder containing lead is restricted by laws and regulations. Therefore, research on lead-free solder not containing lead has been actively conducted as an alternative material for solder containing lead. However, the melting temperature of lead-free solder is generally 200 to 220 ° C., which is 20 to 40 ° C. higher than solder containing lead. Therefore, it is difficult to mount an electronic component having a heat resistant temperature of 150 ° C. or less on a substrate using lead-free solder.

  When an electronic component is mounted on a substrate using lead-free solder, the entire substrate is uniformly heated by using a reflow apparatus that has been generally used. Therefore, the temperature of the electronic component rises to the same level as the melting point of lead-free solder (about 220 ° C.). Therefore, if an electronic component having a heat resistant temperature of 150 ° C. or lower is to be mounted on the substrate, the electronic component may be damaged.

  Therefore, when joining an electronic component with a low heat-resistant temperature to the substrate, it is possible to heat the substrate abruptly from the back side of the substrate on which the electronic component is placed to ensure a temperature difference between the electronic component and the substrate. It has been proposed (see Patent Document 1). However, since the melting point of lead-free solder is 200 ° C. or higher, it is difficult to maintain the temperature of electronic components with low heat resistance such as a CCD module at 150 ° C. or lower.

  On the other hand, Sn-58% Bi (tin alloy containing 58 wt% Bi) solder having a low melting point of 138 ° C. has also been developed. However, Sn-58% Bi solder contains a large amount of Bi having a hard and brittle nature, and Bi segregates inside the solder when the solder is cooled. Therefore, when the electronic component and the substrate are bonded using Sn-58% Bi solder, the reliability of the bonded state is lowered.

  Therefore, it has been proposed to secure bonding strength by applying a minute vibration to the solder to suppress segregation of Bi when the molten solder is cooled (see Patent Document 2). Further, as a method for applying a minute vibration to the solder, a method for transmitting the vibration by bringing an ultrasonic horn into contact with one side of a printed board has been proposed.

  Furthermore, a reflow apparatus having an impedance matching mechanism as shown in FIG. 4 has been proposed so that ultrasonic vibration is efficiently transmitted to the substrate (see Patent Document 3). 4 includes a minute vibration generating unit 41, a minute vibration applying unit 42, and an impedance matching mechanism 43. The impedance matching mechanism 43 includes a holding member 43a that holds the substrate and an urging member 43b such as a spring.

The impedance matching mechanism 43 has a function of aligning each mounted material 45 on which the mounting object 44 conveyed to the reflow apparatus is placed. The impedance matching mechanism 43 finely adjusts the load applied to the mounted material 45 from the biasing member 42b in real time, so that the impedance to the vibration in the minute vibration applying unit 42 and the impedance to the vibration in the mounted material 45 are the same. Then, the vibration energy from the minute vibration applying unit 42 is efficiently transmitted to the mounted material 45. The mounted material 45 is transferred to the next step after the reflow step.
Japanese Patent No. 3529633 (Japanese Patent Laid-Open No. 2000-15431) Japanese Patent No. 3580731 (Japanese Patent Laid-Open No. 2000-351065) JP 2003-46228 A

  In the reflow apparatus disclosed in Patent Document 3, the mounting material 45 and the minute vibration applying unit 42 are heated and thermally expanded during soldering heating, and the wavelength of the minute vibration changes. When the wavelength of the minute vibration changes, it becomes difficult to accurately control the impedance in the mounted material 45 and the minute vibration applying unit 42. As a result, vibration energy concentrates on the connecting portion 46 between the mounted material 45 and the minute vibration applying portion 42, and the reflow device may be damaged.

  Further, since the mounted material 45 is only in contact with the minute vibration applying unit 42 on one side, the contact state between the mounted material 45 and the minute vibration applying unit 42 is not stable. If the contact state is different, the transmission state of the minute vibration changes, so that there is a problem that the reflow process cannot be performed stably.

  In view of the above, an object of the present invention is to provide a reflow device that can perform soldering stably and can realize a high-quality bonded state without performing accurate impedance control.

  The present invention relates to a processing unit for placing an attachment to be attached and a material to be attached to each other by solder, a minute vibration applying unit for applying minute vibration to the processing unit, and a minute vibration transmitted to the minute vibration applying unit. The present invention relates to a reflow apparatus including a minute vibration generating unit that generates, and in which a processing unit and a minute vibration applying unit are integrated.

  The processing unit mainly has an action of applying a minute vibration to the solder when the solder in a molten state cools. The processing section is preferably plate-shaped having a flat surface, and it is desirable to apply minute vibrations to the solder in a state where the mounting material is placed on the flat surface. In this case, for example, the processing unit and the minute vibration applying unit are integrated by mechanically connecting or physically joining the peripheral portion of the plate-shaped processing unit and the minute vibration applying unit. It is desirable that the connecting portion between the processing unit and the minute vibration applying unit coincides with the minute vibration node.

  The reflow apparatus of the present invention preferably further includes a heating mechanism for heating the solder below the processing unit. Moreover, it is desirable that the reflow apparatus of the present invention further includes a cooling mechanism for cooling the mounted object above the processing unit.

  It is desirable that the structure including the processing unit and the minute vibration applying unit is fixed by holding mechanisms installed at at least two locations of the structure.

  The present invention also relates to a method for joining an attachment to a material to be attached using solder. In this method, the object to be mounted is placed on the processing unit, the step of heating the solder, and the micro-vibration is applied to the processing unit. When a certain solder cools, it has a step of applying a minute vibration to the solder.

  In the reflow apparatus of the present invention, the processing unit having an action of applying a minute vibration to the solder and the minute vibration applying unit are integrated, and the attached object and the attached material to be joined by the solder are processed. Placed on the part. Therefore, it is easy to stabilize the minute vibration applied to the mounted material without using an impedance matching mechanism as in the past. As a result, minute vibrations are efficiently transmitted to the solder, segregation of components generated inside the solder is suppressed, and the state of bonding between an attachment (for example, an electronic component) and a material to be mounted (for example, a printed board) is improved. Further, since it is not necessary to control impedance for each material to be mounted, productivity is also improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Embodiment 1
FIG. 1 shows a schematic diagram of a reflow apparatus according to an embodiment of the present invention.
The reflow apparatus 10 includes a processing unit 11 having an action of applying a minute vibration to the solder, a minute vibration generating unit 12, a minute vibration applying unit 13 for applying the minute vibration generated by the minute vibration generating unit 12 to the processing unit 11, And two holding portions 17a and 17b. The processing unit 11 has a plate shape having a flat surface, and the mounted material 15 is placed on the flat surface. An attachment 14 having a solder material (for example, a solder ball) on its lower surface is placed at a predetermined position of the attachment material 15.

  The reflow apparatus includes heating means (not shown) for heating and melting the solder. Heating by the heating means may be performed before the mounted material 15 is carried into the processing unit 11, or may be performed after the heating unit is installed around the processing unit 11 and carried into the processing unit 11. Good. After the solder is melted by the heating means and wets and spreads between the attachment and the material to be attached, the minute vibration generator 12 generates minute vibrations until the temperature of the molten solder decreases and solidifies. The generated minute vibration is transmitted to the processing unit 11 via the minute vibration applying unit 13. The vibration is transmitted from the flat surface of the processing unit 11 to the solder through the mounted material 15. In addition, it is desirable to provide, for example, a fixing mechanism that presses the mounted material 15 downward from the upper surface so that the mounted material 15 is stabilized when a minute vibration is applied to the processing unit 11.

  The minute vibration applying unit 13 has a column shape and is connected to one side of the peripheral portion of the processing unit 11. The minute vibration applying unit 13 may be mechanically connected to the processing unit 11 using screws or the like, or may be physically joined by welding or the like. Further, the processing unit 11 and the minute vibration applying unit 13 may be cut out from the same material in an integrated state.

  As described above, since the processing unit 11 and the minute vibration applying unit 13 are integrated, the state of the transmission path of the minute vibration hardly changes. Therefore, the minute vibration is stably transmitted from the minute vibration applying unit 13 to the processing unit 11. A stable vibration is transmitted from the flat surface of the processing unit 11 to the solder through the entire lower surface of the mounted material 15. Therefore, unlike the conventional reflow apparatus, it is not necessary to strictly control the impedance against vibration for each mounted material, and the productivity is improved.

  In addition, it is preferable that the connection part of the process part 11 and the minute vibration application part 13 corresponds with the node of minute vibration. By making the connecting portion coincide with the vibration node, the transmission path of the minute vibration can be further stabilized. Further, when the connecting portion becomes a node, energy is not concentrated on the connecting portion, and the apparatus is hardly damaged. The wavelength of vibration propagating through the processing unit 11 and the minute vibration applying unit 13 varies depending on the materials constituting them, but by appropriately selecting the frequency of vibration generated by the minute vibration generating unit 12 and the size of the processing unit. The connecting portion between the processing unit 11 and the minute vibration applying unit 13 can be made to coincide with the minute vibration node.

  When the processing unit 11 has a plate shape with a flat surface, the size of the flat surface is preferably larger than the mounting material 15. In the processing unit 11, the part on which the mounted material 15 is placed may be recessed from other parts, or may protrude in a convex shape. Moreover, although the plate-shaped processing unit is shown in FIG. 1, the shape of the processing unit is not particularly limited as long as the mounting target material can be placed. Further, the top view of the processing unit 11 may be any shape such as a rectangle, a circle, and an ellipse. The shape of the minute vibration applying unit 13 is not particularly limited, and may be a columnar shape or a wide plate shape.

  The material which comprises the process part 11 is not specifically limited. For example, a metal material or a resin molded product may be used. If it is a metal material, titanium, stainless steel, aluminum, etc. can be used, for example. It is desirable that the thickness of the processing unit 11 is appropriately changed depending on the constituent material. For example, when the processing unit 11 is made of a material having a relatively low strength such as aluminum, it is preferable to increase the thickness of the processing unit 11 in order to increase the strength of the processing unit 11. The minute vibration application unit 13 may be made of the same material as the constituent material of the processing unit 11, or may be made of a material different from the constituent material of the processing unit 11.

  For the minute vibration generator 12, for example, a device that can generate minute vibrations having a frequency of 10 to 60 kHz is used. For example, various ultrasonic generators can be used as the minute vibration generator 12. The amplitude (wavefront) of the vibration generated by the minute vibration generator may be in any direction. For example, the amplitude of vibration may be parallel to the flat surface of the processing unit or may be perpendicular.

  The structure including the processing unit and the minute vibration applying unit is fixed to a stable object (for example, a frame unit of a reflow apparatus) by two holding units 17a and 17b. By fixing the structure in two or more places in this way, two or more fixed ends of minute vibrations are formed, so that a stable standing wave can be obtained. The holding units 17a and 17b may be integrated with the processing unit 11. The holding parts 17a and 17b may be made of any material.

  When the reflow apparatus of the present invention is used, a low melting point lead-free solder containing Bi that easily segregates (for example, Sn-58% Bi solder) is suitable as a solder material for joining a material to be mounted and a mounted object. There is no particular limitation. For example, Sn-Cu-based or Sn-Zn-based lead-free solder or Sn-Pb solder may be used.

Embodiment 2
FIG. 2 shows a schematic diagram of a reflow apparatus according to another embodiment of the present invention. In addition, the same code | symbol is used about the same component as FIG. 1, and description is abbreviate | omitted.
The reflow device 20 includes a heating device 21 for heating the solder below the processing unit 11, and a cooling device 23 for cooling the mounted object above the processing unit 11. According to such an apparatus, melting and cooling of the solder can be performed almost synchronously, which is advantageous in terms of productivity.

  The heating device 21 is, for example, a type of heating device that blows hot air onto the processing unit 11, and the hot air is blown through the plurality of pipes 22. The heat is sequentially transmitted from the lower surface of the processing unit 11 to the upper surface of the processing unit 11 and the mounted material 15 to heat the solder material included in the attachment 14. The temperature of the hot air depends on the heat resistance temperature of the attachment 14, but when the heat resistance temperature is about 150 ° C., it is preferable to blow a controlled hot air of 150 to 250 ° C. The heating method of the heating device 21 is not particularly limited.

  The cooling device 23 has a role of cooling so that the temperature of the mounted article 14 does not rise excessively while the mounted material 15 is heated. In other words, according to the reflow device 20, it is possible to provide a temperature difference between the mounted material 15 and the mounted article 14 during solder reflow. Furthermore, after the heating is completed, it is possible to immediately lower the temperature of the attachment 14 while applying minute vibrations to the solder. The cooling method of the cooling device 23 is not particularly limited.

  A columnar body 24 is attached to the cooling device 23 as a fixing mechanism for fixing the workpiece 15 to the processing unit 11. The cooling device 23 can move up and down. When the mounted material 15 is transported onto the processing unit 11, the cooling device 23 is in the ascending position and descends at the same time as the mounted material 15 is transported onto the processing unit 11. . At that time, the processed material 15 is fixed to the processing unit 11 by the columnar body 24 attached to the cooling device 23 pressing the mounted material 15 downward from above. Thereafter, the solder is melted, and then the solidification of the solder and the application of a minute vibration to the solder are performed at the same time. Thereafter, the solder is carried out from the processing unit 11 to the next process path.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to an Example.
Example 1
An electronic component having a heat-resistant temperature of 170 ° C. was soldered to a predetermined printed circuit board using a reflow device including a heating device and a cooling device as shown in the second embodiment. In this reflow apparatus, the connecting portion between the processing unit 11 and the minute vibration applying unit 13 is controlled to be a node of minute vibration.

  The processing unit 11 of the reflow apparatus was a plate shape (made by Nippon Alex Co., Ltd.) having a width of 120 mm, a length of 250 mm, and a thickness of 15 to 20 mm. The micro-vibration application unit 13 was a column having a diameter of 25 mm (manufactured by Nippon Alex Co., Ltd.). These were connected by bolts. As the minute vibration generator 12, an ultrasonic generator that generates ultrasonic waves having a frequency of 35 kHz was used.

  Specifically, an electronic component having a plurality of solder balls is arranged at a predetermined position on the printed circuit board so that the printed circuit board and the solder ball are in contact with each other. As the solder, Sn-58% Bi solder (melting point: 138 ° C.) was used. Thereafter, the printed circuit board on which the electronic component was placed was carried onto the processing unit 11.

  Immediately after the printed circuit board was carried into the processing unit 11, the cooling device 23 was lowered, and hot air of 180 ° C. was blown from the heating device 21 and blown to the lower surface of the processing unit 11. Moreover, from the cooling device 23, the cold air of 25 degreeC was always sent toward the downward direction.

The blowing from the heating device 21 was stopped after 100 seconds. From 5 seconds before, application of minute vibrations to the processing unit 11 was started, and application of minute vibrations was continued for 20 seconds. The application of vibration was performed for 20 seconds between 95 seconds after the start of heating and 115 seconds later.
In the meantime, the temperature of the molten solder decreased and solidified below 138 ° C., and the electronic component was bonded to the printed circuit board. FIG. 3 shows the temperature profile (curve A) of the electronic component and the temperature profile (curve B) of the junction between the electronic component and the substrate.

  In FIG. 3, the temperature of the junction reaches a maximum temperature (154 ° C.) higher than 138 ° C., which is the melting point of the solder, 105 seconds after the start of heating. On the other hand, the temperature of the electronic component at that time is 138 ° C. That is, even when the solder is melted, the temperature of the electronic component is maintained at 170 ° C. or less, which is the heat resistant temperature.

Next, the initial bonding strength between the printed circuit board and the electronic component after soldering, the bonding reliability, the ease of equipment control, and the stability of the operating state of the equipment were investigated. In this example and the following comparative examples, a quad flat package (QFP) in which leads are arranged at a pitch of 0.5 mm was used as an electronic component.
As the initial bonding strength, the bonding strength of the lead portion of the QFP immediately after fabrication was examined using a push-pull gauge (manufactured by Aiko Engineering Co., Ltd.).
The bonding reliability is determined by repeating the temperature cycle of maintaining the printed circuit board with QFP at 85 ° C and -40 ° C for 30 minutes each for 1000 cycles, and then determining the bonding strength of the lead part of QFP by push-pull gauge. The evaluation was conducted by examining with (Aiko Engineering Co., Ltd.).
The obtained results are shown in Table 1.

In Table 1, each symbol indicates the following. In addition, about the initial joining strength and joining reliability of Table 1, it shows also about the value of joining strength.
Initial bond strength: ◎ indicates that the bond strength is very excellent, ○ indicates that the bond strength is excellent, and X indicates that the bond strength is low.
Bonding reliability: ◎ indicates very high reliability, ○ indicates high reliability, and X indicates low reliability.
Stability of the operating state of the equipment: ◎ indicates that the stability is very high, and X indicates that the stability is low.

<< Comparative Example 1 >>
Soldering was performed under the same conditions as in Example 1 except that the minute vibration applying device shown in FIG. 4 was used. In other words, in this comparative example, a minute vibration was applied from one minute vibration application unit 42 to one side of the substrate for 20 seconds. Further, as in Example 1, the initial bonding strength, bonding reliability, etc. between the printed circuit board and the electronic component were examined. The results are shown in Table 1. In this comparative example, the maximum temperature of the joint was 156 ° C., and the temperature of the electronic component at that time was 139 ° C.

<< Comparative Example 2 >>
Soldering was performed using a general hot air circulation type reflow furnace (Panasert-RSN manufactured by Matsushita Electric Industrial Co., Ltd.). That is, in this comparative example, no minute vibration was applied to the substrate. However, the temperature of the hot air was the same as in Example 1. Moreover, the used reflow furnace was equipped with the cooling device, and the temperature of the cooling air was about 110 degreeC.
As in Example 1, the initial bonding strength, bonding reliability, etc. between the printed circuit board and the electronic component were examined. The results are shown in Table 1. The maximum temperature of the solder joint was 160 ° C., and the temperature of the electronic component at this time was 160 ° C.

The reflow device of Comparative Example 1 needs to be provided with an impedance matching mechanism that adjusts a load applied to the printed circuit board when a minute vibration is applied to the printed circuit board. Specifically, a feedback mechanism (impedance matching mechanism) is provided to measure the pressing force of the minute vibration application unit on the mounted material and adjust the position of the minute vibration application unit so that the measured value becomes constant. There is a need. For this reason, equipment control becomes difficult. Furthermore, since the reflow apparatus of the comparative example 1 requires the above feedback apparatus, the stability of the operation state of an installation is low.
On the other hand, in the reflow apparatus according to the first embodiment, the minute vibration applying unit and the processing unit are integrated. For this reason, it is possible to efficiently transmit stable minute vibrations to the printed circuit board only by placing the printed circuit board on the processing unit without requiring the feedback mechanism as described above. That is, the reflow apparatus of Example 1 was easy to control the equipment, and the stability of the operating state of the equipment was also good.
In addition, since the reflow furnace of the comparative example 2 did not assume applying a micro vibration to a board | substrate, the structure was simple, equipment control was easy, and the stability of the operation state of the equipment was also favorable.

  Example 1 was the most excellent in terms of bonding strength and bonding reliability between the printed circuit board and the electronic component. In Comparative Example 2, it was considered that Bi contained in the solder was segregated because stable minute vibration could not be efficiently applied to the printed circuit board after the solder was melted and solidified. On the other hand, in Example 1, since it was possible to efficiently transmit stable minute vibrations to the printed circuit board, it is considered that the segregation of Bi was remarkably suppressed.

  In both Example 1 and Comparative Examples 1 and 2, the temperature of the electronic component was lower than its heat-resistant temperature (170 ° C.), but in particular, the temperature of the electronic component in Example 1 was the lowest. .

  INDUSTRIAL APPLICABILITY The present invention can be applied to a general reflow apparatus for joining various attachments to a material to be attached with solder, but is particularly useful when joining using lead-free solder. According to the present invention, for example, even when a brittle solder material containing Bi is used, a highly reliable bonding state can be stably realized.

It is a longitudinal section showing a reflow device concerning one embodiment of the present invention roughly. It is a longitudinal cross-sectional view which shows schematically the reflow apparatus which concerns on another embodiment of this invention. In Example 1, it is a temperature profile of the junction part and electronic component when soldering is performed using the reflow apparatus shown by FIG. It is the schematic which shows the micro vibration application part contained in the conventional reflow apparatus. It is an enlarged view of the part enclosed with the broken line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 20 Reflow apparatus 11 Processing part 12, 41 Micro vibration generating part 13, 42 Micro vibration application part 14, 44 Attachment 15, 45 Mounted material 16, 46 Connection part 17a, 17b Structure holding mechanism 21 Heating apparatus 22 Pipe 23 Cooling device 24 Columnar body 40 Micro-vibration applying device 43 Impedance matching mechanism 43
43a Holding member 43b Biasing member

Claims (9)

A processing unit for mounting an object to be attached and a material to be attached to each other by solder, a minute vibration applying unit for applying a minute vibration to the processing unit, and a minute vibration transmitted to the minute vibration applying unit are generated. With a minute vibration generator,
A reflow apparatus in which the processing unit and the minute vibration applying unit are integrated.   The reflow apparatus according to claim 1, wherein the processing unit has an action of applying a minute vibration to the solder when the solder in a molten state cools.   The reflow apparatus according to claim 1, wherein the processing unit has a plate shape having a flat surface, and the mounted material is placed on the flat surface.   The reflow apparatus according to claim 3, wherein a peripheral portion of the plate-like processing unit and the minute vibration applying unit are mechanically connected or physically joined.   The reflow apparatus according to claim 1, wherein a connection portion between the processing unit and the minute vibration applying unit coincides with a node of minute vibration.   The reflow apparatus according to claim 1, further comprising a heating mechanism for heating the solder below the processing unit.   The reflow apparatus according to claim 6, further comprising a cooling mechanism for cooling the mounted object above the processing unit.   The reflow apparatus according to claim 1, wherein a structure including the processing unit and the minute vibration applying unit is fixed by a holding mechanism installed in at least two places of the structure. It is a method of joining an attachment to a material to be attached using solder,
A process of mounting a mounted material on which a mounted object is disposed via solder on the processing unit;
Heating the solder;
A method of applying a minute vibration to the solder when the solder in a molten state is cooled by applying the minute vibration to the processing unit.

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