JP2007098450A - Soldering method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soldering method which can suppress an occurrence of dewetting and bridging during flow soldering using a Sn-Zn based solder. <P>SOLUTION: In the soldering method, a jet wave of a Sn-Zn based molten solder containing mainly Sn and Zn is spouted in a direction opposite to the transferring direction of the printed wiring board 1 to be transferred from a nozzle body 8, which has a slit type nozzle 14 with a fixed width stretching in a direction rectangular to a transferring direction of wiring board 1 and can rotate and adjust a position of the nozzle 14 in relation to the wiring board 1. The soldering is carried out by touching the jet wave on the bottom surface of the wiring board 1. In this case, an angle α, formed by a vertical line Y which passes the center of rotation of the nozzle body 8 and a line X which passes the center of rotation and an opening edge (an upper end edge) 12a of the nozzle 14 located in the lower stream side of the transferring direction of the wiring board 1, is kept in a state adjusted, taking the vertical line Y as a base, between 0 degree and 5 degree or less to the upper stream side in the transferring direction of the wiring board 1, and then the flow soldering is performed by the jet wave spouted from the nozzle 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of performing flow soldering using Sn—Zn based solder mainly composed of Sn (tin) and Zn (zinc).

  Conventionally, Sn—Ag solder and Sn—Zn solder are known as so-called lead-free solders that allow lead containing impurities to be contained but do not contain lead as a main component. Compared with the high melting temperature of Sn-Ag solder of 217 ° C. to 221 ° C. (eutectic point temperature), Sn—Zn solder has a flow of about 199 ° C. as its eutectic point temperature is about 199 ° C. Since the soldering temperature at the time of soldering can be set as low as around 230 ° C., it is preferable in that it is less likely to cause thermal damage to the printed wiring board and the electronic components thereon.

  In the flow soldering using this Sn—Zn solder, in order to suppress the bridging phenomenon which is one of the soldering defects, the direction opposite to the transport direction of the printed wiring board is performed in an inert gas atmosphere with a low oxygen concentration. A technique is known in which a reverse solder jet wave flowing in the direction of is used and the flow velocity of the jet wave is set to 18 cm / sec or more (see, for example, Patent Document 1).

  In addition, in flow soldering, there is also known a technique in which the jet wave ejected from the blowing port can be switched in the same direction (forward direction) and the reverse direction as the transport direction of the printed wiring board (for example, patents). Reference 2).

In the technique of this Patent Document 2, a pair of jet fluids that can rotate around a rotation axis in a direction orthogonal to the conveyance direction of the printed wiring board is provided in the jet tank, and the pair of jet fluids are rotated to position the jet fluid. By individually changing the above, it is possible to adjust the width of the blowing port formed between the pair of jet fluids and the direction of the jet wave ejected from the blowing port in the forward direction or the reverse direction. In addition to this, in the technique of Patent Document 2, a single jet fluid that is rotatable around a rotation axis in a direction orthogonal to the conveyance direction of the printed wiring board is provided in the jet tank, and the jet fluid is rotated. By changing the position, the width of the air outlet formed between this and the front fixed part of the water jet tank, and the position of the air outlet that directs the jet wave injected from this air outlet in the forward or reverse direction can be adjusted. It is possible. Since the jet wave in the reverse direction is provided so that the front fixed portion intersects the vertical line passing through the rotation axis, the forward direction side (that is, downstream of the printed wiring board in the transport direction). It is designed to be ejected with the position close to the side) as the base point.
JP 2001-298267 A (paragraphs 0006-0044, FIGS. 1-8) Japanese Examined Patent Publication No. 4-69509 (column 4, line 23 to column 5, line 2, FIGS. 2a to 2c, FIGS. 3a to 3c)

  Dewetting is one of the solder wet defects. In the dewetting, when the molten solder leaves the soldered portion such as the Cu electrode surface of the printed wiring board, a part of the solder once wet is pulled back by the molten solder, and the remaining Cu electrode surface is soldered later. It is a phenomenon that becomes plated. Dewetting is a phenomenon that is different from non-wetting, which is the phenomenon that the surface of the Cu electrode is not completely wetted by the solder and is the color of the original base metal itself, but the soldering quality is the same as non-wetting Rated as bad.

  The inventors have found that this dewetting tends to occur remarkably when Sn—Zn solder is used as the solder. Therefore, when performing flow soldering using Sn—Zn-based solder, it is required to suppress dewetting.

  On the other hand, Patent Document 1 that discloses a technique for suppressing a bridge and Patent Document 2 that discloses a technique that can select the direction of a jet wave and the like do not describe dewetting at all. It is unclear whether dewetting can be sufficiently suppressed.

  In addition, according to the research of the present inventors, it has been found that the occurrence of bridges in flow soldering and the occurrence of dewetting are in a reciprocal relationship. For this reason, it is difficult to effectively prevent the occurrence of dewetting by the technique of Patent Document 1 aimed at preventing the occurrence of a bridge.

  The objective of this invention is providing the soldering method which can suppress generation | occurrence | production of a dewetting and a bridge | bridging in the flow soldering using Sn-Zn type solder.

  The present invention provides a slit extending in a direction perpendicular to the conveying direction of the workpiece, in the direction opposite to the conveying direction of the workpiece to be conveyed, in a direction orthogonal to the conveying direction of the workpiece, in a direction opposite to the conveying direction of the workpiece. A blower having a uniform width and having a constant width and rotating is ejected from a blower body which can adjust the position of the blower with respect to the work, and the lower surface of the work is brought into contact with the jet wave for soldering. The angle between the straight line passing through the rotation center of the blower body and the opening edge of the blower located at the downstream side in the conveyance direction of the workpiece and the vertical line passing through the rotation center is defined as Flow soldering is performed by using a jet wave ejected from the blowing port in a state where the reference is adjusted from 0 degree to 5 degrees or less upstream in the conveyance direction of the workpiece.

  In this invention, it is preferable to perform flow soldering using the blower body in which the width of the said blower opening along the conveyance direction of the said workpiece | work was set to 3.0 mm or more and 4.0 mm or less.

  The alloy composition of tin / zinc-based solder composed mainly of tin and zinc used in the present invention is not particularly limited with respect to the content of tin and zinc, and has appropriate characteristics as a so-called lead-free solder. If it is. Moreover, metals other than tin and zinc (silver, copper, aluminum, bismuth, indium, nickel, etc.) may be added as appropriate, and the type and amount thereof are not limited at all. For example, ternary alloys such as tin-zinc binary alloy, tin-zinc-bismuth alloy, tin-zinc-aluminum alloy, and quaternary alloys such as tin-zinc-bismuth-indium alloy can be preferably used. Among these tin / zinc-based solders, tin-zinc eutectic solder (91 wt% tin-9 wt% zinc solder, which is abbreviated as tin-9 zinc solder) alloy is a binary alloy solder. Since it is easy to manage the solder alloy composition in the bath, it is particularly preferable.

  In the present invention, examples of the soldering work to be conveyed include a printed wiring board on which electronic components to be soldered are arranged. It is preferable that the workpiece attack angle is set to 5 to 7 degrees with respect to the horizontal line. Moreover, although it is preferable that the conveyance speed of soldering workpieces, such as a printed wiring board, is the range of 0.6-1.2 m / min, it can set suitably in consideration of manufacturability and solderability.

  In the present invention, the amount of solder adhered to the soldering surface of the printed wiring board is greater than the solder jet wave in the same direction (forward direction) as the direction of conveyance of the printed wiring board. , So that the occurrence of dewetting can be suppressed.

  When the angle α is less than 0 degrees, that is, the straight line passing through the rotation center of the blower body and the opening edge of the blower located on the downstream side in the conveyance direction of the work prints the vertical line Y passing through the rotation center. If the second blower body is disposed in a state where the wiring board 1 is beyond the downstream side in the conveyance direction, the angle at which the molten solder jet wave hits the printed wiring board is too large, resulting in excessive solder, bridges and horns. It was confirmed that it was easy to generate drag solder. On the contrary, the opening edge of the downstream side wall located on a straight line passing through the rotation center of the blower body and the opening edge of the blower located downstream in the workpiece conveyance direction forms a vertical line on the upstream side in the conveyance direction of the printed circuit board. In addition, when the angle α formed by the straight line and the vertical line exceeds 5 degrees, it was confirmed that the hitting of the jet wave against the printed wiring board becomes weak and dewetting is likely to occur.

  In the present invention, it was confirmed that dewetting is likely to occur because the amount of solder attached to the printed wiring board is small when the width of the air outlet is less than 3.0 mm. On the other hand, if the width of the blowing port exceeds 4.0 mm, the amount of solder jet of the reverse jet wave increases, but the opening area of the blowing port 14 increases, so the height of the jet wave decreases and dewetting occurs. It has been confirmed that is likely to occur.

  ADVANTAGE OF THE INVENTION According to this invention, the soldering method which can suppress generation | occurrence | production of a dewetting and a solder bridge in the flow soldering using Sn-Zn type solder can be provided.

  FIG. 1 is a diagram conceptually showing a flow soldering apparatus for carrying out the soldering method of the present invention. By this apparatus, a large number of electronic components (see FIG. As an electronic component to be mounted through a flux coating process, a preheating process, and primary and secondary soldering processes in sequence, the terminal pin is provided. Examples thereof include an electronic component 2 that is set to penetrate through a printed wiring board, and an electronic component 3 that is surface-mounted such as a chip component. In relation to the flow soldering, the electronic component 2 is set on a surface opposite to the soldering surface of the printed wiring board 1, and the electronic component 3 is mainly set on the soldering surface of the printed wiring board 1.

  In the flow soldering apparatus of FIG. 1, the printed wiring board 1 is transported by forming a predetermined transport angle of attack θ with respect to a horizontal line by a transport conveyor 4 that is disposed through and inclined through the flow soldering apparatus. . The conveying direction is indicated by an arrow A in FIGS. The transport attack angle θ is set to 5 degrees, for example. The conveyance speed of the printed wiring board 1 is preferably in the range of 0.6 to 1.2 m / min, but can be appropriately set in consideration of manufacturability and solderability.

  The flux application process is a process in which flux is applied by the flux application device 5 to the lower surface of the printed wiring board 1 carried into the flow soldering device, that is, the soldering surface. The flux is applied by a method such as spraying or foaming. The flux may contain a matting agent, a surfactant, an antioxidant, a rust inhibitor, a flame retardant, or an antifungal agent for preventing generation of wrinkles on the printed circuit board 1 as necessary. There is no problem.

  After the flux is applied to the soldering surface, the printed wiring board 1 is transported to the preheating process section by the transport conveyor 4. In the preheating step, the printed wiring board 1 to which the flux is applied is preheated from the soldering surface side by the heater 6 to pre-activate the flux and the printed wiring board 1 and the electronic components 2. 3 to reduce thermal shock. The temperature of the soldering surface of the printed wiring board 1 in this preheating step is preferably in the range of 90 ° C to 130 ° C. Further, in order to perform flow soldering with good wettability, the preheating step is configured to work in an atmosphere of an inert gas having a low oxygen concentration, such as a nitrogen gas, and the oxygen concentration is 1000 ppm or less. It is preferable to make it.

  The pre-heated printed wiring board 1 is transported to the soldering process section by the transport conveyor 4. The soldering process for bringing the Sn—Zn-based molten solder into contact with the printed wiring board 1 is performed by supplying Sn—Zn-based molten solder to the soldering surface of the printed wiring board 1 in a solder jet wave state. It is a process to do. This soldering process is also configured to work in an atmosphere of an inert gas having a low oxygen concentration, such as a nitrogen gas, and the oxygen concentration is 500 ppm or less in order to perform flow soldering with good wettability. It is preferable to make it.

  In the soldering process part, there is a solder tank containing Sn-Zn solder which is heated and melted by a heater, and this solder tank has a first blowing body for forming solder jet waves. 7 and the 2nd blowing body 8 are installed. The temperature of the molten solder of Sn—Zn solder in the soldering step is preferably in the range of 220 ° C. to 245 ° C.

  The first blower body 7 disposed on the upstream side in the transport direction of the transport conveyor 4 with respect to the second blower body 8 ejects molten solder in the vertical direction through the upward blower port that the first blower body 7 has. A solder jet wave (first jet wave W1) is formed. The open defect in soldering can be suppressed by the first jet wave W1. In the soldering process in the flow soldering apparatus, the flow soldering may be performed using only the second blower body 8 in a state where the use of the first blower body 7 is stopped. .

  The second blower body 8 disposed on the downstream side in the transport direction of the transport conveyor 4 with respect to the first blower body 7 is a solder jet that performs a soldering finish by ejecting molten solder as will be described later. A wave (second jet wave W2) is formed. As the second jet wave W2 for finishing, a solder jet wave jetted in the direction opposite to the transport direction of the printed wiring board 1 is used. The printed wiring board 1 that has been soldered in the soldering process is unloaded from the flow soldering apparatus.

  The second blower body 8 that forms a solder jet wave that jets in the direction opposite to the transport direction of the printed wiring board 1 as the second jet wave W2 in the soldering process has a second jet depending on the transport attack angle θ and the like. It can be rotated to finely adjust the jet direction of the jet wave W2, and the position of the slit-like nozzle having a constant width can be changed by adjusting the rotation angle.

  That is, as shown in the cross-sectional view of FIG. 2, the second blower body 8 includes an upstream side wall 11 and a downstream side wall 12 opposed to the upstream side wall 11 based on the transport direction (indicated by arrow A) of the printed wiring board 1. , And a pair of end plates (not shown) that are connected to each other at both ends in the longitudinal direction, and a support shaft 13 (only one is shown) protruding from the center of these end plates.

  The upstream side wall 11 has a circular arc shape that protrudes toward the upstream side in the conveyance direction of the printed wiring board 1, and the downstream side wall 12 has a circular arc shape that protrudes toward the downstream side in the conveyance direction of the printed wiring board 1. Yes. The lower end edges of the upstream side wall 11 and the downstream side wall 12 are largely separated by forming an inlet gap 8a therebetween, so that the molten solder is filled into the second blower body 8 through the gap 8a. It has become. A slit-shaped air outlet 14 is formed between the upper end edges of the upstream side wall 11 and the downstream side wall 12. The upper end edge 12a of the downstream side wall 12 forming the opening edge on the downstream side in the transport direction of the blower port 14 is shifted upward with respect to the upper end edge 11a of the upstream side wall 11 forming the opening edge on the upstream side in the transport direction of the blower port 14. Yes.

  The second blower body 8 is supported through the pair of support shafts 13 so as to be able to rotate through the walls of the solder bath. As a result, the second blower body 8 is extended in the axial direction of the second blower body 8 (direction in which the pair of support shafts 13 are connected by a straight line) and the blower opening 14 in a direction perpendicular to the transport direction of the printed wiring board 1. The mouth 8 is supported by the solder bath.

  Reference numeral 15 in FIG. 2 denotes a skirt-shaped air outlet base. A second blower body 8 is rotatably sandwiched between the upper parts of the blower base 15. This blower base 15 can be omitted. Although not shown, the solder tank is provided with supply means, for example, a pump, for supplying molten solder to the inside of the blow hole base 15 and applying energy to the solder to be ejected from the blow hole 14. The number of rotations of the pump for forming the solder jet wave is not particularly limited, but is adjusted so as to maintain a height at which the second jet wave W2 strikes the soldering surface of the printed wiring board 1 exactly. If the height of the second jet wave W2 is too high, the solder becomes excessive, and bridging and horn soldering are likely to occur. Conversely, if the height of the second jet wave W2 is too low, the amount of solder is insufficient. However, dewetting is likely to occur.

  The second blower body 8 is a straight line that passes through the center of the support shaft 13 that forms the center of rotation and the opening edge of the blower 14 that is located downstream in the transport direction of the printed wiring board 1 (that is, the upper edge 12a). With the angle α sandwiched between X and the vertical line Y passing through the rotation center adjusted to 0 ° or more and 5 ° or less, the second jet wave W2 is blown out in the direction opposite to the transport direction of the printed wiring board 1 14 erupts. In this case, the angle α is adjusted to 5 degrees or less on the upstream side (plus side) in the transport direction of the printed wiring board 1 with respect to the vertical line Y. Therefore, the angle α when the straight line X and the vertical line Y coincide with each other and the upper end edge 12a is positioned on the vertical line Y is 0 degree.

  FIG. 2 shows a state in which the second blower body 8 is rotated and the blower 14 is arranged at a position where the straight line X is perpendicular to the printed wiring board 1. The angle α in the adjusted state is equal to the transport attack angle θ of the printed wiring board 1. For this reason, as described in relation to the transport attack angle θ of the printed wiring board 1, the angle α may be adjusted in a range from 0 degree to the maximum plus the transport attack angle θ.

  Adjustment of the angle α is performed by operating an adjustment lever (not shown) attached to one of the support shafts 13 outside the solder bath and rotating the entire second blowing body 8 according to the scale. By operating the adjustment lever outside the soldering device, it is possible to perform adjustment without opening the nitrogen atmosphere in the soldering part, and it is excellent in workability when performing continuous soldering work. . In addition, it is preferable that the rotation angle of the second blower body 8 is restricted by appropriate means so that it does not rotate outside the range of the angle α. In this case, the second blowing body 8 can eject only the second jet wave W <b> 2 in the direction opposite to the conveyance direction of the printed wiring board 1 through the blowing hole 14.

  The width L of the blower port 14 that forms the slit of the second blower body 8 is fixed and cannot be changed. Here, the width L indicates the shortest distance between the upper end edge 11 a of the upstream side wall 11 and the upper end edge 12 a of the downstream side wall 12 that form the air outlet 14. Since the width L of the air outlet 14 is fixed, the width of the air outlet 14 does not change regardless of the adjustment of the angle α by the rotation of the second air outlet body 8. Reproducibility can be secured. In other words, the width of the air outlet 14, which is one of the conditions for ejecting the target second jet wave W2, does not change depending on the adjustment of the angle α. Thereby, the angle α can be adjusted by a simple operation of rotating the entire second blower body 8.

  Since the upper end edges 11a and 12a are shifted up and down as described above, the air outlet 14 is provided obliquely with respect to the printed wiring board 1 to be conveyed as shown in FIG.

  Thus, since the 2nd blowing body 8 was formed between the said upper end edges 11a and 12a from which the blowing outlet 14 shifted | deviated up and down, ejection of the 2nd jet wave W2 ejected from this blowing opening 14 Although it is excellent in that the direction can be more reliably directed in the direction opposite to the direction in which the printed wiring board 1 is conveyed, the second blower body 8 shown in FIG. 3 may be used instead. it can. 3 differs from the second blower body 8 shown in FIG. 2 in that the upper end edge 11a of the upstream side wall 11 and the upper end edge 12a of the downstream side wall 12 are substantially the same. The part and the angle α are the same as those of the second blower body 8 shown in FIG.

  When changing the width L of the air outlet 14, several kinds of second air outlet bodies 8 having the air outlets 14 having different widths L are prepared in advance and are suitable for the soldering conditions. What is necessary is just to select the 2nd blowing body 8 and to replace with a soldering apparatus. The width L of the air outlet 14 is preferably set to 3.0 mm or more and 4.0 mm or less.

  FIG. 4 shows the result of the test conducted under the following conditions using the second blower body 8 shown in FIG. 2 in the flow soldering apparatus shown in FIG.

  The printed wiring board 1 used in this test has 1000 soldering lands (Cu electrodes) for the electronic component 2 having the terminal pins set therein and the surface-mounting electronic component 3. In this test, the tin-9 zinc solder was used as the Sn—Zn solder. As the second blower body 8, a constant one having a width L of 3.25 mm was used. The conveyance speed of the printed wiring board 1 was 0.8 m / min. The preheating temperature was 110 ° C., the oxygen concentration in the soldering atmosphere was 200 ppm, and the temperature of the molten solder was 230 ° C.

  Under this condition, the second blower body 8 is rotated to change the angle α in the range of −5.0 degrees to +8.0 degrees mainly every 2.5 degrees, and the angle α is changed at each angle. The number of occurrences of wetting and the number of occurrences of solder bridges were evaluated.

  In this case, the dewetting was performed by observing the soldered state of the joint portion of the printed wiring board 1 and evaluating with “◯” and “×” depending on how the solder repels. The number of bridges generated indicates the average number of generations per printed wiring board. When the angle α is − (minus), the upper end edge 12a of the downstream side wall 12 is shifted to the downstream side in the transport direction of the printed wiring board 1 (right side in FIG. 2) with respect to the vertical line Y of the support shaft 13. In contrast, the angle α is + (plus) when the blowing port 14 is disposed. On the other hand, the upper edge 12a of the downstream side wall 12 is shifted to the upstream side in the transport direction of the printed wiring board 1 (left side in FIG. 2). This is a case where the mouth 14 is arranged.

  As can be seen from FIG. 4, it is found that by setting the angle α of the air outlet 14 in the range of 0 to 5 degrees, dewetting can be suppressed and there are few bridges, and good solderability can be obtained. did. When the angle α is set to minus 5 degrees or less, dewetting is suppressed, but it has been found that as the minus angle increases, the number of bridges increases. It was found that when the angle of the air outlet 14 exceeds +5 degrees, the occurrence of bridging is suppressed, but dewetting occurs.

  FIG. 5 shows the result of the test conducted under the following conditions using the second blower body 8 shown in FIG. 2 in the flow soldering apparatus shown in FIG.

  A large number of second blower bodies 8 having different widths L of the blower openings 14 every 0.25 mm in the range of 2.75 mm to 4.50 mm are prepared. It was arranged in a solder bath so as to be .5 degrees, and the number of occurrences of dewetting at each width L was evaluated. In this case, dewetting was performed by observing the soldered state of the joint portion of the printed wiring board 1 and evaluating with “◯” and “×” depending on the solder repelling condition. The other conditions were the same as those described in Example 1.

  As can be seen from FIG. 5, it was found that dewetting was suppressed when the width L of the air outlet 14 was set to a range of 3.0 mm to 4.0 mm. It has been found that dewetting occurs even when the width L of the air outlet 14 is set to be less than 3.0 mm or when the width L of the air outlet 14 is set to exceed 4.0 mm. That is, it has been found that if the width L of the air outlet 14 is too narrow or too wide, the amount of solder on the printed wiring board 1 is insufficient and dewetting is likely to occur.

The figure which showed notionally the flow soldering apparatus which enforces the soldering method of this invention. Sectional drawing which shows an example of the blowing body used for implementation of the soldering method of this invention in the flow soldering apparatus of FIG. Sectional drawing which shows the other example of a blower body used for implementation of the soldering method of this invention. The figure which shows the relationship between the angle of the blowing port in the soldering performed using the blowing body of FIG. 2, and the generation | occurrence | production number of dewetting and a bridge | bridging. The figure which shows the relationship between the width | variety of the blowing port in the soldering performed using the blowing body of FIG. 2, and the generation | occurrence | production number of dewetting.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Printed wiring board (soldering workpiece), 2, 3 ... Electronic component, 4 ... Conveyor, 8 ... 2nd blower body, 11 ... Upstream side wall of blower body, 11a ... Upper end edge (opening) of upstream side wall Edge), 12 ... downstream side wall of the blower body, 12a ... upper end edge (opening edge) of the downstream side wall, 13 ... support shaft of the blower body, 14 ... blower opening, X ... upper end edge (opening edge) 12a and support shaft A straight line passing through the center of the support shaft, Y a vertical line passing through the center of the support shaft, α an angle between the straight line X and the vertical line Y, W2 a second jet wave in the direction opposite to the workpiece transfer direction

Claims (2)

In a direction opposite to the conveying direction of the soldering work to be conveyed, a jet of molten Sn—Zn solder mainly composed of Sn and Zn is formed in a slit shape extending in a direction perpendicular to the conveying direction of the work. Is a method of spraying from a blower body having a constant blower opening and adjusting the position of the blower hole relative to the work by rotation, and bringing the lower surface of the work into contact with the jet wave and soldering. ,
The angle between the straight line passing through the rotation center of the blower body and the opening edge of the blower located on the downstream side in the conveyance direction of the workpiece and the vertical line passing through the rotation center is from 0 degrees with respect to the vertical line. A soldering method, wherein flow soldering is performed by a jet wave ejected from the air outlet in a state adjusted to 5 degrees or less to the upstream side in the conveyance direction of the workpiece.   The soldering according to claim 1, wherein flow soldering is performed using a blow body in which a width of the blow hole along a conveyance direction of the workpiece is set to 3.0 mm or more and 4.0 mm or less. Method.

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