JP2005353706A - Soldering method of printed board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a matter that since molten solder does not spreads easily to the corner of a through hole or a chip component, a jet nozzle is used for spreading molten solder to a hard-to-spread part but low fluidity lead solder cannot spread perfectly, and when molten solder is jetted from the nozzle at the time of standby where a printed board does not reach a solder tub yet, a large quantity of oxides is generated due to stirring of molten solder and entraining of air. <P>SOLUTION: Molten solder jet from a nozzle is stopped when a printed board does not reach a primary nozzle yet and when it reaches the nozzle, the molten solder is spread to a hard-to-spread part as a low jet flow at first and then as a high jet flow. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of soldering a printed circuit board with molten solder, and more particularly to a soldering method suitable for the case of using lead-free solder.

  In general, when soldering a printed circuit board and an electronic component with molten solder in a solder bath, the back surface of the printed circuit board is brought into contact with the molten solder jetted from the nozzle of the solder bath. Examples of electronic components mounted on the printed circuit board include discrete components having long leads and chip components having electrodes installed on both side surfaces of the main body.

  When soldering a discrete component to a printed circuit board, a lead is inserted into a through hole formed in a land of the printed circuit board, and the lead and the land are soldered with molten solder. At this time, if the printed circuit board is a double-sided board with lands on the front and back sides and conducting between the lands, when the discrete component is inserted into the through-hole and soldered, the molten solder in contact with the back surface will be through-hole. You have to penetrate the inside and reach the surface.

  Further, when soldering the chip component to the printed circuit board, the solder must adhere so as to completely form a fillet between the land on the back surface of the printed circuit board and the electrode of the chip component. In other words, when soldering a chip component to a printed circuit board, after applying an adhesive between the lands of the printed circuit board on which the chip component is mounted, one electrode of the chip component is placed on the land and the other electrode is adjacent to the printed circuit board. The main body is temporarily fixed to the printed circuit board between the lands so as to be placed on the lands. Then, the printed circuit board on which the chip component is mounted on the back surface of the printed circuit board is brought into contact with the molten solder jetted from the nozzle of the solder tank, and the land of the printed circuit board and the electrode of the chip component are soldered.

  By the way, not only is the gap between the discrete part and the through hole narrow, but the length of the through hole is long, so that the molten solder does not easily penetrate into the through hole and reach the surface from the back surface of the printed circuit board. In addition, since the soldering part between the chip part and the land is a right-angled corner, even if solder is applied to the corner, the air and flux present in the corner will interfere with the intrusion of the molten solder. It may become. As described above, the printed circuit board has a portion where the molten solder is difficult to enter (hereinafter, referred to as a difficult-to-enter portion) such as a through hole or a corner of a chip part.

  Conventionally, the solder used for soldering the printed circuit board in the solder bath is Pb-Sn solder. This Pb-Sn solder has a low melting point and good fluidity, so it does not cause thermal damage to electronic components and printed circuit boards during soldering, and it is difficult to penetrate through corners of through holes and chip components. It is easy to invade the part. However, Pb-Sn solder has been reluctant to use in the electronics industry due to the problem of lead pollution, and recently, lead-free solders that do not contain lead have been increasingly used. This lead-free solder is composed mainly of Sn, to which Ag, Cu, Sb, Bi, In, Zn, Cr, Ni, Co, Fe, Mo, Ge, Ga, P, etc. are appropriately added. . Sn-based lead-free solder has poorer fluidity than Pb-Sn solder, so it is hard to penetrate into difficult-to-penetrate parts, and soldering may occur when soldering using conventional soldering methods. .

  Conventionally, there is a method of soldering using a jet jet as a method of injecting molten solder into a portion where entry is difficult (Patent Documents 1 and 2). In this jet jet, the nozzle outlet of the solder tank is narrowed, and the molten solder flows out vigorously from here to allow the solder to enter the difficult-to-enter part. In the soldering method using this jet jet, the molten solder penetrates to some extent in the penetration difficult part in the Pb-Sn solder, but the penetration is almost impossible in the lead-free solder having poor fluidity.

  Further, the conventional method of soldering a printed board, that is, the method of soldering by bringing the printed board into contact with the molten solder jetted from the nozzle of the solder bath has a problem that a large amount of oxide is generated in the solder bath. In other words, the conventional soldering method is performed by an automatic soldering apparatus in which a solder bath is installed. Here, a large number of printed boards are intermittently run along the transport rail at regular intervals. Was continuously jetted from the nozzle.

  By the way, in the solder bath, the solder is melted at a high temperature, and the molten solder flows down from the jet port located at the high position of the nozzle to the liquid surface of the molten solder. It has entered deeply and entrained air in the molten solder. Even solder that is in a molten state at high temperature is easy to oxidize when exposed to air, but in the solder bath, there is agitation and air entrainment when it flows down from the nozzle, so intense oxidation occurs near the nozzle. A large amount of solder oxide was generated.

  When a large amount of oxide is generated in the solder bath, it overflows from the solder bath, scoring the wiring under the solder bath and shorting it, or soiling the vicinity of the solder bath. Also, if a large amount of oxide is generated in the solder bath, it reaches the jet pump together with the molten solder that enters the liquid surface deeply from the nozzle and is sucked into the jet pump, and comes out of the nozzle and adheres to the printed circuit board. It may be a cause. Furthermore, when a large amount of oxide is generated in the solder bath, it is troublesome for the operator to scoop up the oxide with a handle or net at regular intervals. This scooped oxide also has a post-treatment problem that must be treated as an industrial waste by an industrial waste collector for a fee.

  As described above, there are many problems due to the large amount of oxides generated in the solder bath. However, despite the fact that the printed circuit board is sent intermittently, molten solder is constantly jetted from the nozzle of the solder bath. This is because oxides are always generated. In other words, the printed circuit board sent by the transport device is sent at regular intervals, and a large amount of oxide is generated even when the printed circuit board has not arrived in the solder bath (hereinafter referred to as standby). . Therefore, in the solder bath, if only a printed circuit board arrives (hereinafter referred to as “operation”), the amount of oxide is reduced as much as it is jetted. It was proposed. (Reference: Patent Documents 3 to 4)

  In Patent Document 3, two detection means are installed across a solder tank, and molten solder is jetted when an object to be soldered exists between these detection means. In Patent Document 3, at the time of standby, the molten solder is lowered to the lowest position of the nozzle, that is, the liquid level of the molten solder.

Patent Document 4 is provided with a sensor for detecting the presence or absence of a printed circuit board. When the printed circuit board is not detected, the molten solder is prevented from being ejected and kept at a position where it does not flow out of the nozzle. When the sensor detects the printed circuit board, the molten solder is ejected. It is made to let you. The motor that rotates the jet propeller is supplied with electric power through a frequency converter to adjust the rotation speed. In this patent document 4, at the time of standby, the molten solder stays at the top of the nozzle, that is, at the highest position where the molten solder does not flow down from the nozzle.
JP-A-58-178593 Japanese Patent Laid-Open No. 14-134898 JP 56-163074 A JP 59-174270 A

  In the soldering method using a jet jet as in Patent Documents 1 and 2, if the jet jet has a low momentum, the molten solder cannot be penetrated to a difficult-to-enter part, but the molten solder is allowed to penetrate to a difficult-to-enter part. When the momentum is increased, the lead of the discrete component inserted into the through hole is moved upward, or the chip component temporarily fixed with the adhesive is peeled off. Also, in soldering using a jet jet, even if it is attempted to jet molten solder only during operation, it takes time to rotate the pump that was stopped in molten solder with a high specific gravity at high speed, so a short intermittent operation is required. Could not handle printed circuit boards sent by conveyance. Further, in the case where the jet flow from the nozzle is stopped at the time of standby as in Patent Documents 3 and 4, the generation of oxide can surely be reduced, but the molten solder cannot penetrate into the difficult-to-penetrate portion.

  The present invention can not only allow molten solder to easily enter into difficult-to-enter parts, such as lead-free solder, but also allows molten solder to be removed from the nozzle only during operation. It is an object of the present invention to provide a method for soldering a printed circuit board in which generation of oxides can be extremely reduced because it can be jetted.

  In the soldering of a printed circuit board using a solder bath, the present inventor can easily infiltrate the molten solder into the difficult-to-intrude portion by performing the molten solder jet stepwise, and the molten solder can be used only during operation. The present invention was completed by paying attention to the fact that it can be jetted from a nozzle.

  According to a first aspect of the present invention, in the method of performing soldering in a solder bath in which molten solder is introduced while running the printed circuit board, the molten solder in the primary nozzle is removed until the running printed circuit board approaches the solder bath. Lower the solder bath to the liquid level, and if the printed circuit board is close to the primary nozzle, the molten solder is jetted from the primary nozzle to a height that does not cover the printed circuit board, and the printed circuit board is further run to move the molten solder jet height If the molten solder reaches the position where it does not cover the printed circuit board even if the height is increased, the molten solder is completely penetrated to the part where the molten solder is difficult to penetrate by further increasing the jet height of the molten solder, and the printed circuit board is melted. Before leaving the solder, reduce the molten solder jet height to a level where the molten solder does not cover the printed circuit board. Once separated, a method of soldering a printed circuit board, characterized in that to lower the molten solder to the liquid surface of the solder bath.

  According to a second aspect of the present invention, there is provided a method of performing soldering in a solder bath in which molten solder is introduced while running a printed circuit board, and the molten solder in the primary nozzle until the running printed board approaches the solder bath. If the printed circuit board approaches the primary nozzle, the molten solder is jetted from the primary nozzle to a height where it does not cover the printed circuit board. If the molten solder reaches the position where it does not cover the printed circuit board even if the height is increased, the molten solder jet height is further increased to completely penetrate the molten solder until the molten solder is difficult to enter. Before moving away from the molten solder, the molten solder jet height is lowered to a level where the molten solder does not cover the printed circuit board. If There away from the molten solder, a soldering method of a printed circuit board, wherein the lowering to a position which does not flow down the molten solder from the nozzle.

  According to the present invention, when soldering a printed circuit board in a solder bath, molten solder is not jetted from the nozzle during standby until the printed circuit board reaches the solder bath. Less oxidation. Therefore, in the present invention, not only the consumption of the solder due to the generation of oxide is reduced, but the oxide is not caught in the molten solder and attached to the printed circuit board. Further, in the present invention, after the molten solder comes into contact with the running printed board, the jet height becomes high when the soldered portion of the printed board is located at the upper part of the primary nozzle, so the momentum of the jet becomes stronger. As a result, the molten solder easily enters the difficult-to-penetrate part and does not become unsoldered. Further, in the second invention of the present invention, since the molten solder is kept on the upper part of the nozzle that does not flow down from the nozzle during standby, the molten solder in the nozzle always heats the nozzle and does not cool the nozzle. As a result, in the second invention, the molten solder jetted from the nozzle during operation adheres to the printed circuit board at a predetermined temperature without lowering the temperature, and the soldering failure caused by the low temperature of the molten solder is eliminated.

  In the present invention, the molten solder jet is stopped during standby, and when the printed circuit board reaches the nozzle, the molten solder is jetted at an intermediate strength that does not cover the printed circuit board, and the printed circuit board further travels. Even if the molten solder that is being jetted is further strengthened, if it reaches a position where it does not cover the printed circuit board, a three-stage jet is performed in which the molten solder is jetted to a height at which the molten solder can penetrate. If the soldered part of the electronic component has passed, the jet height of the molten solder is lowered to a height at which the molten solder does not cover the printed circuit board, and then the position of the molten solder is further lowered if the printed circuit board passes the nozzle. It is.

  In the first invention of the present invention, the position of the molten solder in the nozzle is lowered to the same position as the liquid level of the solder bath during standby. In the second invention of the present invention, the position of the molten solder in the nozzle is lowered to a position where the molten solder does not flow down from the nozzle during standby. When the molten solder is held on the upper part of the nozzle during standby as in the second aspect of the invention, the nozzle is heated by the molten solder, so that the molten solder jetted from the nozzle during operation is not cooled and soldered at a predetermined temperature. Can be attached.

  In order to finely adjust the height of the molten solder, a motor whose rotation can be controlled is used as a motor for rotating the pump. A motor suitable for use in the present invention is a servo motor or an inverter motor.

  Hereinafter, the soldering method of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an operating state in a solder bath, FIG. 2 is a diagram for explaining a printed circuit board soldering method in the first invention, and FIG. 3 is a diagram for explaining a printed circuit board soldering method in the second invention. It is.

  First, the soldering of the printed circuit board will be briefly described. The printed circuit board includes a process of mounting electronic components on the printed circuit board before the soldering process. In this process, the printed circuit board on which electronic components are mounted is transferred to a transfer device of an automatic soldering apparatus. In the automatic soldering apparatus, processing devices such as a fluxer, a preheater, a solder bath, and a cooler are installed, and a conveying device is installed on these processing devices. The printed circuit board is soldered by being fluxed by a fluxer, pre-heated by a pre-heater, solder is deposited in a solder bath, and cooled by a cooler while being transported by the transport device.

  The solder tank 1 shown in FIG. 1 is provided with a primary nozzle 2 and a secondary nozzle 3, and molten solder 4 is introduced into the solder tank. The molten solder jetted from the primary nozzle and the secondary nozzle has its jet state controlled independently by a pump (not shown). The primary nozzle 2 has a large number of holes 5 at the nozzle outlet so as to roughen the molten solder that is jetted. The rough wave of the primary nozzle makes it easy for the molten solder to penetrate into the difficult-to-penetrate part, but the molten solder cannot completely penetrate into the difficult-to-penetrate part with this rough wave alone. In particular, in the case of poor fluidity such as lead-free solder, unsoldering occurs when soldering with a primary nozzle. Since the wave jetted from the primary nozzle is rough, the solder does not adhere uniformly and forms a tsura or bridge. Therefore, these icicles and bridges are corrected by gentle waves jetting from the secondary nozzle. Since the secondary nozzle 2 has a wide nozzle outlet and there are no obstacles at the nozzle outlet, the molten solder that flows is a gentle wave. The printed circuit board travels from the primary nozzle to the secondary nozzle as indicated by the one-dot chain line arrow.

  In the present invention, molten solder is jetted when the printed circuit board reaches the nozzle, and the timing at which the molten solder is jetted from the nozzle is performed by a sensor and a control device installed in the automatic soldering apparatus. That is, after the printed circuit board is transferred from the previous process to the conveying device of the automatic soldering apparatus, a sensor installed in the automatic soldering apparatus detects the printed circuit board and sends a signal to the control apparatus. The control unit calculates how many seconds it takes to reach the nozzle after the signal that detects the printed circuit board is sent, and if it reaches the arrival time after detecting the printed circuit board, it sends a signal to the motor that rotates the pump. The molten solder is jetted from the nozzle.

Next, the first invention will be described with reference to FIG.
(A) The printed circuit board 6 is transported as shown by a one-dot chain line by a transport device (not shown). At this time, since the printed circuit board 6 does not reach the primary nozzle 2, the molten solder 4 in the primary nozzle is at the same position as the liquid level of the solder bath.
(B) When the printed circuit board 6 reaches the primary nozzle 2, a motor (not shown) rotates by a signal from a control device (not shown) to rotate the pump, and the molten solder 4 jets from the primary nozzle 2. The jet height (h ₁ ) of the molten solder at this time is a height at which the molten solder contacts the back surface of the printed circuit board but does not cover the front surface of the printed circuit board.
(C) If the printed circuit board further travels and the molten solder reaches a point where the molten solder does not cover the surface of the printed circuit board even if the height of the molten solder is further increased, the motor is accelerated to remove from the primary nozzle. Increase the height of the molten solder. The height (h ₂ ) of the molten solder at this time is as shown by a dotted line when measured when there is no printed circuit board. When the height of the molten solder jetted from the primary nozzle is increased in this way, the molten solder becomes stronger, so that it completely penetrates to the difficult entry portion.
(D) In the case where the printed circuit board further travels and the jet flow is high enough to enter the difficult-to-enter part, if the molten solder comes to a position where the rear surface of the printed circuit board is covered, the rotational speed of the motor is reduced and the molten solder Lower the jet. The jet height at this time is substantially the same as the jet height (h ₁ ), and is a height that touches the back surface of the printed circuit board but does not cover the surface.
(E) If the printed circuit board is separated from the primary nozzle, the molten solder 4 is lowered to the same liquid level as the solder bath by a signal from the control device.

Next, the second invention will be described with reference to FIG.
(A ′) The printed circuit board 6 is transported as indicated by a one-dot chain line by a transport device (not shown). At this time, since the printed circuit board 6 does not reach the primary nozzle 2, the molten solder 4 is in a position where it does not flow down from the nozzle in the primary nozzle.
(B) When the printed circuit board 6 reaches the primary nozzle 2, a motor (not shown) rotates by a signal from a control device (not shown) to rotate the pump, and the molten solder 4 jets from the primary nozzle 2. The jet height (h ₁ ) of the molten solder at this time is a height at which the molten solder contacts the back surface of the printed circuit board but does not cover the front surface of the printed circuit board.
(C) If the printed circuit board further travels and the molten solder reaches a point where the molten solder does not cover the surface of the printed circuit board even if the height of the molten solder is further increased, the motor is accelerated to remove from the primary nozzle. Increase the height of the molten solder. The height (h ₂ ) of the molten solder at this time is as shown by a dotted line when measured when there is no printed circuit board. When the height of the molten solder jetted from the primary nozzle is increased in this way, the molten solder becomes stronger, so that it completely penetrates to the difficult entry portion.
(D) In the case where the printed circuit board further travels and the jet flow is high enough to enter the difficult-to-enter part, if the molten solder comes to a position where the rear surface of the printed circuit board is covered, the rotational speed of the motor is reduced and the molten solder Lower the jet. The jet height at this time is substantially the same as the jet height (h ₁ ), and is a height that touches the back surface of the printed circuit board but does not cover the surface.
(E ′) If the printed circuit board is separated from the primary nozzle, the molten solder is lowered to a position where it does not flow down from the primary nozzle 2 by a signal from the control device.

  In the present invention, the jet state of the molten solder at the primary nozzle has been described. However, stepwise jet control is not necessary for the secondary nozzle. In other words, the secondary nozzle is used to correct tsura and bridges generated by the primary nozzle.Since solder has already penetrated into difficult-to-enter parts by soldering with the primary nozzle, the secondary nozzle has a higher height than necessary. There is no need to gain momentum. Therefore, in the secondary nozzle, it is only necessary to jet the molten solder to a predetermined height during operation and to lower the jet to a predetermined position during standby.

  In general, lead-free solder containing Sn as a main component has a high melting point, so it must be used at a high temperature of the solder to be put into the solder bath. The present invention is suitable for soldering printed circuit boards using lead-free solder because it is effective in suppressing oxidation in the solder bath, but Sn-Pb solder having a lower melting point than lead-free solder is used. Needless to say, it can also be used for soldering.

It is a figure explaining the state at the time of the operation | movement in a solder tank. It is a figure explaining the soldering method of the printed circuit board in 1st invention. It is a figure explaining the soldering method of the printed circuit board in 2nd invention.

Explanation of symbols

2 Primary nozzle 4 Molten solder 6 Printed circuit board

Claims (2)

In the method of soldering in a solder bath in which molten solder is introduced while running the printed circuit board, the molten solder in the primary nozzle is lowered to the liquid level of the solder bath until the running printed circuit board approaches the solder bath. If the printed circuit board approaches the primary nozzle, the molten solder is spouted from the primary nozzle to a height that does not cover the printed circuit board, and even if the printed circuit board is run to increase the molten solder jet height, When reaching the position where it does not cover the printed circuit board, the molten solder jet height is further increased so that the molten solder completely penetrates to the difficult-to-penetrate portion of the molten solder. If the molten solder jet height is lowered to a level where it does not cover the printed circuit board, and if the printed circuit board is separated from the molten solder, it will melt Soldering of a PCB, characterized in that lowering the I to the liquid surface of the solder bath. In the method of soldering in a solder bath in which molten solder is introduced while running the printed circuit board, the molten solder in the primary nozzle is kept in a position where it does not flow down from the primary nozzle until the running printed circuit board approaches the solder bath. If the printed circuit board approaches the primary nozzle, the molten solder is spouted from the primary nozzle to a height that does not cover the printed circuit board, and even if the printed circuit board is run to increase the molten solder jet height, When reaching the position where it does not cover the printed circuit board, the molten solder jet height is further increased so that the molten solder completely penetrates to the difficult-to-penetrate portion of the molten solder. The molten solder jet height is lowered to a height that does not cover the printed circuit board, and the printed circuit board is separated from the molten solder. Mules, soldering of a PCB, characterized in that to lower the molten solder to a position which does not flow down from the nozzle.

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