JP2006073898A - Method of locally soldering printed board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of locally soldering a printed board for preventing such poor soldering as insufficient soldering, uneven soldering, solder shorts, or the like to achieve stable soldering in local soldering by jet solder. <P>SOLUTION: A region L to be soldered of a printed board b on which an electronic component d is mounted is brought near to the opening 32a of a nozzle 32 for jetting molten solder h while the region L is maintained in a horizontal state, and then exposed to the liquid surface of the molten solder h. Then, the printed board is moved away from the exposure position to a position where the printed board is not separated from and kept in contact state with the surface of the jetted molten solder, and where the molten solder can stably maintain the jetting shape due to surface tension while a horizontal state is held. After it is moved away, a predetermined clearance (separation distance) is obtained between the region to be soldered and the opening of the nozzle. At the position, the printed board begins to be peeled back from the molten solder. During the peeling back, control may be performed such that the jetting pressure of the molten solder is reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the technical field of soldering of electronic components mounted on a printed circuit board, and in particular, local soldering of a printed circuit board in which molten solder is jetted and soldered by bringing a soldered part of the printed circuit board into contact therewith. Regarding the method.

  In the technology for mounting electronic components (SMT (Surface Mount Technology) components) on a printed circuit board, solder paste is applied to the printed circuit board, the electronic components are placed, and the whole is heated and soldered by melting the solder paste. In recent years, mounting by this technique has become the mainstream.

  However, depending on the specifications of the printed circuit board, some electronic components must be mounted via leads after reflow processing. In this case, only the mounting location is immersed (contacted or dipped) in molten solder. It was mounted by flow soldering technology.

  Mounting on a printed circuit board by such a flow soldering technique has been performed by a jet type local (or partial) soldering apparatus in order to improve the efficiency of the mounting process. This local soldering apparatus is mainly configured to include a solder bath provided with a nozzle for jetting molten solder, a conveying means for the printed circuit board, and a lifting means for moving the solder tank or the printed circuit board up and down while maintaining its horizontal state. .

  Further, in recent years, this local soldering apparatus is provided with an inclined detachment (peelback) mechanism of the printed circuit board in order to promote solder shortage after detachment from the molten solder and to suppress a so-called solder short (bridge) that shorts between leads. The thing that has become mainstream.

  Various jet-type local soldering devices as described above have been disclosed. For example, the apparatus shown in Patent Document 1 includes an elevating mechanism and a transport mechanism that bring a printed circuit board close to a solder bath having a molten solder gate, and the printed circuit board is inclined to prevent a solder short when the printed circuit board is pulled away from the molten metal gate. An inclination separation mechanism for performing separation is provided.

Further, the apparatus shown in Patent Document 2 jets molten solder from a large number of nozzles, conveys the printed circuit board to the upper part of the nozzle group of the solder tank, brings it close, and causes the printed circuit board to be inclined and detached from one side. In this configuration, a printed circuit board is installed on a pair of rails that slide and run with respect to the solder tank, and a suspension plate suspended from the rails.
JP 2004-071683 A (page 3-7, FIG. 1) Japanese Patent Laid-Open No. 2003-273503 (page 3-4, FIG. 1)

  However, in recent years, in addition to the fact that the mounting interval has become narrower with the high-density mounting of electronic components on a printed circuit board, there is a tendency to use lead-free solder with poor fluidity due to environmental considerations. For this reason, in order to maintain the quality of soldering, it is necessary to keep the distance between the soldering part of the printed circuit board and the nozzle appropriately. If this distance is not properly maintained, even if the printed circuit board is tilted and removed, the molten solder will not be sufficiently dipped in the unsoldered or unpainted area. The problem of spreading and soldering to other electronic components was caused.

  In particular, a solder short at the time of tilt separation has occurred due to the following phenomenon. Conventionally, the distance between the soldered portion of the printed circuit board b and the opening n1 of the nozzle n is set to be short in order to prevent unsoldering and non-wetting. When the tilt separation is started from this nozzle position, as shown in FIGS. 4A and 4B, the rising behavior of the molten solder h occurs due to the pressure release of the opening n1, and a so-called dragging state of the solder surface occurs. It was. In the portion where this dragging state has occurred, the solder temperature is drastically lowered, and a solder short or a so-called icicle state has occurred in the lead 1 of the electronic component d. This is because there is a difference between the dipping position that prevents unsoldering and non-wetting and the start position of the inclination separation that prevents the solder short.

  Accordingly, the present invention has been made in view of such problems, and in the local soldering by jet solder, it reduces solder defects such as unsoldering, unpainting, and solder shorting, and realizes stable soldering. A method for local soldering of a printed circuit board is provided.

  In order to solve the above problems, the method of local soldering of a printed circuit board according to the present invention is performed as follows.

  That is, the soldered portion (L) of the printed circuit board (b) on which the electronic component (d) is mounted is close to the opening (32a) of the nozzle (32) that jets the molten solder (h) while maintaining the horizontal state. And immersed in the liquid surface of the molten solder (h).

  Next, the printed circuit board (b) is kept in contact with the molten solder (h) from the liquid level of the jetted molten solder (h) from the above immersion position, and the molten solder (h) stably maintains the jet shape by the surface tension. The horizontal state is maintained as far as possible and separated, and after this separation, a predetermined clearance (separation distance) is provided between the soldering portion (L) and the opening (32a) of the nozzle (32).

  Finally, the printed circuit board (b) is tilted away (peeled back) from the position where the clearance is obtained.

  In other words, the soldering method of the present application is characterized in that the immersion position of the soldering part (L) in the molten solder (h) and the start position of the tilted separation from the molten solder (h) are set in two stages. is there.

  Furthermore, at the time of tilt separation, control may be performed so as to reduce the jet pressure of the molten solder (h) jetted from the nozzle (32).

  Note that the reference numerals in parentheses described in the claims and the means for solving the above-described problems are added with reference numerals for easy understanding of the configuration of the invention. Of course, it is not limited to the above form.

Since the local soldering method for a printed circuit board according to the present invention is the method described above, the following effects are exhibited.
That is, since the soldering part of the printed circuit board is sufficiently immersed in the molten solder that is jetted in the vicinity of the nozzle, the effect of preventing the unsoldered or unpainted state of the lead portion is obtained.

  Further, a clearance is taken between the soldering portion and the nozzle until the shape of the molten solder jet is stabilized, and then the inclination separation (peel back) is performed, and the jet pressure is controlled. For this reason, the starting point of the inclination separation is stabilized and the occurrence of the drag state of the solder surface is suppressed. As a result, it is possible to prevent solder shorts and short circuits between electronic components adjacent to each other at high density.

  The above effects make a significant contribution to quality control and cost reduction by reducing the defect occurrence rate of the entire printed circuit board.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for locally soldering a printed circuit board according to the present invention (hereinafter abbreviated as “soldering method”) will be described in detail with reference to the drawings.

  FIG. 1 is a schematic view showing an apparatus for realizing the soldering method of this embodiment, FIG. 2 is an explanatory view (A) and (B) showing the operation state of the apparatus of FIG. 1, and FIG. It is explanatory drawing which shows the process of the example soldering method.

  First, an apparatus 1 (hereinafter referred to as “this apparatus”) that realizes the soldering method of the present embodiment will be described.

  Reference numeral 3 denotes a solder bath. The solder tank 3 is formed in a container shape and is arranged on the upper side of the frame 2 which is constructed in a frame shape and keeps the entire apparatus. The solder tank 3 stores therein the molten solder h and has a nozzle board 31 formed in a box shape. On the upper surface of the nozzle board 31, a nozzle 32 made of a cylindrical body is arranged in a standing manner so as to communicate with the inner side of the nozzle board 31. The standing position of the nozzle 32 is adapted to the arrangement position of the electronic component d on the substrate b. The opening 32a of the nozzle 32 is formed separately so as to form an opening surrounding the soldering portion L of the substrate b.

  The molten solder h stored in the solder tank 3 passes through the nozzle plate 31 while maintaining a molten state by a circulating means or a melting means (pump, heater, not shown) arranged in the apparatus 1 and is a nozzle. It is jetted from 32 openings 32a. The jet pressure (jet velocity) of the molten solder h is appropriately controlled by control means (not shown) in the present apparatus 1.

  Elevating mechanisms 4 are arranged on both sides of the frame 2. The elevating mechanism 4 is provided with an inclination separation (peelback) mechanism 5 and a transport mechanism 6 described later on the upper side, and moves up and down while maintaining the horizontal state with respect to the frame 2 and the solder tank 3 (see FIG. 2. Arrow a) The elevating mechanism 4 includes a conventional servo motor, ball screw, and the like.

  On the upper part of the elevating mechanism 4, an inclination detaching mechanism 5 for the substrate b is disposed. This tilting and detaching mechanism 5 forms a frame 51 so as to surround the solder tank 3 from above, and a rotating shaft 51 a that is rotatable with respect to the lifting mechanism 4 is disposed on one side of the frame 51. On the side, a tip of a rod 51b that moves forward and backward in a vertical direction is brought into contact. The contact side of the rod 51b in the frame 51 is configured to be separated from the lifting mechanism 4 by the advance movement of the rod 51b (arrow b in FIG. 2). With this configuration, the frame 51 rotates with respect to the lifting mechanism 4 about the rotation shaft 51a (FIG. 2, arrow c).

  A conveyance mechanism 6 is disposed on the inner side of the frame body 51 of the tilting separation mechanism 5 and above the solder tank 3. The transport mechanism 6 carries the substrate b in and out of the pre-process or the post-process, and holds and holds the substrate b in a parallel state with respect to the tilt separation mechanism 5 during soldering. In addition, since the structure of this conveyance mechanism 6 is also constructed | assembled by the existing technique, the detailed description beyond this is abbreviate | omitted.

  Since the apparatus 1 is configured as described above, it is possible to move the soldered portion L of the substrate b carried in close to the opening portion 32a of the nozzle 32 by the lifting mechanism 4 while maintaining the horizontal state. It is also possible to move away from the nozzle 32 while maintaining the above or if necessary, by performing an inclination separation (peel back) operation. It is also possible to appropriately control the jet pressure of the molten solder h in conjunction with each operation.

  Next, the local soldering method which is the main point of the present invention will be described below with reference to FIG.

  First, the substrate b on which the electronic component d held by the transport mechanism 6 is mounted is brought close to the opening 32a of the nozzle 32 while maintaining the horizontal state by the elevating mechanism 4, and the soldering site L is immersed in the molten solder h. (Contact). Through this process, the molten solder h adheres to the lead 1 of the electronic component d. The clearance C1 (separation distance) between the soldering part L and the opening 32a during immersion is set to be narrower than usual, for example, 0.3 to 1.0 mm in order to prevent unsoldering and unpainting. In addition, the jet pressure of the molten solder h may be increased to prevent unsoldering and non-coating.

Next, the substrate b is horizontally moved from the above immersion position to a position where the soldering portion L does not leave the liquid surface of the molten solder h and does not leave, and the molten solder h stabilizes its jet shape by surface tension. It is raised by the elevating mechanism 4 while maintaining the state. Here, the position where the molten solder h stabilizes its jet shape by the surface tension indicates that the molten solder h in the opening 32a of the nozzle 32 has obtained a predetermined curved surface shape by the surface tension.
Due to this rise, the separation distance between the soldering portion L and the opening 32a is longer than the immersion position, for example, a clearance C2 of about 1.5 to 2.5 mm.

  Then, the tilting separation mechanism 5 is operated from this position, and the soldering portion L of the substrate b is detached while being tilted from the liquid surface of the molten solder h. Since the molten solder h has a stable jet shape due to surface tension, the phenomenon that the molten solder h near the edge of the opening 32b is dragged to the soldering site L does not occur, and the separation point is also constant. Can keep. As a result, in the lead 1 of the electronic component d, the occurrence of defects such as a solder short and an icicle phenomenon is suppressed.

  Further, in addition to the above-described inclination separation method, control is performed to reduce the jet pressure of the molten solder h in order to prevent the molten solder jet state from fluctuating as much as possible by releasing the nozzle pressure.

  Note that the numerical values of the clearances C1 and C2 described above are exemplary, and in actuality, it is necessary to set appropriately according to the area of the soldering portion L, the shape of the opening 32a of the nozzle 32, the type of the molten solder h, and the melting temperature. is there.

It is the schematic which shows the apparatus which implement | achieves the soldering method of a present Example. It is explanatory drawing (A) which shows the operation state of the apparatus of FIG. 1, (B). It is explanatory drawing which shows the process of the soldering method of a present Example. It is explanatory drawing which shows the soldering state by the conventional soldering method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 This apparatus 2 Frame 3 Solder tank 31 Nozzle board 32 Nozzle 32a Opening part 4 Lifting mechanism 5 Inclination release mechanism 51 Frame 51a Rotating shaft 51b Rod 6 Transport mechanism b Substrate C1 Clearance (dipping)
C2 clearance (withdrawal)
d Electronic component h Molten solder l Lead L Soldering part n Nozzle (conventional example)
n1 opening

Claims (2)

The soldering part (L) of the printed circuit board (b) is brought close to the opening (32a) of the nozzle (32) into which the molten solder (h) is jetted, and is brought into contact with the liquid surface of the molten solder (h).
After separating the soldering part (L) to a position where the molten solder (h) does not leave and to a position where the jet shape is stabilized by surface tension,
A method for locally soldering a printed circuit board, wherein the soldered part (L) is detached from the molten solder (h) while the printed circuit board (b) is inclined. At the time of detachment of the soldered part (L) from the molten solder (h),
The local soldering method for a printed circuit board according to claim 1, wherein the jet pressure from the nozzle (32) is reduced.

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