JP2597695Y2 - Reflow furnace - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflow furnace for heating a printed circuit board on which a solder paste is applied to solder electronic components and the printed circuit board.

[0002]

2. Description of the Related Art A conventional electronic component inserts a long lead into a hole of a printed circuit board and solders the lead to a copper foil portion behind the hole. So-called surface mount components in which the leads and the copper foil are soldered by directly mounting the components on a surface.
ed Device (hereinafter referred to as SMD).

[0003] As a method of soldering the SMD and the printed circuit board, there are a flow method and a reflow method. The flow method is a soldering method using an automatic soldering device.
In the flow method, first the SM
D is temporarily fixed with an adhesive and mounted, and flux is applied to the mounting surface with a fluxer and preheated with a preheater.
The SMD and the printed circuit board are soldered by bringing the mounting surface of the SMD into contact with the molten solder being jetted from the jet soldering bath. This flow method is a method excellent in productivity because soldering can be performed on all soldered portions simply by passing a printed board through an automatic soldering apparatus. However, since the SMD has been miniaturized, the space between adjacent leads has become narrow, and if molten solder has adhered between the narrow leads, the solder may solidify as it is to form a bridge. Also, in the flow method, if the electrodes to be soldered are square, such as chip components, molten solder cannot enter the corners of the electrodes, which may result in unsoldered defects without solder. there were. Therefore,
The flow method is not very suitable for soldering SMDs.

[0004] The reflow method is a method of soldering in a reflow furnace. Soldering in a reflow oven is performed by printing and applying solder paste to the soldering part of the printed circuit board with a silk screen or a metal mask, or by applying by discharging with a dispenser, and mounting the SMD on the solder paste application part. By passing the printed board through a reflow furnace to melt the solder paste,
This is a method of soldering D and a printed board. In this reflow method, solder paste is applied only to the soldering part, so even if the solder paste melts, no bridge is formed unless the solder paste spreads around the soldering part, and the solder paste melts. If it does, it will not be unsoldered. Therefore, the reflow method has come to be widely used for soldering SMDs today.

The reflow furnace used in the reflow method has a preheating zone, a main heating zone, and a cooling zone in a long tunnel, and a heater is installed in the preheating zone and the main heating zone, and a cooling zone is provided in the cooling zone. Vessels are installed. And a pair of conveyors which convey a printed circuit board run in a tunnel. The reflow furnace conveyor is
The endless chain is provided with claws for holding a printed circuit board. However, when the travel only in a long tunnel in the chain, since thereby to drop the printed circuit board or causing vibrations loosened, is in the tunnel have been installed a pair of rails, conveyor along the rail It is designed to run stably.

[0006] A conventional reflow furnace, as shown in FIG.
A rail fixed rail S ₁ can not move one of the pair of rails, the other rail is a movable rail S ₂ movable parallel to the transverse direction relative to the fixed rail. That was supposed to be conveyed firmly hold the printed circuit board by moving the movable rail S ₂ in accordance with the size of the printed circuit board for transporting the tunnel as indicated by an arrow A.

By the way, in a reflow furnace, if all the solder paste applied to the printed circuit board is melted at the same time, a defect such as unsoldering is eliminated. For this purpose, the entire printed circuit board must be heated uniformly so that the temperature distribution becomes uniform.

[0008] A graph drawn by measuring the temperature of the printed circuit board is called a temperature profile. When a temperature profile is taken at many points on the printed circuit board, the temperature difference between the highest temperature portion and the lowest temperature portion in the main heating zone is obtained. It is desirable that (Δt: delta tee) is as small as possible. This is because if this Δt is small, all the solder paste applied to the printed board can be melted simultaneously without thermally damaging the SMD or the printed board.

In a conventional reflow furnace, it is difficult to reduce Δt when thermocouples are attached to a large number of locations on a printed circuit board to obtain a temperature profile. The cause lies in the heater installed in the reflow furnace. That is, as shown in FIG. 4 (the lower part of the graph is the horizontal width of the heater), the temperature at both ends of the heater is low, and the temperature is in the middle of a high stable temperature range. In the conventional reflow furnace, the fixed rail side is located above the portion near the end of the heater. Therefore, the portion of the printed circuit board held by the fixed rail conveyor is heated by a heater having a small heat capacity, and the temperature does not rise.

When a small printed circuit board is heated in a conventional reflow furnace, the portion of the printed circuit board held by the fixed rail conveyor is unlikely to rise in temperature as described above, but is held by the moving rail side conveyor. The part is hotter. This is because the conveyor on the moving side rail is located in the middle of the heater, so that the heater is heated at a stable high temperature.

However, when a large printed circuit board is heated in a conventional reflow furnace, the temperature of the portion held by the conveyor on the side of the moving rail does not rise because the moving rail is located above the end of the heater having a low temperature. There was something.

If the temperature of both ends of the heater is lower than that of the central portion, heating using only the stable high temperature portion of the central portion reduces the Δt of the printed circuit board. In the reflow furnace disclosed in Japanese Unexamined Patent Publication No. 62-92068, the tunnel portion where the heater is installed is moved in accordance with the printed circuit board, so that the entire printed circuit board can be heated at the center of the heater. In this reflow furnace, one of a pair of conveyors is fixed, and the other conveyor is movable.

[0013]

[Problems to be Solved by the Invention] Since the temperature of the tunnel itself is high because the heater is installed inside the reflow furnace, the reflow furnace for moving the tunnel involves danger in the operation of moving the tunnel. Was. An object of the present invention is to provide a reflow furnace capable of heating a printed circuit board at the center of a heater having a stable temperature without moving a dangerous tunnel.

[0014]

SUMMARY OF THE INVENTION The present inventor has paid attention to the fact that if the printed circuit board can be adjusted to the middle heater portion where the temperature is stable, the printed circuit board can be uniformly heated without moving the tunnel. The present invention has been completed.

[0015] The present invention includes a pair of rails are installed in a tunnel, in a reflow furnace conveyor for printed circuit boards conveyed along the tunnel is traveling, for both the longitudinal direction of the tunnel both the pair of rails horizontal A reflow furnace characterized in that the reflow furnace can be moved in a parallel direction .

The pair of rails may be moved laterally symmetrically with respect to the center of the pair of rails, or may be independently moved horizontally in parallel.

[0017]

The printed circuit board can be placed on a high temperature portion where the temperature of the heater is most stable since both of the pair of rails can be moved horizontally in parallel .

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a plan sectional view of the reflow furnace of the present invention, and FIG. 2 is an enlarged sectional view of the same side.

The reflow furnace is a tunnel 1, in which a preheating zone P, a main heating zone R and a cooling zone C are provided. Heaters 2 are installed in the upper and lower portions of the preliminary heating zone P and the main heating zone R, and a cooler 3 is installed in the cooling zone C. A pair of rails 4 and 4 are installed in the tunnel, and endless conveyors 5 and 5 are running along the rails by a driving device (not shown).

On one side of the conveyors 5, 5, pin-shaped claws 6 are provided.
The pawls are for holding the printed circuit board 7 on the conveyor between the opposing conveyors. The printed circuit board 7 is transported in the direction of arrow B by the conveyors 5 and 5.

The pair of rails 4, 4 have ball screws 8, 8.
Are screwed together, and one end of one ball screw protrudes to the outside, and a handle 9 is installed on the protruding portion. The two ball screws 8, 8 are linked by a chain (not shown). When the handle 9 of one ball screw is rotated, the other ball screw linked by the chain rotates the same in the same direction.

The ball screws 8 have a forward screw 10 on one side from the center and a reverse screw 11 on the opposite side. Accordingly, when the pole screws 8, 8 are rotated, the rails 4, 4 screwed to the ball screws 8, 8 indicate arrows X,
X or Y, sideways against the longitudinal direction of the tunnel as Y
And translated, or each other close to each other, respectively, will be so that or Tsu far <br/> slope.

In the reflow furnace of the present invention, the pair of rails are lateral.
When the distance between the rails is adjusted, the conveyor of the reflow furnace does not coincide with the conveyor of another processing apparatus installed before and after the reflow furnace. That is, when processing devices before and after the reflow furnace, for example, an electronic component automatic mounting device is installed in the front and an inspection device is installed in the rear, a pair of conveyors of these processing devices has one conveyor fixed, Since the other conveyor moves and adjusts the width, the track is shifted from the reflow furnace of the present invention in which the pair of rails are moved in parallel in the horizontal direction . Therefore, in the reflow furnace of the present invention, after adjusting the rail width, the entire reflow furnace is moved sideways so that the trajectory matches the front and rear processing devices.

In the embodiment, an electric heater is used as a heater. However, it goes without saying that the present invention can be applied to a reflow furnace equipped with a heater using hot air.

Next, the use state of the reflow furnace having the above structure according to the present invention will be described. The distance between the conveyors is adjusted to the width of the printed circuit board by rotating the handle 9 to translate the pair of rails 4 and 4 horizontally . When the rails move, the pair of rails move symmetrically, that is, move in the directions of arrows X and X when the distance between the rails is reduced, and move in the directions of arrows Y and Y when the distance between the rails is expanded. Therefore,
The center between the rails is always above the center of the heater, and if the printed circuit board is held by a conveyor, the printed circuit board will be located in the middle of the heater.

In the reflow furnace in which the distance between the rails was adjusted as described above, thermocouples were attached to a large number of locations on the printed circuit board, and a temperature profile was obtained.
° C. On the other hand, when a temperature profile in a conventional reflow furnace was taken, Δt was 15 ° C.

[0027]

As described above, the reflow furnace of the present invention can uniformly heat the entire printed circuit board to reduce Δt, so that when the printed circuit board coated with the solder paste is heated, S mounted on
It is possible to perform highly reliable soldering, in which the solder paste can be completely melted without causing thermal damage to the MD or the printed circuit board itself.

[Brief description of the drawings]

FIG. 1 is a cross-sectional plan view of the reflow furnace of the present invention.

FIG. 2 is an enlarged side sectional view of the reflow furnace of the present invention.

FIG. 3 is an enlarged side sectional view of a conventional reflow furnace.

FIG. 4 is a graph showing a temperature distribution of a heater for a reflow furnace.

[Description of Signs] 1 Tunnel 2 Heater 3 Cooler 4 Rail 5 Conveyor 6 Claw 7 Printed Circuit Board 8 Ball Screw 9 Handle 10 Forward Screw 11 Reverse Screw P Preheating Zone R Main Heating Zone C Cooling Zone

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05K 3/34 B23K 1/008 F27B 9/24

Claims (3)

(57) [Scope of request for utility model registration] 1. A pair of rails are installed in a tunnel,
In the reflow furnace conveyor for printed circuit boards conveyed along the tunnel is traveling, a reflow furnace, characterized in that is movable parallel to the horizontal direction against the longitudinal direction of both the pair of rails tunnel. 2. The reflow furnace according to claim 1, wherein the pair of conveyors move symmetrically and horizontally . 3. The reflow furnace according to claim 1, wherein a ball screw having a positive screw on one side and a reverse screw on the other side from the center is screwed to the pair of rails.