JP2767293B2 - heating furnace - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a heating furnace used for reflow soldering of a surface mount printed circuit board, in particular, to obtain an appropriate heating condition for a printed circuit board having various mounting contents. Development of a device suitable for

[Prior art and its problems] Conventionally, in a reflow furnace in which components and solder are placed on a printed circuit board and conveyed in a heating furnace, and then heated and soldered together, the temperature of the soldering pad in the printed circuit board surface caused by the conveyance is increased. The design of the profile and its stabilization are important. For example, Electric Onyx Volume 31 (19
1986) pages 26 to 30 (Electri Onics, 31 (9), pp.
26-30, 1986). Reflow furnaces with various heating principles (heat sources) were devised,
Although commercially available, when focusing on the design of the temperature profile and its stability, the main items are as follows.

(A) A reflow furnace is generally divided into a preheating section, a solder melting section, a cooling section, and the like, and the length of each of those zones.

(B) Heating power, such as heat generated by heat transfer, heat radiation, and heat condensation in each zone, and the following is representative of only a heating furnace based on heat transfer and heat conduction, which is represented by a heat transfer coefficient.

(C) Thermo-optical characteristic values (specific heat, specific gravity) of the object to be heated such as a printed circuit board or a component and each dimension.

(D) The speed of the conveyor because it is common.

(E) The positional relationship by moving in the furnace.

And so on.

Therefore, in order to design the temperature profile for printed circuit boards with various mounting contents, thermocouples are actually installed at each position on the printed circuit board, and the temperature profile is sampled for each furnace operating condition. There is no other way but to determine the appropriate conditions and the shape of the temperature profile by comparing the mounting quality and the presence or absence of thermal damage to the components and the printed circuit board. This requires a lot of effort, and nevertheless, the operating conditions of the furnace are not only to reduce emissivity and voltage fluctuation due to contamination of the heater surface and reflectors, but also to suck indoor air. There are constant fluctuations, such as the resulting atmospheric fluctuations. For this reason, for printed circuit boards with various types of mounting contents,
Stabilizing the temperature profile has the disadvantage that it is not easy.

As described above, the prior art does not consider real-time control of the temperature of the object to be heated actually occurring in the furnace. There was a problem that resulted in quality deterioration.

The object of the present invention is to measure the real-time temperature distribution reached in the preheating zone at least in the preheating final zone immediately before the melting zone of the solder at least, and make a judgment on the distribution, so that the distribution is temporarily insufficient. If so, a means for performing a fixed stop heating is provided,
Another object is to provide means for automatically performing this.

[Means for Solving the Problems] According to the configuration of the present invention for solving the problems of the prior art, at least a preheating zone, a melting zone, and a cooling zone are used in order to continuously heat a printed circuit board to a desired temperature profile by a carrier. In a heating furnace in which these are arranged in series,
On one side of the carrier, a carrier rail is provided over substantially the entire length of the carrier, the carrier rail runs on the carrier rail in synchronization with the printed board transport speed of the carrier, and returns from the transport end to the transport start end. A carrier is mounted on the carrier, and the carrier is brought into contact with the upper surface of the printed circuit board to measure the temperature of the printed circuit board. At least the printed circuit board temperature at the end of the preheating zone (final preheating zone) is measured. Compared with the above, the transfer body, until the printed circuit board temperature in the preheating final zone reaches the set temperature, and provided with a temperature sensor for temporarily stopping the transfer drive of the carrier, the transfer body, the transfer start end of the printed circuit board From the starting point of the melting zone to the end of the cooling zone. The signal in degrees sensor is characterized in that so as to suspend only the carrier corresponding to the preheating zone.

As described above, the temperature profile generated by transporting the printed circuit board on which components are mounted in the furnace by the conveyor is affected by the configuration of the heating furnace, the properties of the heat source, and the thermo-optical characteristic values of the material to be heated. In addition, a difference in temperature occurs at least between the leading portion and the trailing portion due to the transport. Therefore, if there is a temperature difference in the preheating final zone, the temperature difference in the next melting zone increases.

FIG. 9 compares the temperature profiles of the printed circuit boards 1 and 2 in which the components are not mounted with respect to the positions 1 and 2 in the printed circuit board. 5 ° C., and the conditions for making this uniform are: (a) At least stop heating for a certain time under a heat source under certain conditions is required.

(B) The heating power of the object to be heated, which the heat source has, is not significantly affected by the thermo-optical characteristic value of the material to be heated.

It is.

The latter suggests that radiation heating, which is susceptible to the optical absorptance and surface properties of the material to be heated, should be avoided, and uses only heat transfer and heat conduction, which provides heating power under a heat source in the far-infrared region. This is an advantage and is one of the solutions to the problem.

[Operation] A typical example of a far-infrared furnace is a hot-air heating furnace in which air is sent to a heater coated with a material that attenuates near-infrared wavelength components such as alumina, and the resulting heat flow is returned to a printed circuit board. Will be described.

In FIGS. 1 and 2, the furnace is divided into four parts. First to third
The zone is a preheating zone for sequentially heating the printed circuit board to a predetermined preheating temperature.

The fourth zone is a melting zone for rapidly heating to a temperature approximately 30 to 50 ° C. higher than the solder melting temperature after the end of preheating. The main object of the present invention is to make the temperature of the soldering pad in the printed circuit board uniform in the printed circuit board at the final position of the preheating zone, and the first means is to stop the conveyor in the preheating zone, The second means is a system for automatically measuring the temperature distribution in the printed circuit board in a stopped state in a high temperature environment, and confirming a means for analyzing the temperature value and the distribution, and then automatically moving the conveyor. A third means is to measure the temperature distribution with a temperature sensor in contact with the upper surface of the printed circuit board.

The first means detects the presence or absence of a printed circuit board at the rear of the preheating final zone, stops the conveyor using the signal, and simultaneously sets another printed circuit board mounted on the conveyor in front of the preheated zone to the preheating zone. It is required to stop it so that it is not transported. Also, it should be understood that the other conveyor, which is split and passes over the melting zone, should always be kept at operating conditions.

Next, the second means comprises a temperature measuring device, a computer system for analyzing a thermal image thereof, and a heat-resistant filter provided between the temperature measuring device and the object to be heated.

The third means is that the heating furnace is generally made of a refractory metal, the heat flow of which is directed to the conveyor, and needs to be recirculated. In essence, the blowing fan and the heater are: The structure must not block the upper part of the preheating zone and the printed circuit board mounted on the conveyor.

Example Next, an example of the present invention will be described in detail with reference to the drawings.

1 and 2 are schematic explanatory views of the heating furnace of the present invention, FIG. 3 is a perspective view of a carrier structure, FIG. 4 is a vertical sectional front view of the same, FIG. FIG. 6 is a rear perspective view of the same, FIG. 7 is an exploded perspective view of the same, and FIGS.
FIG. 9 is a flow chart showing the operation of the temperature sensor, FIG. 9 is a temperature profile diagram of two portions on a printed circuit board without components mounted thereon, and FIG. 10 is a temperature profile of two portions on a printed circuit board with components mounted thereon.

FIG. 1 shows an embodiment in which a printed circuit board is conveyed from a conveyance start end to a conveyance end by one conveyance body, that is, a conveyor. Reference numeral 1 denotes a heating furnace main body constituting a heating furnace;
Is divided into four, A is the first preheating zone B is the second preheating zone, C is the third preheating final zone, and the preheating zones are A,
It consists of zones B and C. D is the melting zone,
E is a cooling zone. The heating furnace main body 1 is provided with a printed circuit board conveyor 2 from the first preheating zone A to the cooling zone E. The first and second preheating zones A and B are constituted by a blowing fan 3 and a heater 4, and the third preheating final zone C and the melting zone D are provided with blowing fan heaters 5 and 6, respectively. .

FIG. 2 shows the conveyor 2 divided into two parts, a conveyor 2a corresponding to the first and second preheating zones A and B and a third preheating final zone C, and a conveyor 2b corresponding to the melting zone D and the cooling zone E. In this embodiment, the conveyors 2a and 2b are divided at the boundary between the third preheating final zone C and the melting zone D.
As described later, the operation is stopped immediately below the preheating final zone C.

A carrier rail 8 is disposed on one side of the conveyor composed of the conveyor 2 or the conveyors 2a and 2b over substantially the entire length thereof, and the printed circuit board transport of the conveyors 2, 2a and 2b is carried on the carrier rail 8. Carrier 9 traveling in synchronization with the speed and returning from the transport end to the transport start
With. As is clear from FIGS. 3 and 4, the carrier rail 8 is formed in a channel structure having an upward U-shaped cross section, and the carrier 9 is movably inserted into the groove of the carrier rail 8. At the same time, the rolling wheels 10 are pivotally supported at the front, rear, left and right of the upper portion of the carrier 9, and the respective rolling wheels 10 are supported.
Are rollably mounted on the upper edge of the carrier rail 8 respectively. The lower surface of the carrier 9 is fixed to a central portion of a carrier transport belt 11 inserted into the carrier rail 8, and one end of the carrier transport belt 11 is provided on a transport start end side of the carrier rail 8, and ,
Winding and rewinding reel driven by motor 12
13, the other end of the carrier transport belt 11,
The carrier rail 8 is provided on the transport end side and wound around a reel 15 with a clutch for winding and rewinding driven by a motor 14.

In the upper center of the carrier 9, a shaft 16 orthogonal to the conveying direction of the carrier 9 is rotatably supported through a shaft 16. An inner end of the shaft 16, that is, an end on a side corresponding to the printed circuit board 7. At the end, a base of a pipe 18 made of a metal material having high thermal conductivity constituting a temperature sensor having a bent portion 18a at the tip is attached, and inside the pipe 18, for example, a temperature sensor 17 such as a thermocouple is mounted. Enclose. Also, the shaft 16
At the outer end of the cam rod 19, a central portion of a cam rod 19 having a cam surface 19a at one side end is fixed, and the pipe 18 simultaneously rotates by the rotating action of the cam rod 19, and the temperature sensor 17 is printed. It is configured to be pressed against or separated from the upper surface of the substrate 7. As is apparent from FIG. 7, the shaft 16 is housed in a cavity 9a formed in the carrier 9 and has one end hung on the shaft 16 and the other end hung on a pin 20 provided in the cavity 9a. The one-way turning action is applied by the stopped mainspring 21. In the figure, reference numeral 22 denotes a stopper pin, which restricts the cam rod 19 from hitting the stopper pin 22 and rotating the cam rod 19 approximately one rotation or more. In addition, on the outer side of the transport start end and the transport end of the carrier rail 8,
The cam rod 19 contacts the cam surface 19a formed on the cam rod 19 and
A cam rod 23 in a horizontal position having an upward cam surface 23a for rotating the shaft 16 via the shaft and a cam rod 24 in a horizontal position having a downward cam surface 24a are provided.

In the figure, reference numeral 17a denotes a cable connected to the temperature sensor 17, and the cable 17a connects a temperature detection signal on the upper surface of the printed circuit board 7 to a microcomputer (not shown). Then, the temperature detection signal is processed by a microcomputer, and the drive of the conveyer 2 or 2a and the transport motor 14 of the carrier 9 is performed until the temperature of the printed circuit board 7 in the preheating final zone C falls within a predetermined temperature difference. Is stopped, and the conveyors 2, 2a, 2b and the carrier 9 are transported by a signal indicating that the temperature difference has reached a predetermined value or less. At this time, in the embodiment shown in FIG. 2, since the conveyor 2b is constantly driven, the printed circuit board 7 is transferred to the conveyor 2b and the solder is melted.

In addition, the temperature of the preheating final zone C can be set to be equal to or higher than the solder melting temperature, and the temperature distribution and the change during the solder melting can be measured.

In this embodiment, if the conveyor stop time in the preheating final zone C is determined, this time value is stored,
The stop time is automatically set for printed circuit boards of the same lot.

Further, although the present embodiment has been described with respect to the far-infrared heating furnace, this is merely related to the properties of the heater, and it is needless to say that the present invention can be similarly performed even if a near-infrared heater or a vapor is used. Absent.

FIG. 10 shows an example of the temperature profile of the present embodiment. There is no temperature difference at the end of the preheating final zone C of C and D,
Further, the subsequent melting temperature difference is about 2 ° C.

Next, the relationship between the temperature sensor 17 and the printed circuit board 7 and the change in the attitude of the cam rod 19 and the temperature sensor 17 when the carrier 9 returns will be described with reference to FIGS.

FIG. 8a shows a state in which the carrier 9 is stopped at the transport start end. At this time, the carrier rod 19 provided on the carrier 9 is in parallel contact with the lower surface of the cam rod 23, and the temperature sensor Reference numeral 17 is separated from the upper surface of the principal board 7 to be conveyed. In this state, when the carrier transport belt 11 of the carrier 9 and the conveyors 2, 2a, 2b are driven synchronously, the shaft 16 is rotated by the one-way rotation urging action of the mainspring 21 as shown in FIG. Then, the temperature sensor 17 reaches the transport end while being pressed against the upper surface of the printed circuit board 7. When the carrier 9 arrives at the transport end, the cam surface 19a of the cam rod 19 in the posture as shown in FIG. 8b is guided to abut against the downward cam surface 24a of the cam rod 24 disposed at the transport end. The rod 19 rotates so as to be parallel to the lower surface of the cam rod 24, and is brought into contact with the lower surface of the cam rod 24. With this operation, the shaft 16 rotates,
As shown in FIG. 3C, the temperature sensor 17 is separated from the upper surface of the printed circuit board 7, and the printed circuit board 7 that has been cooled after the completion of the soldering is carried out of the heating furnace body 1 from the transfer end as it is.

Next, when returning the carrier 9 to the transport start end, the clutch of the clutch-equipped reel 15 around which the carrier transport belt 11 has been wound is disengaged, and the motor 12 drives the carrier transport belt.
When the reel 11 is wound on the reel 13, the cam rod 19 comes off the cam rod 24 as shown in FIG. 8d. At this time, the temperature sensor 17
Since there is no printed circuit board 7 with which the shaft 16 contacts, the shaft 16 rotates approximately one rotation by the action of the mainspring 21 until the end of the cam rod 19 hits the stopper pin 22.
At this time, as shown in FIG. 8e, the temperature sensor 17 is in a substantially horizontal posture. In this state, when the carrier 9 returns and the cam surface 19a of the cam rod 19 comes into contact with the upward cam surface 23a of the cam rod 23,
As shown in FIG. 8f, the cam rod 19 rotates in the direction of the arrow,
It is housed under the cam rod 23. This is the same state as FIG. 8a.

[Effects of the Invention] According to the configuration of the present invention as described above, the following effects can be obtained.

It is possible to detect the temperature profile in the printed circuit board necessary for reflow soldering of various types of mounted printed circuit boards, in particular, the temperature in the preheating final zone, and to reliably reach a constant temperature. For this reason, since the temperature difference in the subsequent solder melting zone can be suppressed to the minimum, the temperature difference in the melting zone can be kept within about 2 ° C by correcting the preheating final temperature, and unjoined due to excessive or insufficient solder melting and solder lift to the lead There is an excellent effect that defects such as defects can be completely eliminated.

[Brief description of the drawings]

1 and 2 are schematic explanatory views of the heating furnace of the present invention,
3 is a perspective view of the carrier structure, FIG. 4 is a vertical sectional front view of the same, FIG. 5 is a front perspective view of the carrier part, FIG. 6 is a rear view of the same, FIG. 7 is an exploded perspective view of the same, FIG. a to f are flow charts showing the operation of the temperature sensor, FIG. 9 is a temperature profile diagram of two portions on a printed circuit board alone on which components are not mounted, and FIG. 10 is a temperature profile of two portions on a printed circuit board on which components are mounted. A: First preheating zone, B: Second preheating zone, C: Last preheating zone, D: Melting zone, E: Cooling zone, 1, Superheating furnace body, 2, 2a, 2b ... Conveyor , 3 …… Blower fan, 4 ……
Heater, 5,6 …… Blower fan heater, 7 …… Printed circuit board, 8
…… Carrier rail, 9 …… Carrier, 10 …… Roller wheel, 11 ……
Carrier transport belt, 12 …… Motor, 13 …… Reel, 14…
… Motor, 15 …… Reel with clutch, 16 …… Shaft, 17 ……
Temperature sensor, 17a …… Cable, 18 …… Pipe, 19 …… Cam rod, 19a …… Cam surface, 20 …… Pin, 21 …… Spring spring, 2
2 ... Stopper pin, 23 ... Cam rod, 23a ... Upward cam surface, 24 ... Cam rod, 24a ... Downward cam surface.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kaoru Sato 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi, Ltd. Production Engineering Research Laboratory (72) Inventor Kyoji Imai 7-13-8 Ginza, Chuo-ku, Tokyo Koukinai Co., Ltd. (56) References JP-A-2-263569 (JP, A) JP-A-2-151366 (JP, A) JP-A-62-144876 (JP, A) JP-A-1-124727 (JP) , A) JP-A-1-159586 (JP, A)

Claims (2)

(57) [Claims] In order to continuously heat a printed circuit board to a desired temperature profile by a carrier, at least a heating furnace in which a preheating zone, a melting zone, and a cooling zone are arranged in series in this order. Side, a carrier rail is disposed over substantially the entire length of the carrier rail, and the carrier rail is mounted with a carrier that travels in synchronization with the printed circuit board transfer speed of the transfer body and returns from the transfer end to the transfer start end. At the same time, the carrier is brought into contact with the upper surface of the printed circuit board to measure the temperature of the printed circuit board, and at least the printed circuit board temperature at the end of the preheating zone (final preheating zone) is compared with the actually measured temperature data. The temperature at which the conveyance body and the carrier conveyance drive are temporarily stopped until the printed circuit board temperature in the final zone reaches the set temperature. A heating furnace provided with a sensor. 2. The temperature sensor according to claim 1, wherein said carrier is divided into a carrier extending from a start point of the printed circuit board to an end of a preheating zone and a carrier extending from a start end of a melting zone to an end of a cooling zone. 2. The heating furnace according to claim 1, wherein only the carrier corresponding to the preheating zone is temporarily stopped by the signal of (1).