JPH0216854Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Field of Industrial Application) The present invention relates to an improvement of an infrared heating type reflow oven. (Conventional technology and its problems) As electronic devices become smaller, small leadless chip components are increasingly used for circuit boards.
Discrete components (e.g. aluminum electrolytic capacitors) and mechanical parts (e.g. switches, jacks, etc.), which were difficult to make into chips in the past, are now being made into chips rapidly, and a wide variety of chip parts are now packed together on circuit boards at high density. It has become common practice to implement it. These leadless chip components generally have poor heat resistance, so it is difficult to solder them directly with a solder dip.Soldering involves attaching these leadless chip components to the component mounting land of the circuit board through solder paste. One method is to mount the device on a circuit board by placing it on a circuit board and performing reflow soldering. Reflow soldering methods include the belt method, which conducts heat through a belt for board transfer, the infrared heating method, which heats by irradiating infrared rays, and the vapor phase method, which uses an inert solvent. The disadvantage of the vapor phase method is that heat conduction will be affected if there is a gap between the board and the belt due to warpage, and it cannot be applied to double-sided mounting boards.Also, the vapor phase method uses an inert solvent used during soldering. Generally, infrared heating type reflow ovens are widely used because of problems such as being expensive. Figure 3 shows an example of an infrared heating type reflow oven that has been commonly used in the past, where 1 is the reflow oven body, 2 is the substrate intake port 1a and the substrate output port 1.
A chain belt (or stainless steel mesh belt) for transferring substrates is stretched between drive pulleys 3a and 3b. The inside of the reflow oven 1 includes a reflow section 4 that melts the solder paste on the circuit board 100 and performs reflow soldering, a preheat section 5 that preheats the circuit board 100 before inserting it into the reflow section 4, and a reflow section 4. It consists of a cooling section 6 that cools the soldered circuit board 100. The preheat section 5 heats the circuit board 100 to an appropriate temperature (usually 150°C) before reflow soldering.
The purpose is to gradually heat the circuit board up to 30 degrees (before and after), to alleviate the shock to parts and boards caused by sudden changes in temperature, and to activate the flux _. Heaters 7a to 7b for irradiation are arranged above and below the chain belt 2. A ceramic heater or the like is usually used as the far-infrared illumination heater. Further, in the reflow section 4, a halogen lamp 8 is installed below the belt ₂ , which irradiates, for example, near infrared rays on the circuit board 100, which has been heated to an appropriate temperature by the preheat section 5, and heats it to a temperature sufficient for melting the solder. together with the reflector plate 9. On the upper surfaces of the preheat section 5 and the reflow section 4, lids 51b and 41b are provided in the openings 51a and 41a, respectively.
Dampers 51 and 41 are provided for adjusting the temperature inside the furnace, each of which is attached so as to be openable and closable.
By adjusting the release amount of b and 41b and controlling the inflow of air, the temperature inside the furnace can be adjusted to a certain extent. In addition, outside air taken in from the air intake port 61 is supplied to the cooling unit 6 to cool the soldered circuit board 10.
A fan 10 is attached together with a motor 11 to cool the air by blowing air onto the air. Therefore, when actually performing reflow soldering, the circuit board 100 placed on the component mounting land is attached to the chain belt 2 using solder paste, and the circuit board 100 is attached to the chain belt 2 using a holding means (not shown). transport inward. The circuit board 100 is preheated in the preheat section 5 by ceramic heaters 7a to 7d, and then rapidly heated in the reflow section 4 by a halogen lamp 8 to solder the lands for mounting each component on the board. The paste is melted and the electronic components are soldered. In addition, in order to avoid overheating of the weak heat-resistant components placed on the circuit board 100, the weak heat-resistant components are attached only to the top surface of the circuit board 100, and during reflow soldering, the circuit board 100 is mounted in the reflow section 4.
Near-infrared rays are irradiated from the lower surface _side where the weak heat-resistant parts are not placed, thereby suppressing the temperature rise of the weak heat-resistant parts as much as possible. However, when a circuit board containing a variety of leadless chip components including components with low heat resistance is soldered using the infrared heating type reflow oven as described above, the following problems occur. In other words, mechanical parts that use plastic, such as aluminum electrolytic capacitors, switches, and jacks, which are heat-resistant parts, are easily damaged and deformed due to heat (heat-resistant temperature 200 to 240°C). Since they are components, they often have a large heat capacity and a slow temperature rise. Furthermore, infrared heating type reflow ovens cannot heat only the component mounting lands of the circuit board, and the inside of the oven is also heated uniformly, resulting in an increase in the ambient temperature. Therefore, when reflow soldering a circuit board that contains the above-mentioned weak heat-resistant components, it is recommended to lower the temperature of the heater during reflow soldering to prevent damage to the weak heat-resistant components due to overheating in the furnace. The temperature of the mounting part, that is, the electrode part of the component is difficult to rise, and there is a risk of a solder non-melting accident due to uneven solder melting. In addition, when the temperature inside the reflow oven is raised to sufficiently melt the solder, the temperature rises throughout the entire interior of the oven in an infrared heated reflow oven.
There is a risk that the temperature of the parts themselves will rise too much, causing damage and property deterioration. Note that even if the component is not particularly heat resistant, a component with a small heat capacity may become overheated and its characteristics may deteriorate in the same way as a component with weak heat resistance. For example, aluminum electrolytic capacitors use electrolyte, which increases the internal pressure of the element, which can cause the electrolyte to leak or destroy the element itself, while switches, jacks, etc. use plastic. It may be deformed due to the Furthermore, during reflow soldering, the flux mixed in the solder paste is vaporized by the heat, but in the above-mentioned reflow oven, the volatile components of this flux fill the oven and stagnate, causing damage to electrical contacts such as switches and jacks. This substance adhered to the parts and caused poor contact. In order to solve this problem, measures have been taken to open the dampers 41, 51, etc. on the top of the reflow oven to lower the temperature inside the oven and exhaust the flux gas, and to further enhance this effect, the opening area of the damper is Countermeasures were taken, such as making the dampers wider and increasing the number of dampers, but simply opening the dampers did not create active convection in the furnace, so it was not possible to obtain a sufficient flux gas discharge effect, and the opening area was also reduced. If the temperature inside the furnace was lowered by enlarging the furnace, most of the heat emitted by the heater would be wasted, which would be unfavorable from an economic point of view. (Purpose of the invention) The purpose of the invention is to eliminate the above-mentioned drawbacks, and to provide an infrared heating reflow oven that does not damage or deteriorate heat-resistant weak parts and is highly economical. . (Summary of the invention) An infrared heating type reflow oven consisting of a preheat section that preheats a circuit board, and a reflow section that heats the circuit board preheated by the preheat section to a solder melting temperature and solders it,
By providing an exhaust means for forcibly discharging hot air in the reflow section to the outside through the preheat section, the hot air in the reflow section is prevented from stagnation and heating in the furnace is prevented. , a new infrared heating type reflow oven configured so that preheating can be assisted by hot air passing through a preheating section. (Embodiment) FIG. 1 is a side view showing an embodiment of an infrared heating type reflow oven of the present invention, and the same parts as in the conventional example will be described using the same reference numerals. The reflow furnace 20 has a basic configuration similar to the conventional example shown in FIG.
1, a preheating section 22 that preheats the circuit board 100 before inserting it into the reflow section 21 to alleviate temperature shock, and a cooling section 23 that cools the circuit board 100 soldered in the reflow section 21. ing. Then, the circuit board 100 is transferred into the reflow oven 20 by a chain belt (or stainless steel mesh belt) 2 for board transfer, which is stretched by pulleys 3a and 3b between the board intake port 20a and the board exit port 20b. , preheat section 22, reflow section 2
1, cooling section 23. Inside the preheat section 22, ceramic heaters 7a to 7d are arranged above and below the belt 2 to irradiate the circuit board 100 with far infrared rays _l1 to preheat it. is 7a
It is sufficient to operate only 7b to 7d, and they can be omitted). In the reflow section 21, a halogen lamp 8 is installed below the belt ₂ , which irradiates near-infrared rays on the circuit board 100, which has been heated to a predetermined temperature by the preheat section 22, to heat it to a temperature sufficient for melting the solder. together with the reflector plate 9. Also, in the cooling section 23, a cooling fan 10 is installed together with a motor 11, which cools the circuit board 100 by blowing outside air taken in through an air intake port 231 onto the circuit board 100, as in a conventional reflow oven. Before the preheat section 22, that is, the board intake port 2
A fan 24 serving as a forced exhaust means for forcibly exhausting hot air in the reflow section 21 through the preheat section 22 is provided between Oa and the preheat section 22. The fan 24 is rotated by a motor 25 (control means for the motor 25 is not shown), thereby directing high-temperature hot air in the reflow section 21 through the preheat section 22 to an exhaust port. It is designed to be discharged from 26 onwards.
A lid 22 is provided in the openings 221a and 211a on the upper surfaces of the preheat section 22 and the reflow 21, respectively.
1b, 211b are provided with dampers 221, 221 for adjusting the temperature inside the furnace, which are attached so as to be openable and closable.
Furthermore, there are openings 2 in the partition walls between the fan 24 and the preheat section 22, between the preheat section 22 and the reflow section 21, and between the reflow section 21 and the cooling section 23.
7a, 28a, 29a have lids 27b, 28, respectively.
b, damper 27 attached to 29b so that it can be opened and closed,
28 and 29 are provided, thereby communicating between each block. Therefore, by adjusting the opening area of these dampers, it is possible to control the inflow amount, flow speed, etc. of hot air and outside air, and to adjust the temperature. The infrared heating type reflow oven of the present invention is constructed as described above, and when mounting electronic components on a circuit board, the electronic components are placed on the component mounting land via solder paste using well-known means. This can be done by mounting the circuit board on the chain belt 2 and transferring it into the reflow oven 20 through the board intake port 20a. The parts are sequentially transferred to the factory, preheated, and then reflow soldered. In addition, in the present invention, by gathering the weak heat-resistant components on the top side of the circuit board, the near-infrared rays of the halogen lamp ₈ can alleviate overheating of the weak heat-resistant components of the circuit board during reflow soldering in the reflow section 21. Both methods are used. On the other hand, by driving the fan 24, the hot air and flux gas in the reflow soldering section 21 flow into the preheating section 22 through the damper 28, as shown by the arrow in the figure, and the damper 29 and the cooling Outside air from the substrate outlet 20b flows in through the portion 23. This prevents hot air and flux gas from accumulating in the reflow section 21, lowering the ambient temperature within the reflow section 21, and preventing damage to weak heat-resistant parts due to overheating and contact failures of switches and jacks due to adhesion of flux gas. It can be prevented. Further, the hot air flowing from the reflow section 21 into the preheat section 22 passes through the preheat section 22,
The gas is discharged outward from the exhaust port 26 through the opening 27 . At this time, the circuit board 100 in the preheat section 22 is heated by the passing hot air (approximately 250° C.), and a preheating action is performed. As a result, the efficiency of preheating in the preheating section 22 is greatly increased.

[Table] However, the temperature of the circuit board surface is the temperature of the board surface when heated from the bottom side where no heat-resistant components are placed, and is approximately the same temperature as the component mounting land. Further, the component surface temperature indicates the surface temperature of the component itself, which is a heat-resistant component (aluminum electrolytic capacitor, switch, jack, etc.) that has a relatively large heat capacity and is weak against heat, which is the object of the present invention. The reflow section internal temperature indicates the ambient temperature within the reflow section. In the reflow section, when infrared heating is applied from the bottom side of a circuit board on which a component with low heat resistance and high heat capacity is placed on the top surface, the bottom surface of the circuit board, that is, the surface facing the halogen lamp 8,
It is heated to about 250 to 270°C, and at the same time, the ambient temperature rises not only on the substrate surface but also throughout the reflow part. In the reflow section 4 of the conventional reflow oven 1, there is almost no convection or inflow of outside air, so the temperature inside the oven rises to about 340 to 350 degrees Celsius, and the temperature of the component body on the top surface of the circuit board, which is not directly irradiated with infrared rays, also rises to 230 degrees Celsius. ~
The temperature rises to around 240℃. Therefore, there is a risk that damage, deformation, characteristic deterioration, etc. may occur in heat-resistant parts. On the other hand, according to the reflow oven 20 of the present invention, the hot air in the reflow section 21 is discharged through the preheat section 22, so the lower surface side of the circuit board can be heated to 250 to 270 degrees Celsius similarly to the conventional reflow oven. However, since the atmospheric temperature within the reflow section 21 is prevented from rising, the actual temperature of the circuit board surface is suppressed to about 240 to 260°C. Therefore, the temperature of the weakly heat-resistant component itself can be suppressed to about 190 to 200°C, and damage, deformation, and characteristic deterioration due to overheating can be prevented. It can be seen that as the temperature within the reflow section 21 decreases, the temperature of the terminals of the components on the circuit board also decreases slightly. Figures 2 a to c are graphs comparing the temperature characteristics of the conventional reflow oven 1 and the reflow oven 20 of the present invention. Figure 2 a shows the atmospheric temperature distribution in each reflow oven; is the temperature of the circuit board surface (land for mounting parts) at each part in the reflow oven,
Figure c shows the surface temperatures of low heat resistant parts and large heat capacity parts (aluminum electrolytic capacitors, switches, jacks, etc.) on the circuit board in various parts of the reflow oven. As shown in Figure 2a, the temperature inside the preheat section is constant in any reflow oven.
The surface temperature of the circuit board is maintained at about 200℃, as shown in Figure 2b.
The circuit board is heated to a temperature of 150°C, and the heat-resistant parts (those with large heat capacity) on the circuit board are also preheated to about 150°C, as shown in FIG. 2c. Note that the rise of the graph in FIG. 2c is slower than in FIGS. 2a and 2b, which indicates that the temperature rise is slow because the heat capacity is large even though the component is a weakly heat resistant component. On the other hand, in the reflow section, as shown in Fig. 2b, the temperature of the circuit board surface is approximately 260°C in a conventional reflow oven, and the ambient temperature inside the reflow section at this time is as shown in Fig. 2a. As you can see, the temperature has risen to about 350℃. Therefore, Figure 2c
As shown in Figure 2, the surface temperature of heat-resistant components rises to about 240°C, and there is a risk of component damage, deformation, and property deterioration. On the other hand, in the reflow oven of the present invention, the forced exhaust means prevents hot air from accumulating in the reflow section, so it is heated by the same heater as in the conventional reflow oven, and the temperature of the circuit board surface is reduced as shown in Figure 2. Although the temperature has risen to about 250°C, which is sufficient for melting the solder, as shown in Fig. 2b, the atmospheric temperature within the reflow section can be suppressed to about 250°C, as can be seen from Fig. 2a. As a result, the surface temperature of the heat-resistant components placed on the top side of the circuit board can be suppressed to approximately 200℃, which is a significant reduction compared to the approximately 240℃ of conventional reflow ovens. can. As described above, the reflow oven of the present invention can reliably perform reflow soldering without overheating the weak heat resistant components themselves, and is therefore ideal for reflow soldering of circuit boards containing a mixture of weak heat resistant components. (Effects of the invention) As described above, the infrared heating type reflow oven of the invention includes a preheating section for preheating a circuit board, and a circuit board preheated by the preheating section to a solder melting temperature. In an infrared heating type reflow oven consisting of a reflow section for heating and soldering, the hot air in the reflow section is forcibly discharged through the preheat section, so that the circuit board is not heated during reflow soldering. At the same time, forced exhaust can suppress the temperature rise in the reflow section and suppress the overheating of the parts themselves, and can especially prevent heat-induced damage, deformation, and characteristic deterioration of parts with low heat resistance and small heat capacity. . Incidentally, since the flux gas volatilized during soldering is discharged to the outside without staying in the reflow section, contact failures caused by flux gas adhering to electrical contacts such as jacks and switches can be prevented. In addition, since the hot air discharged from the reflow section passes through the preheat section and is discharged, the preheating of the preheat section can be assisted by the heat exhaust, which greatly improves the efficiency of the preheat section. The heater in the preheat section can be downsized.

[Brief explanation of the drawing]

Figure 1 is a side sectional view for explaining the configuration and operation of the infrared heating reflow oven of the present invention, Figure 2a
~c is a temperature characteristic graph that compares the reflow oven of the present invention and a conventional reflow oven in terms of the furnace atmosphere temperature, circuit board surface temperature, and heat-resistant weak component surface temperature. FIG. 3 is a side sectional view for explaining the configuration and operation. Explanation of symbols, 2...Chain belt, 3a, 3
b... Drive roller, 7a to 7d... Ceramic heater, 8... Halogen lamp, 20... Infrared heating type reflow oven, 21... Reflow section, 22...
Preheat section, 24...fan (forced exhaust means),
27, 28, 29, 211, 221... damper,
100...Circuit board.

Claims (1)

[Scope of utility model registration request] a preheating section that preheats an electronic circuit board on which electronic circuit components are mounted via solder paste;
a reflow section that irradiates the electronic circuit board with infrared rays to heat the solder paste on the component mounting land portion of the board to melt it; the electronic circuit board is preheated in the preheat section; In a reflow furnace that is introduced into the reflow section to perform reflow soldering, a forced exhaust means is provided upstream of the preheat section, and hot air in the reflow section is exhausted through the preheat section. An infrared heating reflow oven characterized in that it is configured to prevent hot air from stagnation in the reflow section and to assist preheating with hot air passing through the preheat section.