JPH07131149A - Reflow soldering device - Google Patents

Abstract

PURPOSE:To provide the satisfactory reflow soldering step capable of suppressing the unfavorable thermal effect on a body part without laying a solder bridge at all even if in a narrow pitch electronic component. CONSTITUTION:A printed-wiring substrate 1 loaded with narrow pitch electronic components 2 through the intermediary of a creamy solder is carried in a reflow furnace A. Next, individual lead of narrow pitch electronic components 2 is pressurized by plural local heating nozzles 8 in a local heating head 7. Finally, the leads are sprayed with hot helium He in high thermal conductivity from respective local heating nozzles so as to reflow-solder the leads onto the printed- wiring substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflow soldering apparatus for mounting electronic components on a printed wiring board, and particularly, a reflow soldering method effective for mounting SMT components having narrow pitches (0.5 mm or less). The present invention relates to a soldering device.

[0002]

2. Description of the Related Art FIG. 4 shows a schematic structure of a conventional reflow soldering apparatus. In FIG. 4, 81 is a printed wiring board,
Reference numeral 82 is an electronic component mounted on the printed wiring board 81 via cream solder, B is a reflow furnace, 83 and 84 are preheating sections, 85 is a reflow section, 86, 87 and 88 are heaters, 89, 90 and 91. Is a suction circulator, 92 is a cooling unit,
93 is a conveyor.

O ₂ concentration in reflow furnace B, heater 8
The operator sets conditions such as the temperature of 6, 87, 88 and the speed of the conveyor 93. The printed wiring board 81 on which the electronic component 82 is mounted is carried into the reflow furnace B by the conveyor 93,
The reflow furnace B is transported. In this process, the printed wiring board 81 is preheated in the preheating units 83 and 84 and reflowed in the reflow unit 85. At this time, in the convection by the suction type circulation machines 89, 90, 91,
Preheating and reflow are performed. Furthermore, electronic components 8
The printed wiring board 81 to which 2 is reflow-soldered is cooled by the cooling unit 92 and is carried out of the reflow furnace B by the conveyor 93. Preheating section 83, 84
Further, in the reflow section 85, the processing by the whole heating method is performed.

FIG. 5 is a flow chart showing the operation of the conventional reflow soldering apparatus described above. Start soldering start, and the operator decides the next item at the start. Temperature setting of the heaters 86, 87 of the preheating units 83, 84, temperature setting of the heater 88 of the reflow unit 85,
These are the speed setting of the conveyor 93 and the O ₂ concentration setting. Step S31 is a setting work in which the worker performs each condition determined above on the apparatus. In step S32, the temperature of the first heater 86 is set, and after it is stabilized,
In step S33, the temperature setting of the second heater 87 is executed and waits for stabilization, and in step S34 the temperature setting of the heater 88 of the reflow unit 85 is executed and waits for stabilization.

Then, in step S35, it is visually confirmed that the O ₂ concentration, each heater temperature, and the conveyor speed are stable. Then, in step S36, the first temperature measurement is performed by the worker, and in step S37, the worker analyzes and determines the temperature and time as the measurement result. In step S38, the second temperature measurement is performed by the operator, and in step S3
At 9, the operator analyzes / determines the temperature and time as the measurement result.

[0006]

In the conventional reflow soldering apparatus, since the whole heating method is used, the heat source of the overall convection from the heating medium (heater) causes both the body and the leads of electronic parts with narrow pitches to be obtained. It will be heated at the same time. That is, it is inevitable that the electronic components are adversely affected by heat.

Further, a solvent (flux) which is a component of the paste solder printed on the lower surface of the lead of the electronic component.
Is softened by conduction heat, so that the flux flows out between the leads. Solder particles and the like also tend to be carried by the outflowing flux. As the pitch of electronic components becomes narrower, it is necessary to reduce the diameter of solder particles, so measures against solder balls become important. Further, when the solder reaches the liquidus line from the solid phase line and the solder is completely melted, the molten solder spreads between the leads.

Further, when the solder solidifies, the surface tension of rosin or the like causes the solder spread between the leads to agglomerate and return to each land. However, heating unevenness, solder activity, surface tension balance, etc. There is a risk that solder bridge will occur due to

Further, in the case of a narrow pitch electronic component (lead pitch 0.5 mm or less), good soldering becomes difficult due to the narrow lead pitch and the thin body.

The present invention was devised in view of such circumstances, and even in a narrow-pitch electronic component, it is possible to suppress a thermal adverse effect on the body portion and to prevent a solder bridge. An object of the present invention is to provide a reflow soldering device that can perform good reflow soldering.

[0011]

SUMMARY OF THE INVENTION A reflow soldering apparatus according to the present invention is a solder for performing reflow by heating while carrying a printed wiring board on which a narrow-pitch electronic component is mounted via cream solder in a reflow oven. A reflow soldering device to attach, by bringing the local heating nozzle of the local heating head close to or in contact with each of the leads of the narrow pitch electronic component, and supplying hot helium from the local heating nozzle, It is characterized by reflow soldering.

[0012]

Function: The local heating nozzle is brought close to or in contact with each lead, and hot helium having a very high thermal conductivity is supplied from the local heating nozzle, so that the leads of the narrow-pitch electronic component are applied to the printed wiring board. On the other hand, since reflow soldering is performed, even in a narrow pitch electronic component, thermal adverse effects on the body are suppressed, and good reflow soldering can be performed without causing a solder bridge.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the reflow soldering apparatus according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a narrow pitch electronic component (S
FIG. 2 is a side view showing a schematic configuration of the reflow soldering apparatus corresponding to the MT component).

In these figures, 1 is a printed wiring board,
2 is an electronic component with narrow pitch leads mounted on the printed wiring board 1 via cream solder, A is a reflow furnace, and A is a reflow furnace.
Reference numeral 1 is a local heating portion, and A2 is a whole heating portion. 3 is a conveyor for carrying the substrate, 4 is a shutter on the substrate loading side, 5 is O ₂
Exhaust port, 6 is an inert gas (helium He) supply port, 7
Is a local heating head, 8 is a local heating nozzle, 9 is a preliminary nozzle, and 10 is a heating head lifting device. Two such local heating units are installed side by side. 11 is a heat-resistant glass, 12 is a temperature sensor, and 13 is an infrared camera.
The temperature sensor 12 and the infrared camera 13 are heat-resistant glass 11
It is enclosed inside. A pair of such temperature measuring units is arranged vertically. Reference numeral 14 is a cooling device, and 15 is a substrate positioning stopper.

Reference numeral 16 is a remelting prevention shield jig processing device,
Reference numeral 17 designates a jig for pushing a division jig, 18 a jig plate for integrated heat load / remelting prevention, and 19 for a jig plate 1 integrated heat load / remelting prevention
8 is a slide path when setting 8 to the heater.

Reference numeral 20 denotes a moving heater for heating the entire body, which is arranged above and below the conveyor 3 so as to circulate and move. Reference numeral 21 is a heat-resistant glass, 22 is a temperature sensor, and 23 is an infrared camera. The temperature sensor 22 and the infrared camera 23 are enclosed in the heat resistant glass 21.
A pair of such temperature measuring units is arranged vertically.

Reference numeral 24 is a cooling device, and 25 is a shutter on the outlet side.

Reference numeral 30 is a personal computer (personal computer), which includes a data input unit 31, a comparison / determination unit 32, a first memory unit 33, a second memory unit 34, and a correction data unit 35.

Next, the operation will be described with reference to the flow chart shown in FIG.

The reflow soldering apparatus for a narrow pitch electronic component according to the present embodiment, before starting the actual manufacturing process, is in an atmosphere of an inert gas (He) in the reflow furnace A, the local heating section A1 and the whole. The conditions for optimal soldering including the total condition of the heating part A2 are analyzed and judged using the personal computer 30. Therefore, at the start of production, the following data is input from the data input unit 31 and stored in the first memory unit 33. That is, the O ₂ concentration, the material of the printed wiring board (paper phenol, glass epoxy, etc.), the size of the board (length × width ×)
(Thickness), lead pitch of narrow-pitch electronic parts that are target mounting parts, number of pins, land area, body material, lead material, number of parts, XY coordinates, reference temperature (preheating temperature, reflow temperature, time specification), etc. Is input (step S1).

The local heating nozzle 8 is automatically moved and positioned based on the input data as described above for the narrow pitch electronic component. In addition, in order to shield the target narrow-pitch electronic component from the shield, the split jig portion push rod 17 in the remelting prevention shield jig processing device 16 is operated based on the input data, and the printed wiring board 1 The heat load / remelting prevention integrated jig plate 18 is processed in accordance with the arrangement of the narrow pitch electronic components 2 mounted via the cream solder. The remelting prevention shield jig processing device 16 that has completed this processing automatically slides along the slide path 19 and sets it on the overall heating moving heater 20 in the overall heating section A2. In parallel with this, the O ₂ is a factor of the oxidation than O ₂ outlet 5 as well as discharged from the reflow furnace A, supplied from the inert gas supply port 6 helium He reflow furnace A. In the oxygen-less atmosphere, after the atmosphere of helium He is stabilized, a calculation process is performed in consideration of the thermal conductivity data and the input data depending on the material difference from the material registered in the personal computer 30 in advance, and the local heating unit A1 Estimate the temperature rise curve during heating. Furthermore, in parallel with this,
Based on the input data, the temperature rise curve during heating of the moving heater 20 for whole heating in the whole heating unit A2 is estimated. Then, the data of the reference temperature condition (preheating temperature, reflow temperature, time) of the input data and the estimated data are compared and analyzed, whereby the optimum condition at this point (the local heating unit The temperature conditions of A1 and the overall heating unit A2, the speed of the conveyor 3) are determined (above, step S2).

Next, a plurality of simulations are carried out based on the optimum conditions determined as described above. After setting the O ₂ concentration (step S3), wait until it stabilizes, set the temperature of the local heating head 7 (step S4), wait until it stabilizes, and set the whole heating part A
The temperature setting of the moving heater 20 for whole heating of No. 2 is executed (step S5), the stabilization is waited, the speed setting of the conveyor 3 is executed (step S6) and the stabilization is waited.

Next, the first simulation is started.
The printed wiring board 1 on which the narrow-pitch electronic components 2 are mounted is automatically carried into the reflow furnace A by the conveyor 3 and conveyed in the reflow furnace A. After the carry-in, the board positioning stopper 15 positions the printed wiring board 1. The heating head elevating device 10 operates and the local heating head 7 descends.
The helium He supplied from the inert gas supply port 6 is heated by the local heating head 7, and the hot helium H
e is a large number of local heating nozzles 8 in the local heating head 7.
From each of them, the leads are sprayed onto each lead of the narrow pitch electronic component 2, these leads are locally heated, and the leads are soldered. Since it is a heating method for each lead, there is no direct thermal adverse effect on the body of the narrow pitch electronic component 2. In addition, since the heating medium is helium He, which has no oxidation factor,
The activity can be efficiently given to the solder. Also in terms of thermal conductivity, when comparing the conventional nitrogen N ₂ with the helium He of this embodiment, the nitrogen N ₂ is 286 kcal / mh3.
Helium He is 1649kca while it is 50 ℃
1 / mh 350 ° C., which is about 5.7 times that of helium He is superior in heat conduction. In addition, since helium He has a higher thermal conductivity, hot helium He sprayed on the leads is used.
The temperature rises in a short time, the amount used is small, and the processing time is short. As described above, by combining helium He having excellent heat conduction characteristics and local heating by the local heating nozzle 8, it is possible to solder the leads of the narrow pitch electronic component 2.

Next, the infrared camera 13 measures the distribution of the front surface temperature and the rear surface temperature of the printed wiring board 1 that has been locally heated (step S7). The infrared camera 13 is covered with the heat-resistant glass 11,
The infrared camera 13 is cooled by supplying cooling air to the inside of 1 through a cooling nozzle (not shown). As described above, the data obtained by measuring the temperature immediately after soldering is the personal computer 30.
Is transmitted to the first memory unit 33 from the data input unit 31 and is compared and judged with the temperature data as the optimum condition in the comparison / judgment unit 32. As a result, the correction data unit 35 outputs appropriate correction data. Is output in a feedback manner (step S8). The printed wiring board 1 whose temperature has been measured by the infrared camera 13 is sent to the cooling device 14 and cooled, so that reliable and highly reliable soldering is performed.

Subsequently, the printed wiring board 1 is automatically carried into the overall heating section A2 by the conveyor 3. The moving heater 20 for whole heating has a structure capable of performing heating for each circuit block. It has a large number of nozzle-shaped hot air jets arranged vertically and horizontally. And already the local heating part A
1 has a structure for preventing application of heat load and re-melting to the narrow pitch electronic component 2 to which the leads are soldered. This is the remelting prevention shield jig processing device 16. Further, the other electronic component 2 has a function of uniform heating.

The upper and lower moving heaters 20 for whole heating are both circulated in the same direction as the direction in which the printed wiring board 1 is conveyed by the conveyor 3. In the process of circulation, the moving heater 20 for heating the entire body is mounted on the printed wiring board
The circuit blocks are heated separately. That is, this is to efficiently perform preheating, which is one of the most important steps in reflow soldering. It is no exaggeration to say that the quality of soldering is determined by whether preheating is performed correctly.

In the case of reflow solder, paste-like flux (natural / synthetic resin + solvent + thickener + thixotropic agent + activator) and solder powder are kneaded. Natural / synthetic resin, which is the main component of the flux, means pine resin and activated rosin, which is also a viscous material for fixing parts, but it is also used for cleaning copper oxide and soldering parts during reflow. It also has the function of preventing reoxidation. Furthermore, adjustment is performed using a solvent (carbitol-based, ether-based).
Next, a thickener and a thixotropic agent are added in order to suppress the separation of flux from the solder powder and improve the thixotropy, and an activator is added to further improve the solderability.

As the above-mentioned flux adjusting agent, it is convenient that the paste is formed by automatically applying the copper foil surface to the printed wiring board 1, so that a solvent is used. . Therefore, the excess solvent is volatilized during preheating to prevent the occurrence of scattering due to the residual solvent during reflow, and the bending and warpage caused by the rapid heating during reflow on parts and boards. We try to prevent problems such as minute cracks.

From the above, if the preheating is not efficiently performed, good soldering becomes difficult. In this embodiment, helium He having a much higher thermal conductivity than that of the conventional nitrogen N ₂ is used as well as the heating for each circuit block, so that the uniform heating property is sufficiently high.

The printed wiring board 1 that has been preheated is carried into the reflow section at the end by the conveyor 3 and is uniformly heated by the moving heater 20 for overall heating.

In the reflow step, an intermetallic compound layer is formed by the phenomenon that tin (Sn) in the solder diffuses into the base metal at an appropriate temperature (uniform heating degree) and time.

That is, with respect to the degree of formation of the intermetallic compound layer, a temperature factor (uniform heating) is particularly important. In this embodiment, since the helium He as the inert gas is preheated and reflowed, the heating for each circuit block using the hot helium He is performed, so that more efficient uniform heating can be performed. That is, since the thermal conductivity is good, the electronic component 2
The heating time may be short and the amount of spraying may be small. Therefore, the damage given to the electronic component 2 can be significantly reduced. Further, the uniform heating improves the degree of formation of the intermetallic compound layer, and enables high quality soldering.

When the soldering in the reflow section is completed,
The distribution of the front surface temperature and the rear surface temperature of the printed wiring board 1 immediately after the reflow is measured by the infrared camera 23 located behind the reflow section (step S7). The infrared camera 23 is also covered with the heat resistant glass 21.
The infrared camera 23 is cooled by supplying cooling air from a cooling nozzle (not shown). As described above, the temperature measured data immediately after the reflow is transmitted to the personal computer 30, stored in the first memory unit 33 from the data input unit 31, and compared with the temperature data as the optimum condition in the comparison / determination unit 32. The determination is made, and as a result, appropriate correction data is output as feedback from the correction data unit 35 (step S8). The printed wiring board 1 whose temperature has been measured by the infrared camera 23 is sent to the cooling device 24 to be cooled and further carried out to the outside of the reflow furnace A. With the above, the first simulation of reflow soldering is completed.

Next, the second simulation will be performed.
Based on the judgment data of the first simulation, the next optimum condition is determined after comparison and judgment with the measurement data.
Similarly to the above, the temperature setting of the local heating head 7 is executed (step S9), and after waiting for stabilization, the entire heating unit A
The temperature setting of the moving heater 20 for whole heating of No. 2 is executed (step S10), and after waiting for stabilization, the conveyor 3
The speed setting is performed (step S11), and the process waits until it stabilizes. Then, again, the printed wiring board 1 on which the narrow-pitch electronic components 2 are mounted is automatically carried into the reflow furnace A by the conveyor 3 and conveyed in the reflow furnace A. In the same manner as described above, soldering is performed between the local heating section A1 and the overall heating section A2, the simulation ends, and the optimum condition which is the final purpose is analyzed and determined.

As described above in detail, according to the present embodiment, (1) it is possible to solder a narrow pitch electronic component (SMT component: lead pitch 0.5 mm or less).

(2) Since the lead is pressed by the local heating nozzle 8, the lead can be prevented from rising.

(3) Since the local heating method is adopted, the thermal adverse effect on the body portion of the electronic component 2 is small.

(4) Since helium He having a very high thermal conductivity is used as the heating medium, the thermal conductivity to the solder portion is good and uniform heating is possible.

(5) Since the simulation system is used, it is possible to approach the optimum conditions in the reflow soldering device which has conventionally been difficult to control the temperature.

(6) By inputting the basic soldering data, the optimum conditions can be approximated even if the soldering conditions are different.

(7) Since the local heating system is adopted,
There is no solder bridge.

(8) Since the local heating system is adopted,
No solder balls are generated.

(9) Since the local heating system is adopted,
It is easy to handle TAB and plastic packages.

(10) It can be used as a reflow soldering device using only the local heating method, or can be used as a reflow soldering device using only the entire heating method.

[0046]

As described above, according to the present invention, even in the case of a narrow pitch electronic component, it is possible to suppress an adverse thermal effect on the body portion and to print the electronic component in a good state in which a solder bridge does not occur. Can be reflow soldered to the wiring board.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a reflow soldering device for a narrow pitch electronic component according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a reflow soldering device according to an embodiment.

FIG. 3 is a flowchart for explaining the operation of the reflow soldering device of the embodiment.

FIG. 4 is a schematic configuration diagram showing a conventional reflow soldering device.

FIG. 5 is a flowchart for explaining the operation of a conventional reflow soldering device.

[Explanation of symbols]

A ... Reflow furnace A1 ... Local heating part A2 ... Whole heating part 1 ... Printed circuit board 2 ... Narrow pitch electronic parts 3 ... Conveyor 4 ... Shutter 5 ... O ₂ exhaust port 6 ... Inert gas ( Helium) supply port 7 ... Local heating head 8 ... Local heating nozzle 9 ... Spare nozzle 10 ... Heating head lifting device 11 ... Heat-resistant glass 12 ... Temperature sensor 13 ... Infrared camera 14 ... Cooling device 15 ... … Substrate positioning stopper 16 …… Remelting prevention shield jig processing device 17 …… Split jig push rod 18 …… Heat load / remelting prevention integrated jig plate 19 …… Slide path 20 …… Movement for whole heating Heater 21 ...... Heat-resistant glass 22 ...... Temperature sensor 23 ...... Infrared camera 24 ...... Cooling device 25 ...... Shutter 30 ...... Personal computer 31 ...... Data input part 32 ...... Comparison and judgment 33 ...... first memory unit 34 ...... second memory unit 35 ...... correction data unit

Claims (1)

[Claims] 1. A reflow soldering device for heating a printed wiring board having a narrow-pitch electronic component mounted thereon via a cream solder to carry out reflow soldering while conveying the printed wiring board in a reflow oven. A reflow soldering device characterized in that reflow soldering is performed by bringing a local heating nozzle of a local heating head close to or in contact with each lead of a component and supplying hot helium from the local heating nozzle.