JPH03221292A - Method for monitoring surface temperature of material to be heated in reflow furnace - Google Patents

Abstract

PURPOSE:To smoothly carry out the productive control for reflow soldering by measuring the maximum surface temperature of a material to be heated, comparing the value with the average value of output signals of a radiation thermometer to adjust an output and using the radiation thermometer to monitor the surface temperature of an actual product. CONSTITUTION:The material 9 to be heated is carried into a reflow furnace 1. The maximum surface temperature is measured by a thermocouple in the material 9 to be heated in this actual heating area 4 to obtain the average value of the temperature output signal of the radiation thermometer 10. These measured values are compared with the average value and the output of the radiation thermometer 10 is controlled so that the average value of the temperature output signals is equivalent to the measured value of the maximum surface temperature. Thereafter, the surface temperature of the material (product) 9 to be heated carried into this actual heating area 4 is monitored. In this way, the temperature width to be monitored can be set suitably.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for monitoring the surface temperature of an object to be heated in a reflow oven, and more specifically, the surface temperature of an object to be heated in a heating area for main heating is determined by adjusting the radiation temperature. Concerning how to monitor with a meter.

(Prior Art) A method using a reflow oven (reflow soldering) is known as a method for surface mounting various semiconductor components on a circuit board by soldering.

This process is generally performed using a reflow oven, such as the one not shown schematically in FIG. That is, in the reflow oven 1, there is a heating area 2 for raising the temperature, which includes surface heaters 2a and 2b such as infrared heaters and far-infrared heaters arranged vertically opposite each other, surface heaters 3a and 3b;
A soaking heating area 3 formed by vertically combining heaters 4c and 3d, and a heating area 4 for main heating comprising surface heaters 4a and 4b vertically opposed to each other are arranged in this order.

Between each side heater, a con hair 8 is arranged which is wound around a driving roller driven by a motor 6 and a feed roller rough and runs in the direction of arrow p1. An object to be heated 9 such as a circuit board is placed thereon,
It is transported at a predetermined speed from the inlet 1a of the furnace toward the outlet 1b.

Here, the object to be heated 9 carried in from the entrance 1a of the furnace is rapidly heated to a predetermined temperature in the heating area 2 for temperature rise through which it passes first due to radiant heat from the surface heaters 2a and 2b on the upper surface. heated. However, in the case of the heated object 9, for example, a circuit board on which semiconductor components are mounted, the heat capacity is different within the surface of the circuit board or between the circuit board and the mounted components, so the object passes through the heating area 2 for temperature rise. Immediately after
There is a temperature difference between them.

Therefore, by passing the object to be heated 9 through the soaking heating area 3, the temperature difference in the object to be heated 9 is reduced and the temperature of the object to be heated is uniformed as a whole.

The object to be heated 9 that has passed through the heating area 3 for soaking is finally transported to the heating area 4 for main heating, where it is heated to a predetermined temperature and, for example, the leat part of the mounted component and the circuit board are heated. The solder that existed between them is remelted and the mounted components are soldered to the circuit board.

Therefore, the temperature profile during the process of transporting the object to be heated 9 in the furnace generally shows a tendency as shown in FIG. 3. In this temperature profile, an important problem in temperature control of the heated object 9 is the heated object 9 measured in the heating area 4 for main heating.
surface temperature Tm.

If this Tm is lower than the soldering temperature, the soldering of mounted components may be defective or impossible, and if Tm is excessively high, problems such as poor soldering may occur. However, this is because the on-board components and circuit boards may be damaged by heat.

For this reason, it is necessary to measure the surface temperature of the object to be heated 9 in the heating area 4 for main heating for production control purposes. A radiation thermometer is used that measures the radiation from the air to obtain an output signal related to temperature, which is then converted into temperature.

In that case, as shown in FIG.
A radiation thermometer 10 is set so as to face the object 9 to be heated.

In this state, the length of the arrow pI in the transport direction is l
When the heated object 9 is conveyed, the surface temperature of the heated object 9 is determined by the radiation jFA temperature meter 10 from the downstream end 11 of the heated object 9 to the upstream side, as shown in FIG. The end portion 12 is scanned.

As a result, from the radiation meter lO, the end l of the object to be heated 9
, an output signal is obtained indicative of the surface temperature at the end 12. That is, the distribution of the surface temperature from the end portion 11 to the end portion 12 can be obtained as an output signal. In other words, the distribution of the surface temperature of the object to be heated can be known from the output signal obtained from the radiation thermometer 10.

At this time, the output signals obtained from each point in the conveyance direction of the object to be heated 9 generally exhibit a tendency as shown in FIG. As is clear from FIG. 5, the central portion of the object to be heated is at a low temperature, and the closer it gets to the ends 12+ and 12, the higher the temperature becomes.

(Problem to be solved by the invention) By the way, in the case of a heated object or a circuit board on which semiconductor element parts are mounted, as mentioned above, the inside of the board surface of the circuit board itself, the contact between the circuit board and the mounted parts. Because the heat capacities of the circuit board, the leat part of the mounted component, and the solder attached to it are different, the circuit board is passed through the soaking heating area and then uniformly heated in the main heating heating area. However, there are differences in temperature, and the surface temperature of the circuit board varies depending on the location and is not constant.

In addition, the heating element has an emissivity specific to its material.

The radiant energy from the surface of the circuit board itself, the surface of mounted components, the surface of leads, and the solder surface are not the same but have different values due to differences in their emissivity. Generally, the radiant energy from the leat surface and the solder surface is smaller than the radiant energy from the former two surfaces.

For this reason, in the output signal shown in Fig. 5 obtained by scanning the surface temperature of the circuit board with a radiation thermometer, the output shows the output horn signal curve from end 11 to end 12. The signal value indicates the surface temperature of the circuit board surface, mounted component surface, lead surface, or solder surface located along the scanning line, and corresponds to the position of each surface along the scanning line. It is shown as follows.

On the other hand, a radiation thermometer is generally a device that outputs radiant energy unique to a heating element to be measured, emitted by the heating element, as an output signal that is a temperature signal.

Now, if the surface temperature of the heating element is Ts and its emissivity is ε, then the radiant energy E from the surface of the heating element is E-εTs
' becomes.

If this radiant energy is received by a radiant thermometer and an output signal J is obtained, the radiant thermometer will produce J=E−
The relationship εTs' holds true. Here, is the conversion coefficient for converting the radiant energy from the heating element into the output signal of the radiation thermometer, and as is clear from the above equation, ε
and Ts.

Therefore, when measuring the surface temperature of a heating element with a radiation thermometer, the surface temperature of the heating element is actually measured in advance by some means, and then the output signal shown by the radiation densitometer is used to calculate the The output is adjusted by determining a specific value of /ε. After that, the radiation thermometer may be operated under the set output adjustment.

Based on the above, when considering the measurement of the surface salinity of a circuit board using a radiation thermometer in an actual reflow oven,
There are the following problems.

That is, this problem is based on the fact that when the loft of the circuit board is changed, the type of board, the type of mounted components, the arrangement relationship, etc. change accordingly.

For example, even if the surface salinity of each circuit board is measured properly at the n-th loft, the output adjustment of the radiation thermometer at that time may be difficult to indicate the accurate temperature at the next (n+1)-th loft. It happens that proper output adjustment cannot be achieved.

In addition, even when measuring temperatures within the same lot, as mentioned above, the temperature of the surface of the circuit board, the surface of the mounted components, the surface of the reed part, and the solder surface are different. There is also the question of whether temperature can be controlled.

The present invention solves the above-mentioned problems when monitoring the surface salinity of a circuit board with a radiation thermometer, and compares the surface temperature of the heated object actually measured with a thermocouple and the output signal of the radiation thermometer. The purpose of this project is to provide a method for monitoring the surface temperature of objects to be heated in a reflow oven. do.

(Means for Solving the Problem) In order to achieve the above-mentioned object, in the present invention, a heating area for temperature start-up, a heating area for soaking, and a heating area for main heating are provided along the conveyance direction of the object to be heated. A radiation thermometer is installed in the main heating heating zone of a reflow oven in which zones are arranged in this order, and the surface temperature of the object to be heated is monitored with the radiation thermometer, the method comprising: (A) First, the object to be heated is transported into the reflow oven with a thermocouple attached to the object, and the surface temperature of the object in the heating area for main heating is determined by the thermocouple and the radiation temperature. (B) actual measurement of the maximum surface temperature by the thermocouple; and the average value of the temperature output signal obtained from the radiation thermometer, and adjust the output of the radiation thermometer so that the average value of the temperature output signal corresponds to the actual measured value of the maximum surface temperature. (C) After that, the radiation thermometer whose output has been adjusted is used to monitor the surface temperature of the object to be heated, which is being transported to the heating area for main heating. A method for monitoring the surface density of a heated object is provided.

(Function) In the method of the present invention, a thermocouple is first attached to the object to be heated on which mounted components are mounted in a reflow oven, and the maximum surface temperature of the object to be heated is actually measured by this thermocouple. The surface temperature of the heated object is measured.

The output signal obtained from the radiation thermometer generally shows a tendency as shown in FIG. 5, and the overall average value is determined based on the integrated amount.

Then, assuming that the average value of this output signal indicates the maximum surface temperature which is the above-mentioned actually measured value, an output adjustment corresponding to /ε of the radiation thermometer is performed with respect to the radiation thermometer.

After these adjustments have been made, the heated object (product) on which the mounted components are mounted without a thermocouple attached is transported into the furnace, and its surface temperature is measured with the adjusted radiation thermometer. .

The output signal obtained at this time is based on the above-mentioned average value, that is, the actually measured maximum surface temperature.

Set an upper limit and a lower limit for the above average value,
If the output signal from the actual product exceeds the above limit value, it means that an abnormality has occurred in the reflow conditions such as conveyor speed, surface heater temperature, and heater surface condition.
By notifying the driver of this using a buzzer or the like, it becomes possible to monitor the surface temperature of the object to be heated in the heating area for main heating.

(Example) As shown in FIG. 2, a radiation thermometer IO is set in the heating area 4 for main heating. A heated object 9 is conveyed above this radiation thermometer as shown in FIG. 4, and its surface temperature is monitored.

First, a circuit board having a length l is placed in a furnace with thermocouples attached to the surface of the circuit board, the surface of the mounted components, the surface of the leat part, and the solder surface. Then, in the heating area 4 for main heating, the maximum surface temperature (Tmax) of the circuit board is actually measured using a thermocouple.

Meanwhile, the radiation thermometer 10 scans the surface temperature of the circuit board. As a result, for example, an output signal as shown in FIG. 1 is obtained. Then, the average value (J) of this output signal
seek.

Assuming that this temperature corresponds to the above-mentioned 1" max, the output of the radiation thermometer 10 is adjusted. With this output adjustment,
When the surface temperature of the circuit board to be measured is Tmax, the output signal of the radiation thermometer 10 indicates j.

Damage to mounted components or circuit board Tmax + Δ
T is the melting temperature of solder or Tmax-ΔT', and the wheel load is
If the output signals of the thermometer 10 corresponding to the above-mentioned temperatures are +ΔJ and J-ΔJ°, respectively, an alarm will be issued if the output signal of the thermometer 10 deviates from each of the above values. Connect the radiation thermometer lO to the alarm system.

In this state, the circuit board with mounted components is placed inside the furnace and its surface temperature is monitored.

If the output signal obtained from the radiation thermometer 10 has a value between J and J+ΔJ and J−ΔJ° in FIG.
It is between T' and is in an appropriate heating state.

However, when the output signal J is obtained outside of J + ΔJ and J - ΔJ', the surface temperature of the circuit board or T m
It is out of the range of aw + ΔT and Tmax - ΔT°. This state is due to an abnormality occurring in the reflow conditions described above. This is notified to the furnace operator by a warning from the alarm system, so the operator can check the reflow conditions and correct the abnormality.

(Effects of the invention) As is clear from the above explanation, when performing reflow solder linking, Kazuo Kinoe first measures the maximum surface temperature of the circuit board on which the mounted components are mounted, and The value is compared with the average value of the output signal from the radiation thermometer to adjust the output of the radiation thermometer, and the adjusted radiation thermometer is then used to monitor the surface temperature of the actual product. By appropriately setting the temperature monitoring width, reflow soldering production management can be performed smoothly.

[Brief explanation of drawings]

Fig. 1 shows the profile of the output signal from the radiation thermometer according to the method of the present invention in the length direction of the circuit board, Fig. 2 is a schematic diagram of a reflow oven equipped with the radiation thermometer, and Fig. 3 shows the output signal in the reflow oven. Temperature profile of the heated object, Figure 4 is a schematic diagram showing the state in which the surface temperature of the heated object is measured with a radiation thermometer, and Figure 5 shows the output signal of the radiation thermometer in the length direction of the heated object. It is a profile. l・Reflow oven, la...inlet, lb...outlet, 2
・Heating area for temperature startup, 3... Heating area for soaking, 4.
Heating area for main heating, 2a, 2b, 3a, 3b
, 3c. 3d, 4a, 4b --- Surface heater, 5... Motor, 6
Drive roller, 7... Feed roller, 8... Conhair, 9... Heated object (circuit board), 10... Radiation thermometer, 10a... Measurement side tip of radiation thermometer, l ...Length of the circuit board (object to be heated) in the transport direction, 11...
- Downstream end, 12... Upstream end, J... Average value of the output signal.

Claims (1)

[Claims] The main heating of the reflow oven, in which a heating area for temperature rise, a heating area for soaking, and a heating area for main heating are arranged in this order along the conveyance direction of the object to be heated. A method for monitoring the surface temperature of the object to be heated using the radiation thermometer by installing a radiation thermometer in The object is transported into the reflow oven, and the surface temperature of the object to be heated in the heating area for main heating is measured by the thermocouple and the radiation thermometer, and the temperature of the surface of the object to be heated is measured from the thermocouple. (B) calculate the actual value of the maximum surface temperature measured by the thermocouple and the average value of the temperature output signal obtained from the radiation thermometer; By comparison, the output of the radiation thermometer is adjusted so that the average value of the temperature output signal corresponds to the actual measured value of the maximum surface temperature; A method for monitoring the surface temperature of an object to be heated in a reflow oven, the method comprising monitoring the surface temperature of an object to be heated that is transported to a heating area for main heating using a radiation thermometer.