JPH0539829Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a reflow soldering device for soldering leads of an integrated circuit or the like to connection parts of a printed circuit board or the like to which solder has been applied in advance.

(Technical background of the invention) Conventionally, solder connections on printed circuit boards, etc. are plated with solder or paste solder is applied in advance, and leads of integrated circuits, etc. are pressed onto these connections and heated to solder. There is a reflow soldering equipment. In one such device, a heater made of a high-resistance material such as molybdenum is provided in the lifting drive means that can be pressed against and separated from the soldered joint, and a temperature sensor such as a thermocouple is fixed to this heater. A heating time setting device is separately provided to set the heating time of the heater, and a voltage corresponding to the heater temperature detected by the temperature sensor is fed back during this heating time, and this feedback voltage is used to melt the solder separately set in advance. Based on the difference signal between the voltage and the voltage corresponding to the required temperature, the heating current supplied to the heater is phase-controlled and the amount of current is continuously controlled to keep the temperature at the tip of the heater constant. There is an instant heating type reflow soldering device that presses a solder onto a solder joint and supplies a heating current for a set time with a heating time setting device to perform soldering.

According to such a device, after the heater comes into contact with the solder connection by lowering the lifting drive means, a pulse current flows through the heater only when the set pressure is reached, and the heater is instantaneously activated by this module heat. heated. The heat generated in the heater instantaneously melts the solder at the solder joint due to thermal conduction, and at the same time, the pressure of the heater performs soldering, and after the molten solder solidifies, the heater is raised, so that integrated circuits, etc. The leads do not lift up, and the heat effect is less compared to those that are constantly heated, such as ordinary soldering irons.

In such a device, if it is desired to increase the speed of repeated operations, the current capacity supplied to the heater is increased to shorten the time it takes to reach the set temperature. However, in the initial stage of energization when the heater temperature rises to the set temperature, a large current momentarily flows, causing an overshoot, and the heater may be heated above the set temperature.

Such overheating of the heater not only shortens the life of the heater, but also damages the integrated circuit element to be soldered because it places a large thermal load on the element.
It also burns the base material of the printed circuit board, causing the conductor to rise from the base material, causing serious damage such that the printed circuit board must also be replaced.

For this reason, the voltage on the secondary side of the output transformer is generally adjusted by switching a tap provided on the secondary side of the output transformer to supply the maximum heating current commensurate with the heat capacity of the heater. However, with this method, it is difficult to finely adjust the optimal heating voltage to suit each heater, and it is not possible to completely eliminate overshoot as described above. It was difficult to heat the heater to the set temperature.

(Purpose of the invention) The present invention was developed in view of the above circumstances, and the maximum overheating current at the initial stage of energization, when the temperature of the heater that heats the solder joint rises to the set temperature, is determined according to the heat capacity of the heater used. It is an object of the present invention to provide a reflow soldering device which can completely eliminate overshoot during energization by finely adjusting the temperature, and can heat a heater to a set temperature in the shortest time.

(Configuration of the Invention) According to the invention, this object is achieved by a reflow soldering apparatus of an instantaneous heating type which comprises a heater attached to a lifting drive means which can be pressed against and separated from a solder connection portion, a temperature sensor fixed to the heater and detecting the heater temperature, a heating time setter which sets the heating time of the heater, and temperature control means which phase controls a heating current supplied to the heater based on a phase control voltage which is inversely proportional to a differential voltage between a voltage equivalent to the heater temperature detected by the temperature sensor during the heating time and a voltage equivalent to a temperature required to melt the solder which is separately set in advance, to keep the heater temperature constant, and which presses the heater against the solder connection portion based on a start signal and supplies a heating current for the time set by the heating time setter to perform soldering, characterized in that a reference voltage generating circuit which generates a predetermined reference voltage which is equal to or lower than a voltage equivalent to the temperature required to melt the solder is connected to a line which sends the phase control voltage to the phase control means, and the reference voltage is sent to the phase control means when the phase control voltage is lower than the reference voltage.

(Function) The phase control voltage, which is inversely proportional to the difference voltage between the feedback voltage from the heater that heats the solder joint and the voltage corresponding to the predetermined temperature setting, melts the solder predetermined by the reference voltage generation circuit. If the reference voltage is lower than a predetermined reference voltage which is equal to or lower than a voltage corresponding to the temperature required for the heating, the reference voltage is supplied to a phase control means for controlling the heating current, and a heating current commensurate with the heat capacity of the heater is supplied to the heater. and heats the heater to the set temperature without overshooting.

(Example) Figure 1 is a block diagram showing an example of the present invention.
FIG. 2 is a timing chart of its operation.

In FIG. 1, reference numeral 1 denotes an electric heater, which is made of molybdenum or other heat-resistant material that does not easily wet with solder.

Reference numeral 2 denotes an AC power supply, and 3 a transformer. The AC output of the power supply 2 is supplied to the primary side of the transformer 3 via a triax 4. The secondary side of the transformer 3 is connected to the heater 1. The triax 4 controls the phase of the primary current supplied to the transformer 3 in accordance with a gate signal g output from a phase control circuit 12, which will be described later, and adjusts the amount of heating current supplied to the heater 1.

Reference numeral 5 denotes a temperature control means, which controls the phase of the gate signal g output to the triax 4 so as to maintain the temperature of the heater 1 constant. The heater 1 includes a thermocouple 6 as heater temperature detection means.
is attached, and the output voltage of this thermocouple 6 is applied to the amplifier 7.
is fed back and amplified. The output voltage of this amplifier 7 indicates the heater temperature t. Reference numeral 8 denotes a temperature setting device, which is composed of a variable resistor that sets an appropriate heater temperature t _p according to the melting temperature of the various solders used. Reference numeral 9 denotes an adder to which the output of the amplifier 7 and the output of the temperature setting device 8 are input, and the difference voltage between them is determined. This differential voltage indicates the difference (t _p -t) between the heater temperature t and the set temperature t _p .

Reference numeral 10 denotes a level adjustment inverting amplifier which converts the voltage level of the difference (t _p -t) into a phase control voltage inversely proportional to the difference voltage according to a predetermined gain and outputs it.

Reference numeral 11 denotes a synchronization signal generation circuit, which outputs a synchronization signal CL in synchronization with the alternating current of the AC power supply 2. 12 is a phase control circuit which outputs a gate signal g with a phase directly proportional to the input voltage from the level adjustment inverting amplifier 10 in synchronization with this synchronization signal CL.

Reference numeral 13 denotes a start switch, which outputs a start signal a when turned on. 14 is a timer consisting of a monostable multivibrator, etc., and this timer 14 measures the time required for soldering, that is, the time required for heater 1.
The set time T is made variable by a time setter 14a made of a variable resistor. This timer 14 starts integrating time in response to the start signal a, and the set time T
When the phase control circuit 1 reaches the stop signal j, the phase control circuit 1
Output to 2. That is, when the output signal of the timer 14 is at H level, the operation of the phase control circuit 12 is allowed, and when it is at L level, the operation is prohibited.

15 is a reference voltage generating circuit which is a feature of the present invention, and one end of which is grounded, and the other end 1 of a variable resistor 16 is grounded.
7 is applied with a voltage to be supplied to the phase control circuit 12 in order to supply the heater 1 with a heating current according to the heat capacity of the heater 1 expected to be used. The anode of a diode 18 is connected to the slider of the variable resistor 16, and the cathode of the diode 18 is connected to a line 19 connecting the level adjustment inverting amplifier 10 and the phase control circuit 12. The voltage at the point tapped from variable resistor 16 is therefore algebraically added to the output of leveling inverting amplifier 10 at junction 20.

Next, the operation of this embodiment will be explained with reference to FIG. It is now assumed that the set time T of the timer 14 is set longer than the time (rise time) required for heating the heater 1 to the set temperature _tp .

In addition, the temperature setting device 8 is made of, for example, 60% tin and 40% lead.
When using this solder, its melting point is 183°C, so the set temperature t _p of the heater 1 is set at about 300 to 350°C to instantly melt the solder.

When the start signal a is input by the start switch 13, the timer 14 starts integration, and the phase control circuit 12 starts operating and outputs the gate signal g to the triac 4. Therefore, heater 1
As the current I flows and the heater temperature t rises, the feedback voltage t generated by the thermocouple 6 also rises.
The initial feedback voltage t through amplifier 7 at this time is 0.6V
That's about it. The feedback voltage t of the thermocouple 6 is amplified by an amplifier 7 and then inputted to an adder 9, and a voltage signal c of 5.4V difference from the output voltage _tp (6V in this embodiment) from the temperature setting device 8 is generated. is output. This output voltage c is inverted in a level adjustment inverting amplifier 10, and the level is adjusted by adding a predetermined constant so that the output voltage of the amplifier 10 falls within a predetermined output voltage range (0 to 6V). Therefore, the output voltage d of the level adjustment inverting amplifier 10 is inversely proportional to the differential voltage c, and the lower the temperature of the heater 1, the closer to 0V.
As the temperature of heater 1 increases, it approaches 6V. The output voltage d for phase control of the level adjustment inverting amplifier 10 is inputted to the phase control circuit 12. A reference voltage generation circuit 15 is connected to this line 19, and a reference voltage e (e.g. 4.5V), the input voltage value d from the level adjustment inverting amplifier 10 is applied to the reference voltage generation circuit 1 at the junction point 20, which is the current summation point.
The set voltage value e of the reference voltage generating circuit 15 is maintained until it matches the reference voltage value e from 5 (shown as f in FIG. 2). For this reason, a voltage e (reference voltage) commensurate with the heat capacity of the heater 1 is input to the phase control circuit 12 at the initial stage of heating, and the conduction rate of the triax 4 is set based on the output voltage e of the reference voltage generation circuit 15. Since the phase is controlled, the heater current I
will not flow beyond the heat capacity of heater 1,
Due to overshoot, heater 1 reaches the set temperature t _p
It will not get heated any higher.

When the heater 1 reaches the set temperature _tp , the feedback voltage t of the thermocouple 6 and the output voltage _tp of the temperature setter 8 match, so the output of the adder 9 becomes zero, and the output of the level adjustment inverting amplifier 10 d becomes 6V. Therefore, at the junction 20, the output voltage d of the level adjustment inverting amplifier 10 is lower than the reference voltage e set by the reference voltage generation circuit 15, as shown as f' in FIG.
Since the voltage is high, no current flows from the reference voltage generation circuit 15. This level adjustment inverting amplifier 1
The output d from 0 is input to the phase control circuit 12,
Since the phase is controlled so that the conduction rate of the triax 4 is greatly limited, the heater current I is controlled at the set temperature t _p
The current required to hold the heater 1 is the only current required.
The temperature t of is maintained at a constant temperature _tp .

After a certain period of time T has elapsed since the start signal a,
The timer 14 outputs a stop signal j, the phase control circuit 12 stops outputting the gate signal g, and the heating current is cut off.

(Effects) As described above, the present invention includes a phase control circuit that controls the heating current of the heater, and a voltage that is inversely proportional to the voltage value according to the difference between the preset heater temperature and the heater temperature returned from the heater. Between the circuits that adjust the level and output to the phase control circuit, we installed a reference voltage generation circuit that limits the phase control amount of the phase control circuit to the maximum heating current commensurate with the heat capacity of the heater. The maximum heating current at the initial stage of energization, when the heater temperature rises to the set temperature, can be finely adjusted according to the heat capacity of the heater used, completely eliminating overshoot when energizing. The heater can be heated to the set temperature in the shortest possible time without causing any overheating.

Therefore, it is possible to reliably prevent the heater from overheating, eliminate thermal damage to integrated circuits and printed circuit boards, and increase the speed of repetitive work, so this device can be applied to automatic machines to great effect. can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a reflow soldering apparatus according to the present invention, and FIG. 2 is a timing chart showing the operation thereof. 1... heater, 5... temperature control means, 6... thermocouple as temperature detection means, 8... temperature setter,
9: adder; 10: level adjustment inverting amplifier;
12: phase control circuit; 15: reference voltage generating circuit; 19: line; 20: junction.

Claims (1)

[Scope of utility model registration request] A heater provided in the lifting drive means that can be pressed against and separated from the solder connection part, a temperature sensor fixed to the heater to detect the heater temperature, a heating time setting device to set the heating time of the heater, and a heating time setting device for setting the heating time of the heater. The heater is controlled based on a phase control voltage that is inversely proportional to the voltage difference between the voltage corresponding to the heater temperature detected by the temperature sensor within the time period and the voltage corresponding to the temperature required to melt the solder, which is separately set in advance. and temperature control means to keep the heater temperature constant by controlling the phase of the heating current supplied to the heater, and presses the heater to the solder joint based on a start signal, and controls the heating current for the time set by the heating time setting device. In an instant heating type reflow soldering device that supplies solder by supplying the solder, a predetermined voltage equal to or lower than the temperature required to melt the solder is connected to the line for sending the phase control voltage to the phase control means. A reflow soldering apparatus, characterized in that a reference voltage generation circuit that generates a reference voltage is connected, and when the phase control voltage is lower than the reference voltage, the reference voltage is sent to the phase control means.