SU1731496A2 - Electric head - Google Patents

Abstract

Usage: wiring and dismounting of smart chips under conditions of high accuracy of measuring the temperature of the working end. Summary of the Invention; between the output of the heater 4 and the tip 3 is included a section 11 of the guide wire of the heater material with a diameter at least twice the diameter of the heater wire. The junction of the guide wire with the blade forms a thermocouple junction. 1 il.

Description

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The invention relates to soldering, in particular to devices for soldering paired connections with solder suction when dismantling integrated circuits, and is an improvement of the invention according to star. No. 1465214.

Known electric flax head for soldering solder joints with suction solder. The flax head has a sting in the form of a hollow cylindrical hollow two-stage cup with an open narrow working end, on which a sleeve is fitted with a radial clearance. On the outer surface of the wide part of the glass there is a resistive heater in the form of a spiral, one end of which is connected to the glass on the surface of its narrow part, with the formation of a thermocouple spa between the materials of the glass and the heater, the emf of which is measured against the background voltage of the heater and The quality of the feedback signal to the source of heat is the temperature of the working end of the head.

During desoldering, in the process of melting the solder, the temperature of the working end decreases and, accordingly, the emf of the thermo-spike falls. This serves as a feedback signal for raising the temperature of the heater, heating the gas (air) in the bulk of the wide part of the hollow cup, expanding it, and squeezing the molten solder into the gap between the working part of the head and the sleeve.

The main parameter of the head is a dynamic characteristic of the rate of increase in gas pressure, which determines the efficiency of the suction, in particular the desoldering time.

The lack of such a head is low efficiency due to the lack of accuracy in measuring the temperature of the working end. This is due to a design flaw - the thermo-spike is formed by the hot output of the heater. When the desoldering point touches the working end of the head, its temperature decreases and, accordingly, the temperature of the thermoset decreases. A decrease in the thermoset emf serves as a feedback signal to increase the power of the heat, the temperature of the heater, and the increase in gas pressure. However, an increase in the temperature of the heater leads to an increase in the temperature of the thermoset during its heating by the hot output of the heater. As a result, the feedback signal decreases rapidly, the temperature of the heater decreases, the gas pressure drops and the head switches to dynamic equilibrium with the environment. A decrease in gas pressure inevitably leads to an increase in the desoldering time and, as a result, to overheating and detachment of the contact pads.

The purpose of the invention is to increase the efficiency of the electric head by increasing the accuracy of tracking the temperature of the tip of the tip.

The essence of the invention is to exclude the thermostat heating by the hot output of the heater. This is achieved by reducing the release of Joule heat in the area directly forming the thermo-spiking output of the heater by reducing its electrical resistance by changing the geometry. For this, between the output of the heater and the tip, there is included a section of the guide wire of the heater material having a diameter at least two times larger than the diameter of the heater wire. As a result, the temperature of the thermal spike-forming end of the conductor becomes independent of the temperature mode of the heater and the accuracy of tracking the temperature of the working tip of the tip is increased.

Let us estimate the degree of increase in the operating efficiency of such an electron head as follows. The transfer function of the head is the change in temperature of the thermospe DTS at the time of desoldering - the change in temperature of the LTI heater is

.(one)

where a is a coefficient having a value of at least 5.

For the prototype, the change in spa temperature will be

, (2)

where DTZH is the cooling of the tip during the desoldering process;

 - the heating coefficient of the thermospa by the hot output of the heater, approximately f 0.3.

The rate of change of gas pressure is

DT

(3)

1 + a / At For the proposed construction, c O and this speed is 2.5 times higher than that of the prototype. Therefore, the desoldering time is also reduced by approximately two times, and this results in an increase in the operating efficiency of the electric head.

The drawing shows the design of the power head.

The electric head includes a body of 1 cup, an expansion volume of 2, a working end 4 of the tip, and a pin 5 of the heater.

current lead 5, thermospike 6, second current lead 7, sleeve 8, insulator 9, head holder 10, wire guide section 11 of the heater material.

The head is made in the form of glass 1 and has a closed expansion volume 2 connected to the end of the working part of the tip

3 thin channel. One output heater

4 is connected to the current lead 5. The second output of the heater is connected to one end of the conductor 11 from the material of the heater, and its second end is connected to the tip 3, forming a thermoset 6. The current lead 7 is connected to the tip

in its widest part. The sleeve 8 with a small gap is fixed at the working end of the sting. The head through heat and electric insulator 9 is fixed in the holder 10.

Electro flax head works as follows.

When the end face touches the working end of the head of the contact pad of the printed circuit board, heat loss leads to cooling of the tip and thermospace 6. The electronic device, striving to return the spa temperature to its original value, increases the power of the heater. At the same time, the temperature of the heater and its output, connected with the wire conductor 11 of the material of the heater with an increased diameter, increases. The resistance of conductor 11, which is small relative to the heater itself, leads to the fact that

the heating power does not cause it to heat up with Joule heat, and the temperature of the spa 6 is independent of the heating mode of the heater, and the thermopower of the spa corresponds to the temperature of the working end of the head.

Electric flax head is made of nickel and has a working end length of 10 mm. The 30W maximum power heater is made of nichrome 0.15 mm in diameter. A piece of conductor made of nichrome with a diameter of 0.3 mm and a length of 10 mm is welded at one end to the output of the heater, and the other to the working part of the sting, forming a thermospray.

The use of the invention will make it possible to create devices for dismantling integrated circuits during the repair of radio equipment.

Claims (1)

Invention Formula Electric flax head auth.St. No. 1465214, characterized in that, in order to increase efficiency in operation by increasing the accuracy of monitoring the temperature of the working end of the tip, it is provided with an end attached to the output of the heater, and the other to the tip of the boiler with the formation of a thermocouple layer of a wire conductor, made of heater material, while the diameter of the conductor wire is not less than twice the diameter of the heater wire.