Vacuum Pump for Desoldering Gun

This invention relates to a desoldering tool, and more particularly to a vacuum pump for removing melted solder from a joint.

To remove electrical components from a printed circuit board, for example, the solder forming the connection between the component and circuit board must be removed to free the connection. A soldering iron or gun is used to melt the solder and the solder is then withdrawn from the joint while still in the molten state. This may be done with a copper wick, or by a suction tool. An example of a hand-held solder removing tool is described, for example, in U.S. Pat. No. 3,114,026, in which a manually compressed spring is released to drive a piston in a direction to produce a or partial vacuum at an orifice or tip which is applied to the solder joint. The vacuum sucks the molten solder into the tip. Tools of this type provide a single vacuum impulse and then must be manually recocked. This is an awkward and tiring operation where large numbers of soldering joints are being desoldered using this type of tool.

Desoldering guns have been developed which can be held in one hand against the solder joint. The gun is connected through a hose to a vacuum source and a valve in the gun is opened to apply suction to the gun tip when it is needed. Another type of desoldering gun utilizes a venturi-type pump which operates from a source of compressed air. These types of guns have not proved to be entirely satisfactory for several reasons. First, a source of compressed air must be available to operate the device, and the vacuum impulse provided by the venturi is limited in the amount of vacuum that could be produced and the time required to reach peak vacuum.

The present invention is directed to an improved desoldering gun assembly and in particular to a mechanized pump device for generating a vacuum impulse for removing the molten solder from a solder joint. A vacuum pump for applying a vacuum pulse to the desoldering iron tip comprises a cylinder and a motor driven piston movable in the cylinder. A spring is connected between the piston and cylinder for urging the piston away from the closed end of the cylinder to increase the volume and thereby reduce the pressure within the cylinder. The spring is held in a compressed position by a latch mechanism with the piston positioned at the end of the cylinder to provide minimum volume. When a motor driven linkage is energized, it first trips the latch mechanism, releasing the spring and moving the piston rapidly away from the closed end of the cylinder to generate a suction at desoldering tip. The motor then recompresses the spring and latches the piston in position for the next cycle of operation.

FIG. 1 is a front prospective view of the hand held desoldering gun and vacuum pump unit according to the present invention;

FIG. 2 is a section view of the vacuum pump unit; and

FIG. 3 and 4 illustrate the mechanism which provide for the impulse operation of the vacuum pump unit.

Referring to FIG. 1, the numeral 10 indicates generally a hand held desoldering gun which includes a pistol type grip 12 from which projects a soldering iron heater assembly 14. The heater assembly includes a tip 16 having a passage 18 which connects through a tube 20 to a solder collecting chamber 22. The chamber 22 preferably includes a removable glass cylinder containing a fibre glass or cotton filter which collects any molten solder sucked into the chamber through the hollow soldering iron tip. The gun is connected to a vacuum pump and control unit indicated generally at 24 by means of an electrical multiple connector cable 26 and a hollow vacuum tube 28. The tube 28 communicates at one end with the chamber 22 and is connected at the other end to the vacuum pump, in the unit 24, for applying a vacuum to the chamber at the appropriate time to withdraw molten solder through the soldering iron tip into the chamber. An electrical thumb-operated switch 23 at the desoldering gun controls the vacuum pump, in a manner hereinafter described, through the electrical cable 26. The vacuum pump, with operation of the switch, momentarily drops the pressure in the chamber to provide a vacuum impulse to suck the molten solder into the chamber where it is trapped by the filter material.

Referring in detail to FIGS. 2-4 the vacuum pump includes a cylinder 30 closed at one end by an end wall 32. Movable in the cylinder 30 is a piston 34. The cylinder 30 is secured to an outer frame or housing 36 by a mounting bracket 37. The space between the end wall 32 of the cylinder and the piston 34, indicated at 38 is fluid connected to the tube 28 extending to the desoldering gun through a nipple 40. A flap valve 41 allows air to be drawn through the nipple 40 into the cylinder during the suction stroke of the piston 34. A second flap valve 42 allows air to escape from the cylinder during the compression stroke of the piston 34.

The piston 34 is normally positioned as shown in FIG. 2 to provide minimum volume in the end of the cylinder. When a vacuum impulse is required to remove the molten solder at the gun, the piston 34 is moved abruptly to the right as viewed in FIG. 2 to the dotted position indicated at 34'. This is accomplished by means of a compression coil spring 44 which engages a guide bracket 46 attached to the piston 34 by connecting rod 48. The bracket 46 includes a slide member 50 which slidably engages an opening 51 in a Teflon guide block 52 anchored to the housing 36. The spring 44 pushes the piston and guide bracket 46 outwardly to the dotted position 46' against the stop 54.

The spring 44 is compressed and the piston 34 moved to its standby position by means of a drive assembly 56 which includes a gear-head motor 58 having an output shaft 60. The shaft is attached to a crank arm 62. A roller 64 is attached to the arm adjacent one end and moves into rolling engagement with the surface of the guide bracket 46 as the crank arm is rotated by the motor.

Referring to FIG. 3 which shows the guide bracket in the position in which the spring 44 is fully compressed, a latch mechanism including a latch arm 66 pivotally attached to the guide block 52 at 68 supports a roller 70 that engages a notch 72 at one corner of the guide member 50. In this position, the roller 70 prevents the guide member 50 and guide bracket 46 from moving under the urging 44. A tension spring 74 holds the roller 70 in the notch 72.

When the motor is energized, the arm 62 is rotated clockwise from the position shown in FIG. 3, moving a roller 76, attached to the arm 62, against the latch release arm 66. The roller 76 forces the arm 66 downwardly against the tension of the springs 74, moving the roller 70 out of the notch 72. This releases the guide bracket 46, allowing the bracket and piston 34 to move to the right, as viewed in FIG. 4, under the urging of the compressed spring 44. This results in a rapid expansion of the volume behind the piston 34, dropping the pressure within the cylinder and applying a suction at the desoldering iron tip through the tube 28.

Operation of the motor 58 is provided by a control circuit 80 from an electrical power source. When the crank arm 62 is rotated into the position shown in FIG. 3, power to the motor 58 is interrupted. This is accomplished by a sensing unit 82 which preferably includes a light source directing a beam at a light sensor, the beam being interrupted by a pin 84 projecting from the crank arm 62. The sensing unit 82 provides a signal to the control circuit 80 which causes the power to the motor 58 to be interrupted.

When the switch 23 on the desoldering gun is actuated by the operator, the control circuit 80 starts the motor 58 running, causing the roller 76 to be moved into engagement with the latch release arm 66, releasing the latch roller 70 and allowing a vacuum impulse to be generated by the release of the compression spring 44. The motor continues to rotate the arm 62, bringing the roller 64 into engagement with the surface of the guide bracket 46, as shown in FIG. 4. As the motor continues to rotate the arm 62 in a clockwise direction, the roller 64 forces the guide bracket 46 to the left as viewed in the Figure, thereby compressing the spring 44 and allowing the roller 70 to move into the latched position. The motor is stopped when the arm completes one revolution, bringing the pin 84 back into light interrupting position in the sensing unit 82. It will be noted that the arm 62 moves the roller 64 out of engagement with and out of the path of the guide bracket 46 before the roller 76 trips the latch assembly. The motor 58 preferably is of a type having a brake mechanism which releases when the motor is energized and engages automatically when the motor is de-energized so as to lock the arm 62 in position instantly when the control circuit interrupts the power to the motor. By making the piston relatively large in diameter, the change in volume in the cylinder becomes quite large with very little movement of the piston compared with the fixed volume of the tube 28 and chamber 22. Thus a sharply defined and relatively high pressure drop can be produced at the desoldering iron tip. This rapid and large drop in pressure at the tip allows the molten solder to be efficiently and completely removed from a soldered joint or terminal.