Chip removal and replacement system

A chip removal and replacement system is designed for safely and easily removing or reattaching components from a printed circuit board. The system includes an automatic suction system for lifting a component which has been removed. A nozzle connection and replacement mechanism is provided for interchanging nozzles. The system is also provided with an improved circuit board holder, a circuit board auxiliary preheater, and a simplified control system with one touch removal and replacement.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to an apparatus for separating and removing
 integrated circuit chips from circuit boards and for replacing the
 integrated circuit chips, and more particularly, the invention relates to
 a system including a heating device for generating a flow of heated air, a
 circuit board holder for positioning a circuit board during chip removal,
 and a auxiliary preheater for heating the circuit board.
 2. Brief Description of the Related Art
 Hot gas desoldering tools are known for removing integrated circuit chips
 from circuit boards. Generally these tools direct a jet of hot gas at a
 component to melt the solder which connects the component leads to the
 circuit board. However, these known tools have a tendency to melt or
 otherwise damage the component being removed, the surrounding components,
 or the circuit board by overheating. These known desoldering tools have
 the additional disadvantage that they are difficult to adjust to a proper
 location and temperature and are generally difficult to use.
 Integrated circuit chips that are to be removed may be traditional dual
 inline packages (DIP) with metal leads protruding from two sides, may have
 leads extending from all sides, or may be surface mount devices. Surface
 mount devices have leads at the perimeter of the device which are flush
 with the bottom surface of the device. Surface mount devices may also have
 connection points in the form of conductive pads on a bottom surface of
 the device allowing connection to the circuit board directly under the
 component. These surface mount devices allow the components to be more
 compact but are more difficult to remove without damage. It is desirable
 to be able to remove a variety of different component sizes and types with
 a single desoldering tool. Therefore, tools are provided with
 interchangeable nozzles for accommodating different chips. However, known
 tools with different nozzles do not provide systems for easily
 interchanging the nozzles even when hot. Accordingly, it would be
 desirable to provide a system of interchangeable nozzles which are easy to
 change.
 Desoldering tools also may include a suction removal system for lifting a
 component off of the circuit board after the solder has been melted.
 However, these suction systems must be manually advanced into contact with
 the component risking component damage and adding an additional step for
 the user. Accordingly, it would be desirable to provide a fully automatic
 suction removal system for lifting a desoldered component off of a circuit
 board.
 It would also be desirable to provide a system for desoldering which is
 easy to use, prevents damage to the circuit board or components, and
 easily accommodates components and circuit boards of different sizes and
 types.
 SUMMARY OF THE INVENTION
 The present invention relates to a safe and easily used system for removing
 and/or reattaching components, such as surface mount technology (SMT)
 components, from a printed circuit board.
 In accordance with one aspect of the invention an automatic vacuum pickup
 system is provided for removing a component from a circuit board after
 desoldering. The system includes a desoldering device for directing a
 heated gas through a nozzle and focusing the gas to solder connection
 areas of a component on a circuit board to melt solder connections, a
 suction source connected to the desoldering device, a suction tip provided
 in the nozzle of the desoldering device for automatically applying suction
 to the component without manual lower of the suction tip, a suction path
 extending from the suction source to the suction tip, and a lifting device
 for applying a predetermined upward force to the suction tip after the
 application of the suction to the component, wherein the predetermined
 force is sufficient to lift the component after the solder connections
 have all been melted but insufficient to lift the component before all the
 solder connections have been melted.
 In accordance with another aspect of the present invention, a desoldering
 tool includes a tool head, a heating element within the tool head, a fan
 for passing a gas over the heating element to provide a heated gas stream
 for desoldering of components from a circuit board, a nozzle removably
 connected to the tool head for directing the heated gas stream to the
 component to be removed, a nozzle connection on the tool head for
 receiving the nozzle, the nozzle connection including at least one spring
 element for forming a snap-in connection with the nozzle, and a nozzle
 release mechanism including a rotatable member which rotates about the
 axis of the nozzle to disengage the at least one spring element and
 release the nozzle.
 In accordance with an additional aspect of the present invention, a
 desoldering tool includes a tool head, a heating element within the tool
 head, an adjustable speed fan for passing a gas over the heating element
 to provide a heated gas stream for desoldering of components from a
 circuit board, a nozzle for directing the heated gas stream to the
 component to be removed, a temperature sensor positioned to sense a
 temperature of the gas stream exiting the nozzle, and a controller for
 adjusting the speed of the fan based on an output of the temperature
 sensor to achieve a predetermined temperature for desoldering.
 In accordance with a further aspect of the invention, a circuit board
 holder for positioning circuit boards during attachment or removal of
 components includes a frame for supporting the circuit board above a work
 surface, two parallel movable side rails supported on the frame and
 movable toward and away from one another to accommodate circuit boards of
 varying sizes, and at least two movable clips positioned on each of the
 movable side rails for grasping the circuit board, wherein the clips are
 movable along the rails to a position at which the clips can grasp the
 circuit board without contacting components on the circuit board.
 According to another aspect of the invention, an auxiliary preheater is
 provided for warming a circuit board in preparation for removal of
 components from the circuit board. The auxiliary preheater includes a
 ceramic positive temperature coefficient heating element, and a variable
 speed fan for directing gas over the heating element toward a circuit
 board which is positioned above the auxiliary preheater.
 In accordance with a further aspect of the invention, a method of
 controlling a desoldering tool includes the steps of:
 providing a desoldering tool with a variable speed fan and a heating
 element;
 providing a plurality of interchangeable nozzles for connection to the
 desoldering tool to direct heated gas over a component, each of the
 nozzles configured to provide an airflow profile for a particular size and
 type of component, the nozzles each having a coded portion which is
 recognized by the desoldering tool;
 inserting one of the nozzles into the desoldering tool; and automatically
 setting an airflow profile of the fan based on the recognition of the
 coded portion of the nozzle by the desoldering tool.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The chip removal and replacement system according to the present invention
 allows the safe and easy removal or reattachment of components such as
 integrated circuits on circuit boards using focused hot air. The system
 shown in FIG. 1 includes a soldering and desoldering tool 10, a circuit
 board holder 12, and a controller 14. Preferably, the system also includes
 an auxiliary preheater 16, shown in FIGS. 3-5, which is placed beneath the
 circuit board.
 The soldering and desoldering tool 10, which is referred to below as the
 tool, is shown with a head 18 of the tool in a lowered position in FIG. 2.
 The tool 10 includes a nozzle 20 positioned on the head 18 for directing a
 flow of hot air over a component to be removed or reflowed. The nozzle 20
 is removably connected to the head 18 by a connection and release
 mechanism 26 which will be described in further detail below with respect
 to FIGS. 7 and 8. The head 18 is connected to a base 22 of the tool 10 by
 an arm 24 which allows the head to be moved between the two positions
 shown in FIGS. 1 and 2. A fan 32 as illustrated in the base 22 is
 positioned for directing air through the arm 24 and the head 18 to the
 nozzle 20. The head 18 includes a heating element illustrated as reference
 numeral 46, which heats the air for heating of the component to be removed
 or reflowed.
 The arm 24 is designed as a four bar linkage which allows the head 18 to
 move upward and back toward the base 22 so that the tool 10 is more
 compact in the non-use storage position illustrated in FIG. 1. The head 18
 is connected to the arm 24 by a Z-axis adjustment mechanism 28 for fine
 Z-axis adjustment including adjustment knobs 30 on both sides of the head.
 The adjustment knobs 30 engage teeth (not shown) on a back side of the
 head 18 such that rotation of the knobs 30 raises and lowers the head on
 the arm 24. The Z-axis adjustment mechanism 28 allows the nozzle 20 to be
 manually adjusted to a position adjacent a component to be removed.
 Additional adjustment of the nozzle 20 is provided by rotation of the
 nozzle connection and release mechanism 26 to rotationally align the
 nozzle with the component to be removed.
 FIGS. 3-5 illustrate a auxiliary preheater 16 which is configured to fit
 below the circuit board holder 12 and blow warm air up around the circuit
 board. The auxiliary preheater includes a variable speed fan 34 which
 blows air over a constant temperature heating element 36. The heating
 element 36 is preferably a ceramic positive temperature coefficient (PTC)
 heater having a plurality of heat exchange fins through which air is
 blown. The PTC heater provides has a fixed maximum temperature. The PTC
 heater provides an advantage over prior art heaters by preventing
 overheating and the associated damage to circuit boards and components
 which may occur with known heaters if not carefully controlled. One
 example of a PTC heating element is available from David+Baader, GmbH of
 Germany and is identified as a finned resistor heating element Type HR 01.
 This heating element operates at 1500 W, with an operating voltage range
 of 100V to 120V, and provides a maximum surface temperature of 230.degree.
 C. with no air flow.
 The auxiliary preheater 16 includes a housing 38 with a screen 40 over the
 heating element 36. The housing 38 includes an on/off switch 42 and a fan
 speed control 44. Although the auxiliary preheater 16 can be controlled
 manually, the auxiliary preheater is preferably connected to the tool 10
 and is controlled by the tool controller 14. The controller 14 is able to
 coordinate the heating profiles of the auxiliary preheater 16 and the
 heater 46 in the tool 10 by controlling fan speeds and thus the rate of
 heat transfer by convective means rather than changing the temperatures of
 the heaters themselves.
 The tool 10 is also provided with an automated vacuum system which lifts a
 component off of the circuit board once the solder connections have been
 completely melted. This automated vacuum pickup system 50 is illustrated
 in FIG. 6. The system 50 includes a suction inlet tube 52 which delivers
 suction from a vacuum source in the base 22. The suction inlet tube 52 is
 connected to an upper end of a vertically movable rigid suction tube 54
 which extends from an interior of the tool head 18 through the heating
 element in the head and out of the bottom of the head in the center of the
 nozzle 20. The bottom end of the suction tube 54 is provided with a
 removable vacuum cup 76 and is positioned so that it is adjacent the top
 of a component when the nozzle 20 is properly adjusted for component
 removal. The suction tube 54 is fixed to a first plate 56 which is
 vertically movable and connects the suction tube 54 to a rod 58. A
 solenoid linear actuator 60 of the pickup system 50 is fixed in the tool
 head 18 and provides a vertical lifting force to lift the component off of
 the circuit board. A piston 62 of the linear actuator 60 is connected to a
 second plate 64 of the pickup system 50. The second plate 64 is provided
 with an opening 66 which allows the rod 58 to pass through the plate.
 In operation, once the tool 10 has been positioned with the nozzle 20
 adjacent a component to be removed the vacuum source is activated to
 create a suction in the suction tube 54 causing the component to be
 grasped by the vacuum cup 72. After the suction is applied, the solenoid
 linear actuator 60 is activated moving the second plate 64 upward in the
 direction of the arrow A. Since the component is still connected to the
 circuit board by the solder connections which have not yet been melted,
 the component applies a downward force in the direction of the arrow B on
 the suction tube 54. This causes the spring 68 to be compressed between
 the second plate 64 and a sensor member 70 on the rod 58. The spring 68
 continues to apply a constant upward force on the suction tube 54, and
 thus, the component until the component is released from the circuit
 board. The force applied by the spring 68 is sufficient to lift the
 component after the solder connections have all been melted but
 insufficient to lift the component before all the solder connections have
 been melted.
 The automated vacuum pickup system 50 also includes a sensing mechanism for
 sensing when the component has been removed from the circuit board. This
 sensing system includes a sensor member 70 on the vertically movable rod
 58 and a corresponding sensing element 72 fixed in the tool head 18. When
 the component has been released by desoldering of all of the solder
 connections, the spring 68 causes the rod 58, the plate 56, and the
 suction tube 54 to be lifted. In the lifted position, the sensor member 70
 on the rod 58 is adjacent the sensing element 72 causing a signal to be
 sent to the controller 14 indicating that the component has been removed.
 The heating system is then automatically shut off.
 FIGS. 7 and 8 illustrate the nozzle connection and release mechanism 26
 which allows different nozzles 20 to be snapped-in, rotated for
 positioning, and released without touching the hot nozzle. The elements of
 the connection and release mechanism 26 include a rotatable ring 76,
 spring biased pins 78, a retaining ring 80, a release ring 82, and a
 handle 84. As shown in FIG. 7, an upper end of the release ring 82 is
 fixed to an exterior of the cylindrical heater housing 86. A space is
 provided between the lower end of the release ring 82 and the housing 86
 for inserting the upper end of the nozzle 20. A rotatable portion of the
 nozzle connection and release mechanism 26 includes the rotatable ring 76
 with spring biased pins 78 and the retaining ring 80. The rotatable
 portion is placed over the fixed release ring 82 and secured by a C-clip
 88, shown in FIG. 7.
 According to the embodiment illustrated, three spring biased pins 78
 provide the snap-in connection by snapping into a circumferential groove
 96 in the nozzle 20. However, other numbers or shapes of spring biased
 members may also be used. The three pins 78 each include a stem 90 which
 is sized to be received in the three slots 94 in the rotatable ring 76,
 and a head 92 which has a disk shape with beveled edges. A spring 98, as
 shown in FIG. 7, biases the pins 78 inward toward the groove 96 in the
 nozzle 20.
 The handle 84 fits into an opening 102 in the rotatable ring 76 and is used
 to rotate the nozzle 20 to adjust the orientation of the nozzle to match a
 component being removed or replaced. The handle 84 is also used to rotate
 the ring 76 to release the nozzle 20 from the tool head. Rotation of the
 ring 76 by the handle 84 until it stops causes the heads 92 of the pins to
 each engage one of the six ramps 104 on the release ring causing the pins
 to be disengaged from the groove 96 in the nozzle allowing the nozzle to
 be released from the nozzle connection and release mechanism 26.
 According to one embodiment of the invention, the nozzles 20 may be coded
 for the size and type of component which is to be removed. The nozzles 20
 may include a coded portion which is recognized by the desoldering tool
 upon insertion. The coded portion may be an electronically readable code,
 a mechanically readable code, or other code. When the coded nozzles are
 inserted into the tool 10, the tool reads the code and automatically sets
 a temperature and an airflow profile of the fan based on the recognition
 of the coded portion of the nozzle by the tool.
 The circuit board holder 12, illustrated in FIGS. 9 and 10, allows a
 printed circuit board to be easily fixed in place for removal or
 replacement of components without contacting any of the components. The
 board holder 12 includes a frame 108 having four legs 110 and two sliding
 parallel rails 114 which move toward and away from each other to
 accommodate the printed circuit board. Each of the rails 114 is provided
 with two sliding clips 116 which are configured to receive an edge of the
 circuit board. An enlarged side view of one of the clips 116 is shown in
 FIG. 11. The clips 116 are preferably formed of a flexible material
 allowing the clips to flex outward to securely retain a circuit board.
 The circuit board holder also includes a threaded rod 120 which extends
 through threaded bores 126 in each of the sliding rails 114. A wheel 118
 is connected to the threaded rod 120 at each end. The circuit board holder
 12 is provided with an optional sliding indicator 124 having a pivoting
 board support arm 122.
 In use, the wheel 118 is rotated so that the rails 114 are spaced to
 accommodate the size of the circuit board to be reworked. The clips 116
 are then moved along the rails 114 to a position at which they can grasp
 the edge of the circuit board without contacting any components on the
 board. The wheel 118 is then rotated to tighten the clips 116 onto the
 circuit board. The clips 116 flex to accommodate thermal expansion of the
 circuit board during the rework process. The circuit board holder 12 can
 accommodate circuit boards of odd shapes such as L-shaped boards by
 adjusting the positions of the clips 116.
 FIG. 12 illustrates the controller 14 for controlling the operation of the
 tool 10 and optionally the auxiliary preheater 16. The controller 14
 includes a mode selector knob 130 for selecting removal mode or reflow
 mode. In the center of the mode selector knob 130 is a start/stop button
 132. The controller also includes time control up/down buttons 134 and an
 airflow control knob 136 which controls the fan speed. A display screen
 138 or LCD displays time and temperature information. Time is displayed on
 the screen 138 and will count either up or down depending on the mode of
 operation. In the removal mode, the display time will count up and in the
 reflow mode the display time will count down. The time control buttons 134
 allow the user to adjust the time for the reflow mode only.
 The air temperature exiting the nozzle 20 is preferably sensed by a
 temperature sensor 48 which is positioned either on the circuit board or
 within the nozzle 20, preferably at a bottom edge of the nozzle. The
 temperature sensor provides a signal to the controller 14 and the
 controller displays the temperature on the screen 138. According to one
 embodiment, the controller 14 may automatically control the fan speed of
 fan 34 based on the information provided by the temperature sensor 48, as
 schematically shown in FIG.
 The operation of the system in the component removal mode is as follows.
 The vacuum cup 76 is installed on the suction tube 54 as shown in FIG. 6
 for grasping of the removed component. A removal nozzle 20 is chosen that
 corresponds to the component to be removed and the nozzle is snapped onto
 the head 18 of the tool 10. The circuit board is placed in the circuit
 board holder 12, or alternatively on a conventional workstand. The head 18
 is lowered until it locks in the down position illustrated in FIG. 2. The
 board holder 12 or workstand is manipulated until the component to be
 removed is centered below the nozzle 20 so that the leads do not hit the
 nozzle when the component is lifted from the board. The nozzle 20 is
 rotated to a proper orientation by the handle 84. The Z-axis adjustment
 knob 30 is then used to lower the reflow head 18 until the nozzle
 completely encapsulates the component. Preferably, the nozzle 20 remains
 about 1 mm above the component leads and does not come into contact with
 the component. The mode selector knob 130 is placed in the removal
 position, the airflow control 136 is adjusted for the particular
 application, and the start button 132 is pressed.
 Once the setup is complete for the removal mode and the start button 132
 has been pressed the system will proceed to automatically remove the
 component. If the auxiliary preheater 16 is connected, the auxiliary
 preheater will start automatically. Hot air will begin to flow from the
 nozzle 20 and the timer will begin counting up. When the solder
 connections have been melted the component will be automatically lifted
 from the circuit board, the auxiliary preheater will shut down, and hot
 air from the tool will automatically stop. The removal time will be stored
 for use in the subsequent reflow cycle. The vacuum cup 72 will continue to
 hold the component until the head 18 is raised and the start/stop button
 132 is pressed. Preferably, a scoop or tray is used to receive the hot
 component when the component is released from the vacuum cup 72. Removal
 is now complete.
 In the reflow or reattachment mode the attachment site on the circuit board
 is prepared and the component to be attached is placed on the circuit
 board. The mode selector knob 130 is rotated to the reflow mode causing
 the suction tube 54 to automatically raise so that it will not cause any
 obstruction during reflow. The head 18 is lowered to the down position,
 the nozzle 20 is rotated with the handle 84, and the Z-axis adjustment
 knobs 30 are used for fine adjustment of the vertical position of the
 nozzle. As in the removal mode, the nozzle 20 is preferably positioned
 about 1 mm from the leads and no part of the nozzle should be in contact
 with the component. The time recorded during the previous removal cycle is
 recorded on the controller display screen 138. Once the start button 132
 is depressed, the hot air cycle will begin and the timer will count down
 to zero and then will shut off.
 The system will operate at a set temperature, which is preferably between
 about 300.degree. C. and 400.degree. C. However, the system may be
 calibrated by the user to other temperatures depending on the application.
 During the removal or reflow process, the temperature may be controlled by
 adjustment of the airflow control 136.
 While the invention has been described in detail with reference to the
 preferred embodiments thereof, it will be apparent to one skilled in the
 art that various changes and modifications can be made and equivalents
 employed, without departing from the present invention.