Abstract:
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.

Description:
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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in greater detail with reference to the preferred embodiments illustrated in the accompanying drawings, in which like elements bear like reference numerals, and wherein: 
     FIG. 1 is a perspective view of a chip removal and replacement system according to the present invention; 
     FIG. 2 is a perspective view of the desoldering tool of FIG. 1 with an arm of the tool in a lowered position; 
     FIG. 3 is a perspective view of a auxiliary preheater for use with the system of FIG. 1; 
     FIG. 4 is a top view of the auxiliary preheater of FIG. 3; 
     FIG. 5 is a cross sectional view of the auxiliary preheater taken along line  5 — 5  of FIG. 4; 
     FIG.  6 . is a perspective view of an automatic vacuum pickup linkage for the tool of FIG.  1 . 
     FIG. 7 is a side cross sectional view of the nozzle connection and release system of the tool of FIG. 1; 
     FIG. 8 is an exploded view of the nozzle connection release system of FIG. 7; 
     FIG. 9 is a top view of the circuit board holder; 
     FIG. 10 is a perspective view of the circuit board holder of FIG. 9; 
     FIG. I 1  is an enlarged side view of a portion of the circuit board holder showing one of the movable clips; 
     FIG. 12 is a perspective view of the system controller; and 
     FIG. 13 is a block diagram of the controller operation. 
    
    
     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° 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° C. and 400° 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.