Surface mount device removal tool

A surface mount device desoldering and removal tool includes a flexible carrier plate and a plurality of heated legs attached to the flexible carrier plate for contacting the leads of an electrical component. The flexible carrier plate is sufficiently flexible so that the flexing of the carrier plate allows the plurality of legs to deflect outward to accommodate electrical components of varying sizes. The plurality of legs are heated by electrical resistance heating elements to melt the solder which connects an electrical component to a circuit board. The legs provide a grip on the leads of the electrical component which allows the removal tool to lift the electrical component from the circuit board when all the solder connections have been melted. The flexible carrier plate is advantageously provided with shoulders which allow the electrical component to be easily removed from the removal tool.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates generally to a device for removal of electrical 
components and more particularly to a device for desoldering and removing 
surface mount devices from a circuit board without damaging the circuit 
board. 
2. Description of the Related Art 
Surface mount devices include various electronic circuit components having 
electrical leads protruding from the sides which are attached to printed 
circuit boards by either solder or conductive adhesive. One type of leads 
extend straight down from the chip and form a butt joint with the circuit 
board. Other leads, referred to as gull wing leads extend down from the 
chip to the board and then extend outward a short distance along the board 
where they are joined to the board by solder. Still other leads, referred 
to as J-shaped leads extend down from the chip and curl underneath the 
chip where they are soldered to the circuit board. Surface mount devices 
having J-shaped leads are commercially manufactured having dimensional 
tolerances which are quite large, on the order of 0.01 inches. Therefore, 
the position of the J-shaped leads relative to one another may vary 
substantially in chips of the same size and type. 
When a surface mount device is found to be faulty or malfunctioning, the 
component is removed from the circuit board by heating each of the solder 
connections above its melting temperature. Several methods are available 
for heating the solder including non-contact heating with a hot gas or 
infrared lamps, and direct contact heating with special heated tools 
having tips size to match the individual components. The non-contact 
methods of heating are typically useful only for repetitive component 
removal due to the long setup time required to establish the proper 
operating parameters for these methods. 
Contact heating devices are generally useful for removing a few components 
from a circuit board as the need arises. These contact heating devices 
generally utilize fixed size contact elements which are configured to 
contact all of the leads of a particular size chip and are heated via 
conduction through a conductive stem. The relative large mass of these 
contact elements prevents rapid heating of the device to operating 
temperature. Examples of such contact heating devices having fixed size 
contact elements are disclosed in U.S. Pat. Nos. 3,632,036 and 3,579,795. 
Due to the above-described large tolerances in surface mount components 
having J-shaped leads, the fixed size contact elements must be made to 
accommodate the largest possible component size within the tolerance 
allowance. This tolerance allowance causes the contact element to be too 
large for most components. When the tool tip is too large for a particular 
component, the contact surfaces do not make contact with all of the leads, 
whereby some of the soldered connections are not melted. Many circuit 
boards have been destroyed when trying to remove a component from the 
board when all the soldered connections have not been melted. 
In an attempt to solve this problem, component removal has been conducted 
with either fixed size removal devices which utilize molten solder or 
removal devices having a set of movable contact blocks which are moved to 
contact the leads of the component. In the molten solder type device, 
grooves are provided in the contact portion of the removal device for 
molten solder which is used to fill the gaps between the leads of the 
component and the oversized removal device. The drawback of this device is 
that the molten solder does not flow into all the grooves in a consistent 
fashion. When the solder does not reach all the grooves, some of the leads 
are not contacted, preventing the solder connection from being melted and 
causing damage to the circuit board. 
The grasping type removal devices are provided with grasping contact 
surfaces which are manually moved to accommodate differences in component 
size. Examples of grasping type removal devices are shown in U.S. Pat. 
Nos. 4,034,202 and 3,895,214. These grasping type devices require operator 
experience and technique to properly align the grasping contact edges with 
the component leads without damaging the circuit board or surrounding 
components. Damage to the board can also occur if an attempt is made to 
remove the component before all the connections are melted. 
SUMMARY OF THE INVENTION 
The surface mount device removal tool according to the present invention 
addresses these problems by providing a removal tool which accommodates 
electrical components of varying sizes and provides contact with each lead 
to melt all the solder connections and prevent damage to the circuit 
board. In addition, the removal tool of the present invention allows a 
user to desolder, remove and discard an electrical component while using 
only one hand. 
A preferred embodiment of the present invention includes a flexible carrier 
plate and a plurality of heated legs attached to the flexible carrier 
plate for contacting the leads of an electrical component. The flexible 
carrier plate is sufficiently flexible so that the flexing of the carrier 
plate allows the plurality of legs to deflect to accommodate electrical 
components of varying sizes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The removal tool 10 according to the present invention, as shown in FIGS. 1 
and 2, includes a flexible carrier plate 12, legs 14 extending from the 
flexible carrier plate and a holding assembly 15 for holding the carrier 
plate. Also shown in FIG. 1 is a surface mount component 50 having a 
plurality of J-shaped leads 52 which are each electrically connected to a 
circuit board 54 by beads of solder 56. The removal tool 10 of the present 
invention can accommodate surface mount devices 50 of varying sizes due to 
the flexibility of the carrier plate 12 which allows the legs 14 to move 
apart to accommodate a particular component 50. In use, the removal tool 
10 is positioned on the component 50 with inside surfaces of the legs 14 
engaging the outer surfaces of the leads 52. The legs 14 are then heated 
to melt the solder 56, whereupon the component 50 is removed from the 
circuit board 54 by the removal tool without damaging the circuit board. 
Each of the legs 14 of the removal tool 10 is configured with an upper 
portion which is connected to the carrier plate 12 by connecting members 
such as screws 16. It should be recognized that the legs may be connected 
to the carrier plate by any type of known connecting method. 
Alternatively, the legs and the carrier plate may be formed as a single 
member. The legs 14 are connected to the carrier plate 12 at a distance 
from the edge of the carrier plate, thereby providing a shoulder 66 of the 
carrier plate which extends beyond the legs. Each of the legs 14 also has 
two upper and lower grooves 18,19 which extend along the length of the 
internal surfaces of the legs. Each of the upper grooves 18 is provided 
with a ceramic tubular insert 62, while the lower grooves 19 accommodate a 
divider plate 60. The legs 14 are also preferably provided with a 
projection 21 of a copper material which provides a horizontal welding 
surface for ease of assembly. 
A step 20 between the upper and lower portions of each of the legs 14 
allows the lower portions of the legs to be thinner than the upper 
portions and creates a low mass leg design which allows rapid heat 
transfer through the legs. Opposing internal surfaces of the legs 14 are 
spaced according to the dimensions of the particular component 50 to be 
removed. The spacing S between the opposing legs 14 is preferably slightly 
smaller than the corresponding spacing S' of the minimum sized part. 
Therefore, the legs will contact all of the J-shaped leads 52 on 
components 50 having varying dimensions which are within the tolerance 
allowance. 
As shown most clearly in FIG. 4, when the removal device 10 is lowered onto 
a component 50 having dimensions which are greater than the spacing 
between the legs 14, the leads 52 apply oppositely directed forces to the 
legs 14, and the legs are allowed to move apart under the influence of 
those forces by the flexing of the carrier plate 12. The legs 14 provide 
automatic spring tension or grip on the component leads which provides 
physical contact with each of the leads and also allows the component to 
be lifted from the circuit board. 
The legs 14 are preferably formed of a material which is a good conductor 
of heat such as a copper alloy. Other suitable materials include brass, 
pure copper or other copper alloys such as leaded copper or tellurium 
copper. 
The heating of the legs 14 is provided by electric resistance heating in a 
set of four heating wires 22 which pass through the tubular inserts 62 in 
the legs 14. The electric current is carried from the holding assembly 15 
to the heating wires by the delivery wire 30 and the first and second 
heating wire connectors 26,28. The heating wires 22 heat the tubular 
inserts 62 which in turn heat the legs 14. The tubular inserts 62 are 
preferably ceramic, however, other insulators which are good conductors of 
heat may also be used. 
The holding assembly 15 includes a pin connector 32 for connecting the 
removal tool to a source of electric current in a specifically designed 
handle (not shown). The pin connecter 32 has an internal bore through 
which the delivery wire 30 extends. The delivery wire 30 is soldered at 
the end 34 of the pin connector 32 and provides a first electrical contact 
for electrical connection with the handle. 
A carrier member 36 is attached to the pin connector 32 by an insulating 
collet 38. The insulating collet is preferable a high temperature 
insulator such as glass epoxy. The carrier member 36 provides a second 
electrical contact for a second electrical connection with the handle. The 
carrier member 36 is provided with an annular projection at a lower 
portion thereof and a carrier insulator 40 is mounted on the projection. 
A carrier plate supporting tube 42 is mounted surrounding the carrier 
insulator 40. The flexible carrier plate 12 has a central circular hole 
configured to receive the supporting tube 42, so that, the flexible 
carrier plate abuts a flange 44 at the end of the tube. The carrier plate 
supporting tube 40 is preferably constructed of a thin sheet of stainless 
steel which results in a cool gripping area on the holding assembly 15 so 
that the holding assembly can be easily removed from the handle. 
Also mounted on the carrier member 36 is a smaller conductor tube 46, made 
of a conducting material which connects the carrier member 36 to the 
second heating wire connector 28 completing the electrical circuit. The 
second heating wire connector 28 is preferably welded to the exterior 
surface of the conductor tube 46. The conductor tube 46 is provided with a 
ceramic insert tube 48 which isolates the delivery wire 30 from the 
conductor tube 46 and the second heating wire connector 28. 
The heating and delivery wires are connected to heat the legs 14 as shown 
most clearly in FIG. 2 which shows a bottom view of the removal tool with 
the divider plate 60 removed. The delivery wire 30 extends from the solder 
connection 34 at the end of the pin connector 32, through bores in the pin 
connector, the carrier member 36 and the conductor tube 46. The delivery 
wire 30 bends at an angle of approximately ninety degrees (90.degree.) at 
the exit of the conductor tube 46 to a contact position where it is 
mounted on the horizontal projection 21 on one of the legs 14 in 
electrical contact with a first heating wire connector 26. 
The delivery wire 30 is preferably copper wire, however, other materials 
which are good conductors may also be used. The four heating wires 22 pass 
through the ceramic tubular inserts 62 in each of the four legs 14 and 
extend at either end of the tubular inserts. The heating wires 22 are each 
provided with a straight end 23 and a curved or bent end 24. The straight 
end 22 of one heating wire is positioned to contact the curved end 24 of 
the neighboring heating wire in a movable connection which accommodates 
relative motion of neighboring legs 14. 
The first heating wire connector 26 is mounted preferably by welding at one 
end on the projection 21 on one of the legs 14 in electrical contact with 
the delivery wire 30. This connection is preferably made by welding, 
however, other known connecting methods may also be used. The other end of 
the first heating connector wire 26 provides a flexible connection with a 
straight end 23 of one of the heating wires 22. The second heating wire 
connector 28 is connected at one end to the conductor tube 46 and provides 
a movable connection at the other end with a curved end 24 of one of the 
heating wires 22. The heating wires 22 and the first and second heating 
wire connectors 26,28 are preferably made of stainless steel. 
Electric current is supplied to the heating wires 22 from a specially 
designed handle unit which engages the upper end of the holding assembly 
15. Three electrical contacts are provided between the holding assembly 15 
and the handle. The first two electrical contacts are provided by the pin 
connector 32 and the carrier member 36, and the third contact provides a 
ground for the holding assembly. 
The electrical connection between the first heating wire connector 26 which 
is preferably stainless steel and the delivery wire 30 which is preferably 
copper provides a thermocouple point 64 due to the different materials of 
the connected wires. This thermocouple 64 is used as a temperature sensor 
to provide temperature feedback to an external temperature controlling 
circuit. The external temperature controlling circuit is preferably a 
circuit which is known to those in the art which measures a voltage 
created by the thermocouple in response to the temperature and turns the 
electrical current supplied to the heating wires on and off depending on 
the sensed temperature. The location of the thermocouple 64 at a position 
close to the working surface of the heated legs 14 allows rapid and 
accurate temperature control of the tool. 
The divider plate 60 is loosely mounted in the lower grooves 19 provided in 
the upper portion of the legs 14 for the purpose of hiding the wires and 
preventing foreign matter from entering the interior of the tool. The 
divider plate 60 is preferably formed of a somewhat flexible material such 
as stainless steel. The grooves 62 are of a sufficient depth that the 
divider plate 60 is maintained in the grooves in a floating position even 
when the legs 14 are spread apart by contact with a component 50. 
Although the present invention has been particularly designed for the 
removal of surface mount devices having J-shape leads because of their 
high dimensional tolerances, it should be understood that the present 
invention can be used for the removal of many different types of 
electrical components. The removal tool of the present invention is 
preferably made available in a variety of sizes for removing electrical 
components of different sizes and types. However, all of the different 
size removal devices preferably will fit in the same handle unit. 
The operation of the surface mount device removal tool 10 of the present 
invention is shown in FIGS. 3-5. In particular FIG. 3 shows a schematic 
side view of the removal tool positioned above an electrical component 50 
which is to be removed from a circuit board 54. As shown in FIG. 3, the 
distance S between the legs 14 is slightly smaller than the distance S' 
between the external surfaces of the J-shaped leads 52 on opposite sides 
of the device. 
FIG. 4 shows a schematic view of the removal tool 10 positioned for removal 
of a component 50. As shown in FIG. 4, the plate 12 has flexed and legs 14 
have been spread apart in the direction of arrows A, by contact with the 
component 50, and the legs are in contact with all of the J-shaped leads 
52 regardless of the size of the component 50. Once the removal tool 10 is 
placed on the component 50 by the exertion of a downward force F, as shown 
in FIG. 4, the heated legs 14 melt the beads of solder 56 on each of the 
leads 52. When all of the solder connections 56 have been melted, the 
component 50 is lifted from the circuit board 54 while the legs 14 of the 
removal device grip the component leads 52. 
The removal device according to the present invention with the flexible 
carrier plate 12 and movable legs 14 prevents removal of the component 50 
before all of the solder connections are melted because if all of the 
solder is not melted the component will slip out of the grip of the legs 
when the tool 10 is raised. This prevents damage to the circuit board 54 
caused when components are removed prior to all of the solder being 
melted. 
FIG. 5 is a schematic view of the release of a removed component 50 from 
the removal tool 10. As shown in FIG. 5, a support surface 68 is provided 
which is used in conjunction with the removal tool 10 to release the 
component from the grasp of the legs 14. The support surface 68 is 
configured to mate with the shoulders 66 of the carrier plate so that when 
shoulders 66 of the removal device are placed on the support surface 68, 
the user may release the component 50 by pressing down on the handle of 
the removal device, with a force F, causing the carrier plate 12 to flex 
and the legs 14 to move apart in the direction of arrows A. In this way 
the component 50 can be desoldered, removed and released from the removal 
tool 10 all with one hand. 
The support surface 68 may be provided in any convenient manner, for 
example, the support surface may be mounted on the top of a receptacle so 
that the removed components 50 may be deposited in the receptacle. 
While the invention has been described in detail with reference to specific 
embodiments thereof, it will be apparent to one skilled in the art that 
various changes and modification can be made, and equivalents employed, 
without departing from the spirit and scope of the invention.