Multi-nozzle surface mount rework system

Apparatus for rapidly and precisely removing and replacing surface mount devices without disturbance to nearby devices on a printed circuitboard, the invention utilizes a multiple nozzle arrangement wherein nozzles arranged for reciprocating motion one each along each edge of a surface mount device direct low velocity hot gas against bond joint locations along the respective edges of the surface mount device, thereby to melt the bonding agent mounting the device to the circuitboard. The multiple nozzle arrangement of the present system thus allows removal and/or replacement of devices of widely varying dimensions without the need for changes in nozzle size such as is inherent in prior art hot gas rework stations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates generally to apparatus for removing surface mount 
devices from circuit boards and particularly relates to a multiple nozzle 
rework system capable of removing devices of widely varying sizes without 
nozzle changes. 
2. Description of the Prior Art 
Hot gas rework stations previously available in the art have been used for 
rapidly and easily attaching and removing surface mounted components to 
and from printed circuit boards without disturbing nearby components or 
damaging the device being removed or mounted to the board. An example of 
such a prior art system is the Model 4460 Hot Gas Rework Station 
manufactured by Semiconductor Equipment Corporation of Moorpark, Calif., 
this prior rework system comprising a sophisticated apparatus utilizing a 
single interchangeable nozzle through which hot nitrogen gas is directed. 
Since a hot nitrogen gas jet must be directed in an extremely concentrated 
area to permit surface mount component removal without heating adjacent 
components, a multiplicity of nozzles which are interchangeable in the 
apparatus must be provided for surface mount components of differing 
dimensions. A fact of life in prior surface mount rework systems is the 
requirement for nozzles of differing sizes which are interchangeable to 
allow an operator to move and replace devices of different sizes on a 
printed circuit board. 
Hot gas reworking tools are disclosed in a number of prior patents 
including those noted as follows: 
4,295,596 Broten et al 
4,366,925 Fanene 
4,426,571 Beck 
4,552,300 Zovko et al 
4,602,733 Slack et al 
4,605,152 Fridman 
4,620,559 Holdway 
4,696,096 Green 
The patents noted above require a change of nozzles or similar 
gas-directing structure in order to work with surface mount devices of 
differing sizes. The patents are thus representative of prior art 
apparatus which require nozzle changes in order that surface mount devices 
of differing sizes can be removed and/or replaced on printed circuit 
boards by precise hot gas techniques. 
The present invention thus provides improvement over the prior art by the 
provision of multiple nozzles arranged for reciprocating movement so that 
hot gas can be precisely directed to bond joint locations of surface mount 
devices, thereby allowing removal and replacement without the requirement 
for maintaining a large inventory of nozzles of differing sizes and 
dimensions and without wasting time necessary for changing nozzles. 
SUMMARY OF THE INVENTION 
The invention provides a universal rework system capable of rapidly and 
precisely removing and replacing surface mount devices of virtually all 
sizes and styles without the need for changing nozzles. Surface mount 
devices mounting on printed circuit boards or similar substrates include 
epoxy bonded die, eutectic bonded die and leadless chip carriers inter 
alia. In common with prior hot gas rework systems, the present apparatus 
preferably uses nitrogen gas directed precisely against bond joint 
locations at low velocity, the temperature of the gas typically being as 
high as 800.degree. C. The present apparatus exhibits versatility not 
previously available in the art by the provision of multiple nozzles which 
allow rework of surface mount devices of varying size and configuration 
and which, in the prior art, could only be reworked through an interchange 
of a large number of different nozzle styles and configurations. With a 
multiple nozzle arrangement, typically four nozzles arranged with each 
nozzle being reciprocable essentially along one side of an imaginary 
rectangle, the apparatus of the invention is capable of directing very hot 
gas to particular locations necessary for removing or replacing surface 
mount devices on a substrate without undue heating of adjacent devices and 
without damage to the device being worked. The apparatus of the invention 
is capable of such performance without the requirement for time-consuming 
interchange of nozzles of differing configurations which previously had to 
be used for rework of devices of differing configuration and size. Use of 
the present apparatus thus eliminates the need for down time involved in 
the interchange of nozzles necessary in the prior art. A user of the 
present rework system is also not required to maintain an inventory of 
nozzles of differing sizes and configurations in order to work a full 
range of surface mounted devices as has been necessary in the prior art. 
Accordingly, it is a primary object of the present invention to provide a 
surface mount rework system capable of removing and replacing surface 
mount devices both quickly and easily without disturbance or damage to 
nearby devices and without the need to change nozzles when working surface 
mount devices of differing styles, sizes and configurations. 
It is another object of the invention to provide a surface mount rework 
system using multiple nozzles arranged to direct low velocity hot gas 
against bond joint locations at edges of a surface mount device in order 
to facilitate rework of the device on a printed circuit board or similar 
substrate. 
It is a further object of the present invention to provide a multi-nozzle 
surface mount rework system which is sufficiently versatile to allow 
rework of surface mount devices without damage to the devices or to 
devices adjacent to the rework location and without the need for 
time-consuming nozzle changes when working with devices of different sizes 
and configurations and further without the need for maintaining an 
inventory of nozzles of differing sizes and configurations which would 
need to be interchanged on a rework apparatus depending upon the size and 
configuration of the devices being reworked. 
Further objects and advantages of the invention will become more readily 
apparent in light of the following detailed description of the preferred 
embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The apparatus of the invention has substantial similarity to the Model 4460 
Surface Mount Rework System produced by Semiconductor Equipment 
Corporation of Moorpark, Calif. 93021 in that a number of subsystems of 
the prior art Model 4460 can be utilized in the present apparatus. As an 
example, the prior art Model 4460 as well as other devices available in 
the art provide means for heating gas to a temperature sufficient for use 
in a rework system as well as providing means for directing the heated gas 
to a nozzle for use. As another example, the prior art provides video 
camera, video monitor and similar subsystems for viewing of the work 
location, such subsystems being similar to subsystems employed in the 
present apparatus. Electronic and vacuum systems employed in prior devices 
such as the Model 4460 and which can be utilized in the present apparatus 
are thus conventional and are not considered to be novel features of the 
present apparatus. Accordingly, the operation of such conventional 
subsystems will not be described herein since the person of ordinary skill 
in the art will readily understand the operation and utilization of such 
subsystems in the embodiments of the present invention. 
Referring now to the drawings, and particularly to FIGS. 1 and 2, the 
present multi-nozzle surface mount rework system is seen at 10 to comprise 
a control console 12 and a work console 14, the work console 14 mounting 
nozzle assembly 16 within nozzle assembly housing 18. The nozzle assembly 
16 will be further described herein to mount a plurality of nozzles, 
preferably four nozzles, which allows the system 10 to rework virtually 
all styles and configurations of surface mount devices without the 
requirement for changing nozzles as has been necessary in the prior art. 
The system 10 allows ready adjustment of the nozzle assembly 16 to 
accommodate surface mount devices of any size from 0.1" on its smallest 
dimension to ob 2.0" on its largest dimension. The system 10 further 
accommodates rectangular as well as square surface mount devices and also 
accommodates devices with contacts on one, two or four sides. These 
capabilities are accomplished without the removal and replacement of 
nozzles. When the system 10 is called on to accommodate a surface mount 
device of differing size or shape, the system 10 is reset via motorized 
adjustment with video display to handle each different style and shape of 
device, the adjustment being accomplished within seconds as will be 
described hereinafter. 
A board holder 20 is configured to hold a printed circuit board (not shown) 
on which surface mount devices (not shown) are to be reworked, that is, to 
be removed or to be replaced with debonding and bonding occurring through 
the precise direction of low velocity hot gas against bond joint 
locations. The board holder 20 forms a part of a two-position work surface 
36 immediately below the nozzle assembly 16. 
As will be described further hereinafter, an optical system comprising a 
video camera 24 and video monitor 26 enables an operator of the system 10 
to view the work area, an image splitter 22 allowing viewing of a surface 
mount device being reworked while simultaneously viewing the nozzle 
assembly 16 as will be described hereinafter relative to FIG. 4. Prior 
rework systems have used video equipment in order to facilitate working of 
surface mount devices. Accordingly, the structure and operation of this 
equipment will not be described in detail. 
A vacuum pick up 30 is provided at a location central of the nozzle 
assembly 16 in order that the surface mount devices can be handled without 
damage to the devices. The vacuum pick up 30 will be further described 
relative to FIG. 3. 
A preparation station 28 can be provided on the work console 14 adjacent to 
the work surface 36. The preparation of section 28 is optional and similar 
structure has been available in the prior art. 
A status panel 32 is disposed on a forward face of the control console 12 
in order that the status of the nozzle assembly 16 can be readily 
determined. Control of the nozzle assembly 16 is accomplished through 
keypad 38 disposed on the work console 14 in a location convenient for 
user manipulation. Position controls 34 are also provided in the work 
console 14 in order to control the location of the board holder 20 in X, Y 
and theta motions. The particular mechanisms employed for printed circuit 
board positioning by the board holder 20 as well as the electronics 
employed for control functions within the system 10 are conventional in 
the art. Accordingly, a detailed discussion of the structure and function 
of these conventional systems need not be provided herein. 
Referring particularly to FIGS. 2, 3 and 4, the nozzle assembly 16 can be 
seen to include nozzles 40 through which low velocity hot gas is directed 
against precise locations along edges of a surface mount device (not 
shown) which is to be reworked according to the invention. In FIGS. 2, 3 
and 4, only two nozzles are shown for ease of illustration of the image 
splitter 22 and the vacuum pick up 30. In a preferred embodiment of the 
invention as will be described hereinafter, four of the nozzles 40 are 
utilized in order to provide the greatest degree of versatility in the 
reworking of surface mount devices of differing size and configuration. 
The vacuum pick up 30 comprises a vacuum tube 42 having a contact head 44 
located at its distal end, the other end of the vacuum tube 42 being 
connected to a source of vacuum (not shown) in a conventional manner. The 
vacuum tube 42 is either curved or "offset" along its length in order that 
the video camera 24 can be provided with an unobstructed view of the 
nozzles 40 and surface mount device 46 positioned on the board holder 20. 
When a device 46 is to be removed, the vacuum pick up 30 is lowered into 
place above the device 46 and vacuum is actuated. Once the hot gases 
emanating from the nozzles 40 cause reflow of bonding material to occur, 
the device 46 is lifted from board 47. An adjustable spring-loaded 
assembly 48 located at the anterior end of the vacuum tube 42 facilitates 
lifting of the device 46 at the exact moment when reflow occurs. The 
curved or offset shaping of the vacuum tube 42 is an important feature of 
the invention in that an operator of the system 10 can readily view the 
device 46 and the nozzles 40 through the video monitor 26 without 
substantial obstruction. When the surface mount device 46 is lifted off by 
the vacuum pick up 30, the nozzle assembly 16 retracts upwardly, thus 
allowing clearance to move the board holder 20 out from under the nozzle 
assembly 16 for ease of inspection, clean up and the like. Contact heads 
44 of differing sizes can be interchanged at the distal end of the vacuum 
tube 42 to allow use of the vacuum pick up 30 with components of differing 
sizes including very small components. 
As can also be seen in FIGS. 2, 3 and 4, an image splitter 22 is seen to be 
retractably disposed between the distal ends of the nozzles 40 and the 
surface mount device 46 which is to be reworked. The image splitter 22 
essentially comprises an image splitting mirror which allows downward 
viewing toward the device 46 while simultaneously allowing upward viewing 
of the nozzles 40 with the two views being superimposed and displayed on 
the video monitor 26. Accordingly, both the device 46 which is to be 
either removed or installed and the nozzles 40 can be simultaneously 
viewed by a user of the system 10 thus guaranteeing alignment of the 
nozzles 40 with respect to the device 46. This viewing occurs with the 
nozzle assembly 16 in an up position. Retraction of the image splitter 22 
and subsequent lowering of the nozzle assembly 16 retains the precise 
alignment of nozzles 40 and surface mount device 46. The sweep range and 
position of the nozzles 40 can be adjusted with the nozzle assembly in the 
up position and with the nozzles in motion once alignment through the use 
of the image splitter 22 has been accomplished. 
The board holder 20 functions to hold printed circuit boards or similar 
substrates such as the board 47 for reworking. Once the board 47 is locked 
into an approximate alignment within the board holder 20, the board 47 can 
be finely located in X, Y and theta by utilizing fine adjustment knobs 
provided by the position controls 34. Knob assembly 50 best seen in FIG. 2 
allows lock down of the board 47 in approximate alignment. 
Although not shown in the drawings, the system 10 can be provided with a 
"backside" heater for preventing thermal shock to surface mounted devices 
on a board such as the board 47. Backside heaters have previously been 
utilized in systems such as the Model 4460 of Semiconductor Equipment 
Corporation referred to above. The backside heater effectively provides 
gas flow and temperature control along with a timing function to prompt 
the operator of the system 10 at the end of the preheating cycle. The 
backside heater is located in a fixed position in close proximity to the 
under side of the board 47, the heater being mounted in the work console 
14 immediately below the board holder 20. The amount of thermal energy 
applied for preheating of the board 47 is controlled by gas flow and 
temperature controls (not shown) as is conventional in the art. Referring 
now to FIGS. 5, 6 and 12, the nozzle assembly 16 is shown in a preferred 
embodiment to comprise four of the nozzles 40 for delivering low velocity 
hot gas to precise locations along edges of a surface mount device such as 
the device 46 as schematically seen in FIG. 12. In FIGS. 5 and 6, the 
nozzles 40 are seen to each reciprocate along one side of an area within 
which a surface mount device 46 is to be removed or replaced on the board 
47. Proper functioning of the system 10 is dependent upon heating of a gas 
such as nitrogen to a very high temperature and applying the concentrated 
thermal energy available in the gas directly to a location where a bonding 
material is to be melted. The nozzle assembly 16 must be accurately raised 
and lowered into position in order to facilitate proper application of the 
low velocity hot gas. In order to allow the nozzles 40 to be more easily 
seen in FIG. 5, the angle of the nozzles 40 shown at approximately 
30.degree. from the vertical. In actual practice, a preferred range of 
angles is between 18 and 20.degree. . As is schematically seen in FIG. 12, 
the four nozzles 40 each have two degrees of motion relative to the 
surface mount device 46. The distance which each nozzle 40 travels along 
an edge of the device 46 is referred to as the "sweep range" while the 
proximity of each nozzle 40 to the surface mount device 46 is referred to 
as the "nozzle position". The nozzles will be referred to for purposes of 
discussion as the right, left, front and rear nozzles 40. In operation, 
the left and right nozzles 40 can be electronically linked together such 
that change of the "sweep range" of the left nozzle 40 correspondingly 
changes the "sweep range" of the right nozzle 40 simultaneously. A single 
adjustment thus controls the sweep range of both the left and right 
nozzles. In a similar manner, the sweep ranges of the front and rear 
nozzles 40 are linked together with one adjustment controlling both 
nozzles. Each pairing of the nozzles 40 as noted above can further be 
linked together such that a change in "nozzle position" of one also 
changes the nozzle position of the other simultaneously. Further, all four 
nozzles 40 can be linked together as to both position and sweep range 
function for rapid alignment in handling surface mount devices 46 which 
are square in conformation. Each pair of nozzles, that is, left and right 
or front and rear, can be retracted and/or functionally disabled when 
removing or replacing a device 46 with contacts on only two sides. 
Further, a single nozzle 40 can be used singly to remove and replace 
"in-line" or very small components on a substrate. 
The sweep cycle of a nozzle is always the same, the sweep cycle being the 
time required for travel of a nozzle 40 down a row of contacts of a device 
46 and back to the initial nozzle position. Accordingly, balancing of 
thermal input and matching of reflow time on adjacent sides of a 
rectangular device requires separate gas temperature and gas flow controls 
with one set of controls for the left and right nozzles 40 and a second 
set of controls for the front and rear nozzles 40. Either of the controls 
can be shut down entirely when working with surface mount devices which 
have contacts on two sides only. When the system 10 is initially actuated, 
all four nozzles can be brought up to a fixed idle temperature for fast 
response. A timer (not shown) can also be provided for associated heating 
equipment for assisting with uniform cycle duration and for preventing 
overheating. As has been noted previously, the lifting of a device 46 by 
the vacuum pick up 30 results in nozzle assembly 16 retraction upwardly 
with heating elements being cut back to an idle temperature. A pressure 
interlock (not shown) can also be provided to prevent heater burnout in 
the event of low gas pressure. 
Referring now particularly to FIGS. 5 and 6, it is to be seen that the 
nozzles 40 are generally located in an orientation corresponding to the 
left, right and front, rear pairings shown in FIG. 12. Movement of the 
pairs of nozzles 40 in the "sweep range" mode occurs through driving of a 
gear motor 52 tied to sprockets 54 and 56 and idler pulley 58 by means of 
cable 60. Manual adjustment of the sweep range is accomplished by range 
setting knobs 62 and 64 associated with the sprockets 54 and 56 
respectively so that the nozzles 40 are controlled as to the extent of the 
sweep range desired in a given rework situation. Nozzle position is 
controlled by the two cable and pulley assemblies 66 and 68. The 
assemblies 66 and 68 have turnbuckle adjustment elements 70 and 72 to 
maintain cable tightness. Each assembly 66 and 68 have respective return 
spring 74 and 76 which return respective nozzles 40 to an initial position 
as set by respective thumbscrew 78. 
Each nozzle 40 is held within a nozzle mounting assembly 80 with the 
assemblies 80 being mounted for reciprocating movement so as to allow 
accomplishment of the sweep range function noted above. It is to be 
understood that electric motors such as miniature stepper motors (not 
shown) can be employed for movement of the nozzles 40, these motors being 
capable of electronic linkage for appropriate positioning of the nozzles 
40. The nozzles 40 can thus be controlled by apparatus other than as 
specifically shown and described herein. 
Referring now to FIG. 7, the status panel 32 essentially comprises a 
membrane switch/display panel which displays information as to the status 
of the nozzles 40. Control of the system 10 can further be provided 
through the status panel 32. As an example, the indicators of system 
functions can be caused to be eliminated or to flash to provide an 
indication of system condition. Further, the positions of the nozzles 40 
can be schematically represented and the condition of gas flow to the 
nozzles can be shown on the panel 32. 
As noted relative to FIG. 8 and FIGS. 9A through 9D, the linkage between 
the pairs of nozzles 40 can be controlled through use of the link control 
panel 82. Sweep range display 84 is noted in FIGS. 9A and 9B as comprising 
pairs of flashing lights 86 which indicate respective linkages of left and 
right nozzles and front and rear nozzles. Both pairs of nozzles 40 can be 
linked together as aforesaid with resultant flashing of all of the lights 
86 either alternately or together depending upon particular linkage of the 
pairs of nozzles 40. Similarly, nozzle position is shown by nozzle 
position display 88 comprising flashing lights 90. 
Referring now to FIGS. 10 and 11, a nozzle 40 is seen in one embodiment of 
the invention to be maintained within inner and outer heat shields 92 and 
94. Heating of the nozzle 40 can be accomplished by means of heater 96 
with heat indication being provided by thermocouple 98. Position 
adjustment of the nozzle 40 within the heat shield 94 can be provided by 
spring loaded adjustment knob 100. 
It is to be understood that the invention can be practiced other than as 
explicitly described herein without departing from the scope of the 
invention. Mechanical and electronic subsystems and features not described 
in detail constitute conventional and readily available subsystems 
including gas heating subsystems, electronic control subsystems, backside 
heating subsystems, vacuum subsystems, etc. In its most basic mode, the 
invention contemplates the provision in a surface mount rework system of 
multiple nozzles capable of independent and coordinate movement for 
directing low velocity hot gas to precisely selected locations for either 
removing or replacing surface mount devices on a printed circuit board or 
similar substrate.