Vision system apparatus and method for component/pad alignment

An improved method and apparatus for the visual alignment and placement of electrical components, such as lead-carrying chip members, and pad members, such as pad-carrying printed circuit boards, for purposes of aligning, placing and soldering said leads to said pads. The method involves supporting the chip member vertically over said pad member, inteposing therebetween a beam splitter cube which provides a simultaneous view of the underside of the chip member and the surface of the pad when viewed through a stereo microscope means, interposing an adjustable polarizing filter means which permits the operator to adjust the visual contrast between the leads and the pads, thereby facilitating the proper X, Y and theta vertical alignment, and moving the component down onto the pad member for soldering thereto.

BACKGROUND OF THE INVENTION 
The present invention relates to an improved method and apparatus for the 
vertical registration or alignment of electrical components, such as 
multi-lead chip members, over pad areas of receptor members such as 
printed circuit boards, each said pad area comprising a contact area 
designed to be contacted with and soldered to one of said leads to 
integrate the chip member into the printed circuit loop. 
It is known to provide vision system devices for supporting multi-lead chip 
members vertically over pad members and for interposing a beam splitter 
cube therebetween for purposes of viewing and aligning the underside of 
the chip member with the surface of the pad member, such viewing being 
done through a solid state camera and monitor system providing a video 
screen image. Such known devices have been commercially-available under 
the trademarks Model 4460 M Rework Station available from Semiconductor 
Equipment Corp., Moorpark, CA, Conceptronic Rover, Explorer and Caps Pick 
and Place Systems available from Conceptronic, Exeter, NH. 
While such systems and devices are designed for the same purposes as the 
present systems, they have the disadvantage of providing video screen 
images of the chip member and the pad member to the operator for purposes 
of facilitating adjustment of the X, Y, theta and Z axes for alignment. 
Such video images are of relatively poor quality, sharpness and fixed 
contrast, which makes it difficult for the operator to visually 
distinguish between the leads and the pad areas, particularly in cases 
where there is a color contrast between the component and the pad member. 
It is also known to provide vision system devices which give the operator a 
direct three dimensional view of the underside of the component and the 
surface of the pad member through a beam splitter cube and a stereo 
microscope means, for the present purposes. Reference is made to the Model 
DRS-22 Surface Mount System available from Air-Vac Engineering Company, 
Inc., Milford, CT, the present applicant. While such devices provide a 
superior stereo view of the component and the pad to the operator for 
alignment purposes, they do not permit any adjustment of the visual 
contrast between the component and the pad member, which makes it 
difficult for the viewer to distinguish between the component and the pad 
member, particularly in cases where there is a color contrast 
therebetween. Also the view provided to the operator varies significantly 
with the ambient light even though the apparatus incorporates external 
small halogen-type lamp source, the light from which illuminates both the 
component and the circuit board. Such light variations are dependent upon 
the location of the apparatus and upon variations of the ambient light 
even when the apparatus is only used in a single location. 
SUMMARY OF THE INVENTION 
The present invention provides a new and improved method and apparatus for 
facilitating the perfect registration or alignment of a multi-lead 
component and a multi-pad receptor area, such as of a printed circuit 
board, in which the operator has a stereo view of the underside of the 
component and the surface of the pad member through a microscope and 
through an interposed beam splitter cube, characterized by the latter 
having an integral adjustable polarizing filter at the underside thereof 
which enables the viewer to adjust the visual contrast of the pad member, 
darkening it or lightening it to produce the best possible visual contrast 
between the leads or contact feet of the component and the pads or 
receptor contact areas of the pad member or board, for purposes of 
improving the visual alignment ability and accuracy by the operator. 
According to a preferred embodiment of the present invention, the beam 
splitter cube is also provided with integral lighting means, preferably 
fiber optic lighting means, for providing a constant and intense direct 
illumination of the underside of the component and the receptive surface 
of the pad member, and surrounding the z-axis therebetween. 
According to another preferred embodiment of the invention, the beam 
splitter cube is also provided with a means for sensing the plane of the 
undersurface of a multi-lead component adjustably supported thereabove for 
purposes of regulating and unifying the supported location of said plane 
regardless of differences in the thickness of the component, whereby the 
distance between the component and the surface of the pad member during 
alignment is always the same regardless of the thickness of the component. 
Verifying the distance in both optical paths through the stereo microscope 
and beam splitter cube gives an image of uniform viewing clarity. 
The other essential and conventional features of the present apparatus and 
method comprise a means for releasably holding the multi-lead component in 
vertical elevation above the pad member and for moving the aligned 
component downwardly along the z-axis into contact with the pad member; 
means for supporting the pad member and for adjusting it in the X, Y and 
theta (rotational) directions for alignment with the multi-lead component 
supported thereabove; means for extending the beam splitter cube to a set 
position along the z-axis between the component and the pad member for 
alignment purposes, and for retracting the cube to permit movement of the 
aligned component down along the z-axis onto the stationary pad member, 
referencing the placement by means of an indicator scale, and heating 
means for causing the reflow of solder present on the multiple pads of the 
pad member while in contact with the aligned leads of the multi-lead 
component, to produce electrical interconnection therebetween.

DETAILED DESCRIPTION 
Referring to the apparatus 10 of FIG. 1, said apparatus, as illustrated, is 
identical in outward appearance and function to the prior-known Surface 
Mount System apparatus DRS-22 referred to hereinbefore. The essential 
differences reside in the beam splitting cube assembly and are only 
apparent when said assembly is extended and used. 
The general apparatus 10 of FIG. 1 comprises a housing 11 including a 
supporting base 12, a rear upright housing member 13 containing a 
pneumatic system and supporting a beam splitting cube housing 14 and a 
nozzle member support 15, both in horizontal extension therefrom overlying 
the supporting base 12. A heater head and nozzle assembly 16 is connected 
to the end of the support 15 by means of precision guide pins. The heater 
head and nozzle assembly 16 ride along precision guide shafts and bushings 
for adjustable vertical movement along the z-axis by means of a vertical 
adjustment knob 17 and for rotation adjustment by means of knob 18. 
The assembly 16 comprises internal heating and vacuum means, an 
interchangeable lower gas nozzle 19 having a component-receiving cavity 
20, shown in FIG. 2, including component-piloting means 21 and a vacuum 
orifice 22. The assembly 16 also includes a releasing ring 23 which 
spreads or closes a clamping finger means thereof to release or engage a 
nozzle 19. As illustrated by FIG. 2, a component 24 preferably is manually 
inserted into or removed from the nozzle pilots 21 by means of a hand-held 
vacuum probe 25 to prevent physical contact with the leads. Once inserted 
the component is secured within the nozzle pilots 21 by the internal 
vacuum through orifice 22. Removal of a component 24 from the cavity 20 is 
accomplished by applying the manual vacuum probe 25 to the underside 
thereof, generating a vacuum therein and discontinuing the vacuum through 
orifice 22, and manually withdrawing the component with the probe. 
Alternatively a component holding tray can be used instead of the vacuum 
probe. 
Alignment is accomplished by clamping a circuit board 26 having a receptive 
pad member 27 within the receptive facing slots 28 present on the inside 
surfaces of spring-loaded carrier arms 29 and 30 as shown in FIG. 3. The 
arms 29 and 30 are commonly-supported on a member engaged within a track 
31 for adjustable movement in the x-direction by turning the fine 
x-adjustment control wheel 32 at the front of the apparatus. The track 31 
is present on a carriage member 33 supported within a track 34 for 
adjustable movement in the Y-direction by turning the fine Y-adjustment 
control wheel 35 at the front of the machine. 
When an electrical component 24 is secured within the nozzle 19 and a PCB 
26 is secured between the clamping arms 29 and 30, adjustment and 
alignment thereof is accomplished by sliding the beam-splitting cube 
member 36 out of its housing 14 to a stop position in which the 
beam-splitting cube 37 thereof is centered along the z-axis between the 
overhead component 24 and the receptive pad member 27 of the PCB 26 
thereunder. The operator has a simultaneous three-dimensional view of the 
underside of the component 24 and the top side of the PCB 26, as they are 
superimposed and viewed through the stereo microscope 38 adjustably 
mounted on the nozzle member 16. External illumination is provided by 
halogen lamps 39 connected to the heater/nozzle assembly 16, and an 
adjustable focus lens 40 is provided on the microscope. 
The view through the microscope 40, as illustrated by FIG. 4, is focused 
against the primary mirror 41 of the optic frame 36 which reflects 
superposed images of the component 24 and the pad member 27 of the PCB. 
The view of the underside of the component 24 is reflected by the upper 
surface of a 50% diagonal mirror 42 and then projected against a vertical 
100% rear mirror 43 of the beam splitting cube section 37 and said 
reflection is viewed through the 50% mirror 42 and reflected by the 
primary mirror 41 as illustrated by FIG. 4. The image strength of the 
component is 25% overall. The view of the top side of the PCB 26 is 
reflected by the under surface of the 50% mirror 42, which surface is 
viewed through the primary mirror 41. The image strength of PCB is 50% 
overall. A polarizing filter cuts this intensity to 25% overall, creating 
equal image strength. The heater/nozzle assembly 16 is rotated slightly, 
if necessary, to produce rotational alignment by turning knob 18. 
Adjustments along the X and Y axes are made to produce perfect 
registration alignment between each of the leads 24a of the component 24 
and each of the individual corresponding pads 27a of the pad member 27 to 
which the leads are to be soldered. Generally all of these features and 
functions are present in the prior known surface mount system apparatus 
disclosed hereinbefore. 
The improvements provided by the novel vision system of the present 
invention are accomplished through modifications in the beam splitting 
cube section 37 of the optic frame 36. Such modifications include upper 
fiber optic lighting means 44 surrounding the z-axis for the direct 
illumination of the underside of the overhead electrical component 24 and 
of the leads 24a thereof; lower lighting means 45 surrounding the z-axis 
for the direct illumination of the top surface of the pad member 27 and 
the pad areas 27a thereof, and an interposed adjustable polarizing light 
filter ring 46 mounted across the z-axis, which polarizes the image of the 
pad member 27 and is rotatably mounted to enable light contrasts to be 
adjusted in the visible reflection of the pad member as viewed by the 
observer, whereby the reflection of the pad areas 27a can be lightened or 
darkened to produce a clearer visual contrast between the superimposed 
reflections of the component leads 24a and of the pad areas 27a. This 
enables the operator to make a more precise alignment of the leads 24a in 
centered position with the pad areas 27a whereas, in the prior known 
apparatus, the lighting of each of these elements was indirectly reflected 
from the external type lamps 39, and the superimposed reflections of the 
leads 24a and the pad areas 27a were of equal contrast and appearance. 
This made precise alignment very difficult, particularly in the case of 
colored printed circuit boards 27 having background areas similar in color 
to the color of the pad areas 27a. 
Most preferably the cube section 37 of the cube member includes both upper 
and lower lighting means 44 and 45. The preferred lighting means 44 and 45 
comprise fiber optic elements mounted around the housing of the cube 
section 37 and surrounding the z-axis, which elements have been found to 
produce a uniform intense illumination of both the component 24 and the 
pad member 27. 
The polarizing filter ring 46 comprises a polarizing filter lens laminated 
to an anti-reflection glass and mounted within a peripheral ring which, in 
turn, is rotatably mounted within the housing of the cube section 37, 
above the lower lighting means 45. 
A final modification of the prior known beam-splitting cube sections 
comprises opposed component position sensors 47 and 48 mounted at the 
upper portion of the housing of the cube section 37, on opposite sides of 
the z-axis, for sensing the precise vertical location of the undersurfaces 
of the leads 24a of the supported component 24 along the z-axis. In the 
illustrated embodiment of FIGS. 3 to 5, the sensor 47 is a light emitter 
or sender and the sensor 48 is a light receiver to provide an electric eye 
beam across the z-axis at a precise fixed position relative to the focal 
point of the diagonal mirror 42 of the cube section 37. When the light 
beam is initially interrupted an LED is activated to indicate the precise 
positioning of the leads 24a. This is important since any apparatus of the 
present type has a plurality of different component fixturing devices, 
i.e., nozzle housings 19 of different sizes to accommodate the containment 
of electrical components 24 of different sizes and shapes and thicknesses. 
Thus a single alignment top position for the heater/nozzle assembly 16 is 
not possible without resulting in variations in the distance between the 
supported component 24 and the focal point of the diagonal mirror 42. The 
present position sensors 47 and 48 provide a means for accurate uniform 
positioning of all components 24 regardless of their thickness or of the 
depth of the nozzle housing 19 in which they are supported. 
The foregoing modifications of the vision system of an alignment apparatus 
for component leads and pad areas to which they are being soldered enables 
the alignment step to be conducted more precisely, more quickly and more 
comfortably by an operator, reducing eye strain and guesswork. Moreover 
the resultant individual solder connections are more perfect, thereby 
preventing the inadvertent connection of more than one lead to each pad 
area or more than one pad area to each lead, with resultant failure. 
The soldering step is accomplished in conventional manner, such as by 
pre-printing each area with solder deposit, and applying sufficient heat 
to reflow the solder after the alignment is finished, the cube element 37 
is pushed horizontally back into its housing 14, and the heater/nozzle 
assembly 16 is moved downwardly by turning adjustment knob 17 until the 
leads 24a contact the pad areas 27a. The alignment devices of the present 
type include upper and lower heating means, the upper heating means 
comprising a heated air means within the nozzle member 16 for expelling 
heated air through slots 49 present at the undersurface of nozzle housing 
19, as shown in FIG. 2, and the lower heating means 50 comprising a heated 
air-expelling conduit which underlies the pad member on the printed 
circuit board, as shown by FIG. 1. Thus the component leads and pads can 
be heated and reflowed from the top side, and the pad member can be 
pre-heated, and/or heating can be applied after the positioning of the 
component on the pad member. 
The present apparatus is also used for the removal of defective components 
from a PCB, whereby the heater/nozzle assembly 16, carrying an empty 
nozzle housing 19 of the required size, is adjusted downwardly over the 
component, heat is applied to remelt the solder connections, vacuum is 
activated and the heater/nozzle assembly 16 is moved upwardly to lift the 
component away from the PCB, the component being held within the nozzle 
housing 19 by the vacuum through orifice 22. 
It is to be understood that the above described embodiments of the 
invention are illustrative only and that modifications throughout may 
occur to those skilled in the art. Accordingly, this invention is not to 
be regarded as limited to the embodiments disclosed herein but is to be 
limited as defined by the appended claims.