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Description  |
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The present invention relates to methods of and systems for kinematically
positioning layered surfaces such as plates or sheets of planar material,
being particularly, though not exclusively, directed to laying up thin
sheets in printed circuit board manufacturing and the like, such that the
relative position and orientation of the sheets is defined with great
accuracy and repeatability.
BACKGROUND
Printed circuit boards (PCB) are the common denominator in virtually all
electronics products and the circuit board manufacturing industry is huge.
It is often seen as "low tech", because the manufacture of circuit boards
has generally been accomplished with rather simple tools; but, with the
growing push towards miniaturization, line widths and pad sizes are
decreasing, with the result that current manufacturing techniques are
struggling to maintain alignment between layers in a circuit board. The
problem arises with the fact that circuit boards are made from many thin
layers which each have unique circuit patterns, and which must align so
that interconnection holes (passages) can be formed between them. These
thin sheets are like large pieces of paper and are typically large
fiberglass sheets coated with copper which is then covered with
photoresist, exposed, and then etched. They are exceedingly difficult to
position repeatably. Typically, overconstrained arrangements of slots and
holes are used to fit over close tolerance posts. Currently, the industry
standard is to use precision-punched holes in sheets and precision
alignment posts, which, due to tooling errors and environmental issues,
result in positioning errors on the order of hundreds of microns. For very
thin flexible sheets conventional fixturing methods are not applicable.
The first problem of tooling errors-tolerances between the slot size and
the post size, and errors in their relative positions and orientations;
and the second problem of post wear residing in the use of fiberglass
which is super abrasive, result in a practical positioning repeatability
of only about 100 to 200 microns. Furthermore, dimensions of punched holes
and slots vary with material thickness due to the mechanics of the
glass-epoxy material that forms the very struicture of the circuit board.
Other industries, such as the aircraft industry, also have similar
positioning problems with large material sheets. These same issues apply,
although on a larger scale. The fixturing method that is the subject of
this invention is equally applicable to such and similar applications, as
well, and is being described illustratively for the example of printed
circuit boards.
A key to the design philosophy that guides the use of this invention in all
its different applications is the recognition that the loading is
succinctly different from that in a traditional kinematic coupling.
Accordingly, it is appropriate to review the mathematical background to
the technology--an area called screw theory. Screw theory asserts that the
motion of any system can be represented by a combination of a finite
number of screws of varying pitch that are connected in a particular
manner. This concept is well illustrated for a plethora of mechanisms by
Phillips (J. Phillips, Freedom in Machinery, Vol. I, Cambridge University
Press, London, 1982, p 90.). Earlier work on screws spanned the latter
half of the 19th century, and a detailed summary of such work on screw
theory was published in 1900 (R. S. Ball, A Treatise on the Theory of
Screws, Cambridge University Press, London, 1900). Ball's treatise
describes the theory of screws in elegant, yet easily comprehensible
linguistic and mathematical terms.
Screw theory is an elegant and powerful tool for analyzing the motion of
rigid bodies in contact, but it is not always easy to apply. With respect
to practical implementation of the theoretical requirement for stability,
for traditional precision three-groove kinematic couplings, such as
described by applicant Slocum (A. Slocum, Precision Machine Design,
Prentice Hall, 1991, Section 7.7), stability, and good overall stiffness
will be obtained if the normals to the plane of the contact force vectors
bisect the angles of the triangle formed by the hemispheres (e.g., balls)
that lie in the grooves.
This works well for kinematic coupling of one rigid body to the next. When
one wants to use a kinematic coupling to define the position and
orientation (yaw) of a body in a plane, and then have the body translate
down and contact a plane, however, one needs to use a translational
kinematic coupling as described in applicant's co-pending U.S. patent
application Ser. No. 568,612 (Dec. 7, 1995).
For thinner sections, it is possible to cut grooves in the body, if the
grooves can still be made to have sufficient rigidity to support contact
on angled force lines. This works for applications such as silicon wafers
as disclosed in, for example, applicant's co-pending U.S. patent
application Ser. No. 324,255 (Oct. 17, 1994). Current state of the art,
however, uses non-kinematic solutions involving use of a post that fits
tightly in a hole to form a pivot point, and then a post that fits tightly
in a groove to form a reaction point, where the tight fit in the hole of
the first pin is supposed to provide planar registration. The problem is
that these accurate fits are very hard to realize in practice with great
accuracy and repeatability.
There remains, however, a powerful need for means to align precisely
different layers in a printed circuit board lay-up prior to heating and
pressing the layers to bond them together, as well as at every step in the
process that creates the layers in the first place. The issue is that the
sheets that make up the PCB layers are very thin and floppy. They are
typically made of fiberglass sheets on the order of a fraction of a
millimeter in thickness. In addition to not being able to support any
normal forces (to the plane of the sheet) it is not possible to form
shaped grooves in the sheet. It is only practical to cut slots into the
sheets, where the cut is straight through the sheet.
In the reprographics industry, when a large stack of paper is to have its
edges aligned, such as prior to binding, the paper is put into a vibrator
with walls on 2 sides at a compound angle. This shakes all the sheets down
into a common corner. Such a technique is not practical for PCB sheets,
however, because the sheets are so difficult to cut that sub-millimeter
registration would never be achievable, though it would be possible to
precision-punch registration grooves into the sheets.
Thus a special design has been needed to develop kinematic couplings
specifically tailored for application to the problems of accurately
positioning and orienting thin sheets of materials.
OBJECTS OF THE INVENTION
An object of the present invention, accordingly, is to provide a new and
improved method of and systems for kinematically positioning and orienting
planar surfaces such as sheets of materials.
A further object is to provide such a technique in which kinematic
preloading and holding in place of a stack of thin sheets of material is
enabled.
Another object of the invention is to optimize the selection of the best
orientation of slots to be cut into the sheet, relative to the direction
which gravity would load the sheet when it is positioned on an inclined
plane with posts or pegs, each post smaller than each of the respective
slots and engaging the slots to form a kinematic (deterministic) fixturing
system to define the position of the sheet with respect to the posts with
a very high degree of repeatability.
Other and further objects will be explained hereinafter and are more fully
delineated in the appended claims.
SUMMARY
In summary, the invention embraces a system for kinematically positioning
planar surfaces such as sheets having, in combination, a planar mount for
resting the surfaces thereupon; each surface having a plurality of
openings spaced along and near edges thereof; the planar mount being
provided with a plurality of protrusions corresponding, located and spaced
similarly to the openings and of less cross-dimension than that between
the walls bounding the openings, such that, as the surface is mounted on
the planar mount, the protrusions thereof are loosely received within the
corresponding surface openings; the mounted surface being subjected to an
applied preload force having a component along the plane of the surface to
cause the protrusions to engage and contact points of the walls of the
corresponding openings, uniquely to define the planar position and
orientation of the surface upon the mount.
With this system and method, thin sheets of material can be positioned
kinematically, such as for laying up sheets in printed circuit board
manufacturing, where each sheet has three precisely formed and positioned
(e.g., punched) slots that fit loosely over three corresponding
cylindrically shaped posts, such that when a bias force, such as gravity
from a tilted plane or a coming action, or expanding bladder on the posts,
is applied, the sheets are referenced against one side of the slots to
effect a planar kinematic coupling with the relative planar position and
orientation of the sheets defined with great accuracy and repeatability.
An entire factory system. indeed, can use this concept, where each piece
of precision manufacturing equipment employs such planar kinematic
coupling to achieve great accuracy in the manufacture of printed circuit
boards (or the like) to allow for the use of ever smaller electronics
components.
Preferred and best mode designs and techniques are hereinafter detailed.
DRAWINGS
The invention will now be described with reference to the accompanying
drawing in which:
FIG. 1 is a schematic view of a traditional prior art kinematic coupling
and the graphical methods used to optimize groove orientation;
FIG. 2 is an isometric view 6f a sheet of material precisely located by
having three precision punched slots spaced along the edges of a sheet,
preferably mounted on an inclined plane to provide a gravity pre-load or
bearing force that enables engagement with three corresponding precisely
located posts on a plane;
FIG. 3 is an isometric view of a sheet of material precisely located by
having the three punched slots at angles in the sheet to form the basis of
a planar kinematic coupling, which then engage three posts on a plane;
FIG. 4 is a schematic diagram of the geometry of the planar kinematic
coupling which defines the convention used in the analysis;
FIG. 5a is an isometric cutaway view of a precision locating post that can
be used with an expandable bladder to contact the edge of a groove in a
planar kinematic coupling, and with the expanding bladder acting to
preload the kinematic coupling so that a stack of kinematically located
sheets will not slip, such as when pressure is applied during thermal
curing;
FIG. 5b is an isometric cutaway of the post in FIG. 5a, where a circular
shaped bladder is used for simplicity;
FIGS. 6a, 6b, 6c, and 6d are plan views that show a progression of
components with kinematic coupling slots and preload force vectors in
order of increasing self-centering action;
FIG. 7 is a plan view that shows the component of FIG. 6d provided with an
added preload slot and actuatable preload post at the bottom of the sheet;
and
FIGS. 8a and 8b are a close-up plan view of an application of the invention
to an electronics package with a ball-grid-array of contacts, and special
ball-grid kinematic features to align chips to contacts on the printed
circuit board, where once again, the key is to use kinematic mounts to
align the flat plane surfaces together.
PREFERRED EMBODIMENT(S) OF THE INVENTION
FIG. 1 is a diagram of prior art kinematic couplings where one object or
body containing 3 vee-grooves 20a, 20b, and 20c mates with corresponding
balls 21a, 21b, and 21c of another object or body to be coupled to the
first. When each ball mates within each respective groove, two points of
contact occur which uniquely define the position of the one body with
respect to the other (six points of contact define six degrees of
freedom). In order to obtain approximately equal stiffness in all
directions, one must properly orient the grooves with respect to one other
in accordance with the following rules. First, to achieve stability, the
planes that pass through the contact points must form a closed triangle
such as 25. Next, the optimal shape of the triangle should be such that
the normals to the sides of the triangles (the groove axes), such as 24,
should bisect the angle of the opposed angle. The result is that the
normals will all meet at the coupling centroid 23 of the triangle 22
formed by the coupling balls 21a, 21b, and 21c.
While the above sets out the geometrical requirements for kinematic
coupling generally, there are significant practical problems, as before
described, in precisely aligning different planar-surface layers in a
printed circuit board lay-up, for example prior to heating and pressing
the layers to bond them together, as well as at every step in the process
of creating the layers in the first place. The issue is that the sheets
that make up the PCB layers are very thin and floppy--typically of
fiberglass sheets on the order of a fraction of a millimeter in thickness.
In addition to not being able to support any normal forces (to the plane
of the sheet), it is not even possible to form shaped grooves in the
sheet; it being only practical to cut slots or other notches into the
sheets, where the cut is straight through the sheet.
FIG. 2 shows such a sheet 30 with rectangular notches or slots 31a, 31b,
and 31c cut in the sides of the planar sheet. These notches can rest
against precisely located corresponding round protrusions or posts 32a,
32b, and 32c of lesser cross dimensions, on an inclined planar mounting or
support surface 27, allowing for precision registration of the sheet 30.
In this embodiment, the two open rectangular notches 31b and 31c are
spaced near opposite ends of the left-bottom edge of the sheet 30, and the
third notch 31a is located near the upper right corner on the right-hand
inclined edge. The posts 32a, 32b and 32c are positioned on the planar
surface (indicated at, say, 45.degree., more or less), to mount the sheet
with opposing diagonal corners along the Y and X axes, respectively.
Such a precision registration, while useful for some sheet materials, may
require modification for thin sheet materials that may be sensitive to
thermal expansion; and, with the position defined along the edges, the
thermal error motion of the critical center position of the sheet can be
very large. With respect to stability, furthermore, while the sheet 30
could be kept from falling off the inclined plane by use of a vacuum chuck
or the like behind the sheet, other than the preload force Mg offered by
gravity, there is no way to force registration against the notches. When
many layers are stacked, they are subject to pressing forces, such as when
they are to be bonded together, and the sheets may slide in the X and/or Y
directions with respect to one another.
Another embodiment of the invention accordingly uses closed slots in the
sheets to create a preloadable kinematic coupling as shown in FIG. 3,
wherein the inclined plane 7 mounts a sheet 8 with its edges respectively
parallel to the X and Y axes, and its rectangular or square slots 6a, 6b,
and 6c receiving and engaging location and alignment posts 5a, 5b, and 5c
protruding from the plane. It is important to note that because the design
is deterministic (kinematic), neither the posts nor slots need be accurate
in size or location in order to acheieve a high degree of repeatability.
This is a major distinction over the prior art which required accurate
pins and holes in order to achieve even mediocre repeatability. They only
have to be accurate in size and position if location accuray is required.
The slots are located and aligned with respect to one other to maximize
kinematic coupling stability according to the angle bisection rules
described earlier in connection with the diagram of FIG. 1. While these
rules are not a condition for repeatability, they are a condition for
optimizing repeatability. In the embodiment of FIG. 3, the centroid 4 is
symmetrically defined with respect to the slots, and the sheet is not in
the compound angle position of FIG. 2, which can be more convenient for
some manufacturing applications. Note that with this type of slot
orientation, with the planes through the contact points forming a closed
isosceles or other triangle, thermal growth errors will radiate out from
the center of the sheet, and the center of the sheet will effectively
remain stationary. This means that the edges of the sheet will experience
half the thermal error of a sheet constrained as shown in FIG. 2.
Furthermore, this type of coupling hangs the sheet, so that it is in
tension, with the lower slot primarily acting to define the angular
orientation; thus a buckling/wrinkling mode is avoided which would
decrease the repeatability of location of the center of the sheet.
In order to optimize the slot location and orientation, the coordinate
system is modeled as in FIG. 4, where there are three generic grooves and
contact points (posts, shown here as arrows) 1, 1' and 2, 2', and 3, 3',
respectively. Each of these pairs has coordinates x.sub.i, y.sub.i and
orientation .alpha..sub.i, where i=1, 2, 3, respectively. The default is
that the coupling would be symmetrically located about the center of mass
4, and have a radius r.sub.c. The convention for the analysis is that
positive forces are oriented in a counterclockwise direction, as is the
orientation angle .alpha..
When the sheets 8 of FIG. 3 are placed on the posts 5 to engage the slots
6, slight vibration will ensure that friction effects are overcome, and
the sheets have settled into place. Where required, a step may be to lock
them in place. To do this, a modified post 15a shown in FIG. 5a can be
used. This post has a central hole and radial slot to accommodate an
expanding bladder 16a, shown here as having a dumbbell shape with an
inside inflatable cavity 17a to ensure it does not get pulled out when it
is deflated. Many other shapes may also be used. As shown in FIG. 5b, a
simple cylindrical bladder 16b with central inflatable cavity 17b, set
back into the post 15b, would also work, although it would have less range
of motion. An alternative to a bladder would be a sliding wedge or cam
action; but, in some applications, this may be too hard for a slot in a
sheet-type material.
Expanding on the issue of self-centering, it is important in the fixturing
of sheets or other components, where the preload force effecting
repeatable location has a component parallel to the plane against which
the sheets or other components are to be fixtured or rested, that the
worker or the robotic placing of the sheet or other component on the posts
to engage the slots achieves a very high degree of repeatability. FIG. 6a
shows a classic arrangement for such a kinematic coupling, where the sheet
or other component 70 has three rectangular slots 101a, 101b, and 101c
that receive and engage round posts 102a, 102b, and 103c, respectively.
Slots 101a and 101b are oriented at appropriate inclined angles at left
and right upper corners so that the top two slots bear the brunt of the
preload force component. The third slot 101c, located mid-way of the
bottom edge, counters any moment about the centroid of the sheet or other
component. When the sheet or other component 70 is placed so the posts are
loosely received in the slots and the preload force is applied as shown
(e.g., gravity), the posts, being of smaller cross-dimension than that
between the walls bounding the slots, engage only points at one side of
the slots, so that the entire system is actually neutrally stable.
Location repeatability, however, is not optimum.
By rotating the slots with respect to the force vector, the situation shown
in FIG. 6b is obtained, where the sheet or other component 80 again has
three slots 111a, 111b, and 111c that engage posts 112a, 112b, and 113c,
respectively, but with the collection of slots/posts rotated 90.degree.
counter-clockwise from the configuration in FIG. 6a. The result is a
condition where the preload force is resisted by post-slot force
components in all three slots. Thus greater repeatability is achieved.
Physically, any one post acts as a pivot point.
Taking this concept of a pivot point, and trying further to maximize the
forces between the posts and the slots, the configuration shown in FIG. 6c
may be obtained. Here, the sheet or other component 90 has a central
bottom edge vertical rectangular slot 121c, and upper right corner
horizontal rectangular slot 121a, and an inclined rectangular upper left
corner slot 121b, receiving and engaging posts 122c, 122a and 122b,
respectively. Slot 121a engaging post 122a acts as the primary pivot
point. It cannot support any load in the X direction. Slot 121b engaging
post 122b minimally resists any moment about the pivot point because its
force vector is substantially aligned towards post 122a. However, because
slot 121a and 121b engaging posts 122a and 122b, respectively, both have
substantial force vectors to resist the preload force (e.g., gravity
acting on every portion of the sheet or other component), the sheet or
other component hangs by these two slots. Thus, if the component is of
sheet material, it would hang without buckling or wrinkling. There is
still a substantial moment to be resisted, and that is countered by the
action of post 122c engaging slot 121c. With the slots widely spaced from
one other, the forces will preload the system, and contact stresses
between posts and slots will be low to prevent such buckling; and thus,
repeatability will be high. To further minimize the chance of buckling,
the slot 121c can be located at the lower left corer of the sheet.
The overall philosophical goal of the invention is thus to create a pivot
point, and an arrangement of slots and posts to create the maximum force
between each slot and post, while hanging the sheet from two upper slots
to prevent buckling and while keeping the slots as far away from each
other as possible also to prevent buckling.
A condensed form is shown in FIG. 6d. Here the sheet 100 has a single
larger hole 131 (such as a tilted square or diamond or a gothic arch to
minimize contact stress and buckling) in one upper corner of the sheet
that engages a smaller post 132a, so the fit is loose. With the use of the
inclined plane of the invention to provide a preload force on the sheet,
the post 132a engages two edges 131a and 131a' of the hole 131. Rotation
of the sheet 100 about the post 132a is then opposed by a post 132b
engaging a rectangular diagonal slot 131b located at the opposite upper
corner of the sheet so the moment is maximized. The slot 131b that
counters the moment could be located at the top of the sheet with an
orientation angle .alpha. of 180.degree., so the sheet completely hangs
and therefore does not buckle. Alternatively, the slot 131b could be
located at the bottom of the sheet with an orientation angle .alpha. of
270.degree.. The prime advantage of this design is that only two features
need to be cut into the sheets. Note that in any hanging design, thermal
growth errors will emanate from the hanging points, so the sheet center
location repeatability will be affected, unless good temperature control
is maintained from sheet-to-sheet.
It may be desirable, furthermore, to provide an additional force to that of
gravity for enhanced preload; or, if the plane must be flat, the effect of
gravity must be added. This can be obtained as shown in FIG. 7, where the
sheet 110 has the same geometry as the system in FIG. 6d, with post 142a
engaging hole 141 at points 141a and 141a', and post 142b engaging slot
142b, and a further slot 141c added at the bottom of the sheet, where an
expandable post 142a, such as shown in FIGS. 5a or 5b, or a rotating
cam-shaped post, or a translating post, engages the bottom side of slot
141c. In FIG. 7, the post 142a is shown provided with a rolling expandable
surface 142a' to provide preload while not creating frictional tractive
forces. This preloads the sheet 110 in tension and locates it
kinematically so that the sheet is not required, if desired, to be located
on an inclined plane. For maximized repeatability, however, the post 142a
should have a rotatable outer sleeve 142a', or free linear motion parallel
to the slot. The concept of not applying tractive forces between the posts
and slots is applicable to any of the above configurations as a means for
further reducing buckling or tractive-force-induced non-repeatable
strains, all of which would reduce repeatability.
It is possible to analyze the design, and for a particular sheet or other
component and loading, one can create different optimization criteria, for
example, by using the SOLVER function in the Microsoft.TM. spreadsheet
Excel.TM.. Such a spreadsheet follows, illustrating how one skilled in the
art of mechanics can optimize the groove location and orientation to
maximize performance.
__________________________________________________________________________
Enter numbers in bold
Weight of sheet (N)
2.00
Incline (deg) (90 is vertical)
45.00
Preload (NO), P (- indicates down)
-1.41
Grooves symmetric about the CG?
yes If "no", manually enter coordinates to
the right
Nominal coupling radius (mm)
100.00
Rotation of coupling (deg)
-30.00 Find below using solver (positive
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ccw)
Coupling Coordinate system is
assumed to be located at the CG of the PCB sheet
Alpha (before
Coupling grooves'
rotate coupling)
coordinates
Location of grooves wrt CS
(deg) x (mm)
y (mm)
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First groove 0.00 100.00
0.00
Second groove 120.00 -50.00
86.60
Third groove 240.00 -50.00
-86.60
Equilibrium equations
.SIGMA.Fx = 0 0.00 -0.87
0.87
0.00
F1 =
0
.SIGMA.Fy = 0: 1.00 -0.50
-0.50
1.00
F2 0
.SIGMA.FM = 0: 100.00 100.00
100.00
0.00
F3 0
Preload from weight, incline
0.00 0.00
0.00
1.00
F4 -1.4
__________________________________________________________________________
Coupling groove forces (should be equal for a balanced design)
Solver can be used to rotate the coupling until the forces are equal in
magnitude
F1 = 0.94
F2 = -0.47
F3 = -0.47
F4 = -1.41
Force equilization (minimize)
0.47
Coupling rotation angle
-30.00
to obtain even groove loading
__________________________________________________________________________
The physical characteristics of the coupling are entered, and then the
equilibrium equations are used to balance the forces and moment on the
system. A strong condition for repeatability is that each groove must bear
a substantial amount of force, or else the same may risk being weakly
stable, or even neutrally stable. Such would be the case, for example, if
the two grooves were symmetric about the positive Y axis, and the third
groove lay along the negative Y axis. To optimize the design, the
spreadsheet seeks to equalize the magnitude of the forces. It does this by
rotating the coupling about the centroid, to in effect rotate the sheet to
virtually obtain the orientation shown in FIG. 2. Note that so long as the
criteria for a closed triangle by the planes through the contact points is
met, as shown in FIG. 1, the groove orientations can be changed to
optimize the forces in the grooves to maximize the self-locating effect of
using gravity to preload the coupling.
For example, in FIG. 3, the groove 6b has an orientation .alpha..sub.2 of
120.degree.. If the angle were 90.degree., the sheet tends to have better
self-centering capability for some larger rectangular sheets. Through a
combination of experimentation and tuning of the desired optimization
criteria, one skilled in the art of kinematics can customize the design to
obtain maximum repeatability for the materials to be positioned with this
novel design.
Once the sheets are positioned, the expanding bladder system, shown in FIG.
5, can be used to preload the coupling, and because the slots are in
effect in tension, there are no buckling issues associated with putting
preload forces on a thin sheet. Once a stack of sheets is preloaded,
operations such as pressing and heating can be completed without worry of
sheet slippage. In fact, for single sheet processes, as in exposure tools
and test tools, it may not be required to use the expanding bladder to
hold position. The plane angle and gravity preload may be sufficient.
These different embodiments may each have their own application niche for
different types and geometries of materials and processes. The fundamental
advancement is that now as a sheet or other component is processed in a
multi-step process that passes it off from machine to machine, whenever
the process (such as printing or drilling) requires precision alignment
with respect to the component, a very high degree of precision, on the
order of microns or less, is obtained with minimal cost and effort. The
exemplary illustration of the manufacture of printed circuit boards where
multiple layers are made individually and then bonded together, has been
described in detail above. The alignment principles of the invention,
however, as before explained, are applicable to other products--for
example to the direct location of silicon chips with ball-grid-array
contacts directly to circuit boards since now the circuit boards can be
made accurately enough to receive the chips; and the chips themselves may
even have kinematic features to align them to the mounting points on the
boards.
FIGS. 8a and 8b illustrate the use of the kinematic concepts described
above for locating other types of flat plane objects with respect to one
other, as for the case of an electrical component to be mounted to a
circuit board. Here, a circuit board 199 has an array of contact points
211, but it also has protruding features 205 and 206. These can be solder
bumps or posts. Electronics component 200 has an array of electrical
contacts 210 that is to be connected to corresponding contacts 211 on
printed circuit board 199. In order to facilitate the relative position
and alignment between electronics component 200 and printed circuit board
199, the electronics component is provided with protrusions 201, 202, 203,
and 204 in one corner, and protrusions 201', 202', 203', and 204' in
another corner. It would also be possible to have two sets of three
protrusions, but here it was desired to keep the same basic pattern. When
the electronics component 200 is flipped over and placed on the printed
circuit board 199, protrusions 201, 202, 203, and 204 effectively surround
protrusion 205 on the printed circuit board. In addition, protrusions
201', 202'. 203', and 204' surround protrusion 206. This particular
embodiment is overconstrained, but enough tolerance is easily built into
the system to obtain sufficient alignment; and when solder balls are used,
they will melt and stay aligned to their respective contacts by the effect
of surface tension. To obtain additional functionality, the alignment
features can also be ground connections for the component.
FIGS. 8a and 8b represent one such particular alignment principle. The mold
kinematic coupling grooves may be molded into the electronics component
package, such as three grooves, or three slots, which could engage
ball-type features on the printed circuit board, or vice versa. The unique
feature, however, as with the printed circuit board layers mentioned
above, is the use of essentially kinematic features built into the printed
circuit board layers, the printed circuit board itself, and the
electronics components, also. Thus, from a coarse (board level) to fine
(component level) scale, all element positions are determined by physical
features.
Further modifications of the invention will also occur to persons skilled
in the art, and all such are deemed to fall within the spirit and scope of
the invention as defined by the appended claims.
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