Invited paper

Kinematic and Elastically Averaged Joints:Connecting the Past, Present and Future
Alexander H. Slocum1
Michael A. Chiu1
Eric D. Hobbs2
Gerald Rothenhöfer3
Akinori Yui4
1

Massachusetts Institute of Technology, Cambridge MA USA
2
FormFactor Inc, Livermore CA USA
3
Carl Zeiss SMT, Oberkochen Germany
4
National Defense Academy, Yokosuka Japan                                     !                                                                                                                            

1.

2.

Introduction.

Servo controlled kinematic coupling alignment system

Kinematic couplings provide exact constraint because they use

One example of a successful kinematic interface used in

six known contact points to locate one component with respect toindustry is the Perfect DockTM system developed by Teradyne,another. They have long been known to provide an economical

Inc. in the late 1990’s to provide a robust and accurate andand dependable method for attaining high repeatability in fixtures

reconfigurable interface between their semiconductor Automatic[1-9] and helping to reduce design and manufacturing costs. On

Test Equipment (ATE) and a wide variety of material handlingthe other hand, contact stresses are often very high and noequipment, including wafer probing stations and package

lubrication layer remains between the elements that are in point

handlers. At the time, state of the art bond pad pitches were 40contact. For high-cycle applications it is advantageous to have themicrons and advanced microprocessors might have in excess ofcontact surfaces made from corrosion-resistant materials (e.g.,

5000 electrical connections distributed along the periphery of a 1

stainless steels, carbides, or ceramic materials). When non-cm^2 die. In volume test applications, multiple die may be tested

stainless steel components are used, one must be wary of frettingin parallel at typical rates of once/second.

at the contact interfaces, so steel couplings should only be used

Because of the batch-process nature of volume semiconductor

Less well known are dynamic

test and packaging manufacturing; equipment is reconfigured andkinematic couplings, which allow for servo controlled fine motion

tooling changed at least once per shift by operators who often[10-13].

have little training or education. Contemporary solutions typicallyfor low-cycle applications.

Elastically averaged joints support a system at many points,used pin and bushing interfaces with manually actuated cam-thus preventing large deformations sometimes associated withclamps to lock two sides of the interface; either to align tooling tosupporting a system at only a few points. Many machine

tester or between two pieces of equipment. The non-repeatability

components are made far more accurate than any of theirof this design could result in poor gage reliability, damaged

components by elastic averaging: Hirth or Curvic couplings use

tooling and lost yield. Figure 1 shows a typical image of probe

essentially two face gears that are forced together to allow one

needles with a tip diameter of approximately 40 um, and die bondsurface to be indexed with respect to another and achieve anpads with needle scrub marks.

accuracy (number of gear teeth)1/2 better than either gear itself,

Teradyne developed a reconfigurable interface based on

because of the high forces used to preload the gears together

kinematic couplings using modular ball and groove components

Spline-type flexible couplings can eliminate backlash if theirthat also integrated latching, preload, error sensing and alignment

elements radially flex to create a preload effect [14].

Of[11]. Each module consists of a single ball-groove couple, withparticular interest for the future is the ability of elastically

two contact points on hardened, gothic-arch ground and polishedaveraged joints to be used in semiconductor systems and devices

surfaces to increase contact area and stiffness. Grooves were[15].

typically pinned and bolted to the handling equipment on a single
plane and balls mounted on the tester. The position of each ball

ISUPEN 2013International Symposium on Ultraprecision Engineering and Nanotechnology, Tokyo, Japan, March 13, 2013.

1Invited paper

was adjustable in translational 3 axes. Other surfaces of the ballwill require small adjustable alignments [16]. The fundamental

and groove were shaped to help guide them to safely final

importance of these ultra stiff, adjustable machine elements isposition while minimizing risk of damage or binding as the tester

demonstrated in the design of a grinding machine for 450mm

can weigh more than 500kg and be constrained by a large cablediameter silicon wafers. A new generation of silicon wafer

bundle.

grinding machines is needed to back-grind large (450mm

Figure 2 shows an example of a single ball-groove couple.

diameter) wafers from the production thickness of up to 1mm

Note the outer diameter of the ball has a hardened rim and recess

down to less than 50μm so as to reduce the cost of Si-wafer basedthat engages raised walls on the groove. Prior to reaching its finalcomponents. The grinding process needs to be done in about

position, this rim-wall interface constraints the motion of the90sec (fine-grinding, e.g. -200micron) to 160sec (coarse grinding,tester to +/- 1mm, and thus reducing the lateral motions during thee.g. -600micron). After completion of the fine grinding process

final compression of electrical connectors. Figure 2 also shows

the wafer must be flat to 0.1m/45mm and parallel to 0.6the final version of the production system with covers removed.

m/450mm diameter. The surface roughness must be less thanThis version includes a latching pin through the center of the ballRymax 0.1m and Ra 0.01m. Even though the requiredthat locks to a floating washer in the groove. A DC servo motor

machining forces are <10N, the machine must be extremely rigid

and leadscrew are used to apply a fixed preload force and sensors

in order to achieve the necessary surface quality with a reasonable

can detect whether the system was accurately latched.

grinding feed-rate. Assuming a feed-rate of 5m/min and a total

The above production systems allow only ‘static adjustments’,

allowable error motion of 5nm, a stiffness of >1N/nm is required,

i.e. the final position can be set using a fixture or adjusted in thewhich is many times stiffer than a typical machine tool (0.1 tofield by a technician, but there is otherwise no closed-loop,

0.3N/nm).

adjustment possible. Aversion with 3 z-axis actuators was also

In cooperation with industry, this work had the aim of creating

developed that allowed z-axis motion and planarization in the rolla new machine design philosophy, with an example applicationand pitch axes. This is useful in probe applications where thethat focuses on nano- adjustable kinematic couplings andprober has the ability to move in the translational and yaw axes.

feedback controlled water hydrostatic bearing technology. ThisFigure 3 shows an early version of this system.

new design philosophy is needed to enable the design of a

For most applications, the required accuracy is determined by
the mating geometry of a spring-pin (pogo pin) electrical

relatively small footprint, compact precision machine shown in
Figure 4 [17, 18].

connector and it’s mating pad. The budgeted tolerance for thisIn particular, a ball screw preloaded height adjustable kinematic

mate is typically 40-200um, though some specialized applications

coupling and a magnetically preloaded hydrostatic thrust bearing

may require <40um repeatability. Test systems typically had large

were designed and built. The adjustable kinematic coupling

cable bundles, up to 16” in diameter, for power, signals, andallows for up to 8mm of vertical height adjust and 7N/nm

cooling, that also apply large lateral and rotational loads on thestiffness at 26kN preload. By varying the preload on the coupling

tester. Field tests were performed with repeatability results wellby +/- 10%, in-process nm to micron height and tilt adjustment atwithin the required specification, both as a free body and under>95% of the nominal stiffness is possible.

expected loads, as shown in Table 1.

Under the assumption of a constant flow supply, the hydrostatic

The Perfect Dock system was applied to the portfolio of

bearing achieves a theoretical stiffness of 1N/nm at a 20micron

Teradyne test platforms and continues to be used today, withbearing gap and 7000N combined gravitational and magnetic

many thousands of systems in the field. Furthermore, the general

preload. In practice, the stiffness is limited by the pressure flow

concept of modular kinematic interfaces for macro-docking

characteristics of the supplying pumps. To increase the bearing

applications has since gained broad acceptance in the ATE

stiffness to a required 4N/ nm, various control loops have beenindustry and multiple versions of this system have been adopted

developed and tested, although we find that there is much roomby competitors.

for more advanced pump/control system development [19].

The challenges of the test industry continue to grow and thus
do the opportunities for high repeatability kinematic interfaces.

4.

Elastic averaging based thermocentric fixturing

For example, massively parallel testing of memories requires
repeatable positioning of high density probe cards and emerging

Probe cards are used to test semiconductor die and arearray camera technology will methods to achieve accurate andcomposed of ~3,000 to 80,000 probes that provide electricalrepeatable positioning of multiple lenses and image sensors

signals from a tester to chips on a wafer to test the functionality

during assembly and tests. Modular kinematic interfaces offer aand determine subsequent yield of the wafer manufacturing

robust and easy to apply solution to reconfigurable and repeatableprocess. One of the main constraints is the Interposer pitch. Theinterfacing of manufacturing equipment.

role of the interposer is to provide electrical interconnection fromthe Printed Circuit Board (PCB) to the Space Transformer (SxF).

3.

Servo controlled kinematic coupling for advanced machine tools

The smaller the interposer pitch, the more signals that can be sentfrom the PCB to the SxF.

Next generation precision machines will require ever more

The challenge is to make sure that 60,000-80,000 interposers

rigid elements to achieve the required machining tolerances, yetmake connection to electrical pads on the PCB and the SxF. The2ISUPEN 2013
International Symposium on Ultraprecision Engineering and Nanotechnology, Tokyo, Japan, March 13, 2013.

Invited paper

connections must be reliable, for the life of the probe card as it is“Design of a kinematic coupling for precision applications”,

thermally cycled over a wide temperature range: from -40oC toPrecision Engineering, Vol. 20, pp 46-52.

150oC. The native machining tolerances in the PCB or SxF can[9] Ziegert, J., Tymianski, Vadim., “Air bearing kinematic

not provide sufficient accuracy and therefore it was decided to use

couplings”, Precision Engineering, Vol. 31, No. 2, April 2007,

an elastically averaged connection such as described in [15], butPages 73-82 M.A. Chiu, MIT Mechanical Engineering Doctoral

applied to PCB manufacturing.

thesis, “Roadmap of Mechanical Systems Design for theAs shown in Figure 5, posts were added to a PCB and flexureslots to the SxF.

The flexure slots provide radial degrees ofSemiconductor Automatic Test Equipment Industry”, February
1998.

freedom for differential thermal expansion between the PCB and[10] Culpepper, M.L., Slocum, A.H., and DiBiasio, C.M.,

SxF. The flexure slots also have lateral stiffness and are designed“Design of Detachable Precision Fixtures which Utilize Hard andto provide alignment between the parts and lateral stiffness. The

Lubricant Coatings to Mitigate Wear and Reduce Friction

accuracy of location is about the accuracy of any post/slot pair

Hysteresis,” Proc. of the 2003 Annual Meeting of the American

divided by the square root of the number of posts/slots.

Society for Precision Engineering, Portland, OR, October 2003,

The

solution

wasimplemented

onFormfactor

Inc.’spp. 47–50.

SmartMatrixTM and TouchMatrixTM probe card products that are[11] Chiu, M.A., “Roadmap of Mechanical Systems Design for theused to test semiconductor chips. Alignment accuracy is <50μm

Semiconductor Automatic Test Equipment Industry”, MIT Mech.

and Alignment Repeatability is <2μm.

Eng., Ph.D. thesis, February, 1988.

The cards can beassembled quite easily, without special tooling, therefore enabling[12] G. Rothenhöfer, A. Slocum, M. Paone, X. Lu, A. Yui,field repair. Furthermore, this solution has enabled us to reduce“Elements for the Design of Next Generation, High Stiffness andinterposer pitch by a factor of 2; thereby providing 4x the number

High Accuracy Precision Machines”, 2011 euspen annual mtg, Como,of signals per area compared to previous solutions. This allows

Italy.

for an increase in test parallelism and enhances customer’s
manufacturing throughput.

[13] A. Honda, A. Yui, T. Koiwai, S. Okuyama, G. Okahata, H.
Kobayashi, T. Kitajima, A. Slocum, “Development of Grinding
Machine for 450mm Wafer - 2nd Report: Numerical Analysis of5.

Static Stiffness and Load Capacity of Water Hydrostatic Table”,

Conclusions

There are many applications of deterministic design that can befound in the use of kinematic couplings and their reciprocal,

JSME 9th Manufacturing & Machine tool Conference, Akita
prefecture October 26-27 2012.

elastically averaged interfaces. The key is to keep an open mind

[14] M. Balasubramaniam, H. Dunn, E. Golaski, S. Son, K.

and try both options to find the best solution to use for a given

Sriram, A. Slocum, "An anti backlash two- part shaft withproblem (opportunity).

interlocking elastically averaged teeth", Precis. Eng., Volume 26,
No. 3, pp. 314-330, 2002.

6.

[15] Slocum, A., Weber, Alexis, “Precision Passive Mechanical

References

Alignment of Wafers”, IEEE JMEMS, Dec. 2003, Vol. 12, No. 6,[1] Slocum, A.H., ”Kinematic couplings: A review of designprinciples and applications”, Int. Jou. of Machine Tools andManufacture (2009), doi:10.1016/j.ijmachtools.2009.10.006.
[2] Slocum, A.H., "Design of Three-Groove KinematicCouplings", Precision Engineering, Vo. 14, No. 2, pp 67-76.

pp 826-834.
[16] G. Rothenhöfer, “Elements for the Design of Precision
Machine Tools with High Required Loop Stiffness and their
Application to a Prototype 450mm Si-Wafer Grinder”, PhD
Thesis, Massachusetts Institute of Technology, Aug 2010.

[3] Hale, L, Slocum, A.H., "Optimal design techniques for[17] G. Rothenhöfer, A. Slocum, M. Paone, X. Lu, A. Yui,

Kinematic Couplings", Precision Engineering, Vol. 24, number 2,“Elements for the Design of Next Generation, High Stiffness andpp 114-127.

High Accuracy Precision Machines”, 2011 euspen annual mtg,[4] Schmiechen, P., Slocum, A.H., "Analysis of Kinematic
Systems: a Generalized Approach", Precision Engineering, Vol.
19, No. 1, pp 11-18.

Como, Italy.
[18] G. Rothenhofer, A.H. Slocum, “An Adjustable Kinematic
Coupling for Use in Machine Tools with a Tight Structural Loop”,[5] Slocum, Alexander H. "Kinematic Couplings for Precision
Fixturing -- Part I: Formulation of Design Parameters", Precision
Engineering, Vol. 10, No. 2, 1988, pp 85- 91.

Precision Engineering, Volume 37, Issue 1, January 2013, Pages
61-72.
[19] A.Yui, S. Okuyama1, T. Kitajima1, E. Fujita, A.H. Slocum,[6] Slocum, Alexander H. and Alkan Donmez. "Kinematic

G. Rothenhofer, “Study on Precision Machine Table Equipped

Couplings for Precision Fixturing - Part 2: Experimental

with Constant-Flow Hydrostatic Water Bearings”, Advanced

Determination

Materials Research Vols. 76-78 (2009) pp 664-669, online atof

RepeatabilityandStiffness",

Precision

Engineering, Vol. 10, No. 3, 1988, pp 115-122.

http://www.scientific.net.

[7] Barraja, M. and Vallance, R. "Tolerancing kinematic
couplings." Precision Engineering, Vol. 29, No. 1, 2005, pp 101 –112.
[8] Schouten C.H., Rosielle P.C.J.N., Schellekens P.H.J..
ISUPEN 2013
International Symposium on Ultraprecision Engineering and Nanotechnology, Tokyo, Japan, March 13, 2013.

3

Invited paperFigure 1: Bond pads and probe needles

Figure 4: Servo kinematic coupling height and tilt
adjustable wafer grinding machine.

Figure 2: Z axis servo controlled cinematic coupling unit

Figure 5: elastic slots and pins used in multitude forthermocentric design
Figure 3: “Perfect Dock” three Z axis servo controlled
cinematic coupling units for adjusting height and tilt

Table 1: Perfect Dock adjustable kinematic coupling test results

Condition
No external loads
Side Cable Load
Longitudinal Cable
Load
Vertical Cable
Load4

X
(in.)
.0004
.0006
.0032

Y(in.)
.0002
.0014
.0019

Z
(in.)
.0002
.0006
.0019

θx(arc-sec)2
13
25

θy(arc-sec)21340

θz(arc-sec)
2
27
14

.0027

.0006

.0009

161116

ISUPEN 2013
International Symposium on Ultraprecision Engineering and Nanotechnology, Tokyo, Japan, March 13, 2013.