WO2005068958A1 - Structure and method for packaging micro strain sensors - Google Patents

Structure and method for packaging micro strain sensors Download PDF

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Publication number
WO2005068958A1
WO2005068958A1 PCT/US2005/000256 US2005000256W WO2005068958A1 WO 2005068958 A1 WO2005068958 A1 WO 2005068958A1 US 2005000256 W US2005000256 W US 2005000256W WO 2005068958 A1 WO2005068958 A1 WO 2005068958A1
Authority
WO
WIPO (PCT)
Prior art keywords
sheet base
sensor
strain
substrate
tensile strength
Prior art date
Application number
PCT/US2005/000256
Other languages
French (fr)
Inventor
Wen H. Ko
Jun Guo
Hung-I Kuo
Original Assignee
Case Western Reserve University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Case Western Reserve University filed Critical Case Western Reserve University
Publication of WO2005068958A1 publication Critical patent/WO2005068958A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
    • G01L1/2287—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges constructional details of the strain gauges
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
    • G01L1/2287—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges constructional details of the strain gauges
    • G01L1/2293—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges constructional details of the strain gauges of the semi-conductor type

Definitions

  • the present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to a structure and method of packaging a micro
  • micromachined sensors (hereinafter “micro sensors”) are sold worldwide in very large volumes, and are used in a wide variety of
  • micro sensors is the packaging which effects reliability, cost, and performance of such micro
  • the present invention provides a micro strain sensor package generally comprising a
  • the sheet base is configured for attachment to a substrate and has a given length L and a given tensile strength. An opening extends through the sheet base.
  • the senor has first and second anchors with at least one sensor element therebetween.
  • the sensor has a given length Ls and a given tensile strength.
  • the sheet base given length L is greater than
  • the sensor given length Ls and/or the sheet base given tensile strength is greater than the sensor
  • the sensor is attached to the sheet base with the anchors positioned on opposite sides of the opening through the sheet base.
  • the present invention further provides a method of securing a micro strain sensor
  • the method comprises the steps of providing a sheet base having first and second spaced apart weld zones. Attaching a strain sensor to an upper side of the sheet base between the first and second weld zones. Applying a soft adhesive to an underside of the sheet
  • FIG. 1 is a side elevational view of a micro strain sensor package according to a first
  • Fig. 2 is a top plan view of the sensor package of Fig. 1 with the protective cover
  • FIG. 3 is a top plan view of a micro strain sensor package according to a second
  • Fig. 4 is a side elevational view of the sensor package of Fig. 3.
  • Fig. 5 is a graph comparing the output of a metal foil strain sensor with and without
  • strain enhancement packaging of the present invention is the strain enhancement packaging of the present invention.
  • the sensor package 10 is configured for attachment to a substrate 12, for example, a steel substrate.
  • the preferred method of attachment of the sensor package 10 to the substrate 12 will be described hereinafter.
  • the sensor package 10 includes a
  • the sheet base 30 is preferably manufactured
  • the stainless steel sheet base is preferable to protect the sensor from
  • strain sensor 20 interface electronics 50, for example, an integrated circuit 52, cables 54 and a
  • electronics 50 are preferably attached using conventional adhesives, but may be attached in other
  • a protective cover 34 preferably covers the strain sensor 20 and, if provided, the
  • interface electronics 50 and is attached to the sheet base 30.
  • the strain sensor 20 generally comprises sensor elements 26 extending between
  • anchors 22 and 24 are attached to the sheet base 30 on opposite sides of
  • the strain sensor 20 may have various configurations
  • foil strain sensors including, but not limited to, foil strain sensors, capacitive strain sensors, and piezoresistive
  • the sensor element 26 has a length L s between the anchors 22 and 24.
  • the sheet base 30 is preferably configured to enhance the strain detected by the
  • strain sensor 20 that is, the design malces the strain seen by the sensor element 26 larger than the
  • the sheet base 30 has a length
  • the mechanical strength of the base sheet 30 under the sensor 20 is reduced, for example, by controlling the size of the opening 32. Additionally, it is preferable to provide a base sheet 30 having a tensile strength relatively larger than the tensile strength of the sensor element 26 and the base support under the sensor 20.
  • Enhancement factor can be designed with various values and is preferably designed to be 1.5 to
  • the enhancement factor can be controlled by controlling the length L of the sheet base 30
  • FIGs. 3 and 4 illustrate a sensor package 110 that is a second embodiment of the
  • the sensor package 110 is similar to that of the previous embodiment, but
  • the strain sensor 120 utilizes a metal foil strain sensor 120 attached to the sheet base 130.
  • the strain sensor 120 utilizes a metal foil strain sensor 120 attached to the sheet base 130.
  • sensor elements 126 extending between anchors 122 and 124 that are attached to a foil
  • the foil sheet 128 is in turn attached to the sheet base 130 with the anchors 122 and
  • the sensor element 124 positioned on opposite sides of the opening 132 in the sheet base 130.
  • a preferred method for rapid bonding of sensor package 10, 110 to the substrate 12 is described with reference to Figs. 1-4.
  • the sensor 20, 120 is bonded on to the sheet base 30, 130
  • a "soft” adhesive 40 is applied to the center portion of the sheet
  • both ends of the sheet base 30, 130 are spot welded, as illustrated at 42, on to the substrate 12.
  • the welded spots 42 provide "hard” attachment of sensor package 10, 110 to the substrate 12, and allow the package 10, 110 to follow the strain of the substrate 12 at both ends.
  • Additional hard bonding material 44 may be added under welded spots 42 to supplement the
  • the whole process can be completed in/under 30 seconds.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

Abstract

A micro strain sensor package generally comprising a sheet base and a sensor. The sheet base is configured for attachment to a substrate. An opening extends through the sheet base. The sensor has first and second anchors with at least one sensor element therebetween. The sensor is attached to the sheet base with the anchors positioned on opposite sides of the opening through the sheet base. The present invention further provides a method of securing a micro strain sensor package to a substrate.

Description

STRUCTURE AND METHOD FOR PACKAGING MICRO STRAIN SENSORS
BACKGROUND
[0001] The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to a structure and method of packaging a micro
strain sensor.
[0002] Sensors have been under intense development during the last two decades, and many
devices have been developed and commercially produced. Micromachined sensors (hereinafter "micro sensors") are sold worldwide in very large volumes, and are used in a wide variety of
application areas. One of the most important manufacturing steps for the mass production of
micro sensors is the packaging which effects reliability, cost, and performance of such micro
sensors.
SUMMARY
[0003] The present invention provides a micro strain sensor package generally comprising a
sheet base and a sensor. The sheet base is configured for attachment to a substrate and has a given length L and a given tensile strength. An opening extends through the sheet base. The
sensor has first and second anchors with at least one sensor element therebetween. The sensor has a given length Ls and a given tensile strength. The sheet base given length L is greater than
the sensor given length Ls and/or the sheet base given tensile strength is greater than the sensor
tensile strength. The sensor is attached to the sheet base with the anchors positioned on opposite sides of the opening through the sheet base.
[0004] The present invention further provides a method of securing a micro strain sensor
package to a substrate. The method comprises the steps of providing a sheet base having first and second spaced apart weld zones. Attaching a strain sensor to an upper side of the sheet base between the first and second weld zones. Applying a soft adhesive to an underside of the sheet
base between the first and second weld zones. Adhering the sheet base to the substrate with the
soft adhesive. Applying at least one spot weld between the sheet base and the substrate in each
weld zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Fig. 1 is a side elevational view of a micro strain sensor package according to a first
embodiment of the present invention.
[0006] Fig. 2 is a top plan view of the sensor package of Fig. 1 with the protective cover
removed for clarity.
[0007] Fig. 3 is a top plan view of a micro strain sensor package according to a second
embodiment of the present invention.
[0008] Fig. 4 is a side elevational view of the sensor package of Fig. 3.
[0009] Fig. 5 is a graph comparing the output of a metal foil strain sensor with and without
the strain enhancement packaging of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] The present invention will be described with reference to the accompanying drawing figures wherein like numbers represent like elements throughout. Certain terminology, for
example, "top", "bottom", "right", "left", "front", "frontward", "forward", "back", "rear" and
"rearward", is used in the following description for relative descriptive clarity only and is not intended to be limiting.
[0011] Referring to Figs. 1 and 2, a sensor package 10 that is a first embodiment of the present invention will be described. The sensor package 10 is configured for attachment to a substrate 12, for example, a steel substrate. The preferred method of attachment of the sensor package 10 to the substrate 12 will be described hereinafter. The sensor package 10 includes a
strain sensor 20 positioned on a sheet base 30. The sheet base 30 is preferably manufactured
from stainless steel. The stainless steel sheet base is preferable to protect the sensor from
mechanical abrasion, electrical interference, and chemical reactions, and to have material
properties close to the steel substrates. Other materials may also be selected. In addition to the
strain sensor 20, interface electronics 50, for example, an integrated circuit 52, cables 54 and a
cable clamp 56, may also be attached to the sheet base 30. The strain sensor 20 and interface
electronics 50 are preferably attached using conventional adhesives, but may be attached in other
manners. A protective cover 34 preferably covers the strain sensor 20 and, if provided, the
interface electronics 50, and is attached to the sheet base 30.
[0012] The strain sensor 20 generally comprises sensor elements 26 extending between
anchors 22 and 24. The anchors 22 and 24 are attached to the sheet base 30 on opposite sides of
an opening 32 in the sheet base 30. The strain sensor 20 may have various configurations
including, but not limited to, foil strain sensors, capacitive strain sensors, and piezoresistive
strain sensors. The sensor element 26 has a length Ls between the anchors 22 and 24.
[0013] The sheet base 30 is preferably configured to enhance the strain detected by the
strain sensor 20, that is, the design malces the strain seen by the sensor element 26 larger than the
strain applied to the substrate 12. To facilitate strain enhancement the sheet base 30 has a length
L that is longer than the sensor element length Ls. Additionally, the mechanical strength of the base sheet 30 under the sensor 20 is reduced, for example, by controlling the size of the opening 32. Additionally, it is preferable to provide a base sheet 30 having a tensile strength relatively larger than the tensile strength of the sensor element 26 and the base support under the sensor 20. When the strain/stress is transferred from substrate 12 to the base sheet 30 and to the sensor 20,
most of the strain/displacement corresponding to the length L is transferred to the sensor with
length Ls. The ratio of strain seen by the sensor element 26 and that of the substrate 12 is enhanced, with the enhancement factor expressed as K = f (L /Ls) wherein f is the empirical
coefficient depending on the adhesives used and the base and sensor material properties. The
enhancement factor can be designed with various values and is preferably designed to be 1.5 to
3. The enhancement factor can be controlled by controlling the length L of the sheet base 30
relative to the sensor element length Ls, and by controlling the relative strength of the sheet base
30 relative to the sensor element 20 strength and the strength of the base supporting the sensor
element 20.
[0014] Figs. 3 and 4 illustrate a sensor package 110 that is a second embodiment of the
present invention. The sensor package 110 is similar to that of the previous embodiment, but
utilizes a metal foil strain sensor 120 attached to the sheet base 130. The strain sensor 120
includes sensor elements 126 extending between anchors 122 and 124 that are attached to a foil
sheet 128. The foil sheet 128 is in turn attached to the sheet base 130 with the anchors 122 and
124 positioned on opposite sides of the opening 132 in the sheet base 130. The sensor element
120 has a length Ls that is equal to the length of the foil sheet 128. Again, strain enhancement
can be controlled by controlling the length L of the sheet base 130 relative to the sensor element
length Ls, and by controlling the relative strength of the sheet base 130 relative to the sensor
element 120 strength and the strength of the base supporting the sensor element 120.
[0015] A preferred method for rapid bonding of sensor package 10, 110 to the substrate 12 is described with reference to Figs. 1-4. The sensor 20, 120 is bonded on to the sheet base 30, 130
using conventional adhesive. A "soft" adhesive 40 is applied to the center portion of the sheet
base 30, 130 and attaches the sheet base 30, 130 to the substrate 12. The "soft" adhesive helps to prevent buckling of the sheet base 30, 130 under compression and to allow the sheet base 30, 130 to slide horizontally with small sheer force. After the sheet base 30, 130 is attached onto the substrate 12, both ends of the sheet base 30, 130 are spot welded, as illustrated at 42, on to the substrate 12. The welded spots 42 provide "hard" attachment of sensor package 10, 110 to the substrate 12, and allow the package 10, 110 to follow the strain of the substrate 12 at both ends.
Additional hard bonding material 44 may be added under welded spots 42 to supplement the
strength of the spot welding bonds. The whole process can be completed in/under 30 seconds.
[0016] Metal foil strain sensor packages similar to that shown in Figs. 3 and 4 were manufactured and tested on a computer controlled four point bend beam apparatus. Preliminary
testing results using foil and piezoresistive sensors confirmed the strain enhancement factor of
1.3 to 2.1 as shown in Fig. 5. A sensor package bound to the substrate 12 as illustrated has been
found to survive cycles of test, from 0 to 2500με.

Claims

What is claimed is:
1. A micro strain sensor package comprising: a sheet base configured for attachment to a substrate, the sheet base having a given length
L and a given tensile strength; an opening through the sheet base; and a sensor having first and second anchors with at least one sensor element therebetween,
the sensor having a given length Ls and a given tensile strength, the sheet base given length L
being greater than the sensor given length Ls or the sheet base tensile strength being greater than
the given tensile strength; wherein the sensor is attached to the sheet base with the anchors positioned on opposite
sides of the opening through the sheet base.
2. The micro strain sensor package of claim 1 wherein the sheet base given length L is greater than the sensor given length Ls and the sheet base tensile strength is greater than the
given tensile strength.
3. The micro strain sensor package of claim 1 wherein the sensor is selected from the group
of foil strain sensors, capacitive strain sensors and piezoresistive strain sensors.
4. The micro strain sensor package of claim 1 wherein the sheet base is manufactured from stainless steel.
5. The micro strain sensor package of claim 1 wherein the sensor and sheet base are each manufactured from a desired material and the sensor is bonded to the sheet base with a bonding agent and the sensor senses a strain applied to the substrate with an enhancement factor of K wherein K = f(L/Ls) with f being an empirical coefficient dependent on the sheet base and sensor
materials and the bonding agent material.
6. The micro strain sensor package of claim 5 wherein the enhancement factor K is between
1.5 and 3.
7. A method of securing a micro strain sensor package to a substrate comprising the steps
of: providing a sheet base having first and second spaced apart weld zones; attaching a strain sensor to an upper side of the sheet base between the first and second
weld zones; applying a soft adhesive to an underside of the sheet base between the first and second weld zones; adhering the sheet base to the substrate with the soft adhesive; and applying at least one spot weld between the sheet base and the substrate in each weld zone.
8. The method of claim 7 further comprising the step of providing hard bonding material
about the respective spot welds.
PCT/US2005/000256 2004-01-05 2005-01-05 Structure and method for packaging micro strain sensors WO2005068958A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US53425204P 2004-01-05 2004-01-05
US60/534,252 2004-01-05

Publications (1)

Publication Number Publication Date
WO2005068958A1 true WO2005068958A1 (en) 2005-07-28

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1285762A (en) * 1969-02-12 1972-08-16 Central Electr Generat Board Improvements in strain gauges
US3878711A (en) * 1973-09-24 1975-04-22 Jr George J J Randolph Extensometer
US4295117A (en) * 1980-09-11 1981-10-13 General Motors Corporation Pressure sensor assembly
JPS61150382A (en) * 1984-12-25 1986-07-09 Agency Of Ind Science & Technol Method of connecting tactile sensor and substrate
FR2792068A1 (en) * 1999-08-30 2000-10-13 Commissariat Energie Atomique Force measuring device has intermediate support placed between deforming part and sensitive component, having local thinning extending along its width

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1285762A (en) * 1969-02-12 1972-08-16 Central Electr Generat Board Improvements in strain gauges
US3878711A (en) * 1973-09-24 1975-04-22 Jr George J J Randolph Extensometer
US4295117A (en) * 1980-09-11 1981-10-13 General Motors Corporation Pressure sensor assembly
JPS61150382A (en) * 1984-12-25 1986-07-09 Agency Of Ind Science & Technol Method of connecting tactile sensor and substrate
FR2792068A1 (en) * 1999-08-30 2000-10-13 Commissariat Energie Atomique Force measuring device has intermediate support placed between deforming part and sensitive component, having local thinning extending along its width

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 010, no. 352 (E - 458) 27 November 1986 (1986-11-27) *

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