WO2000042636A9

WO2000042636A9 - Micromachined device and method of forming the micromachined device

Info

Publication number: WO2000042636A9
Application number: PCT/US2000/000670
Authority: WO
Filing date: 2000-01-11
Publication date: 2001-08-23

Abstract

An apparatus (10) that includes a substrate (12) having first and second surfaces and a micromachined device (14) integral with the first surface (18) of the substrate (12), and wherein the second surface (20) is an outer portion of the apparatus (10). The apparatus (10) also has a cover (16) connected to the substrate (12). A method of forming a micromachined device (14) includes providing a substrate (12), fabricating the micromachined device (14) on the substrate (12), and connecting a cover (16) to the substrate (12).

Description

MICROMACHINED DEVICE AND METHOD OF FORMING THE MICROMACHINED DEVICE

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention is directed generally to a micromachined device and,

more particularly, to a micromachined device that is integral with a portion of its

package. The present invention is also directed generally to a method of forming a

micromachined device and, more particularly, to a method of forming a

micromachined device in which the device and a portion of the package are integral. Description of the Background

Electromechanical relays are used in a wide variety of applications, such as

automatic test systems, instrumentation equipment, telecommunications, wireless

technologies, and automotive and medical electronics. Electromechanical relays,

however, are typically fabricated on an individual basis by either manual or automated

processes. This often results in undesirable unit-to-unit variability. In addition,

conventional electromechanical relays are relatively large compared to other

electronic components, and are increasingly becoming a limiting factor as the

packaging density of electronic devices continues to increase.

Solid state relays (SSRs) provide one solution to this problem, by providing

for batch fabrication of the devices and reducing the overall size of the device. SSRs,

however, often suffer from higher offset voltages, lower maximum off-state

resistance, higher contact capacitance, and higher contact power dissipation in

comparison to electromechanical relays. This makes SSRs unsuitable for many

applications.

Micromachined relays are electromechanical relays produced by batch

fabrication techniques. Micromachining commonly refers to the use of semiconductor

processing techniques to fabricate devices known as micro electromechanical systems

(MEMS), and may include any process which uses fabrication techniques such as, for

example, photolithography, electroplating, sputtering, evaporation, plasma etching,

lamination, spin or spray coating, diffusion, or other microfabrication techniques. In

general, known MEMS fabrication processes involve the sequential addition or removal of materials from a substrate layer through the use of thin film deposition and

etching techniques, respectively, until the desired structure has been achieved.

Micromachined relays seek to combine the best attributes of electromechanical

relays and SSRs. That is, micromachined relays provide the decreased size of solid-

state devices and the increased off resistance and lower on resistance of typical

electromechanical relays, in addition to the lower contact capacitance of

electromechanical relays. These advantages are especially important for applications

utilizing relays to test semiconductor chips, which have decreased in size and

increased in frequency response over the years. Micromachined relays also provide

an advantage in that they can be manufactured at a relatively low cost because they

can be batch fabricated using established micromachining techniques. Also,

micromachined relays allow for the interconnection of large relay arrays during

fabrication, thus reducing other fabrication steps needed for typical relay arrays.

MEMS fabrication techniques largely follow the fabrication techniques of the

semiconductor industry. For example, micromachined devices are typically batch

fabricated on a substrate. The substrate is then sectioned, or diced, to form multiple

MEMS devices. The individual devices are then packaged in the same manner as a

semiconductor die, such as, for example, on a lead frame, chip carrier, or other typical

package. The additional packaging associated with MEMS fabrication minimizes two

of the advantages that micromachined relays enjoy over conventional

electromechanical relays. First, the overall size of the device is increased, and second,

additional steps in the packaging process are incurred, which consequently increases

production costs. In addition, the substrate on which the micromachined relay is formed and the package in which it is housed are often made of similar materials,

which leads to duplicative processing steps and associated additional costs.

Furthermore, the additional packaging step results in an increased signal path length,

thereby increasing the response time, electrical resistance, and capacitance of the

relay.

Accordingly, there exists a need in the relevant art for the packaging of

micromachined devices such that the size of the package is decreased and which

reduces cost. There also exists a need in the relevant art to decrease the length of the

inputs to a micromachined device to minimize parasitic effects at higher frequencies.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to an apparatus including a substrate having

first and second surfaces. A micromachined device is integral with the first surface of

the substrate, and the second surface is an outer portion of the apparatus. The

apparatus also includes a cover connected to the substrate. The present invention is

also directed to a method of forming a micromachined device. The method includes

providing a substrate having first and second surfaces, fabricating the micromachined

device on the first surface of the substrate, and connecting a cover to the substrate

such that the micromachined device is enclosed by the cover and the second surface of

the substrate is not enclosed by the cover.

The present invention has the advantage that it has reduced production costs.

The present invention also has the advantage that the overall size of a micromachined

package can be made smaller. The present invention also has the advantage that the length of the leads of the device can be made small when compared to leads of

relevant art packages for micromachined devices, thus providing better electrical

performance, especially for high frequency applications. The present invention also

has the advantage that yield loss is decreased because less product is damaged as a

result of obviating additional packaging steps.

BRIEF DESCRIPTION OF THE DRAWINGS

For the present invention to be clearly understood and readily practiced, the

present invention will be described in conjunction with the following figures,

wherein:

Figure 1 is a cross-sectional view of an apparatus according to the present

invention; and

Figure 2 is a cross-sectional view of an apparatus according to another

embodiment of the present invention;

Figure 3 is a cross-sectional view of an apparatus according to another

embodiment of the present invention;

Figure 4 is a cross-sectional view of an apparatus according to another

embodiment of the present invention; and

Figure 5 is a perspective view of a substrate and a number of micromachined

devices of the apparatus of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 is a cross-sectional view of an apparatus 10 according to the present

invention. The apparatus 10 includes a substrate 12, a micromachined device 14, and

a cover 16. The substrate 12 may be a non-conductive material, such as, for example,

ceramic, glass, silicon, a printed circuit board, or materials used for silicon-on-

insulator semiconductor devices. The micromachined device 14 is integrally formed

with a first surface 18 of the substrate 12, such as, for example, by batch

micromachining fabrication techniques, which include surface and bulk

micromachining. The micromachined device 14 may be, for example, a

micromachined relay, such as that described in U.S. Patent No. 5,847,631, issued to

Taylor et al. In addition, the micromachined device 14 may be an array of

micromachined relays, or it may be, for example, a valve, switch, actuator, sensor, or

motor. The cover 16 is connected to the substrate 12 and encloses the micromachined

device 14. The substrate 12 and the cover 16 form a housing, or package, for the

micromachined device 14, thus providing a micromachined device 14 that is integral

with its package.

An apparatus 10 constructed according to the present invention, in which the

micromachined device 14 is a micromachined relay, may be used in high frequency

applications, such as up to 20 GHz, and may be utilized in such applications as, for

example, automatic test equipment and cellular telephone equipment. In addition,

where the micromachined device 14 is a relay, the footprint of the apparatus 10 may

approach one millimeter by one millimeter.

The substrate 12 may define a number of holes extending from the first surface

18 of the substrate 12 to a second surface 20. The holes in the substrate 12 may be filled with electrically conductive material, such as metal or conductive polymers, to

form conductive vias 22. The conductive vias 22 may be formed by, for example,

thick film techniques (such as screen-printing of conductive paste) or doctor blading.

The conductive vias 22 may form a grid array and may be connected to conductive

balls 24, such as solder balls used in ball grid array (BGA) arrangements. The

conductive vias 22 and conductive balls 24 form a signal path between the

micromachined device 14 and the outside of the apparatus 10. Of course, the present

invention may be used with other types of packages, such as a pin grid array (PGA),

dual in-line package (DIP), small outline package (SOP), or small outline J-lead

package (SOJ). The BGA embodiment, however, has the advantage that the length of

the signal leads, provided directly through the conductive vias 22, are comparatively

shorter than in other packaging arrangements, thereby enhancing the overall

performance of the apparatus 10 at higher frequencies by reducing the parasitic

capacitance effects associated with longer signal lead lengths.

The cover 16 may be constructed of non-conductive material, such as plastic

or ceramic. The cover 16 may also be constructed of an electrically conductive

material, such as metal, to shield the micromachined device 14 from electromagnetic

interference. The cover 16 may be connected to the substrate 12, such as by epoxy

bonding. Fig. 2 is a cross-sectional view illustrating another embodiment of the

present invention. In the embodiment illustrated in Fig. 2, the cover 16 is formed

from two parts, a wall 30 and a lid 32. The wall 30 and lid 32 may be bonded

together, and the two-part cover 16 may bonded to the substrate 12. If the cover 16

and substrate 12 are both made of ceramic, both the micromachined device 14 and the cover 16 may be batch fabricated and bonded in batch to produce a hermetically

packaged apparatus 10.

The embodiments of Figs. 1 and 2 illustrate the cover 16 connected only to the

first surface 18 of the substrate 12. Fig. 3 is a cross-sectional view of the apparatus 10

illustrating another embodiment of the present invention. In the embodiment

illustrated in Fig. 3, the cover 16 includes a stepped lip 26. The stepped lip 26 may be

connected to both the first surface 18 and the sides 28 of the substrate 12, such that the

substrate 12 fits into the cover 16. For this embodiment, the cover 16 may be

connected to the substrate 12, for example, by epoxy bonding or by mechanical grip.

Fig. 4 is a cross-sectional view of the apparatus 10 according to another

embodiment of the invention. For the embodiment illustrated in Fig. 4, signals are

provided to and from the micromachined device 14 via a number of bond pads 40.

The bond pads 40 are connected to a number of pins 42, thus forming a signal path

between the micromachined device 14 and the outside of the apparatus 10. The pins

42 may be configured, for example, in a fashion similar to a dual in-line package, or

an SOJ package.

The present invention is also directed to a method of forming a

micromachined device 14. The method includes providing a substrate 12, fabricating

a micromachined device 14 on the substrate 12, such as by batch microfabrication

techniques. Examples of microfabrication techniques include surface micromachining

and bulk micromachining. A cover 16 is connected to the substrate 12, such as by

epoxy bonding, thus enclosing the micromachined device 14, such that the

micromachined device 14 is integrated with the package thereof. The method may include, prior to the fabrication of the micromachined device

14, forming holes extending through the substrate 12. Conductive vias 22 may be

formed therethrough by filling the holes, such as by screen printing or doctor blading,

with conductive material, such as metal or conductive polymers. The substrate 12 and

conductive vias 22 may be polished to a desired flatness. The micromachined device

14 may then formed on the substrate 12, as described hereinabove, such that leads to

the micromachined device 14 are connected to the conductive vias. The surface of the

substrate 12 on which the micromachined device 14 is formed may be larger in area

than the micromachined device 14, thus allowing for batch fabrication of the

integrated device 14. Fig. 5 is a perspective view of a substrate 12 having a number

of micromachined devices 14 formed thereon. After fabrication, a conductive

material, such as solder or other materials capable of reflow, may be placed on the

conductive vias 22. The substrate 12 may be cut, such as by a wafer or substrate saw,

into a number of individual devices 14, or an array of devices 14. A cover 16 may be

connected to the substrate 12 to enclose the micromachined device 14. Conductive

balls 24 may be connected to the conductive vias 22 adjacent the second surface 20 of

the substrate 12.

Those of ordinary skill in the art will recognize that many modifications and

variations of the present invention may be implemented. The foregoing description

and the following claims are intended to cover all such modifications and variations.

Furthermore, the materials and processes disclosed are illustrative, but are not

exhaustive. Other materials and processes may also be used to make devices embodying the present invention. In addition, the described sequences of the

processing may also be varied.

Claims

What is claimed is:

1. An apparatus, comprising:

a substrate having first and second surfaces and including a

micromachined device integral with said first surface, wherein said second

surface is an outer portion of the apparatus; and

a cover connected to said substrate and enclosing said micromachined

device.

2. The apparatus of claim 1, wherein said cover is connected to said first surface

of said substrate.

3. The apparatus of claim 1, wherein:

said substrate includes a side adjacent said first surface and said second

surface; and

said cover includes a stepped lip connected to said side of said

substrate.

4. The apparatus of claim 1, further comprising at least one conductive via

between said first surface and said second surface of said substrate and

connected to said micromachined device.

5. The apparatus of claim 4, wherein said conductive via is part of a grid array.

6. The apparatus of claim 5, further comprising at least one conductive ball

connected to said conductive via.

7. The apparatus of claim 1, further comprising:

a plurality of bond pads electrically connected to said micromachined

device; and

at least one pin electrically connected to said bond pads and external of

both said substrate and said cover.

8. The apparatus of claim 7, wherein said pins are mechanically connected to

both said substrate and said cover.

9. The apparatus of claim 7, wherein said pin forms a configuration selected from

the group consisting of dual in-line and small outline J-lead.

10. The apparatus of claim 1, wherein said micromachined device is selected from

the group consisting of a relay, an array of relays, a switch, a sensor, a valve, an

actuator, and a motor.

11. An apparatus, comprising:

a substrate having first and second surfaces and including a

micromachined device integral with said first surface, wherein said second

surface is an outer portion of the apparatus;

a cover connected to said substrate;

at least one conductive via between said first and second surfaces of

said substrate and connected to said micromachined device; and

at least one conductive ball connected to said conductive via adjacent

said second surface of said substrate.

12. The apparatus of claim 11 , wherein said micromachined device is selected

from the group consisting of a relay, an array of relays, a switch, a sensor, a valve,

an actuator, and a motor.

13. A method of forming a micromachined device, comprising:

providing a substrate having a first surface and a second surface;

fabricating the micromachined device on the first surface of the

substrate; and

connecting a cover to the substrate such that the micromachined device

is enclosed by the cover and the second surface of the substrate is not enclosed

by the cover.

14. The method of claim 13, further comprising: forming at least one conductive via between the first and second

surfaces of the substrate; and

connecting the micromachined device to the via.

15. The method of claim 13 , further comprising:

providing a plurality of bond pads connected to the micromachined

device; and

connecting a plurality of pins to the bond pads.

16. The method of claim 14, further comprising connecting at least one conductive

ball to the conductive via adjacent the second surface of the substrate.

17. The method of claim 13 , wherein:

fabricating a micromachined device includes fabricating a plurality of

micromachined devices on the first surface of said substrate; and

connecting a cover includes connecting a plurality of covers.

18. The method of claim 17, further comprising cutting the substrate into a

plurality of packaged micromachined devices.

19. The method of claim 13, wherein fabricating the micromachined device is

selected from the group consisting of surface micromachining and bulk

micromachining.

20. The method of claim 14, wherein forming at least one conductive via includes:

forming at least one hole extending between the first surface and the

second surface of the substrate; and

filling the hole with conductive material.

21. The method of claim 20, wherein filling the hole with conductive material is

selected from the group consisting of screen printing and doctor blading.

22. A method of forming a micromachined device, comprising:

fabricating a plurality of micromachined devices on a first surface of a

substrate, the substrate having a second surface;

cutting the substrate into a plurality of die, each die having a

micromachined device fabricated thereon; and

connecting a plurality of covers to the die to enclose the

micromachined devices.

23. The method of claim 22, further comprising:

forming a plurality of conductive vias between the first surface and the

second surface of the substrate; and

connecting the micromachined devices to the vias.

24. The method of claim 23, further comprising connecting a plurality of

conductive balls to the conductive vias.

25. The method of claim 22, wherein said fabricating includes fabricating a

plurality of devices selected from the group consisting of relays, arrays of

relays, actuators, sensors, motors, switches, and valves.

26. A method of forming a micromachined device, comprising:

fabricating a plurality of micromachined devices on a first surface of a

substrate, the substrate having a second surface;

forming a plurality of conductive vias between the first surface and the

second surface of the substrate;

connecting the micromachined devices to the vias;

connecting a plurality of covers to the substrate to enclose the

micromachined devices;

cutting the substrate into a plurality of packaged micromachined

devices; and connecting a plurality of conductive balls to the vias adjacent the

second surface of the substrate.

27. The method of claim 26, wherein said fabricating includes fabricating a

plurality of devices selected from the group consisting of relays, arrays of

relays, actuators, sensors, motors, switches, and valves.

28. A method of packaging a micromachined device, comprising:

providing a micromachined device on a first surface of a substrate;

connecting a cover to the substrate such that the micromachined device

is enclosed by the cover.

29. The method of claim 28, further comprising;

providing a signal path between the micromachined device and an

external connection.

30. The method of claim 29, wherein providing a signal path includes:

forming conductive vias between the first surface of the substrate and a

second surface of the substrate; and

connecting the micromachined device to the conductive via.