USRE44407E1 - Space transformers employing wire bonds for interconnections with fine pitch contacts - Google Patents

Abstract

Method and apparatus for electrical testing of a device under test (DUT) that employs a connection board with signal contacts for applying test signals and a space transformer that has low pitch contacts arranged on one or more circumferential shelves that define an enclosure in the space transformer. The apparatus has a substrate with fine pitch contacts positioned such that these are within the enclosure. A set of wire bonds is used for pitch reduction by interconnecting the fine pitch contacts with the low pitch contacts arranged on the shelves. The probes are connected to the fine pitch contacts and are used to apply the test signals to a DUT by contacting its pads. In some embodiments, the fine pitch contacts may be embodied by plugs or by blind metal vias.

Description

FIELD OF THE INVENTION

This invention relates generally to apparatus and method using wire bonds for making electrical connections between low pitch signal contacts and fine pitch contacts to probes used for applying test signals to a device under test.

BACKGROUND ART

The testing of semiconductor wafers and other types of integrated circuits (ICs), collectively known as devices under test (DUTs), needs to keep pace with technological advances. Each IC has to be individually tested, typically before dicing, in order to ensure that it is functioning properly. The demand for testing products is driven by considerations of new chip designs and higher volumes.

In particular, chips are getting smaller and they have more tightly spaced contact pads. The pads are no longer located about the circuit perimeter, but in some designs may be found within the area occupied by the circuit itself. As a result, the spacing or pitch of probe arrays required to establish electrical contact with the pads or bumps is decreasing. In addition, the requirements on planarity are increasing.

To address the increasingly fine pitch of the pads, several prior art solutions have resorted to using more effective space transformers for achieving pitch reduction and improved probe performance. Several examples of recent space transformers for probe contact assemblies are found in the patent literature, including U.S. Pat. Nos. 6,676,438 and 6,917,102 to Zhou et al. These teachings include several contact structures and production methods, including an embodiment using the flip-chip bonding process to attach the space transformer. Still other prior art, such as U.S. application Ser. No. 2006/0033516 to Rincon et al. teaches a probe and universal tester contact assemblage that is capable of testing multiple chips. This assemblage employs a wire bond between the end of a trace that is connected to a probe and a fan-out trace that belongs to an intermediate element or interposer made of a dielectric material to step up from low pitch contacts to fine pitch contacts.

In addition to the finer pitch of the pads to be tested, there has also been a move to increase the test signal frequencies. Some prior art probe devices address the coupling and noise problems arising at such higher frequencies. For example, U.S. Pat. No. 6,714,034 discusses the inclusion of an inductive (magnetic) filter to suppress AC noise on the DUT ground and U.S. application Ser. No. 2005/0012513 to Cheng et al. teaches a probe card assembly with a stiffener ring and a set of coaxial transmitters. Furthermore, U.S. application Ser. No. 2005/0099191 talks about the design of a multi-GHz probe structure for optimizing the signal path to improve bandwidth. Unfortunately, this probe structure can only address a limited number of pads and is thus only suitable for devices with a small number of pads located along the die perimeter. Devices that have a large number of fine pitch pads located along the perimeter or arranged in an array cannot be tested with such probe structure.

Clearly, as more complicated arrays of pads having a fine pitch are to be tested at high frequencies the prior art space transformers and high-frequency handling can not be integrated to produce suitable solutions. In particular, the high-frequency performance of typical wired space transformers that employ via holes and copper wires that use heads equipped with buckling beam or similar probes is insufficient. Even though probe cards employing such space transformers can be made cheaply and relatively quickly, they experience unacceptably high levels of electrical cross-talk and self-inductance with an upper bound on test frequency of about 0.9 GHz at a 3 dB bandwidth. Furthermore, such probe cards can only be made with up to about 1,500 connections, since the wiring process becomes too cumbersome at higher connection counts.

Some probe cards avoid the use of wires and employ instead a space transformer made of an organic substrate (e.g., MLC or MLD) with solder reflow connections to a connection board (typically a printed circuit board to which the test signals are applied). Such probe cards exhibit much improved high frequency performance, typically up to 3 GHz at a 3 dB bandwidth, but are hard to make and require expensive lithographic processing.

Employing wire bonding techniques and wire bonds is in general a very low-cost and mature method of making electrical connections and is used in various related contexts including interposers, probes and space transformers. For example, U.S. application Ser. No. 2002/0125584 discusses using wire bonding to ensure high bond strength between the bonding pads and conducting wires when wire-bonding chips to carriers. Specifically, the weak bonding strength problem is solved by designating a separate section of the IC pad for probing and a separate section for wire-bonding. U.S. application Ser. No. 2002/0194730 teaches how to repair probes mounted on a space transformer that were shaped and made using wire-bonding. U.S. application Ser. No. 2003/0116346 shows how to use a wire-bonding machine to make stud-bumped probes.

Although the prior art solutions individually address some of the problems associated with pitch step up and reliable connections, there is no apparatus or method that combines the requisite characteristics in a single space transformer that can be used in a probe card or testing apparatus. Specifically, what is needed is a space transformer that is compatible with high frequency test signals, easy to make, low cost and can address densely packed pads or bumps arranged in arrays.

OBJECTS AND ADVANTAGES

In view of the above prior art limitations, it is an object of the invention to provide a low-cost method and apparatus for electrically testing devices under test (DUTs) that have densely spaced arrays of contact pads or bumps. More precisely, the object is to provide such apparatus with a space transformer that takes advantage of low-cost wire bonding for interconnections with the fine pitch contacts.

It is another object of the invention, to ensure that the space transformer is capable of handling high-frequency test signals.

It is still another object of the invention to ensure that the method and apparatus can be easily integrated with any conventional head designs to take advantage of any available probe geometry.

These and other objects and advantages of the invention will become apparent from the ensuing description.

SUMMARY OF THE INVENTION

The objects and advantages of the invention are secured by a method and an apparatus for electrical testing of a device under test (DUT). The apparatus has a connection board that has signal contacts for applying test signals and a space transformer with intermediate contacts connected to the signal contacts. The space transformer has low pitch contacts that are connected to the intermediate contacts. The low pitch contacts are arranged on one or more circumferential shelves that define an enclosure. A substrate with fine pitch contacts is positioned such that the fine pitch contacts are within the enclosure. A set of wire bonds is used for pitch reduction by interconnecting the fine pitch contacts with the low pitch contacts on the shelves by any suitable wire bonding or wedge bonding including ribbon bonding for power/ground technique. The probes are connected to the fine pitch contacts and are used to apply the test signals to a DUT by contacting its pads.

In a preferred embodiment, the fine pitch contacts are made of contact plugs that are lodged or secured by epoxy in corresponding vias made in the substrate. The vias can be etched or laser machined, depending on the material of which the substrate is made. The plugs are preferably mico-electro machined, i.e., they are MEMs plugs. The substrate itself, can be made of any suitable material including ceramics, organics such as MLC or MLD, or, preferably Al₂O₃.

The space transformer has a lower circumferential shelf bearing a lower set of low pitch contacts and at least one upper circumferential shelf bearing an upper set of the low pitch contacts. In accordance with the invention, the one or more upper circumferential shelves are recessed or inset from the lower circumferential shelf. The lower set of low pitch contact arranged on the lower shelf usually includes a ground contact.

The wire bonds are made between the lower set of low pitch contacts and the fine pitch contacts and also between the upper set of low pitch contacts and the fine pitch contacts. In particular, the wire bonds include a short set of wire bonds interconnecting a set of the fine pitch contacts proximal the lower shelf with the lower set of low pitch contacts arranged on the lower shelf. Since this set contains the shortest wire bonds it is preferable that the ground contact be included in this set, as mentioned above. The wire bonds further include a long set of wire bonds interconnecting a set of the fine pitch contacts remote from the lower shelf with the upper set of low pitch contacts arranged on the one or more upper shelves. It is preferable for high-frequency operation that the longest wire bonds in the long set of wire bonds be at most a few millimeters in length.

In the fully assembled space transformer according to the invention, the enclosure is preferably filled with a dielectric material. This is done after all the wire bonds have been made in order to ensure stability and insulation.

The step down or pitch reduction from the intermediate contacts to the fine pitch contacts is preferably about ten to one. In numerical terms the intermediate contacts are at a pitch of about 1 mm and the fine pitch contacts are at a pitch of about 0.1 mm or 100 μm.

The apparatus of the invention is preferably employed in a probe card for testing a DUT by delivering the test signals to the pads of the DUT when the pads are contacted by the probes. The DUT is typically an integrated circuit.

The method of invention for electrically testing the DUT includes the steps of providing the connection board with signal contacts and providing the space transformer. The space transformer has intermediate contacts and low pitch contacts connected to the intermediate contacts. The low pitch contacts are arranged on one or more circumferential shelves that define the enclosure, and the signal contacts are connected to the intermediate contacts. Furthermore, a substrate with fine pitch contacts is provided and positioned such that the fine pitch contacts are within the enclosure. The fine pitch contacts are interconnected with the low pitch contacts by a set of wire bonds and the probes are connected to the fine pitch contacts. Then, the test signals are applied to the signal contacts and the probes are contacted with the pads of the DUT for performing the electrical test.

Preferably, the fine pitch contacts are made by producing vias in the substrate and lodging contact plugs in the vias. The vias can be laser machined and the plugs can be made by a micro-electro machining technique. The space transformer has a lower circumferential shelf bearing a lower set of low pitch contacts and one or more upper circumferential shelves bearing an upper set of low pitch contacts. The one or more upper circumferential shelves are recessed or inset from the lower circumferential shelf, and a set of fine pitch contacts proximal the lower shelf is interconnected with the lower set of low pitch contacts by a short set of wire bonds. A set of fine pitch contacts remote from the lower shelf is interconnected with the upper set of the low pitch contacts by a long set of wire bonds. After the interconnections are made, the enclosure is filled with the dielectric material.

A detailed description of the preferred embodiments of the invention is presented below in reference to the appended drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a partial three-dimensional diagram illustrating an apparatus of the invention.

FIG. 2 is cross-sectional side view of a portion of the apparatus ofFIG. 1.

FIG. 3 is a side cross-sectional view of an assembled apparatus according to the invention.

FIG. 4 is a cross-sectional side view of a portion of another apparatus according to the invention.

FIG. 5 is a top plan view illustrating interconnections in a space transformer according to the invention.

DETAILED DESCRIPTION

The present invention will be best understood by first reviewing anapparatus10 of the invention as shown in a partial three-dimensional diagram ofFIG. 1.Apparatus10 has aspace transformer12 withintermediate contacts14 located on aledge16. Space transformer also haslow pitch contacts18 that are arranged on a lowercircumferential shelf20 and an uppercircumferential shelf22. Specifically, alower set18A oflow pitch contacts18 is located on lowercircumferential shelf20 and anupper set18B oflow pitch contacts18 is located on uppercircumferential shelf22. Furthermore,upper shelf22 is recessed or inset fromlower shelf20 to enable easy access by wire bonding equipment tolow pitch contacts18 on both shelves.

Ledge16 andshelves20,22 extend circumferentially (only partially shown inFIG. 1) to define astructure24 that has aninternal enclosure26. Any suitable, mechanically stable dielectric material or materials can be used to constructstructure24 that includesledge16 andshelves20,22. For example,structure24 can be made layer-by-layer, thus defininglower shelf20 first, thenupper shelf22 and finallyledge16. During the formation of the structure, embeddedelectrical connections28 are made to connectintermediate contacts14 with correspondinglow pitch contacts18.

Space transformer12 has asubstrate30 with a number offine pitch contacts32.Substrate30 is positioned belowstructure24 such thatfine pitch contacts32 are withinenclosure26.Substrate30 can be permanently attached to structure24 by any suitable bonding method. It should be noted that in some embodiments it is useful whenstructure24 is removable. For example, this is of value whensubstrate30 is a mini printed circuit board and thecontacts32 are blind metal vias.

A set ofwire bonds34 is used for pitch reduction by interconnectingfine pitch contacts32 withlow pitch contacts18 onshelves20,22. Wire bonding is a technique well known in the art and typically involves one of the following three major techniques: thermocompression bonding, ultrasonic bonding, and thermosonic bonding. In general, ultrasonic bonding will be preferred for Aluminum wire bonding, and thermosonic bonding will be preferred for Au wire bonding. In order to accrue the full benefit of the invention including low electric cross-talk and low self-inductance, the maximum length of anyparticular wire bond34 should not exceed a few millimeters and preferably be at most 5 millimeters. The specific techniques for bonding tolow pitch contacts18 include wire bonding or wedge bonding, including ribbon bonding used for power/ground technique.

In the preferred embodiment,fine pitch contacts32 are made of contact plugs36 that are lodged or secured by epoxide in correspondingvias38 insubstrate30.Vias38 can be etched or laser machined, depending on the material of whichsubstrate30 is made. For example,substrate30 can be made of a ceramic or an organic such as MLC or MLD in which case the “plugs” equivalent would be electroplated vias. In this case there would be no need for MEMS plugs and epoxide. Preferably, however,substrate30 is made of Al₂O₃so that it lends itself well to laser machining, which is the preferred technique due to its high accuracy and speed.Plugs36 are preferably mico-electro machined, i.e., they are MEMs plugs made of a nickel and cobalt alloy plated with gold. In an alternative embodiment, vias38 are filled with metal and thus themselves constitutefine pitch contacts32. In other words, vias38 are blind metal vias and serve asfine pitch contacts32.

A number ofprobes40 are connected tofine pitch contacts32. Specifically, probes40 are connected to the bottoms ofplugs36 orblind metal vias38, depending on the embodiment. Although in the embodiment shown, probes40 are non-linear, it will be appreciated by one skilled in the art that they can be of any variety, including buckling beam probes. Moreover, probes40 can be held together in any suitable mechanical retention device or be otherwise configured in a suitable head unit. Such head unit can be removable or permanently attached tospace transformer12, depending on application.

Referring now to the partial cross-sectional side view ofFIG. 2 for more detail, we see thatapparatus10 also has aconnection board42 withsignal contacts44. Typically,connection board42 is a printed circuit board (PCB) with appropriateprimary contacts46 for applying test signals48.Primary contacts46 are electrically connected tocorresponding signal contacts44 for delivering test signals48. Test signals48 are usually generated by a testing circuit (not shown) and applied toprimary contacts46 with the aid of spring pins or other suitable mechanism.

Intermediate contacts14 ofspace transformer12 are connected to signalcontacts44. In the present embodiment, this is accomplished withsolder reflow junctions50. Thus,primary contacts46 are in electrical communication with correspondinglow pitch contacts18 onshelves20,22. More specifically, lower set oflow pitch contacts18A arranged on lowercircumferential shelf20 and upper set oflow pitch contacts18B arranged on uppercircumferential shelf22 are in electrical communication withprimary contacts46 viasignal contacts44,intermediate contacts14 and embeddedelectrical connections28. Therefore, test signals48 can be delivered directly to the appropriatelow pitch contacts18 ofspace transformer12.

Wire bonds34 between lower set oflow pitch contacts18A andfine pitch contacts32 and also between the upper set oflow pitch contacts18B andfine pitch contacts32 are made in accordance with a certain scheme. In particular,wire bonds34 include a short set ofwire bonds34A interconnecting a set offine pitch contacts32A proximallower shelf20 with lower set oflow pitch contacts18A arranged onlower shelf20. Since this set contains the shortest wire bonds it is preferable that the ground contact be included in this set.

Wire bonds34 further include a long set ofwire bonds34B interconnecting a set of thefine pitch contacts32B remote fromlower shelf20 with upper set oflow pitch contacts18B arranged onupper shelf22. It is preferable for high-frequency operation that the longest wire bonds in long set ofwire bonds32B be at most 5 millimeters in length. This is done in order to reduce cross-talk betweenwire bonds34 and self-inductance to permit the application of high frequency test signals48, e.g., test signals in the range of several GHz.

InFIG. 2, reference Δ denotes the pitch ofintermediate contacts14 and reference δ denotes the pitch offine pitch contacts32. In accordance with the invention, the step down or pitch reduction from pitch Δ ofintermediate contacts14 to pitch δ offine pitch contacts32 is preferably about ten to one. In numerical terms Δ is on the order of about 1 mm and δ is on the order of about 0.1 mm or 100 μm. For peripheral IC pad test application the pitch is as small as 35 μm today. For full grid array flip-chip bump test the minimum pitch is about 140 μm today.

FIG. 3 is a cross-sectional side view of a fully assembledapparatus10. In this fully assembled state,space transformer12 has itsenclosure26 filled with adielectric material52. This is done after allwire bonds34 have been made in order to ensure stability and insulation. Of course, the wires used inbonds34 can be already insulated, e.g., with a non-conductive ink or by other means, thus making the presence ofmaterial52 unnecessary. However, non-insulated wires can also be used, and in thiscase material52 must be used to avoid shorts.Material52 also provides mechanical stability tospace transformer12 andapparatus10 as a whole. This is especially important, to sustain the aggregate forces acting onprobes40 andapparatus10 during normal operation due to the deflection ofprobes40. Such forces can be quite large—for example, with 2000probes40 each exerting 10 grams of force the total force pushing on the assembly ofapparatus10 is about 20 kg. It should be noted that at the present time, as many as 5,000probes40 can be used in oneapparatus10.

Apparatus10 is used for electrical testing of a device under test (DUT)54.DUT54 has a number of pads or bumps56, which have to be contacted byprobes40 to applytest signals48 thereto and thus conduct the test.Apparatus10 is preferably employed in a probe card for testing integrated circuits with high-frequency test signals48. For example,DUT54 is an integrated circuit on a wafer that requires testing prior to dicing. Alternatively,DUT54 is an electronic device or circuit that is already mounted and whose functionality needs to be verified by applyingtest signals48 to a number of its bumps orpads56.

FIG. 4 is a cross-sectional side view of a portion of anapparatus100 according to the invention.Apparatus100 employs aspace transformer102 with astructure104 that has threecircumferential shelves106,108,110 bearinglow pitch contacts112. Aledge114 ofstructure104 bears connectionintermediate contacts116 that are connected to correspondinglow pitch contacts112. Aconnection board118 withsignal contacts120 that are reflow soldered tointermediate contacts116 is used to deliver test signals tolow pitch contacts112.

Space transformer102 employs a mini printedcircuit board122 as a substrate.Board122 is attached to structure104 as shown and positioned such that its set offine pitch contacts124 is contained within anenclosure126 defined byshelves106,108,110.Board122 has a set ofblind metal vias128 that serve as fine pitch contacts. A set ofwire bonds130 interconnectsfine pitch contacts124 or the tops ofblind vias128 withlow pitch contacts112. As before, any suitable wire bonding technique can be employed to accomplish this connection. In this embodiment, the probes (not shown) are attached to the bottoms ofvias128.

As in the previous embodiment, it is preferable to keep the lengths ofwire bonds130 as short as possible, and most preferably under 5 mm. This limitation places the toughest restrictions onwire bonds130 interconnectinglow pitch contacts112 fromtop shelf110 and vias128 that are remote frombottom shelf106. In addition, in this embodiment it is essential to use insulated wire forwire bonds130 to further counteract any possibility of shorts.

As before, adielectric material132 is used for potting wire bonds130. Preferably, the potting is performed sequentially by first interconnecting and potting theshortest wire bonds130 betweenlowest shelf106 and vias128 closest to structure104. Then repeating the process for thesecond shelf108 wire bonds and finally forthird shelf110 wire bonds.

In any of the above embodiments, or in still other embodiments, it is important to optimize the localization of low pitch contacts and fine pitch contacts. One approach involves staggering of contacts, as shown in the top plan view ofFIG. 5. In this example aspace transformer140 has astructure142 with threecircumferential shelves144,146,148.Low pitch contacts150 are staggered with respect to each other and with respect tofine pitch contacts152. Thus, interconnections performed withwire bonds154 are non-overlapping because the wires fromdifferent shelves144,146,148 tend to fall in-between each other. It should be noted that appropriate potting can be employed in this embodiment to further aid in accommodating more shelves and making more secure over-arching wire bonds154.

A person skilled in the art will recognize that the above are merely a few exemplary embodiments and that many other embodiments of the apparatus and method are possible. Therefore, the scope of the invention should be judged by the appended claims and their legal equivalents.

Claims (68)

I claim:

1. An apparatus for electrical testing, comprising:

a) a connection board having signal contacts for applying test signals;

b) a space transformer having intermediate contacts connected to said signal contacts, said space transformer further having low pitch contacts connected to said intermediate contacts and arranged on at least one circumferential shelf, said at least one circumferential shelf defining an enclosure;

c) a substrate having fine pitch contacts and positioned such that said fine pitch contacts are within said enclosure;

d) a set of wire bonds interconnecting said fine pitch contacts with said low pitch contacts;

e) probes connected to said fine pitch contacts.

2. The apparatus ofclaim 1, wherein said fine pitch contacts comprise contact plugs lodged in corresponding vias in said substrate.

3. The apparatus ofclaim 2, wherein said vias are laser machined and said plugs are made by a micro-electro machining technique.

4. The apparatus ofclaim 2, wherein said substrate comprises a material selected from the group consisting of ceramics, organics and Al₂O₃.

5. The apparatus ofclaim 1, wherein said fine pitch contacts comprise blind metal vias.

6. The apparatus ofclaim 1, wherein said space transformer comprises a lower circumferential shelf bearing a lower set of said low pitch contacts and at least one upper circumferential shelf bearing an upper set of said low pitch contacts, said at least one upper circumferential shelf being inset from said lower circumferential shelf.

7. The apparatus ofclaim 6, wherein said lower set of said low pitch contacts comprises a ground contact.

8. The apparatus ofclaim 6, wherein said set of wire bonds comprises a short set of wire bonds interconnecting a set of said fine pitch contacts proximal said lower shelf with said lower set of said low pitch contacts.

9. The apparatus ofclaim 6, wherein said set of wire bonds comprises a long set of wire bonds interconnecting a set of said fine pitch contacts remote said lower shelf with said upper set of said low pitch contacts.

10. The apparatus ofclaim 9, wherein said long set of wire bonds comprises wire bonds of at most 5 millimeters in length.

11. The apparatus ofclaim 1, wherein said enclosure is filled with a dielectric material.

12. The apparatus ofclaim 1, wherein a pitch reduction from said intermediate contacts to said fine pitch contacts is about ten to one.

13. The apparatus ofclaim 1, employed in a probe card for testing a device under test by delivering said test signals to pads of said device under test by contacting said pads with said probes.

14. The apparatus ofclaim 13, wherein said device under test comprises an integrated circuit.

15. A method for electrically testing a device under test, said method comprising:

a) providing a connection board having signal contacts;

b) providing a space transformer having intermediate contacts and low pitch contacts connected to said intermediate contacts, said low pitch contacts being arranged on at least one circumferential shelf, said at least one circumferential shelf defining an enclosure;

c) connecting said signal contacts to said intermediate contacts;

d) providing a substrate having fine pitch contacts and positioned such that said fine pitch contacts are within said enclosure;

e) interconnecting said fine pitch contacts with said low pitch contacts by a set of wire bonds;

f) connecting probes to said fine pitch contacts;

g) applying test signals to said signal contacts; and

h) contacting said probes with pads of said device under test for electrically testing said device under test.

16. The method ofclaim 15, wherein said fine pitch contacts are made by producing vias in said substrate and lodging contact plugs in said vias.

17. The method ofclaim 16, wherein said vias are laser machined and said plugs are made by a micro-electro machining technique.

18. The method ofclaim 15, wherein said space transformer comprises a lower circumferential shelf bearing a lower set of said low pitch contacts and at least one upper circumferential shelf bearing an upper set of said low pitch contacts, said at least one upper circumferential shelf being inset from said lower circumferential shelf, and wherein said method further comprises interconnecting a set of said fine pitch contacts proximal said lower shelf with said lower set of said low pitch contacts by a short set of wire bonds, and interconnecting a set of said fine pitch contacts remote said lower shelf with said upper set of said low pitch contacts by a long set of wire bonds.

19. The method ofclaim 15, further comprising filling said enclosure with a dielectric material.

20. An apparatus for electrical testing comprising:

a layered space transformer;

a first layer of said layered space transformer comprising a substrate;

said substrate comprising a plurality of fine pitch contacts;

a second layer of said layered space transformer comprising a structure disposed around an outside circumference of said substrate;

said structure comprising at least one shelf, said shelf comprising a plurality of low pitch contacts;

said structure further comprising a ledge disposed above said shelf;

said ledge comprising a plurality of intermediate contacts;

said intermediate contacts electrically connected to corresponding said low pitch contacts via electrical connections embedded within said structure; and

a plurality of bonds interconnecting said fine pitch contacts with corresponding said low pitch contacts.

21. The apparatus of claim 20 further comprising an enclosure defined by said shelf.

22. The apparatus of claim 21 wherein said fine pitch contact is within said enclosure.

23. The apparatus of claim 21 further comprising a dielectric material filling the enclosure.

24. The apparatus of claim 20 comprising a pitch reduction from said intermediate contact to said fine pitch contact of about ten to one.

25. The apparatus of claim 20 further comprising at least one signal contact and wherein said signal contact is connected to said intermediate contact.

26. The apparatus of claim 25 wherein said connection between said signal contact and said intermediate contact comprises a solder reflow junction.

27. The apparatus of claim 25 further comprising a connection board connected to said signal contact.

28. The apparatus of claim 27 wherein said connection board comprises a printed circuit board.

29. The apparatus of claim 27 wherein said connection board comprises a primary contact connected to said signal contact.

30. The apparatus of claim 27 further comprising a probe connected to said fine pitch contact.

31. The apparatus of claim 20 wherein said shelf comprises a circumferential shelf.

32. The apparatus of claim 20 comprising an upper shelf and a lower shelf.

33. The apparatus of claim 32 comprising a lower set of low pitch contacts located on said lower shelf and an upper set of low pitch contacts located on said upper shelf.

34. The apparatus of claim 33 comprising a short set of wire bonds interconnecting a set of said fine pitch contacts proximal to said lower shelf with said lower set of low pitch contacts.

35. The apparatus of claim 33 wherein said lower set of low pitch contacts comprises a ground contact.

36. The apparatus of claim 33 comprising a long set of wire bonds interconnecting a set of said fine pitch contacts remote to said lower shelf with said upper set of said low pitch contacts.

37. The apparatus of claim 32 wherein said upper shelf is recessed from said lower shelf.

38. The apparatus of claim 32 wherein said shelves are made layer-by-layer.

39. The apparatus of claim 20 wherein said substrate is positioned below said shelf.

40. The apparatus of claim 39 wherein said substrate is permanently attached to said shelf.

41. The apparatus of claim 39 wherein said substrate is removably attached to said shelf.

42. The apparatus of claim 20 wherein said substrate comprises a circuit board.

43. The apparatus of claim 20 wherein said fine pitch contact comprises a via.

44. The apparatus of claim 43 wherein said via comprises a blind via.

45. The apparatus of claim 44 wherein said blind via comprises a blind metal via.

46. The apparatus of claim 20 wherein said wire bond is equal to or less than 5 millimeters.

47. The apparatus of claim 20 wherein said at least one fine pitch contact comprising a contact plug.

48. The apparatus of claim 47 further comprising a via, wherein said contact plug is secured in said substrate by said via.

49. The apparatus of claim 47 wherein said plug is micro-electro machined.

50. The apparatus of claim 20 wherein said substrate comprises aluminum oxide.

51. The apparatus of claim 20 wherein said substrate comprises ceramic.

52. The apparatus of claim 20 wherein said substrate comprises organics.

53. The apparatus of claim 20 wherein said wire bond comprises a short wire bond for bonding.

54. The apparatus of claim 20 wherein said apparatus is employed in a probe card.

55. The apparatus of claim 20 comprising three shelves.

56. The apparatus of claim 20 comprising a plurality of low pitch contacts staggered with respect to a plurality of fine pitch contacts.

57. The apparatus of claim 20 wherein said bond comprises a wire bond.

58. A method for testing a device under test comprising:

providing a layered space transformer comprising a first layer of the layered space transformer having a substrate, a second layer of the layered space transformer having a structure disposed around an outside circumference of the substrate, the structure comprising at least one shelf, the shelf comprising a plurality of low pitch contacts, the structure further comprising a ledge disposed above the shelf, the ledge comprising a plurality of intermediate contacts;

disposing a plurality of fine pitch contacts on the substrate;

interconnecting the low pitch contacts to corresponding intermediate contacts via electrical connections embedded within the structure;

interconnecting the fine pitch contacts with corresponding low pitch contacts by at least one wire bond; and

applying a high frequency test signal to a device under test.

59. The method of claim 58 further comprising connecting the intermediate contact to a signal contact located on a connection board.

60. The method of claim 59 further comprising applying a test signal to the signal contact.

61. The method of claim 58 further comprising connecting at least one probe to the fine pitch contact.

62. The method of claim 61 further comprising contacting the probe with a pad of the device under test for electrically testing the device under test.

63. The method of claim 58 wherein said fine pitch contact comprises producing a via in said substrate and lodging a contact plug in the via.

64. The method of claim 63 further comprising laser-machining the via.

65. The method of claim 63 further comprising micro-electro machining the plug.

66. The method of claim 58 wherein the space transformer comprises a lower shelf bearing a lower set of low pitch contacts and at least one upper shelf bearing an upper set of the low pitch contacts.

67. The method of claim 66 further comprising interconnecting a set of fine pitch contacts proximal to the lower shelf with the lower set of low pitch contacts by a short set of wire bonds.

68. The method of claim 66 further comprising interconnecting a set of fine pitch contacts remote to the lower shelf with the upper set of low pitch contacts by a long set of wire bonds.

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