US20020070743A1

US20020070743A1 - Testing head having vertical probes

Info

Publication number: US20020070743A1
Application number: US09/921,646
Authority: US
Inventors: Stefano Felici; Giuseppe Crippa
Original assignee: Technoprobe SRL
Current assignee: Technoprobe SRL
Priority date: 2000-08-04
Filing date: 2001-08-03
Publication date: 2002-06-13
Also published as: US20020067178A1; ITMI20001835A1; EP1179734A1; US6674298B2; IT1318734B1; ITMI20001835A0

Abstract

A testing head having vertical probes is presented. The testing head comprises a guide plate having a guide hole formed therethrough, for accommodating a contact probe having a contact tip that is arranged to mechanically and electrically contact a contact pads on a device under test. The contact probe has a pre-deformed section placed in a flexion region between the guide plate and the test device, arranged to further deform as the contact pad of the test device is drawn against the contacting tip.

Description

BACKGROUND OF THE INVENTION

1. Field of The Invention

The present invention relates to a testing head having vertical probes, and more particularly to a testing head for use on semiconductor integrated devices.

2. Description Of The Related Art

As is well known, a testing head is basically a device suitable to electrically interconnect a plurality of contact pads of a microstructure and the corresponding channels of a testing machine arranged to perform the tests.

Integrated circuits are factory tested in order to spot and reject any circuits that show out to be already defective during the manufacturing phase. The testing heads are normally employed to electrically test the integrated circuits “on wafer”, prior to cutting and mounting them in a chip package.

A vertical probes testing head comprises at least a pair of parallel guide plates placed at a given distance apart to leave an air gap therebetween, and a plurality of specially provided movable contact elements. In particular, the guide plate pair comprises a top guide plate and a bottom guide plate, both plates being formed with guide holes receiving the movable contact elements for axial sliding movement therethrough, the contact elements being usually wires made of special alloys having good electrical and mechanical properties. These will be referred to as the testing head probes through the remainder of this description.

A good contact of the testing head probes with the contact pads of a device to be tested is achieved by urging the testing head against the device, with the movable contact probes flexed in the air gap between the two guide plates. Testing heads of this type are commonly known as “vertical probes”.

In other words, conventional testing heads have an air gap where the probes are flexed, with such flexion being assisted by a suitable configuration of the probes or their guide plates, as schematically shown in FIG. 1.

As shown in FIG. 1, a testing head 1 comprises at least a top guide plate 2 and a bottom guide plate 3, both formed with top 4 and bottom 5 guide holes, respectively, through which at least one contact probe 6 slides.

Each

contact probe

6 has at least one contact end or tip 7. In particular, the contact tip 7 is caused to abut against a contact pad 8 of a device to be tested, thereby establishing a mechanical and electrical contact between said device and a testing apparatus (not shown) that has said testing head as end element.

The top and

bottom guide plates

2 and 3 are suitably separated by an air space or gap 9 accommodating the deformation of the contact probe 6. Moreover, the top and

bottom guide holes

4 and 5 are suitable sized to guide the contact probe 6.

The deformed pattern of the probes, and the force required to produce it, depend on a number of factors, such as:

the physical characteristics of the alloy used in the construction of the probes; and

the amount of offset between the guide holes in the top guide plate and the corresponding guide holes in the bottom guide plate, as well as the distance between such holes.

It should be noted that, for a correct testing head operation, the probes must have a suitable degree of free axial movement in the guide holes. In this way, the probes can also be taken out and replaced in the event of a single probe breaking, with no need to replace the whole testing head.

All these features are, therefore, to be taken into due account in the manufacture of a testing head, given that a good electric connection between the probes and the device to be tested is mandatory.

Also known is to use contact probes having a pre-deformed configuration even when the testing head 1 is not contacting the device to be tested, as in the probes 6 b and 6 c shown in FIG. 1. This pre-deformation effectively helps the probe to correctly flex during its operation, i.e. upon contacting the device to be tested.

Thus, the correct operation of a testing head depends on the vertical movement, or overtravel, of its probes, and the horizontal movement, or scrub, of the probe contact tips.

In conventional testing heads, these parameters have inherent limitations. As schematically shown in FIGS. 2A and 2B, the maximum overtravel of a probe is equal to the length of the probe portion A projecting out with respect to the bottom guide plate, this projecting portion A being retracted into the bottom guide plate as the testing head contacts the device to be tested, by virtue of the probe flexion and deformation.

However, the height of such projecting portion is limited by the probe fragility properties, and is usually 300 to 500 μ.

In practice, the above overtravel amount of the probes is only theoretically achievable, and problems due to probes becoming stuck in their guide holes and due to the permanent deformation of the probes already arise for very small overtravel amounts.

This problem has been circumvented by using probes with a deformation in their section lying within the air gap, as schematically shown in FIG. 2C. Such probes utilize almost all the overtravel of the projecting portion from the bottom guide plate, but are complicated to manufacture and maintain.

In addition, the bottom guide plate greatly restricts the horizontal movements of the probe tip, the extent of this movement or scrub being strictly dependent on the difference between the diameters of the hole and the probe.

In some cases, the contact probes are fixedly mounted to the top guide plate of the testing head. This arrangement is known as a testing head having clamped contact probes.

However, testing heads with loose-mounted probes are more widely employed, wherein the probes are interfaced to a “board” by a microcontact strip called the “space transformer”. This is known as a testing head having no-clamped contact probes.

In the latter case, each contact probe has an additional contact tip pointing toward a plurality of contact pads provided on the space transformer. A good electric contact is established between the probes and the space transformer in a similar way as the contact to the device to be tested, i.e. by urging the probes against the contact pads on the space transformer.

The major advantage of a testing head having no-clamped contact probes is that one or more faulty probes, or the whole set of probes, can be replaced with greater ease than is allowed by testing heads having clamped contact probes.

In this case, however, the top and bottom guide plates must be designed to withhold the contact probes in place even while no device to be tested is abutting their contact tips, or when the whole set of probes is removed for replacement.

SUMMARY OF THE INVENTION

Embodiments of this invention provide testing heads for microstructures, which have probes adapted to be deformed on touching contact pads to establish a good electric contact to a device to be tested, and adapted to be held in place without the assistance of a bottom guide plate.

One of the principles on which embodiments of the present invention stand is one of providing a testing head with a plurality of probes, each having a pre-deformed section between the testing head and the device to be tested.

Presented is a testing head comprising a guide plate having a guide hole formed therethrough and adapted to receive a contact probe having a contacting tip arranged to mechanically and electrically contact a contact pad of a test device, said contact probe having a pre-deformed section placed in a flexion region between the guide plate and the test device, said pre-deformed section being arranged to further deform as the contact pad of the test device is drawn against the contacting tip. Additionally presented is a method of creating an electro/mechanical connection between a testing head and a test device.

The features and advantages of a testing head according to the invention will be apparent from the following description of embodiments thereof, given by way of nonlimiting examples with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a testing head according to an embodiment of the prior art; [0033]
FIGS. 2A, 2B and [0034] 2C are cross-sectional views of a testing head according to further embodiments of the prior art;
FIG. 3 is a cross-sectional view of a testing head according to an embodiment of the invention; [0035]
FIGS. 4A, 4B, [0036] 4C, 4D and 4E are cross-sectional views of a testing head according to further embodiments of the invention;
FIGS. 5A and 5B are cross-sectional views of a testing head according to another embodiment of the invention; [0037]
FIGS. 5C and 5D are top plan views of alternative arrangements of a testing head according to an embodiment of the invention; [0038]
FIGS. 6A and 6B is a cross-sectional view of a testing head according to further embodiments of the invention; [0039]
FIGS. 7A, 7B, [0040] 7C and 7D are cross-sectional views of a testing head according to further embodiments of the invention; and
FIGS. 8A. [0041] 8B and 8C are cross-sectional views of a testing head according to further embodiments of the invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 3, a [0042] testing head 10 according to an embodiment of the invention, suitable to be placed in contact with a device 11 to be tested or test device, is shown.
The [0043] testing head 10 comprises at least one guide plate 12 formed with at least one guide hole 13 for receiving a contact probe 14.
The [0044] contact probe 14 has a symmetrical or asymmetrical pre-deformed section 15, placed in a flexion region 19 extending between the guide plate 12 and the device 11 to be tested. This pre-deformed section can also deform during normal operation of the testing head 10. In particular, the contact probe 14 has a contact end or tip 16 intended to abut against corresponding contact pads 17 of the device 11 to be tested and to cause a further deformation of the probe 14 at its pre-deformed section 15.
The [0045] testing head 10 shown in FIG. 3 has no-clamped contact probes, each probe having an additional contact tip 18 pointing toward a space transformer 20. This is given by way of non-limiting example of a testing head according to an embodiment of the invention. Alternatively, it would be plainly possible to provide a testing head 10 having pre-deformed clamped probes.
Advantageously according to embodiments of the invention, the [0046] flexion region 19 lies outside the testing head 10, between the guide plate 12 and the device 11 to be tested. In this way, the problems that beset conventional testing heads, due to probes becoming stuck in their guide holes, or due to the size of the air gap between the guide plates and, hence, the testing head space requirements, are overcome.
Furthermore, since the [0047] flexion region 19 is placed outside the testing head 10, the amount of possible vertical movement or overtravel for the testing head 10 can be increased.
Moreover, the horizontal movement or scrub of the [0048] contact tip 16 on the contact pads 17 is easily controlled by suitably changing the size and shape of the pre-deformed section 15 of the probe 14.
Shown in FIGS. 4A, 4B, [0049] 4C, 4D and 4E are representative embodiments of the testing head 10 according to the invention, specifically providing a range of different shapes for the pre-deformed section 15 of the probe 14.
In particular, the probe shown in the embodiment of FIG. 4A has its [0050] pre-deformed section 15 symmetrical and essentially oval in shape. The contact tip of this probe makes no horizontal movement (scrub), and the probe vertical movement (overtravel) is taken up by a deformation occurring in its pre-deformed section 15, which is in any case symmetrical.
With this configuration, a horizontal movement (scrub) having a preset amount and direction can be obtained by using a [0051] pre-deformed section 15 having one leg with a different cross-section from the other or mirror-image leg.
The probes shown in the embodiments of FIGS. 4B, 4C and [0052] 4E have each a pre-deformed section 15 of asymmetrical shape, and first and second slanted (e.g. vertical) extensions 15 a and 15 b that are suitably offset from each other to cause the horizontal movement (scrub) to occur along a given direction. It is also possible to use a probe 14 having a C-shaped pre-deformed section 15, such section having the first 15A and second 15B extensions suitably slanted (e.g. vertical), so that a horizontal movement (scrub) occurs, which depends on the contact geometry, as shown in FIG. 4D.
Advantageously according to embodiments of the invention, the [0053] probes 14 may be formed with a non-circular cross-sectional shape. In a preferred embodiment, schematically shown in FIGS. 5A and 5B, a probe 14 with a rectangular cross-sectional shape is provided. In this case, its corresponding guide hole 13 in the plate 12 should also have a rectangular cross-sectional shape, the probes 14 passing through such holes being always aligned to the contact pads 17 of the device 11 to be tested.
Using a rectangular cross-sectional probe as shown in FIG. 5A, the deformed of the [0054] probe 14 in the plane of the pre-deformed section 15 is better controlled when the probe contacts the device 11 to be tested, the movement occurring in a predetermined plane such that different rectangular cross-sectional probes will retain the same orientation during their vertical or overtravel movement.
Major advantages of a [0055] probe 14 formed with a non-circular cross-section are:
a better orientation of the probes at the testing head assembling phase by reason of the match provided between the guide holes and the probes; [0056]
a better controlled deformation during the contact of the probe tip to the pads of a device to be tested; and [0057]
easier replacement of faulty probes in a self-centered position, once the relative positions of the guide holes and the contact pads are set, and accordingly, more convenient servicing of the testing head. [0058]
Advantageously according to further embodiments of the invention, a [0059] testing head 10 carries a plurality of probes 14 formed with a pre-deformed section 15 and orientated according to a symmetrical pattern of their deformed sections relative to a row of contact pads, as shown in FIG. 5C, or according to a mirror-image pattern relative to two adjacent rows of contact pads, as shown in FIG. 5D, minimizing the bulk dimensions of the plurality of probes and, therefore, of the testing head.
In a preferred embodiment, wherein the [0060] testing head 10 has probes 14 orientated according to a symmetrical pattern, for example, such probes 14 have non-circular cross-section for more convenient orientation of the deformed sections, each probe 14 being rotated through a suitable angle, e.g. 180°, one from the other. In particular, the cross-sectional shape is a rectangle with the small side in the same plane as the deformed section, as shown in FIG. 5A, to have the probe 14 oriented in the right direction, even when the probe is deformed.
In a further embodiment of the invention, as schematically shown in FIGS. 6A and 6B, an [0061] area 21 of frictional engagement of the probe 14 in its guide hole 13 through the guide plate 12 is provided to prevent the probe 14 from dropping off the guide hole 13 while no device 11 to be tested is positioned.
This further embodiment is specially suitable for use with a [0062] space transformer 20, wherein the probe 14 is held in the guide 12 only by frictional engagement.
According to a preferred embodiment, the [0063] probe 14 is provided with an additional pre-deformed section 22 extending inside the guide hole 13, as shown in FIG. 6A, to form the area 21 of frictional engagement of the probe 14 in the guide hole 13.
A target amount of frictional engagement is obtained by suitably selecting the shape of this additional [0064] pre-deformed section 22 and the dimensions of its guide hole 13.
Alternatively, the [0065] area 21 of frictional engagement could be provided by using guide holes 13 slanting from a perpendicular line to the plane containing the device 11 to be tested, i.e. from the vertical lay of the probes 14, as schematically shown in FIG. 6B. In the same manner, curvilinear guide holes 13 could be also considered.
According to a further embodiment of the invention, slanting or curvilinear guide holes are used for [0066] probes 14 incorporating said additional pre-deformed section 22, so as to increase the frictional engagement generated in said area 21 of frictional engagement of the probe 14 in the guide hole 13.
According to an alternative embodiment, the [0067] guide plate 12 comprises a top guide hole having an S-like pattern; or different patterns, e.g. a curvilinear pattern, for increasing the frictional engagement of the probes in the guide holes.
It should be noted that, although a [0068] single guide plate 12 accommodating the probes 14 has been described thus far, several such guide plates could be used instead.
According to further embodiments of the invention, the [0069] testing head 10 comprises two or more juxtaposed guide plates 12 a, 12 b, . . . , 12 n, which are suitably offset from one another to create a combined area 21 a of frictional engagement between the probes 14 and the guide plates 12 a, 12 b, . . . , 12 n, as schematically shown in FIGS. 7A and 7B.
The [0070] guide plates 12 a, 12 b, . . . , 12 n are in mutual contact relationship, and can be assembled such that each guide hole and each area 21 of frictional engagement have non-straight patterns, according to more or less complicated forms, to increase the probe 14 retaining force in the guide plates.
According to another embodiment of the invention the [0071] guide plate 12 is overlaid by an elastic film 23 to increase the probe 14 retaining force inside the guide hole 13, as schematically shown in FIG. 7C.
This [0072] elastic film 23 would increase the probe-to-hole friction force, and with it, the probe retaining force in the guide plate.
Finally, according to a further embodiment of the invention, two or more [0073] juxtaposed guide plates 12 a, 12 b, . . . , 12 n, not offset from each other, are used to receive at least one probe 14 provided with an additional pre-deformed section 22 for retaining the probe within the guide holes 13, as schematically shown in FIG. 7D.
It should be emphasized that the embodiments of the [0074] testing head 10 described hereinabove increase the probes 14 retaining force within the guide holes 13 without interfering with any of the operations for replacing faulty probes 14, the operations of pulling out and pulling in the probes 14 being here much simpler to perform than in conventional designs, due to the pre-deformed section 15 having been located outside the testing head 10.
To summarize, the [0075] testing head 10, according to a preferred embodiment of the invention, comprises at least one probe 14 having a pre-deformed section 15 located in a flexion region 19 outside the testing head 10, on the same side as a device 11 to be tested. The flexion of this pre-deformed section takes up the probe 14 vertical movement or overtravel upon the probe tip 16 contacting a pad 17 of the device 11 to be tested, whether or not the probe overtravel is accompanied by a horizontal movement or scrub of the contact tip 16 depending on the shape of the pre-deformed section 15.
Broadly speaking, [0076] pre-deformed sections 15 with different dimensions and symmetrical or asymmetrical shapes may be provided, of which some non-limiting examples are shown in FIGS. 8A, 8B and 8C. It is understood, however, that these examples are not exhaustive of all possible shapes for the pre-deformed sections 15 of the probes 14 of a testing head 10 according to the invention.
Changes can be made to the invention in light of the above detailed description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all methods and devices that are in accordance with the claims. Accordingly, the invention is not limited by the disclosure, but instead its scope is to be determined by the following claims. [0077]

Claims

1. Testing head having vertical probes and comprising:

a guide plate having a guide hole formed there through; and

a contact probe adapted to be received in said guide hole and having a contacting tip arranged to mechanically and electrically contact a contact pad of a test device,

wherein said contact probe has a pre-deformed section placed in a flexion region between the guide plate and the test device, said pre-deformed section being arranged to further deform as the contact pad of the test device is drawn against the contacting tip.

2. The testing head of claim 1, further comprising a plurality of probes having pre-deformed sections symmetrically orientated with a row of contact pads.

3. The testing head of claim 1, further comprising a plurality of probes having pre-deformed sections orientated in mirror-image relationship with two rows of contact pads.

4. The testing head of claim 1, further comprising a plurality of probes having pre-deformed sections orientated in mirror-image relationship with two adjacent rows of contact pads.

5. The testing head of claim 1, wherein an area of frictional engagement is provided between said probe and said guide hole to prevent the probe from dropping off the guide hole when no device to be tested is positioned.

6. The testing head of claim 5, wherein said probe comprises an additional pre-deformed section lying inside said guide hole to enhance the frictional engagement in said area.

7. The testing head of claim 5, wherein said guide hole is slanted from a perpendicular line to the plane containing the test device, and produces said area of frictional engagement.

8. The testing head of claim 5, wherein said guide hole is curvilinear from the perpendicular line to the plane containing the test device and produces said area of frictional engagement.

9. The testing head of claim 5, wherein said probe comprises an additional pre-deformed section provided within said guide hole, and said guide hole is slanted from a perpendicular line to the plane containing the test device and produces said area of frictional engagement.

10. The testing head of claim 5, wherein said probe comprises an additional pre-deformed section provided within said guide hole, and said guide hole is curvilinear and produces said area of frictional engagement.

11. The testing head of claim 1, wherein said pre-deformed section is symmetrical in shape.

12. The testing head of claim 1, wherein said pre-deformed section is asymmetrical in shape.

13. The testing head of claim 11, wherein said pre-deformed section is essentially oval and symmetrical in shape.

14. The testing head of claim 12, wherein said pre-deformed section is C-shaped with suitably slanted first and second extensions that are aligned to each other.

15. The testing head of claim 12, wherein said pre-deformed section is C-shaped with first and second vertical extensions that are aligned to each other.

16. The testing head of claim 12, wherein said pre-deformed section is C-shaped with first and second extensions that are suitably slanted and offset from each other.

17. The testing head of claim 12, wherein said pre-deformed section is C-shaped with first and second vertical extensions that are suitably offset from each other.

18. The testing head of claim 1, further comprising two or more guide plates arranged in mutual contact relationship to provide said guide hole.

19. The testing head of claim 18, wherein said guide plates are mutually offset and provide for a guide hole with a non-straight section.

20. The testing head of claim 1, wherein an elastic film overlies said guide plate and enhances the retaining force of said probe in said guide hole.

21. The testing head of claim 1, wherein said probe has a non-circular cross-sectional section.

22. The testing head of claim 1, wherein said probe has a rectangular cross-sectional shape.

23. The testing head of claim 1, wherein said probe has a rectangular cross-sectional shape with the small side of the rectangle lying on the same plane as said pre-deformed section.

24. A testing head having vertical probes and comprising:

a guide plate having a guide hole formed there through; and

wherein, as a contact pad of a test device is placed against the contacting tip of the contact probe, said contact probe is structured to deform in a flexion region between the guide plate and the test device.

25. The testing head of claim 24, wherein said contact probe has a pre-deformed section placed in said flexion region, said pre-deformed section being arranged to further deform as the contact pad of the test device is drawn against the contacting tip.

26. The testing head of claim 24, further comprising a plurality of probes having pre-deformed sections symmetrically orientated with a row of contact pads.

27. The testing head of claim 24, further comprising a plurality of probes having pre-deformed sections orientated in mirror-image relationship with two rows of contact pads.

28. The testing head of claim 24, further comprising a plurality of probes having pre-deformed sections orientated in mirror-image relationship with two adjacent rows of contact pads.

29. The testing head of claim 24, wherein an area of frictional engagement is provided between said probe and said guide hole to prevent the probe from dropping off the guide hole when no device to be tested is positioned.

30. The testing head of claim 29, wherein said probe comprises an additional pre-deformed section lying inside said guide hole to enhance the frictional engagement in said area.

31. The testing head of claim 29, wherein said guide hole is slanted from a perpendicular line to the plane containing the test device, and produces said area of frictional engagement.

32. The testing head of claim 29, wherein said guide hole is curvilinear from the perpendicular line to the plane containing the test device and produces said area of frictional engagement.

33. The testing head of claim 29, wherein said probe comprises an additional pre-deformed section provided within said guide hole, and said guide hole is slanted from a perpendicular line to the plane containing the test device and produces said area of frictional engagement.

34. The testing head of claim 29, wherein said probe comprises an additional pre-deformed section provided within said guide hole, and said guide hole is curvilinear and produces said area of frictional engagement.

35. The testing head of claim 24, wherein said pre-deformed section is symmetrical in shape.

36. The testing head of claim 24, wherein said pre-deformed section is asymmetrical in shape.

37. The testing head of claim 35, wherein said pre-deformed section is essentially oval and symmetrical in shape.

38. The testing head of claim 36, wherein said pre-deformed section is C-shaped with suitably slanted first and second extensions that are aligned to each other.

39. The testing head of claim 36, wherein said pre-deformed section is C-shaped with first and second vertical extensions that are aligned to each other.

40. The testing head of claim 36, wherein said pre-deformed section is C-shaped with first and second extensions that are suitably slanted and offset from each other.

41. The testing head of claim 36, wherein said pre-deformed section is C-shaped with first and second vertical extensions that are suitably offset from each other.

42. The testing head of claim 24, further comprising two or more guide plates arranged in mutual contact relationship to provide said guide hole.

43. The testing head of claim 42, wherein said guide plates are mutually offset and provide for a guide hole with a non-straight section.

44. The testing head of claim 24, wherein an elastic film overlies said guide plate and enhances the retaining force of said probe in said guide hole.

45. The testing head of claim 24, wherein said probe has a non-circular cross-sectional section.

46. The testing head of claim 24, wherein said probe has a rectangular cross-sectional shape.

47. The testing head of claim 24, wherein said probe has a rectangular cross-sectional shape with the small side of the rectangle lying on the same plane as said pre-deformed section.

48. A method for creating an electro/mechanical connection between a testing head and a test device, the method comprising:

holding a contacting tip of a contact probe in the testing head in correspondence to a contact pad on the test device;

causing the contacting tip of the contact probe to abut against the contact pad as the device to be tested is pressed against the contacting tip;

providing a pre-deformed section of the contact probe in a flexion region between the guide plate and the test device; and

causing the contact probe to deform in correspondence of said pre-deformed section, as the device to be tested is further pressed against the contacting tip.

49. The method of claim 48, wherein holding a contacting tip of a contact probe in the testing head comprises holding a portion of the contact probe in a frictional relationship with the guide hole.

50. The method of claim 49, wherein said probe comprises an additional pre-deformed section lying inside said guide hole.

51. The method of claim 49, wherein said guide hole is slanted from a perpendicular line to the plane containing the test device.

52. The method of claim 49, wherein said guide hole is curvilinear.

53. The method of claim 49, wherein said probe comprises an additional pre-deformed section provided within said guide hole, and that said guide hole is slant from a perpendicular line to the plane containing the test device.

54. The method of claim 49, wherein said probe comprises an additional pre-deformed section provided within said guide hole, and that said guide hole is curvilinear.

55. The method of claim 48, further comprising, before the contact pad touches the contacting tip:

inserting a plurality of contact probes having pre-deformed sections through a plurality of guide holes wherein said pre-deformed sections of the contact probes are symmetrically orientated with a row of contact pads.

56. The method of claim 48, further comprising, before the contact pad touches the contacting tip:

inserting a plurality of contact probes having pre-deformed sections through a plurality of guide holes wherein said pre-deformed sections of the contact probes are orientated in mirror-image relationship with two rows of contact pads.

57. The method of claim 48, further comprising, before the contact pad touches the contacting tip:

inserting a plurality of contact probes having pre-deformed sections through a plurality of guide holes wherein said pre-deformed sections of the contact probes are orientated in mirror-image relationship with two adjacent rows of contact pads.

58. The method of claim 48, wherein providing a pre-deformed section of the contact probe comprises providing a pre-deformed section symmetrical in shape.

59. The method of claim 48, wherein providing a pre-deformed section of the contact probe comprises providing a pre-deformed section asymmetrical in shape.

60. The method of claim 58, wherein said pre-deformed section is essentially oval and symmetrical in shape.

61. The method of claim 59, wherein said pre-deformed section is C-shaped with suitably slanted first and second extensions that are aligned to each other.

62. The method of claim 59, wherein said pre-deformed section is C-shaped with first and second vertical extensions that are aligned to each other.

63. The method of claim 59, wherein said pre-deformed section is C-shaped with first and second extensions that are suitably slanted and offset from each other.

64. The method of claim 59, wherein said pre-deformed section is C-shaped with first and second vertical extensions that are suitably offset from each other.

65. The method of claim 48, wherein holding a contacting tip of a contact probe in the testing head comprises providing two or more guide plates arranged in mutual contact relationship to form said guide hole.

66. The method of claim 65, wherein said guide plates are mutually offset and provide for a guide hole with a non-straight section.

67. The method of claim 48, further comprising applying a layer of elastic material to said guide plate.

68. The method of claim 48, wherein said probe has a non-circular cross-sectional section.

69. The method of claim 48, wherein said probe has a rectangular cross-sectional shape.

70. The method of claim 48, wherein said probe has a rectangular cross-sectional shape with the small side of the rectangle lying on the same plane as said pre-deformed section.