WO1998030914A1

WO1998030914A1 - Contact probe assembly for testing electrical devices

Info

Publication number: WO1998030914A1
Application number: PCT/US1998/000499
Authority: WO
Inventors: Peter Hoang Nguyen; Loi Nguyen
Original assignee: Peter Hoang Nguyen; Loi Nguyen
Priority date: 1997-01-13
Filing date: 1998-01-08
Publication date: 1998-07-16
Also published as: AU5912898A

Abstract

A simplified contact probe assembly for testing integrated circuit devices is provided comprising multiple contact needles (4). The contact end of the needles (4) is attached to a fixing plate (1), has a top portion (8), a middle portion (7) and a bottom portion (6) and a contact tip (5) making contact with IC's pads (3). The top portion (8) and a fixing plate form a first angle (9); the top portion (8) and the middle portion (7) form a second angle (10); the middle portion (7) and bottom portion (6) form a third angle (11); a bottom portion (6) and the contact pads (3) form a fourth angle (12), whereby, by adjusting the first, second, third and fourth angles, or the ratios of the lenghts among top, middle, and bottom portions (8, 7, 6), the axial forces of the needles (4), the buckling directions, and the wiping effects are controllably predetermined. Any of the three portions of the contact ends can be linear or precurved, or can be coated with electrical insulating materials.

Description

CONTACT PROBE ASSEMBLY FOR TESTING ELECTRICAL DEVICES

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention generally relates to contact probes for testing electrical devices.

In particular, this invention relates to needle probe assembly used in testing integrated

circuits (ICs) by making contacts with the test points ("pads") of ICs.

2. Description of Related Art

In the semiconductor industry, electrical products or devices such as ICs require testing for working condition and performance during the manufacturing

process. ICs are normally made in group in the form of wafers and then excised into

individual chips. Needle cards or contact probe assemblies are commonly used to test

integrated chips, wafers, and multichip modules. Needle card assemblies consist of a

plurality of contact probes or resilient needles, which exactly correspond to the pads of the ICs being tested. Thus, a new needle card has to be manufactured for each IC pad

contact pattern.

In recent years, because of the increasing needs and complexity in IC or chips,

the density of IC pads, or the probe needles in a contact probe assembly, has been increased significantly. For instance, the demand for high density pads reaches 300

pads in a 10x10 mm² area. The distance between two pads or two probe needles is

called the pitch. The demand for pitch can reach as small as 75 μm or 3 mils in a chip.

In addition, it is not always possible to fill the total area of the test card or contact

probe assembly with contact needles because of the physical limitation of multi- layered, densely arranged needles in the current state of the art contact probe assembly. Thus, manufacturing of needle probes for high density IC pads becomes increasingly complex and expensive because manual work is required in assembling high-precision needle probes. Buckling beam technology is well-known in the art in designing contact probe needles. When axial forces are applied on the needle probes to push the needles

against the IC pads in a predetermined magnitude, the needles will buckle laterally as such that the axial forces against the pads will not increase beyond a certain force magnitude. However, there are concerns in using buckling needle probe, including the possible short circuiting between needles, and needle sliding off the pads due to uneven surface of pads and different length of probe needles. Coating the needles with insulating materials or sheltering the needles by insulating structures may solve the short circuiting problem. Likewise, in order to achieve good contacts between contact probe needles and IC pads, the needle tips must create wiping effects to penetrate an oxide layer on some ICs' pads. Thus, practitioners of the art have been attempting to improve the technologies of IC testing probes to meet the ever increasing demands of high-density IC pads. In U.S. Pat. No. 4,027,935, issued to Byrnes et al on June 7, 1977, a contact for an electrical contactor assembly is disclosed. In the disclosure of the invention, the contact probe has a pivotable end and a pre-curved center section to provide minimal forces on contact pads. The pre-curved center section has a large radius and is arranged such that the privotable end and the contacting end of the contact are offset from one another within the plane including the radius of the center section so that the deflection direction is predetermined. In addition, the disclosed contact probe assembly consists of a guiding plate for the contact probes.

In U.S. Pat. No. 4,843,315, issued to Bayer et al on June 27, 1989, a contact

probe arrangement for testing electrical devices is disclosed. The disclosed contact

probe arrangement includes a stack of perforated plates through which extend a plurality contact probes. The special arrangement of the plates serve to reduce contact

resistance between contact probe and the contact pad of the device to be tested. The

plate arrangement also serves to adapt to irregularities of the contact pad surface. In U.S. Pat. No. 5,367,254, issued to Faure et al. on November 22, 1994, a test probe assembly using buckling wire probes is disclosed. Each test probe unit includes

a wire and a slotted tube containing the wire. The test probe units are inserted into

predetermined respective holes of an apertured block of insulating material according

to a pattern of device points to be tested.

Nevertheless, the advantageous features needed in a contact probe assembly include controllable and predetermined buckling direction, reduced axial forces against

contact pads, controlled wiping effects, reduced costs and high efficiency of

manufacturing, and capability of probe needle high density. However, all the contact

probe assemblies disclosed in the cited prior art do not possess all the advantageous features combined in one contact probe to meet ever increasing complex ICs being tested. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a contact probe assembly capable of testing the contact pads of ever increasing density in more advanced ICs. It is another object of the present invention to provide a contact probe assembly capable of testing a whole wafer.

It is yet another object of the present invention to provide a contact probe

assembly having contact needles capable of buckling in a predetermined direction.

It is a further object of the present invention to provide a contact probe

assembly having controllable and predetermined axial forces against the contact pads of ICs being tested.

It is yet another object of the present invention to provide a contact probe

assembly having contact needles whose wiping effects are controllable and

predetermined when contacting the contact pads of ICs.

It is still a further object of the present invention to provide a simplified contact

probe assembly without any guiding plates or housing for probe needles, hence,

reducing the costs and time of manufacturing contact probes and improving the

efficiency of manufacturing contact probes. The above and other objects of the invention are achieved by a contact probe

assembly for electrically testing a device having a plurality of contact pads, comprising:

electrically conductive wires having a first end and a second end; a fixing plate having a

plurality of apertures, said fixing plate being securely fixed on a printed circuit board;

said first end extending through said apertures of said fixing plate and electrically

SUBSTITUTE SHEET (RULE 26Ϊ connected to said printed circuit board; said second end having a top portion securely attached to said fixing plate, a middle portion, a bottom portion having a contact tip for contacting said contact pads of ICs; said top portion and said fixing plate forming

a first angle, said top portion and said middle portion forming a second angle; said

middle portion and said bottom portion forming a third angle; said bottom portion and

said contact pads forming a fourth angle; said second and third angles being

positioned in opposite directions; said top portion, middle portion, or bottom portion buckling laterally towards a predetermined direction when the contact tips contact the

pads.

Whereby, by adjusting the first, second, third, or fourth angle, or the ratios of

lengths among top, middle and bottom portions, the axial forces are controllably predetermined. By adjusting said third angle, the wiping effects on said pads are controllably predetermined. One or more of said three portions can be linear, or

precurved. The probe needles can be coated with electrically insulating chemicals.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail hereinafter with respect to the

accompanying figures, wherein: FIG. 1 is a schematic illustration of the contact probe assembly in accordance

with the present invention;

FIG 2 is an enlarged view of the contact end of an individual contact probe

needle. The contact end consists of three portions and a contact tip making contact

with a contact pad; FIG 3 is an enlarged view of another example of the contact end of an individual contact probe needle, exemplified as an embodiment of the present invention; FIG 4 is an enlarged view of the contact end of an individual contact probe needle, exemplified as a preferred embodiment in the present invention; FIG. 5 is an enlarged view of the contact end of one individual contact probe needle, of which one portion of the contact end is precurved in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 is an exemplary teaching to assemble probe needles of the present invention into a contact probe assembly. The etching technology is well-known in the art of making contact probe needles. Practitioners in the field are readily capable of etching probe needles of any geometric shapes according to the teaching of the present invention. The probe needles 4 are etched or molded in a predetermined three-portion geometric shape near the end of the contact tips 5 of the needles 4. The probe needles 4 are made of proper metal sheets, such as tungsten, beryllium copper, or other alloys

available in the market. The cross-section of each resulting probe needles 4 can be of any shape, i.e.: cylindrical, trapezoidal, rectangular, circular, or non-circular. The thickness or diameter of the probe needles can vary to meet the specifications of the

ICs pads and can be as small as 25 μm or 1 mil when utilizing the teaching of the present invention.

Following the etching process, preferably, the probe needles 4 are inserted into

apertures of a fixing plate 1, preferably, ceramic, with the aid of microscope. The needles 4 are then securely attached to the fixing plate by epoxy. The apertures on the plate 1 are arranged in a predetermined pattern of contact pads 3 of IC 20 being tested. The contact tips 5 of the probe needles are pointing towards the direction to make contacts with the IC pads 3. The plate 1 is securely attached onto a printed circuit board 17 (PCB).

The other ends of the needle probes distal to the contact tips 5 are electrically

connected to the printed circuit board 17 at PCB solder pads 19. The said fixing plate 1 is securely attached on the printed circuit board 17 by threaded rods 15 and screws

14 and metal washer 16, or by epoxy. The distance between the contact tips 5 and the

fixing plate 1 is a predetermined length for making contact with the contact pads 3

when the printed circuit board 17 is lowered in the direction of the contact pads 3.

Referring to Fig. 2, the geometric shape of the probe needles 4 is custom-

designed to meet specifications for various chips, based upon their axial force

requirements, the wiping effects, and the density of the pads. When the printed circuit

board 17 with the needle probes is lowered to make contacts with the pads 3, the top portion 8, middle portion 7, or lower portion 6 may buckle laterally individually or in

unison, depending on the individual custom-design of the relative lengths of the three

portions.

It is well-known in the art that the buckling beam mechanism controls the

maximum axial force of the probe needles applied to the contact pads. The use of

buckling beam technology reduces the risk of potential damages to the IC pads. The axial forces being transmitted onto the contact pads 3 from the contact needles 4 will

remain constant when the probe needles buckle. However, because of the close proximity of each needle in a high-density contact probe, short circuiting among needles may occur if the probe needles, which do not have an electrically insulating coating, touch each other when buckling excessively and randomly. In the current state of the art buckling beam probe, practitioners of the field attempt to insulate the probe needles by using insulating composite, coating, insulating tubing, or channels. Adding exterior insulating structures to the probe needles, however, may greatly reduce the spacing or pitch of the probes and reduce the density capability of contact pad. Furthermore, friction will be generated between needles and the insulating structures.

In the present invention, because of the geometric arrangement of the three portions 6, 7, and 8 of the probe needles, the buckling directions of the three portions 6,7 and 8 of the probe needles 4 are readily controlled in a predetermined orientation. The three portions can buckle either individually or simultaneously to avoid potential

short circuiting among the needles. No exterior insulating structures are required according to the present invention. During the testing of the ICs, in order to obtain an electrically reliable contact between the contact tip 5 and the IC pads 3, the needle tips 5 have to penetrate through an oxide layer on the contact pad surface of some ICs. When contacting the pads 3, the probe needles 4 generate wiping effects on the contact point, which force

the contact tips 5 rub over the surface of the contact pads 3. The extent of wiping effects is dependent upon the axial force and the geometric design of the probe needles. Some ICs or electrical devices may not need significant wiping effects, as opposed to others, because of the type of metal materials used in making the contact pads. Therefore, it is desirable to control wiping effects by the contact probes when the probe needles 4 are being custom-designed and made for specific type of IC being

tested.. In the current state of art contact probe assembly, practitioners in the field

attempt to control or retain the wiping effects in a contact probe assembly by attaching

guiding plates, tubing or channels to the probe needles. Such added accessories for the probe needles significantly limit the density capability of the probe needles and complicate probe card manufacturing process. However, the present invention teaches

simplified methods to control the wiping effects by varying the lengths and angles of

the three portions of the probe needles.

Referring to Fig 3 and 4, the practitioners in the art will readily understand the general concept of the present invention. The present invention utilizes the relative lengths of the top portion 8, middle portion 7, and bottom portion 6 and the relative

degrees of the first, second, third, and forth angles in order to control the magnitude of

the axial force, the buckling direction, and the wiping effects.

Figure 4 is an example of a preferred embodiment for designing the three

portions 6, 7, and 8 of the probe needles to achieve ideal axial forces and proper wiping effects or wiping distance on the contact pads 3. The relative lengths of the

three portions of the probe needles 4 vary depending upon the specifications and

requirements of the IC being tested. Given a specific type of metal used for the probe

needles, the magnitude of the axial force against the pads can be controlled by

adjusting the length of the middle portion 7 in relation to the top and bottom portions 8, 6. The longer the middle portion 7 is, in relation to the bottom portion 6, the greater the wiping effect or distance will be generated on the surface of the pads as illustrated in Fig 4 when making contacts. In addition, the smaller the fourth angle 12 is, the greater the wiping effect or distance will be generated on the surface of the pads 3 when making contacts. Depending upon how much wiping effects are needed for a specific type of ICs or wafers being tested, the wiping effect can thus be adjusted by adjusting the relative length of the middle and bottom portions 7, 6, or the degree of the fourth angle 12. Different types of pads made of different types of metals requires different magnitude of axial force and wiping distance in order to have effective wiping effects without damaging the pads. Further, the second angle 10 and the third angle 11 have a range greater than 90 degree and smaller 180 degree, while the fourth angle has range smaller than 90 degree and greater than 45 degree. In referring to Fig. 3, the buckling directions of the contact probe needles of the present invention are readily determined. The buckling direction of the upper portion 8 normally points to the opposite direction of the second angle 10. In referring to Fig. 4, the buckling direction of the middle portion 7 points to the opposite direction of the second angle 10, or the direction of the third angle 11. The buckling ability of

the contact probe needles are dependent upon the length of the three portions 6, 7 and 8. In addition, it is well-known in the art that the buckling direction can be controlled by precurving the portion intended to buckle. Thus, the teaching of the present invention will also be applied in the probe assembly whose probe needles are precurved in three portions as illustrated in FIG 5. Among all types of buckling beam contact probe assemblies, each contact

probe assembly has a certain tolerance, which indicates how far the probe needles can buckle before they become short circuiting among each other. The tolerance of a contact probe assembly is normally determined by factors, such as the density of the pad pattern or the pitch of the needles, the diameter or thickness of the probe needles, the length of the needle making contacts, the variation of the length of the needles among themselves, and the variation of the height of the contact pads. Most of the above-mentioned factors are readily controllable. In the present invention, because of

the unique geometric and simplified design of the contact ends of the probe needles,

the pitch of the probe needles can reach a value as small as 75 μm or 3 mils.

Therefore, the contact probe assembly in accordance with the present invention is designed to accommodate unlimited number of probe needles within a predetermined area in a contact probe assembly. Since the contact probe assembly disclosed under the present invention has virtually no physical limitation in needle arrangement, one custom-designed contact probe assembly can test many chips or the whole wafer at the same time. In the disclosure of the present invention, there is shown and described only the preferred embodiment. It should, however, be understood that the invention is capable of changes or modification within the scope of the invention concept. It is therefore desired that the invention not be limited to this embodiment. It is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

Claims

What is claimed is: 1. A contact probe assembly for testing electrical devices having contact pads, comprising: a plurality of electrically conductive wire having a first end and a second end ,

said wire capable of buckling when subject to axially opposing forces;

a fixing plate having a plurality of apertures, said fixing plate being securely

attached on a printed circuit board; said first end extending through said apertures of

said fixing plate and electrically connected to said printed circuit board; said second

end having a top portion securely attached to said fixing plate, a middle portion, and a

bottom portion having a contact tip, whereby said contact tip contacts said contact

pads when said fixing plate is lowered towards said contact pads.

2. The contact probe assembly according to claim 1, wherein said top

portion and said fixing plate form a first angle, said top portion and said middle portion

form a second angle, said middle portion and said bottom portion form a third angle,

said bottom portion and said contact pads form a forth angle, whereby said top

portion, middle portion, or bottom portion buckles laterally towards a predetermined

direction individually or in unison when said contact tips contact said contact pads in a

pre-determined axial force.

3. The contact probe assembly according to claim 2, wherein said first

angle has a range greater than 45 degree and smaller than or equal to 90 degree, said second angle has a range greater than 90 degree and smaller than 180 degree, said

third angle has a range greater than 90 degree and smaller than 180 degree, and said forth angle has a range greater than 45 degree and less than 90 degree to achieve predetermined wiping effects.

4. The contact probe assembly according to claim 3, wherein said top portion, middle portion, or bottom portion is linear in a predetermined length to achieve a predetermined minimum axial force and a predetermined wiping effects on the surface of said contact pads.

5. The contact probe assembly according to claim 4, wherein the length of said middle portion is greater than the length of said top portion and bottom portion to

achieve predetermined axial forces and predetermined wiping effects on said contact pads.

6. The contact probe assembly according to claim 4, wherein the length of said top portion is longer than the length of said middle portion and bottom portion.

7. The contact probe assembly according to claim 4, wherein the length of said bottom portion is longer than the length of said top portion and middle portion.

8. The contact probe assembly according to claim 3, wherein said top portion, middle portion, or bottom portion is precurved in a pre-determined length to achieve a predetermined minimum axial force and a predetermined wiping effect on said contact pads.

9. The contact probe assembly according to claim 8, wherein said top portion, middle portion, or bottom portion is linear in a predetermined length to achieve a predetermined minimum axial force and a predetermined wiping effects on the surface of said contact pads.

10. The contact probe assembly according to claim 8, wherein the length of said middle portion is greater than the length of said top portion and bottom portion to

achieve predetermined axial forces and predetermined wiping effects on said contact

pads.

11. The contact probe assembly according to claim 8, wherein the length of said top portion is longer than the length of said middle portion and bottom portion.

12. The contact probe assembly according to claim 8, wherein the length of

said bottom portion is longer than the length of said top portion and middle portion.

13. The contact probe assembly according to claim 3, wherein said top

portion, middle portion, and bottom portion are coated with electrically insulating

material.