MULTI-BEAM CANTILEVER STYLE CONTACT PIN FOR IC TESTING

Abstract

An integral electrical contact pin for electrically connecting a test terminal of tester load board with an IC terminal of an IC device, adapted for short test height. The integral electrical contact pin comprises an upper cantilever arm and lower cantilever arm connected at a back portion. The upper cantilever arm is movable between a first default position to a second and third position, where the upper cantilever arm is in contact with the lower cantilever arm in the second position. A bracket arm is provided, extending in the opposite direction from the two cantilever arms for engagement with the corresponding socket housing.

Claims

1. An integral electrical contact pin for electrically connecting a test terminal of tester load board with an IC terminal of an IC device, adapted for short test height, the integral electrical contact pin comprising: a resilient upper cantilever arm having a free end and an opposing connecting end; an upper pin tip located at the free end of the upper cantilever arm for contact with the IC terminal of the IC device; a lower cantilever arm having a free end and an opposing connecting end, the lower cantilever arm extending essentially in the same direction the upper cantilever arm, arranged below and spaced apart from the upper cantilever arm; a lower pin tip extending downwardly from the lower cantilever arm for contact with a test terminal of the tester load board; and a back portion connecting the connecting end of the upper cantilever arm to connecting end of the lower cantilever arm wherein the free end of the upper cantilever arm is movable between a default first position where the free end of the upper cantilever arm and the free end of the lower cantilever arm are spaced apart and a second position where the free end of the upper cantilever arm is in contact with the free end of the lower cantilever arm.

2. The integral electrical contact pin of claim 1, wherein the free end of the upper cantilever arm is elastically biased from the default first position to the second position in response to an external load applied onto the upper pin tip.

3. The integral electrical contact pin of claim 1, wherein the closest distance between free end of the upper cantilever arm at its default first position and the free end of the lower cantilever arm is between 0.14 mm to 0.16 mm.

4. The integral electrical contact pin according to claim 2, wherein the upper cantilever arm, the lower cantilever arm and the back forms essentially a “C” shape.

5. The integral electrical contact pin according to claim 2, wherein adapted for test height at 2 mm and below.

6. The integral electrical contact pin according to claim 2, wherein upper pin tip is narrower than the thickness of the main body of the contact pin.

7. A test socket assembly, comprising: a socket housing having a lower surface generally in engagement with a surface of a tester load board, said housing further having an upper surface, generally parallel to, spaced from, and facing oppositely from said lower surface, at least one socket cavity formed in said housing extending through said socket housing between said lower surface and said upper surface, the socket cavity having at least one socket slot and the socket cavity having a roof section on the upper surface; and at least one integral electrical contact pin according to any one of claims 1 to 6 sized to fit within the socket slot, the integral electrical contact pin further comprising a protrusion located on the free end of the upper cantilever arm, wherein when the integral electrical contact pin is mounted within the socket slot, the free end of the upper cantilever arm is in a third position, in between the first default position and the second position due to the protrusion on the upper cantilever arm engaging with the roof section of the socket slot.

8. The test socket assembly according to claim 7 wherein the closest distance between the free end of the upper cantilever arm at its third position and the lower cantilever arm is between 0.1 15 mm to 0.135 mm.

9. The test socket assembly according to claim 7, wherein the socket cavity further comprises a retaining wall planar to and horizontally displaced from a side wall of the socket cavity transverse to the socket slot, the retaining wall extending from the upper surface of the socket housing into the socket cavity and terminating a distance before the lower surface of the socket housing and the integral electrical contact pin further comprises a bracket arm, the bracket arm extending in the opposite direction from the upper and lower cantilever arms, the bracket arm and back portion defining a channel to receive the retaining wall of the socket cavity when the integral electrical contact pin is mounted within the socket slot.

10. The test socket assembly according to claim 9, wherein the bracket arm is a “L” shape extension from the back portion of the integral electrical contact pin.

11. The test socket assembly according to claim 9, wherein the width of the retaining wall is greater than width of the channel defined by the bracket arm and the back portion of the integral electrical contact pin such that the retaining wall is gripped by the integral electrical contact pin when said contact pin is mounted in the socket housing.

12. The test socket assembly according to claim 11, wherein the difference between the width of the retaining wall and the width of the channel defined by the bracket arm and the back portion of the integral electrical contact pin is between 0.01 mm to 0.02 mm.

13. The test socket assembly according to claim 12, wherein during test condition, resilient upper cantilever arm is biased to the second position and the back portion of the integral electrical contact pin disengages from the retaining wall.

14. The test socket assembly according to claim 9, wherein the upper pin tip of the integral electrical contact pin has a wiping length of less than 0.10 mm.

15. The A-test socket assembly according to claim 9, wherein upper pin tip of the integral electrical contact pin has a wiping length between 0.06 mm to 0.07 mm.

Description

DRAWINGS/BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 show a front cross-sectional view of an electrical contact pin in an uncompressed state with an IC chip in a first embodiment of the present invention.

[0021] FIG. 1A is a close-up view of the selected section of FIG. 1.

[0022] FIG. 2 shows a front cross-sectional view of an electrical contact pin in a compressed state during testing of an IC chip in a first embodiment of the present invention.

[0023] FIG. 2A is a close-up view of the selected section of FIG. 2, showing disengagement of the back portion of the electrical contact pin from the socket housing.

[0024] FIG. 3 shows a front cross-sectional view of an electrical contact pin between a partially compressed state (mounted in socket housing) and a fully compressed state (test condition) in a first embodiment of the present invention.

[0025] FIG. 4 is a perspective view of an electrical contact pin of a second embodiment of the present invention.

[0026] FIG. 5A shows an upside-down perspective view of a socket housing in a first embodiment of the present invention.

[0027] FIG. 5B shows a close up upside-down perspective cross-sectional view of a socket housing in a first embodiment of the present invention.

[0028] FIG. 6A shows an upside-down perspective cross-sectional view of the insertion of an electrical contact pin into a receiving slot of a socket housing according to a first embodiment of the present invention.

[0029] FIG. 6B shows an upside-down perspective cross-sectional view of an electrical contact pin fully loaded into a receiving slot of a socket housing according to an embodiment of the present invention

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0030] FIGS. 1 and 2 show a contact pin 10 adapted for 1.4 mm test height (H.sub.T) mounted in a block shaped socket housing 20 having at least one pair of opposed essentially planar and parallel surface 20A and 20B and oriented essentially parallel to one another. Contact pin 10 is arranged to electrically connect to a contact pad (or lead) 40A of IC device 40 which is to be loaded in vertical motion, perpendicular to planar surface 20A to load board 30 located on planar surface 20B. In other embodiments, an interposer may be required to electrically connect load board 30 to contact pin 10.

[0031] Referring to FIG. 1, contact pin 10 comprises an upper cantilever arm 10A and a lower cantilever arm 10B connected by back portion 10C forming essentially a “C” shape. From back portion 10C, upper cantilever arm 10A extends forward, initially curving downwards following the upper arc of a typical “C” shape to an inflexion point where cantilever arm 10A continues extending forward in an upward curve. Upper cantilever arm 10A terminates at an upper pin tip 10D which is arranged to extend outwards beyond planar surface 20A toward the leads or pads of IC devices to be tested.

[0032] Upper cantilever arm 10A includes a protrusion 10E which is located between the inflexion point and upper pin tip 10D Protrusion 10E functions to engage a roof 20C defined by an upper portion of socket housing 20 when contact pin 10 is mounted in socket housing 20. Engagement of roof 20C by protrusion 10E serves to limit the degree of upward movement of upper cantilever arm 10A and the distance that upper pin tip 10D extends beyond planar surface 20A of socket housing 20 when the contact pin 10 is mounted in the housing.

[0033] Lower cantilever arm 10B extends from the back portion 10C, below upper cantilever arm 10A in an upwards curve following the lower arc of a typical “C” and terminating at free contact end 10F at a close distance of approximately 0.1 mm below the free end of upper cantilever arm 10A. Lower cantilever arm 10B includes a lower pin tip 10G extending essentially from the lowest most point of lower cantilever arm 10B to physically contact the electrical traces on load board 30. Lower pin tip 10G is a defined, non-moving positioning of contact pin 10 with respect to load board 30 during both the uncompressed state and compressed state of contact pin 10.

[0034] FIG. 3 is a representation of the contact pin mounted in a housing superimposed on the same contact pin at test condition. When contact pin 10 is not mounted in socket housing 20 (free state), the vertical distance between protrusion 10E and lower pin tip 10G, H.sub.1 is slightly greater than the distance between the inner surface of roof 20C and planar surface 20B (H.sub.i) such that when mounted in socket housing 20, upper cantilever arm 10A is lightly biased against roof 20C at the contact point formed between roof 20C and protrusion 10E. For the present embodiment, H.sub.1 is 1.22 mm when contact pin is in its free state and H.sub.i is 1.2 mm. In its free state, the closest distance between the free end of lower cantilever arm 10B and the free end of upper cantilever arm is in the range of 0.14 mm to 0.16 mm and is approximately 0.15 mm for the present embodiment. When mounted in socket housing 20, the closest distance between the free end of lower cantilever arm 10B and the free end of upper cantilever arm is in the range of 0.115 mm to 0.135 mm.

[0035] A retaining wall 20D planar to and horizontally displaced from inner socket wall 20E of socket housing 20 extends perpendicularly downwards from roof 20C and terminates a short distance before planar surface 20B Extending from a lower part of back portion 10C away from upper and lower cantilever arms 10A and 10B, a “L” shaped bracket arm 10H together with back portion 10C defines a channel for receiving retaining wall 20D.

[0036] D.sub.1 most clearly seen in FIG. 2A, is the closest distance between the vertical part of bracket arm 10H and back portion 10C of contact pin 10. When contact pin 10 is in its free state, i.e. contact pin is not inserted in housing socket 20 and no external forces are exerted on contact pin 10, D.sub.1 is slightly less than the thickness of retaining wall 20D (L.sub.RW) such that retaining wall 20D is lightly gripped by contact pin 10 when contact pin 10 is mounted in socket housing 20. For the present embodiment, D.sub.1 when the pin is in its free state is 0.24 mm and L.sub.RW is 0.25 mm. Bracket arm 10H additionally serves as a stud for impedance control to the contact pin.

[0037] Electrically conductive contact pin 10 is fabricated using wire cut EDM (Electrical Discharge Machining) from a beryllium copper alloy (BeCu) metal sheet of constant 0.2 mm thickness and having essentially identical opposing lateral faces. Depending on the requirements, contact pin 10 may be fabricated using BeCu metal sheet of thickness in the range of 6mil to 20mil (0.15 mm - 0.5 mm). The thin wire used to discharge the electrified current allows for precision cuts, with a positioning accuracy down to +/- 0.01 mm. BeCu alloy is susceptible to oxidization when exposed to air and humidity. A plating process is utilised to seal the outer surface of contact pin 10 in order to eliminate or reduce its oxidization rate. Typically, the outer coating used is gold (Au) and bonding between BeCu and Au is achieved using nickel (Ni) interface. Thus, the base material up to surface layer of contact pin 10 is BeCu—Ni—Au. Other coating compositions are possible and contact pin 10 may be fabricated with any plating at all Fabrication using wire cut EDM produces contact pins 10 with an essentially consistent cross section which leads to reduction of any potential bounced signal and better mechanical stability when in assembly. Other methods of fabrication such as electroforming produces contact pins of less consistent cross sections when the thickness value increases.

[0038] It is to be understood that various types of IC devices including analog IC devices, high frequency IC devices and mixed-signal IC devices can be tested utilising a test socket 20 and contact pin 10 as illustrated by the present embodiment.

[0039] Referring to FIG. 2, fully depressed under test condition, upper cantilever arm 10A is elastically deformed downwardly clockwise such that the free end of upper cantilever arm 10A presses down on free contact end 10F. Free contact end 10F corresponding elastically deforms downwardly clockwise such that a reliable contact point is formed between the free ends of upper and lower cantilever arm 10A and 10B. A parallel circuit whereby electrical signal passes between IC device 40 and load board 30 via upper pin tip 10D through both cantilever arms 10A and 10B and lower pin tip 10G Parallel circuit leads to a reduction of resistance (R); reduction of impedance (L); increase in capacitance (C). The resultant of all 3 variables above is known as impedance (Z.sub.0). As the contribution of C is less significant in comparison to R & L, the impedance (Z.sub.0) of contact pin 10 at test condition is lower compared to its uncompressed state. The dimensions of contact pin 10 are designed such that elastic deformation of contact pin 10 under test condition results in back portion 10C disengaging from retaining wall 20D of socket housing 20. D.sub.1 increases as contact pin 10 elastically deforms and eventually becomes greater than Law, thus optimizing housing lifespan. For the present embodiment, D.sub.1 at test condition is 0.253 mm. In addition, there is minimal issue with load board digging as lower contact tip 10G is stationary with respect to load board 30.

[0040] FIG. 3 illustrates the elastic deforming of upper cantilever arm 10A when contact pin 10 is between a mounted pre-test state and mounted compressed (test) state. The scrubbing/wiping length achieved during elastic deforming of arm 10A of the present embodiment is less than 0.10 mm, preferably in the range of 0.06 to 0.07 mm. Short wiping length has many advantages including less debris generation, less wearing on the pin tip 10D thus resulting in a longer pin tip lifespan, is more accommodating for device offset, for example in the case of worn out alignment plate of the IC device, and allows for testing of IC devices with very short device pad. With less debris and longer pin tip lifespan, the frequency of downtime for cleaning and pin replacement is reduced.

[0041] FIG. 4 illustrates a contact pin 10 of a second embodiment of the present invention. Whilst the width of the contact pin 10 in FIG. 1 is constant across its entire body, step cuts are made at the contact end of upper pin tip 10D such that it is narrower than the thickness of the main body of contact pin 10 (W.sub.B> W.sub.T). W.sub.B is envisaged to be in the range of 0.20 mm to 0.50 mm and W.sub.T may be in the range of 0.15 m to 0.40 mm. For the present embodiment. W.sub.B is 0.20 mm and W.sub.T is 0.15 mm. This arrangement caters to high current testing of IC devices with small contact pads as well as IC devices with small contact pads in general.

[0042] FIG. 5A shows an upside-down perspective view of a socket housing 20 in an embodiment of the present invention. The socket housing 20 has a square configuration, with four socket cavities 201-” cut out near and aligned with each side of socket housing 20. Socket cavity 20F is cut out from a bottom side of socket housing 20 and extends out from planar surface 20A in a series of exit slots (not shown in FIG. 5A but partially shown in FIG. 5B). At each socket cavity 20F, there is provided further a plurality of socket slots 20G that run perpendicular to the length of socket cavity 20F. Retaining wall 20D extends across the full length of socket cavity 20F. Inner socket wall 20E can be seen at outer ends of each socket slot 20F. FIG. 5B is a close-up upside-down perspective cross-sectional view of the socket housing of FIG. 5A showing inner socket wall 20E, retaining wall 20D and roof 20C The invention encompasses socket housings of various configurations, such as socket housings with only two socket cavities 20F located on opposing sides of the socket housing. In other embodiments, the socket cavity 20F may only comprise a single slot 20G and such slot is adapted to receive one or more contact pins 10.

[0043] FIG. 6A shows the insertion of one contact pin 10 into a socket slot 20G. Contact pin 10 is first aligned with the opening of a socket slot 20G, upside down with bracket arm 10H positioned on the outer end of the socket slot. As contact pin 10 is inserted vertically into the slot 20G, bracket arm 10H is guided into the space between inner socket wall 20E and retaining wall 20D The open end of retaining wall 20D is chamfered to improve the ease of insertion of bracket arm 10H. As described D.sub.1, the closest distance between the vertical part of bracket arm 10H and back portion 10C of contact pin 10 at its free state is adapted to be slightly less than the thickness of retaining wall, L.sub.RW. The difference between L.sub.RW and D.sub.1 may be approximately in the range of 0.01 mm to 0.02 mm. The user simply applies a light force to push contact pin 10 into a fully inserted position.

[0044] Contact pin 10 is shown fully inserted into a socket slot 20G in FIG. 6B. Bracket arm 10H and back portion 10C resiliently grips retaining wall 20D hence preventing accidental pin drop Protrusion 10E of upper cantilever arm 10B is also in light resilient engagement with roof 20C.

[0045] While a preferred embodiments of the present invention have been described and illustrated, it should be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are intended to embrace such changes, modifications, and areas of application that are within the scope of this invention.

TABLE-US-00001 List of numbered elements in figures Contact Pin 10 Socket housing 20 Planar surface 20A, 20B Upper cantilever arm 10A Lower cantilever arm 10B Back portion 10C Upper pin tip 10D Protrusion 10E Roof 20C Free contact end 10F Lower pin tip 10G Load board 30 Retaining wall 20D Inner socket wall 20E Bracket arm 10H Socket cavity 20F Slot 20G IC device 40 Device pad (or lead) 40A