Field of the Invention

The present invention relates to an electrical

interconnect assembly for use in testing integrated circuit (IC) devices and to a test contact for use in an electrical interconnect assembly.

Background of the Invention

As part of an IC manufacturing process, it is important to test manufactured IC devices in order to ensure that the devices are operating correctly and to required

specifications. Such testing is generally carried out using an IC test system, the test system having a test assembly and an interconnect assembly arranged to

electrically connect the test assembly with pads/leads of an IC during testing so that characteristics of the IC device in response to input electrical stimuli can be determined and compared with reference responses by the test assembly. The interconnect assembly comprises a series of test contacts which extend between respective test terminals of the test assembly and IC terminals of the IC device. The test assembly is arranged to provide an interface between a test assembly and an IC device whilst minimizing the likelihood of damage to leads/pads of the IC device.

In one arrangement, the interconnect assembly includes first and second arm portions arranged to respectively connect with test terminals and IC terminals. The test contacts are moveably disposed in the interconnect

assembly and resiliently biased such that during use when an IC device is engaged with the test assembly, a biasing force is exerted so as to urge the first arm portion into good electrical contact with an IC terminal of an IC device and so as to urge the second arm portion into good electrical contact with a test terminal of the test assembly. The test contacts- generally have a relatively thin profile of uniform thickness with each test contact being disposed in a test socket of generally uniform and slightly larger width than the test contacts.

However, in recent years, the number of high pin count IC devices has increased dramatically and with it the difficulties in effective IC testing have increased.

For example, for some leaded IC devices such as QFPs and SOICs, both of which are configured using "gull wing" type leads, conventional test assemblies are often unsuitable. This is because IC device leads have a tendency to become trapped between adjacent test contacts if slight

misalignment occurs between the IC device and the test assembly. This can often causes major hardware failure and component damage.

Furthermore, in order to achieve effective electrical testing of IC devices, good electrical contact is required between the interconnect assembly and the IC device, particularly for non-leaded IC devices. This has

traditionally been achieved by increasing the biasing force exerted by the test contacts on the IC device and the test assembly. However, such an increased biasing force can cause damage to the test assembly.

Summary of the Invention

In accordance with a first aspect of the present

invention, there is provided an electrical test contact for electrically connecting a test terminal of an IC test assembly with an IC terminal of an IC device in an

electrical interconnect assembly, the test contact being formed of electrically conductive material and comprising: a substantially planar body portion having a

substantially constant first thickness;

a head portion; and

a foot portion;

at least one of the head portion and foot portion having a second thickness greater than the first

thickness;

the head portion comprising a first electrical contacting portion for electrically engaging an IC

terminal of an IC device during use, and the foot portion comprising a second electrical contacting portion for electrically engaging a test terminal of a test assembly during use, the first and second electrical contacting portions being substantially oppositely located on the test contact.

In one embodiment, the head portion has a second thickness greater than the first thickness.

With this embodiment, the second thickness may be greater than the width of an IC terminal of an IC device desired to be tested. In an alternative embodiment, the foot portion has a second thickness greater than the first thickness.

With, this embodiment, the second thickness may be smaller than the width of an IC terminal of an IC device desired to be tested.

In one embodiment, the test contact is substantially W- shaped. In one embodiment, the test contact comprises a receiving portion arranged to receive a resiliently biasing member during use. The receiving portion may be at least partially circular.

The test contact may be formed of metal material, such as precious metal material.

In one embodiment, the first and/or the second electrical contacting portions is/are arranged to facilitate sliding of the first and/or the second electrical contacting portion relative to the respective IC terminal or test terminal. The first and/or the second electrical

contacting portion may comprise beryllium copper material.

In one embodiment, the second electrical contacting portion comprises a curved surface arranged such that during use rotation of the test contact effects regulation of the contact pressure between the test contact and a test terminal of a test array.

In accordance with a second aspect of the present ^■ invention, there is provided an electrical interconnect assembly for electrically connecting test terminals of an IC test assembly with respective IC terminals of an IC device, the electrical interconnect assembly comprising: a plurality of test contacts, each test contact being formed of electrically conductive material and comprising:

a substantially planar body portion having a substantially constant first thickness;

a head portion; and

a foot portion;

at least one of the head portion and foot portion having a second thickness greater than the first thickness;

the head portion comprising a first electrical contacting portion for electrically engaging an IC terminal of an IC device during use, and the foot portion comprising a second electrical contacting portion for electrically engaging a test terminal of a test assembly during use, the first and second electrical contacting portions being substantially oppositely located on the test contact;

a housing provided with a plurality of contact sockets, each contact socket being arranged to receive a test contact such that the test contact is movable during use relative to the contact socket; and

at least one resilient member arranged to resiliently bias the test contacts towards a test assembly and towards an IC device to be tested during use.

In one embodiment, each resiliently biasing member comprises an elongate elastomeric member, which may be a substantially cylindrical elastomeric member.

In one embodiment, each test contact and associated resiliently biasing member forms a cantilever arrangement.

In one embodiment, the foot portion has a second thickness greater than the first thickness, and each contact socket is configured such that the contact socket is keyed to the foot portion so that the amount of permitted rotation of the test contact relative to the respective contact socket is restricted. In one embodiment, the foot portion and the contact socket are provided with complementary

shoulder portions.

Brief Description of the Drawings The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic cross-sectional view of a test system of the type including a test assembly and an electrical interconnect assembly, and showing an IC device disposed on the interconnect assembly;

Figures 2a and 2b are diagrammatic side and front views respectively of a test contact in accordance with an embodiment of the present invention, the test contact . forming part of the interconnect assembly shown in Figure 1; ^'

Figures 3a and 3b respectively show side views of a conventional test contact and a test contact in accordance with an embodiment of the present invention disposed in electrical communication with an IC terminal of an IC device and a test terminal of a test assembly;

Figure 4 is a diagrammatic perspective view of the test contact shown in Figure 2 disposed between a test terminal of a test assembly and an IC terminal of a leaded type IC device;

Figures 5a and 5b are diagrammatic side and front views respectively of a test contact in accordance with an alternative embodiment of the present invention;

Figure 6 is a diagrammatic perspective view of the test contact shown in Figures 5a and 5b;

Figures 7a and 7b are respective diagrammatic cross- sectional views of a conventional test assembly and a test assembly according to an embodiment of the present

invention, and including the test contact shown in Figures 5 and 6; and

Figure 8 is a diagrammatic perspective view of the test contact shown in Figures 5 and 6 in electrical communication with a test terminal of a test assembly and an IC terminal of an IC device.

Description of an Embodiment of the Invention

Referring to Figure 1, a test system 8 is shown for testing IC devices. The test system 8 is of a type including an electrical interconnect assembly 10 for forming an electrical connection between test terminals 12 of a test assembly 14 and IC terminals 15 of an IC device 16 desired to be tested. The test assembly 14 in this example is of conventional type and is arranged to carry out a series of tests on an IC device 16 connected to the test assembly 14 through the interconnect assembly 10, for example by applying defined signals to the test terminals 12, monitoring response signals and comparing the response signals to reference responses .

The interconnect assembly 10 comprises a housing 18 having a plurality of test contacts 20 movably disposed in respective contact sockets 22 formed in the housing. Each of the test contacts 20 in this example is formed of electrically conductive material, for example a precious metal, and is formed of generally planar sheet-like material. In this example, each test contact 20 is generally W-shaped and includes a first electrical

contacting portion 24 arranged to engage during use with an IC terminal 15 and a second electrical contacting portion 26 arranged to engage during use with a test terminal 12. The test contacts are arranged to engage with a biasing member 28, in this example in the form of an elongate generally cylindrical elastomeric member, which cooperates with the test contacts 20 to urge the first electrical contacting portion 24 towards an IC terminal 15 and to urge the second electrical contacting portion 26 towards a test terminal 12.

While the elastomeric member in the present embodiment is generally cylindrical, it will be understood that any suitable shape is envisaged.

During use, an IC device 16 to be tested is disposed on the interconnect assembly 10 and the IC device 16 is urged towards the interconnect assembly 10, as indicated by Arrow A, and secured in this position in any appropriate way, for example using one or more screws. This causes establishment of good electrical contact between each first contacting portion 24 and an IC portion 15 and between each second contacting portion 26 and a test terminal 12, with each test contact 20 moving from a first position shown by full line ^' 27 iri Figure 1 to a second position shown by dotted line 29 in Figure 1. The test contact 20 and the biasing member 28 form a cantilever arrangement. As the test contact 20 moves between the first position and the second position, a small degree of rotation occurs which causes a wiping action to occur at the IC terminals 15 and at the test terminals 12, thereby ensuring good electrical contact.

A test contact 30 in accordance with an embodiment of the present invention is shown more particularly in Figure 2. The test contact 30 is particularly suitable for use with leaded-type IC devices.

The test contact 30 comprises a first arm portion 32, a second arm portion 34 and an engaging portion 36, in this example' of generally part-circular shape. The engaging portion 36 is configured to receive the biasing member 28 such that during use when an IC device 16 is engaged with the interconnect ^' assembly 10 and the test contact 20 moves from the first position to the second position, the biasing member 28 is slightly compressed and the biasing member 28 thereby exerts a biasing force on the IC

terminals 15 and the test terminal 12.

The test contact 30 also includes a curved contact surface 38, part of which constitutes the second electrical contacting portion 26. The curved contact surface 38 enables the test contact 20 to regulate the contact pressure at the second electrical contacting portion 26 by self-adjusting its orientation relative to a test terminal 12.

The biasing force exerted by the first electrical contacting portion 24 on an IC terminal 15 should be sufficient to achieve good electrical contact, but not so excessive so as to be potentially detrimental to the IC terminal 15. In addition, in order to facilitate good sliding action with some resilience at the IC terminals 15, at least part of the test contact 20 at the first electrical contacting portion 24 may be formed of

beryllium copper material.

The test contact 30 also comprises a body portion 40 of generally constant thickness and a head portion 42 of generally enlarged thickness relative to the body portion 40. The head portion 42 forms part of the first arm portion 32 and includes a surface which constitutes the first electrical contacting portion 24.

It will be understood that for leaded-type IC devices, by increasing the thickness of the test contact at the first electrical contacting portion 24, the likelihood of IC leads becoming trapped between test contacts of the interconnect assembly 10 during use is much reduced.

As shown in Figure 3a, a conventional test contact 50 is ordinarily thinner than the width of a lead-type IC terminal 15 and the width of the conventional test contact 50 is similar to the spacing between adjacent leads. For this reason, the likelihood of IC terminal leads 15 becoming jammed between adjacent test contacts 50 is significant. However, as shown in Figure 3b, the test contact 30 according to the present embodiment has a body portion 40 which is generally thicker than a conventional test contact 50 and a head portion 42 which is generally wider than a lead-type IC terminal 15 and wider than a spacing between adjacent leads.

It will also be understood that by providing a head portion 42 of increased width, the contact surface area is also increased which reduces electrical resistance and reduces the pressure exerted by the head portion 42, thereby improving the lifespan of the test contact 30 and minimizing the likelihood of damage to the IC terminals 15.

A test contact 60 in accordance with an alternative embodiment of the present invention is shown more

particularly in Figures 5 and 6. Like and similar features are indicated with like reference numerals. The test contact 60 is particularly suitable for use with pad/unleaded type IC devices, particularly such devices with relatively high lead counts. Pad/unleaded type IC devices require a higher contact force at the pad - test contact interface than leaded type IC devices and, as such, damage to the IC terminals 15 and/or the test terminals 12 is more likely.

The test contact 60 comprises a body portion 62 of generally constant thickness and a foot portion 64 of generally enlarged thickness relative to the body portion 62. The foot portion 64 forms part of the second arm portion 34 and comprises a surface which includes the second electrical contacting portion 26.

Figure 7a shows part of a conventional electrical

interconnect assembly including conventional test contacts 70 disposed in respective contact sockets 22.

Figure 7b shows part of an electrical interconnect assembly according to the present embodiment and including test contacts 60 disposed in respective contact sockets 72. The contact sockets 72 are configured so as to be keyed with the test contacts 60, in this example by forming a shoulder portion in the contact sockets 72 which is of complementary shape to the enlarged foot portion of a test contact 60. In this way, the amount of rotation of - li the test contacts 60 which is possible during use is restricted.

It will be understood that the thickness of the foot portion 64 is comparable to the thickness of the

conventional test contacts 70 at the second electrical contacting portion 26, but is thinner at the body portion 62 than conventional test contacts. As a consequence, the amount of material between adjacent contact sockets is greater with the present embodiment than with a

conventional interconnect assembly, which increases strength and improves the life span of the interconnect assembly.

It will also be understood that since the test contacts 60 are thinner than conventional test contacts 70 at the first electrical contacting portions 24, the interconnect assembly according to the present embodiment is able to test finer pitch IC devices than is possible with the conventional interconnect assembly shown in Figure 7a.

It will also be understood that since the test contacts 60 are thinner than conventional test contacts 70 at the first electrical contacting portions 24, the contact pressure at the test contact - IC terminal 15 interface is greater with the present embodiment than with conventional test contacts for the same applied force, which is

desirable to obtain efficient testing in pad/unleaded type IC devices.

It will also be understood that the enlarged foot portion also reduces skewing of the test contacts 60 and thereby provides better coplanarity of test contacts.

Furthermore, it will be understood that by maintaining a relatively high width at the second electrical contacting portion, the contact pressure at the test contact - test terminal interface is maintained sufficiently low to avoid damage to the test terminals.

Figure 8 shows an example tdst contact 60 disposed during use between a test terminal 12 of a test assembly 14 and a pad-type IC terminal 15 of an IC device 16. For ease of reference, only one test contact 60 is shown.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.