This invention relates generally to integrated circuit testing using probe cards.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, the approaches described in this section may not be prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In semiconductor integrated circuit manufacturing, it is conventional to test integrated circuits (“IC's”) during manufacturing and prior to shipment to ensure proper operation. Wafer testing is a well-known testing technique commonly used in production testing of wafer-mounted semiconductor IC's, wherein a temporary electrical connection is established between automatic test equipment (ATE) and each IC formed on the wafer to demonstrate proper performance of the IC's. Components that may be used in wafer testing include an ATE test board, which is a multilayer printed circuit board that is connected to the ATE, and that transfers the test signals between the ATE and a probe card assembly. The probe test card assembly (or probe card) includes a printed circuit board that generally contains several hundred probe needles (or “probes”) positioned to establish electrical contact with a series of connection terminals (or “die contacts”) on the IC wafer. Conventional probe card assemblies include a printed circuit board, a substrate or probe head having a plurality of flexible test probes attached thereto, and an interposer that electrically connects the probes to the printed circuit board. The interposer conventionally includes telescopic “pogo pins” or solder bumps that provide electrical connections between conductive pads on the printed circuit board and the interposer and between the interposer and conductive pads on the substrate. The test probes are conventionally mounted to electrically conductive, typically metallic, bonding pads on the substrate using solder attach, wire bonding or wedge bonding techniques
The pogo pin or solder bump connections used with conventional probe card assemblies have some significant limitations. For example, pogo pins use spring components that exert a high aggregate amount of force against the substrate when used in large numbers. The spring components used in pogo pins can also stick or wear out over time, resulting in a “floating contact.” Pogo pins are also generally very labor intensive to install, especially in high density applications, and do not have high planarity. They have high deflection capability but their coplanarity is poor. The high force exerted by pogo pins can deflect, misalign or even crack a substrate. Thus, pogo pins are not a scalable solution for higher density applications. Solder bumps do not have the same spring component-related problems as pogo pins, but solder bumps sometimes do not provide reliable electrical contact, resulting in floating contacts, i.e., an open circuit. Also, solder bumps are not readily repairable, since they are normally created using solder flow techniques that cannot be used to repair an individual solder bump. Solder reflow technology works well only for smaller reflow areas—scalability to 10 and 12 inches would be a problem.
Based on the foregoing, there is a need for a probe card assembly that does not suffer from limitations of conventional probe card assemblies.
In the figures of the accompanying drawings like reference numerals refer to similar elements.
In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention. Various aspects of the invention are described hereinafter in the following sections:
I. OVERVIEW
II. PROBE CARD ASSEMBLY WITH FLEXIBLE INTERCONNECT STRUCTURE
III. ATTACHMENT OF FLEXIBLE INTERCONNECT STRUCTURE
IV. PROBE HEAD STRUCTURES
V. TEST PROBES
A probe test card assembly for testing of a device under test includes a printed circuit board, a space transformer, a probe head structure and a flexible interconnect structure. The printed circuit board has a plurality of electrical contacts disposed thereon. The space transformer has a first plurality of electrical contacts disposed thereon for providing electrical connections with the plurality of contacts disposed on the printed circuit board. The space transformer also includes a second plurality of electrical contacts disposed thereon for making contact with a plurality of test probes. The probe head structure supports the plurality of test probes. Each test probe from the plurality of test probes has a first end for making electrical contact with a device under test and a second end for making electrical contact with one of the electrical contacts from the second plurality of electrical contacts on the space transformer. The flexible interconnect structure provides electrical connections between the first plurality of electrical contacts on the space transformer and the plurality of electrical contacts on the printed circuit board. The probe head structure may include first and second guide plates with apertures in which the plurality of test probes is disposed. The first and second guide plates constrain and align the plurality of test probes with test points on the device under test. The plurality of test probes may be pre-buckled to cause the plurality of test probes to deflect and/or bend in a specified direction.
II. Probe Card Assembly with Flexible Interconnect Structure
As previously described herein, flexible interconnect structure 110 may be implemented using one or more flexible circuits. For example, a single flexible circuit may be used to connect a plurality of electrical contacts on PCB 102 to a plurality of electrical contacts on space transformer 104. Thus, in a situation where PCB 102 and space transformer 104 are rectangular in shape, four flexible circuits may be used. Alternatively, more than one flexible circuit may also be used on each side of PCB 102 and space transformer 104. For example, PCB 102 or space transformer 104 may have multiple rows or “banks” of electrical contacts and a separate flexible circuit may be used for each row or bank of electrical contacts. The flexible circuits may be arranged side by side or may overlap, depending upon the requirements of a particular implementation. Flexible interconnect structure 110 may be connected to PCB 102 and space transformer 104 using a variety of techniques and mechanisms. For example, as depicted in
As another example, as depicted in
Although
As yet another example, as depicted in
A wide variety of probe head structures may be used, depending upon a particular implementation.
First guide plate 210, second guide plate 212 and spacers 214 may have a variety of shapes and dimensions, depending upon a particular implementation. For example, first guide plate 210, second guide plate 212 and spacers 214 may be rectangular or circular in shape, or may have irregular shapes. First guide plate 210, second guide plate 212 and spacers 214 may be made from a variety of materials. Example guide plate materials include, without limitation, plastic, silicon, silicon nitride and quartz. Example processes for making guide plates from silicon include, without limitation, Micro-Electro-Mechanical Systems (MEMS) and Deep Reactive Ion Etching (DRIE) micromachining processes. One benefit provided by the MEMS and DRIE processes is that they allow rectangular apertures or slots to be formed in the guide plates, which are more compatible with rectangular-shaped test probes, e.g., when the test probes are made using semiconductor fabrication techniques. Rectangular apertures or slots also provide further control over the deflection and bending of test probes, as described in more detail hereinafter. For silicon nitride, a laser fabrication process may be used. Other materials may be used, depending upon the requirements of a particular implementation. According to one embodiment of the invention, first guide plate 210 and/or second guide plate 212 are made from a rigid material to provide adequate alignment and thermal stability of the test probes, to ensure proper contact with a device under test. As described in more detail hereinafter, one or more portions or the entirety of first guide plate 210 and second guide plate 212 may be coated, for example, with a non-conductive material. This prevents shorts between test probes if the guide plate material is not sufficiently insulating. Example materials for spacers 214 include, without limitation, metals, such as steel, or other rigid materials that have good flatness and provide stability for first guide plate 210 and second guide plate 212.
Test probes 216 may be fabricated using a variety of techniques, depending upon a particular implementation. For example, test probes 216 may be stamped, electro-formed or fabricated using semiconductor fabrication techniques. Test probes 216 may be any type of test probe, such as cantilever test probes or vertical test probes. Test probes 216 may be made from a wide variety of materials, for example, aluminum or other metals or alloys. Test probes 216 may also have different shapes, depending upon a particular implementation. For example, test probes 116 may be round or rectangular and may be straight, bent or curved. Test probes 116 made from wires are typically round, while test probes 116 made using semiconductor fabrication techniques are typically rectangular. Test probes 116 may be partially or fully coated to change their physical or conductive characteristics. Test probes 116 may also be fabricated with features, e.g., notches, ridges, lips, protrusions, etc., that automatically position the test probes 116 within the first guide plate 210 and second guide plate 212.
According to one embodiment of the invention, test probes 216 are pre-buckled so that they deflect in generally a specified direction when test probes 216 make contact with a device under test. This reduces the likelihood that test probes 216 will deflect and/or bend in different directions and contact each other causing shorts when moved into contact with a device under test. It also increases the predictability of positioning of probe tips on a device under test.
A wide variety of techniques may be used to pre-buckle test probes.
The probe test card assembly with a flexible interconnect structure as described herein has several benefits over conventional probe test cards. In particular, the flexible interconnect structure provides a compliant connection between the printed circuit board and the space transformer without applying a large force load to the space transformer. This allows the PCB and space transformer to be placed at different heights with respect to each other. The flexible interconnect structure also provides control over signal impedance. The use of a clamping mechanism to attach the flexible interconnect structure to the printed circuit board and/or the space transformer reduces the uncontrolled impedance length of the contact and allows removal of the space transformer from the printed circuit board. Use of wire bond or solder connections between the flexible interconnect structure and the space transformer eliminates the need for a clamping mechanism, which reduces the space and alignment tolerance requirements.
In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is, and is intended by the applicants to be the invention is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.