WO2010041188A1

WO2010041188A1 - Wafer probe

Info

Publication number: WO2010041188A1
Application number: PCT/IB2009/054341
Authority: WO
Inventors: Alexander Remmele; Horst Eisermann; Alexander Katzow
Original assignee: Nxp B.V.
Priority date: 2008-10-08
Filing date: 2009-10-05
Publication date: 2010-04-15

Abstract

A wafer probe comprises electric contacts and a replaceable probe tip(4). In order to make handling easier and to obtain better probe results the tip(4) is arranged in a replaceable needle head(1).

Description

WAFER PROBE

DESCRIPTION

FIELD OF THE INVENTION

This invention relates to a wafer probe with electric contacts with a replaceable probe tip for high frequency application.

BACKGROUND OF THE INVENTION Testing or probing a wafer with integrated circuits is an important step during the test production and especially during the mass production of such integrated circuits for testing whether the electric behaviour of each electronic device lies within the desired parameters.

Different types of such wafer probes are known like cantilever wafer probes or the like. For contacting the device under test (DUT) the wafer probe has to establish a good electric contact to all pins. Probes for RF transmitter and receiver devices require additional performance for high frequency as well. After having tested a first device, the wafer is moved relative to the wafer probe in order to test the next device. This process is being repeated continuously in mass production. Therefore the tip is exposed to a strong abrasion or the tip might be bended in an undesired manner. Once the tolerances of probe tip in terms of tip size or position are not being met anymore, the wafer probe has to be replaced. To overcome this problem it is known that such a tip can be replaceably mounted to the wafer probe.

Such a wafer probe with a replaceable tip is disclosed in the US 4,849,689 or in the US 6,242.930 B 1. But in both embodiments the replacement of a worn tip requires an exact mounting of a new tip with extensive adjustment works.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a wafer probe with a simple configuration and an easy handling while still establishing good high frequency behaviour. These problems are solved with a wafer probe as described in claim 1. The core of the invention lies in the fact that the one or more tips are arranged within a replaceable needle head. With this embodiment the needle head itself can be handled to replace a worn tip. It is obvious, that the needle head is largely bigger in size than a single tip so that the handling of the needle head is easier and can be done even by hand. Further the needle head is formed with seats, fitting surfaces, notches or the like to mount the needle head in a desired orientation relative to the wafer probe itself, which is formed correspondingly. It is possible that no further fixation devices for the needle head are necessary. It is to understand that this wafer probe might be a cantilever probe.

The needle head with for example three electric needles with respective electrical contacts and dedicated pins can be shaped as desired corresponding to the electronic devices to be tested. Further it is possible do execute prior to manufacturing the needle head a mathematical simulation in order to elaborate the best shape and arrangement of the needle head with its pins in order to obtain the best high frequency performance for a desired pitch or step from one device to another.

In the scope of the invention the needle head can be shaped by a person skilled in the art in many different ways, but preferably as described below. The advantage of the invention is the simplicity of replacing a tip. Further it is possible to contact wafers at high frequencies which can be applied via the contacts, the needles in the needle head and the respective tips. In order to execute a correct probe, the needle head is mounted on the printed circuit board for example with placement pins and tightening screws to reach a sufficient accuracy. In a preferred embodiment the needle head has a impedance controlled structure, so that it may cooperate with a correspondingly shaped feeding for printed circuit boards (e.g. coplanar). Such a coplanar structure can be easily fulfilled if the needle head is made of a ceramic structure which can be shaped by a person skilled in the art. To arrange the needle with their respective tips relative to the needle head in a desired manner there are holes, preferably drilled holes, in which the metal needles are inserted and fixed, for example with a glue. The holes or bores can be manufactured after forming a massive needle head.

For getting the desired results, there are three needles, which are arranged essentially on a line whereas two electrical ground tips enclose a signal tip for applying a desired high frequency electrical signal and detecting its effects on the device to be tested. For the arrangement of the three pins it is proposed that a middle signal tip is aligned straight and the two neighboured needles with their ground tips have an opening angle α for example 1,5°. It is clear that the rear ends of the ground needles, opposite to their respective tips, form the opening angle α.

Further it is preferred, that the two ground needles are arranged in another plane than the signal needle. Therefore there are formed buckles in the elongated needles to shape them at an angle of essentially 90°. That means that the three tips are orientated substantially perpendicular to the wafer and the three main needle bodies are substantially parallel to the major plane of the wafer. But the vertical distance of the signal needle body to the wafer is larger than the vertical distances of the two neighbouring ground needle bodies. Length, diameter, orientation and arrangement of each needle with its tip may be calculated from a simulation prior to manufacturing the needle body. Also it is possible that the three needles are arranged so that they step up. That means, that the distance of a free end of the needle bodies to the printed circuit board is larger than at the buckles. There the distance could be for example 3,0mm. In order to enhance the electrical properties of the needle head, the needles are mostly covered with the ceramic material. Where they are exposed to the air they can be additionally covered with an epoxy glue in order to reduce a needle length in free space.

For the same purpose and to reduce friction the needle head as well as a feeding for the printed circuit boards may be coated with a metal layer. BRIEF DESCRIPTION OF THE DRAWING

An embodiment of the invention is hereinafter described with reference to the according drawings. The figures show:

Fig.1 : a needle head with a feeding and Fig. 2: an arrangement of needles.

DETAILED DESCRIPTION OF THE DRAWING

In figure 1 is depicted a needle head 1 for example made of a ceramic material. Within the needle head there are arranged three needles 2a, 2b, 2c and they are covered at least partially with an epoxy glue or material to avoid their direct contact with the air in order to achieve the desired electrical properties. The two outer needles 2a, 2c are via not depicted electrical contacts set to electrical ground and the middle needle 2b a high frequency signal is applied to probe a printed circuit board or an integrated circuit on a wafer respectively. With such an arrangement the complete needle head 1 and 2 can be replaced and adjusted easily since it is not soldered.

Further there is a coplanar feeding on the printed circuit board 3 to feed the wafer probe with the desired high frequency signal. The feeding and/or the needle head 1 are preferably equipped with an additional metal layer for best performance.

In figure 2 is shown an arrangement of three needles 2a, 2b, 2c whereas the three tips 4a, 4b, 4c are orientated substantially perpendicular to a major plane of a wafer to be tested and the three needles 2a, 2b, 2c are substantially parallel orientated or they step up slightly. Further there is an opening angle α between the outer ground needles 2a, 2c and the middle signal needle 2b of for example 1,5°. Also the vertical distance of this middle needle 2b to a surface of the wafer is larger than the vertical distance of the two outer ground needles 2a, 2c in order to achieve desired electrical properties. LIST OF REFERENCE SIGNS

1 needle head

2 needle

2a, 2c ground needle

2b signal needle

3 feeding 4 tip α opening angle

Claims

CLAIMS:

1. A wafer probe comprising electric contacts and a replaceable probe tip (4) characterised in that the tip (4) is arranged in a replaceable needle head (1).

2. Wafer probe according to claim 1 characterised in that the needle head (1) has a defined structure for controlled impedance.

3. Wafer probe according to claim 1 or 2 characterised by holes for housing needles (2) in the needle head (1), especially in a needle head (1) made of ceramic.

4. Wafer probe according to any of the claims 1 to 3 characterised in that two ground needles (2a, 2c) form an opening angle (α).

5. Wafer probe according to any of the claims 1 to 4 characterised in that two ground needles (2a, 2c) and a signal needle (2b) are arranged in different planes with respect to a major plane of a wafer to be probed.

6. Wafer probe according to claim 5 characterised in that the signal needle (2b) is displaced from the printed circuit board for 3,0mm.

7. Wafer probe according to any of the claims 1 to 6 characterised in that at least one needle (2) is at least partially covered wit an epoxy material.

8. Wafer probe according to any of the claims 1 to 7 characterised in that the needle head (1) is at least partially equipped with a metallic layer.