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A probe card for testing electrical devices

IP.com Disclosure Number: IPCOM000128431D
Original Publication Date: 2005-Sep-16
Included in the Prior Art Database: 2005-Sep-16
Document File: 4 page(s) / 90K

Publishing Venue

IBM

Abstract

Disclosed is a device for a probe card to test an electrical device. Probes attached to a card consists with a lot of bristles like a brush. Each bristle has a two needles without electrical conductivity, which pair is used in order to sense and force electrical signals. This device enables to discriminate a contact error from a defect. Furthurmore the probe card is so thin and flexible that it enables to make 2-dimensional and 3-dimensional probes that can correspond to a compelx shape of substrates.

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A probe card for testing electrical devices

Problems solved:

   As for testing an electrical device, bonding pads are getting a small and fine pitch. Escpecially such like a thin film transistor array used for an active matrix organic light emission display, pixel electrodes are arranged as a matrix and it is very hard to contact each pixel electrode with an existing contact probe. It means that each small contact probe is really contacting an electrode or not. If it cannot be distinguished a device failure from contact failure, it importantly interferes to the test. In addition pixel electrodes must be kept from any contamination and damages because OLED and other materials will be mounted on it later. So a new contact probe card is needed for testing those electrical devices.

Solution:

   To solve problems above, a brush-type contact probe which bristles consist with sense & force pair electrodes is very effective. A brush-type contact probe is made of soft metal or carbon or polymer coated with metal. Gold is preferable for the metalic material. The structure of a brush-type contact probe is shown in Fig.1. A brush-type contact probe can contact small pixel electrodes easily. However it is very hard to cofirm any bristles are really contacting an electrode without observation visually using an extra microscope equipment. So this invention provides a pair probe inside one bristle, which is called sense & force electrode. As shown in Fig.2, a pair electrode is united with insulator coating. And the dimensions are also shown in Fig.2. Applying this structrue it can be easily found whether a probe is really contacting a pixel electrode or not. The test sequence is following.

1. Allign the probe card and touch it down to a device.
2. Apply a voltage on a force electrode.
3. Scan all sense electrodes to see if the applying voltage is detected or not. And the result is stored in a database.
4. Judge the contact error between each bristle and electrode on a device. And the result is stored in a database.
5. According to the result, reconfigure wires by each switches in a probe card.
6. Do a main test procedure.

For 4th procedure above, there are two ways to detect which pad is not contacted. One is to make sense & force bristles with the same pitch as a test device. In this way the alignment and scannning operation have to be done in a some accuracy, that is about within a few micrometers. And the second is by calculation with a pitch of probe card's bristles and pads on a device. If the bristles' pitch is made smaller than pads' one, it is very easy to find which bristle is placed on a corresponding pad.

When contact error is detected, alignment is retried and do process from the first step. And the number of contact error is more than a defined value, it reports the breakdown and exchange to a new probe card or some pads on a test device is not mounted.

Fig.6 shows the configuration in a probe card. After judging which bristle is really contact...