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I disassembled a cheap digital tire pressure gauge that had quit working (leaking silver oxide cell, as I discovered). After deciding it was unrepairable I removed the circuit board, which had the LCD display on the back. It fell off and seemed to be completely unattached. There was a ribbed rubber strip between a plastic "step" on the the display and the row of contacts.

after detaching circuit board from front of case

Here are some images of the LCD:

Front

Front ↑

Back

Back ↑

Edge view showing step

Edge view showing the "step" ↑

The rubber spacer

The rubber spacer ↑

I happened to view the display under bright light with a specular reflection from the plastic, and saw this:

Are these the electrical contacts?

Since the ribbing on the spacer runs "vertically" from the contacts on the PCB is that how power and signal are delivered to the faint, almost invisible traces on the display? I don't see any embedded wires in the rubber... is each rib designed to conduct along its length but be insulated from its neighbors? The spacer looks and behaves just like a simple piece of rubber.

What is this technology (both the "spacer" and the invisible traces on the LCD) called?

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It's called "zebra strip", and yes, the black areas are conductive while the white areas are insulating. The strips do not need to line up one-for-one with the contacts on the board and the glass, as long as there is at least one for each connection (usually several) and there's enough space between the contacts so that they don't get bridged by a black zone.

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    \$\begingroup\$ The key is that the contacts on the glass need to be aligned with the contacts on the board, so that the conductive stripes connect the proper pins between board and glass. \$\endgroup\$ – jwygralak67 Sep 2 '15 at 18:04
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    \$\begingroup\$ Yup and the gaps between the contacts on either the glass or the PCB need to be wider than the Zebra pitch plus any potential misalignment of the PCB and LCD to prevent a circuit path between two adjacent contacts. The transparent conductor on LCDs is tin oxide often as it can be coated and etched reliably and is almost transparent. \$\endgroup\$ – KalleMP Sep 2 '15 at 18:11
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The more formal name is elastomeric connector, commonly known, as Dave Tweed mentioned, as "Zebra Strips." They are designed to conduct current only in a "vertical" direction and not to conduct current across the length of the strip. In addition to being used for LCD connections, the strips are sometimes used in test sockets for surface mount components.

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