Browse Prior Art Database

SMART TESTER FOR FLEX INTERFACE

IP.com Disclosure Number: IPCOM000006938D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2002-Feb-11
Document File: 3 page(s) / 147K

Publishing Venue

Motorola

Related People

Ron Vanderhelm: AUTHOR

Abstract

Testing a board level interface connection that hap- pens to be the end of a Flex circuit is difficult to auto- mate. But such automation is essential to reducing errors and costs in a high volume electronics factory. On a flex circuit there are no rigid pins or surfaces with which to mate a test jig, only the plated metal traces on the highly flexible plastic substrate. The end of the flex is ticult to feed into an automatic tester by machine because it is often warped in one or two axes, with unpredictable severity. The plastic substrate material bends easily, requir- ing that it be grasped very close to the end, another di&ulty for a machiie.

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MOTOROLA INC. Technical Developments Volume 19 June 1993

SMART TESTER FOR FLEX INTERFACE

by Ron Vanderhelm

   Testing a board level interface connection that hap- pens to be the end of a Flex circuit is difficult to auto- mate. But such automation is essential to reducing errors and costs in a high volume electronics factory. On a flex circuit there are no rigid pins or surfaces with which to mate a test jig, only the plated metal traces on the highly flexible plastic substrate. The end of the flex is ticult to feed into an automatic tester by machine because it is often warped in one or two axes, with unpredictable severity. The plastic substrate material bends easily, requir- ing that it be grasped very close to the end, another di&ulty for a machiie.

  These problems can be solved with the unique com- bination of elements described here that provide the abil- ity to grasp the flex and then automatically mate misaligned connections with remarkable tolerance. Fig- ure 1 shows the complete system.

  The front end of the jig consists of a pair of jaws which clamp down on the flex PC. The jaws are made up of two opposing plates, each of which consist of three layers. The first layer is a "zebra strip"" resilient interconnecting material, the second is a rigid PCB, and the third is a metal support for the PCB. The zebra strip layer on both jaw surfaces face each other so as to con- tact both sides of the Flex under test when clamped together.

  Those who work in the electronics industry may recognize the unique characteristics of zebra strip as this material is commercially available. It comes in strip form with a rectangular cross section. At equally spaced inter- vals down the strip, whose body is made up of a resili- ent non-conductive material, clumps of conductive wires are embedded. These wires are all oriented in one direc- tion as illustrated in Figure 1. The intervals between these wire clumps are chosen to be very small relative to the spacing of the conductors on our flex circuit. The width ofthe wire clumps is also very small.

one conductor on the first surface to any conductor on the second surface that happens to be immediately across from it. The wire bundles are spaced relatively close together so that in practical application more than one bundle is making the same connection. Using this, the sandwich jig can interconnect a flex PC with the con- ductors plated onto a rigid PCB by placing the Flex between two such jaws and applying mild pressure.

  The fundamental problem that remains to make such an interconnection useful is that of alignment of the Flex conductors with the jig conductors. This invention does this electronically. Fit, the conductor spacing and width on the rigid PCB that forms the face of the jaws is altered so as to not match those of the conductors on the Flex. Instead, these widths and spacings are reduced to rou...