Flexible flat cables have gained widespread acceptance and are gaining prevalence over conventional round wire systems because of their compact design, low cost, and ability to bend. Flexible flat cables, for example, are used for electrical connection to components in many consumer electronic applications, such as digital and analog tape heads, inkjet and dot matrix printer heads, mobile phones, the connection between the body of a laptop computer and its lid, and other consumer electronics requiring small and lightweight flexible cables.
In a typical configuration of a flat cable, wires are embedded in a flexible plastic film. One end of the flat cable is connected to a component such as a tape head, print head, etc. typically via ultrasonic bonding or soldering. The other end of the flat cable typically has a contact pad or connector coupled to each wire. The contact pads or connector are later connected to a circuit board which sends signals through the wires to the component to control operation of the component. One type of connector for coupling the circuit board to the contact pads is a compression connector where cable pads are compressed onto a circuit board by a biased non-conductive (e.g., rubber) fitting. Another type of connector is an array of fingers with a conductor on one side which slide into a receptacle on the cable. A third is a connector which is permanently affixed to the cable end and which attaches to a circuit board.
After a flexible flat cable is affixed to a component it is desirable to ensure that all of the cable leads have proper electrical connection to that component. This is because if the manufacturer installs the component/cable combination in the end device and the component does not function, the product must be disassembled and another component/cable combination installed in the end device. To assure this connection, electrical measurements may be made on the unconnected end of the cable through two wires and some portion of the attached component in a particular circuit.
One problem encountered during testing flat cable connections is that when the cable is attached to the testing system, only a single contact is made to each wire in the cable. If the contacts on the cable are dirty (debris), corroded, misaligned, missing contact pad material, or the contacts on the test system are dirty or corroded, the test system will read a high resistance through some part of the component. In other words, a poor connection to the free end of the cable could inadvertently indicate a poor or nonexistent cable attachment to the component. If a bad connection is sensed between the cable and component, the component and cable are often discarded, as the cost of repairing a faulty connection is often more expensive than creation of a new unit. Thus, because it is impossible to tell whether the contact between the cable and the test system is bad, or whether the contact between the cable and the component is bad, the component may be needlessly discarded.
What is therefore needed is a way to avoid false indications of poor or nonexistent cable attachment to the component.