Patch card rework for planar card assembly

Abstract

This paper describes how a new product schedule was protected by incorporating a new approach to carrying out Engineering Changes on a card assembly without the need for wire adds or gluing down components. The Planar Card Assembly or sometimes called Motherboard is the heart of any Personal Computer and contains the microprocessor and interfacing logic to the rest of the system. When a major component on the Planar Card Assembly, such as a Gate Array, does not meet the overall design requirements of the system, the schedule and system testing is impacted until a new level of Silicon for the Gate Array is designed and produced, which can be two to three months. The existing level of Gate Array can normally be used with the addition of extra circuitry to support the out of specification condition. To implement this change, by adding additional circuitry, the Design Engineer has to either produce a new level of printed circuit board or glue down the additional components and attach them with long wire adds to the existing design. These approaches either impact the schedule or degrade the quality of the product. Traditionally, wire adds and attaching additional components with glue have been accepted by Manufacturing as normal practice and with the remoteness of the Design Laboratory went unquestioned. The method adopted here was to use a `Patch Card' which was populated with extra circuitry, bonded to the card and electrically connected without the use of long wire adds. This paper will describe the advantages and also problems encountered while designing the card and establishing the process to attach it.