Automated Wirepull Testing – Parallelogram of Forces-Real Time Application

Abstract

In hybrid electronics, it is a standard practice to perform 100% wire bond pull testing to ensure robust wire bonding of the components. The principle behind Mil-STD-883 method 2023.5 compliant wire bond pull testing is to position the hook underneath the wire and either pull until the wire breaks or, alternatively, pull to a predefined force. With high density layouts, small component geometry or staggered wire bonds, it has been a challenge for manufacturing operations to maintain consistency in “manually” placing the wirepull hook on wires with varying height, looping profiles and wire distances. The influence of loop height and wire distance is a significant factor in determining the true wire pull strength. A low wire loop will result in lower measured pull strength, while a higher loop will result in higher pull strength. Therefore, if we can accurately quantify the loop height and profile then we can place the wirepull hook in the optimum position for pulling. In this study we will demonstrate how the “parallelogram of forces” can affect wirepull measurements. With the advent of the current generation of automated wirebond pull testers, we can accurately determine the appropriate correction factor(s) for varying loop heights in order to position the wirepull hook at the precise location necessary for accurate and meaningful results. In addition, with real time yield monitoring, the new pull testers are capable of locating and identifying missing wires that can often be attributed to the high density of today's circuit designs.