Abstract

Recent packaging requirements for very fine pitch wire bonding has placed considerable demand on both assemblers and wire bonder manufacturers. Close cooperation between these two groups has resulted in wire bonders capable of addressing pad pitches of 70, 60 and even 50 microns, some in volume production and others at the prototype level. What is often overlooked in such evolutions is the effect of other processes on the operation in question. For example, such increased requirements for wire bond precision might see the die attach operation having a critical impact on the wire bond processes. Until now, the bonding operation has been able to adjust parameters for minor die misalignment. At these finer pitches, it becomes essential to understand and determine whether current die attach process windows are sufficient and, if not, what measures are appropriate to improve such windows. This paper addresses current die attach process windows through data collection on die placement accuracy (X-Y and theta) for a number of different die attach machines using different vision systems. Pad layouts of existing fine pitch package designs were also modeled on design workstations to simulate and evaluate the impact of die misalignment on wire bond connection criteria. Results of these studies demonstrate that the die attach equipment must contain a die translation within 25 microns and a rotation within 0.2 degree in order to meet wire bond criteria at pitches as slow as 50 microns. It is also shown that current die attach machines require vision systems with pad recognition in order to meet such requirements and that, even when so equipped, there exist variations between machines that may impact selection at the finest pitches. Finally, die attach measurement techniques are reviewed with regards to recommending appropriate process control.(Author abstract)