The die attach process is a critical step in the manufacturing of electronic materials, and one that presents continual challenges to the industry. In the simplest of terms, die attach is picking a chip from a wafer and setting onto a substrate. Sounds simple enough, but the way that the die is bonded to the substrate, or metal lead frame, defines the success of the process. Some commonly used techniques are epoxy, soft solder, eutectic and flip chip, each used for specific electronic materials manufacturing, and for specific kinds and sizes of chips. Today, there is widespread demand for stacked die in electronic materials. Stacked die are desirable for their space saving benefits, yet they represent distinct challenges for industry.
Semiconductor Adhesion Promoters
Adhesion promoters are used not to act as adherents themselves, but to enhance the bonding of a photoresist to a silicone dioxide surface. How does an adhesion promoter do this? It reacts directly with the substrate material and acts in two ways there. First, it removes moisture that has been absorbed. This is important because it therefore creates a water repellent hydrophobic interface, which in turn prevents etchants from undercutting the photoresist. Using a semiconductor adhesion promoter is therefore smart in terms of the money and worry that it can save. Some specialty adhesion promoters for semiconductors are designed to work uniquely on copper and gold surfaces where a photoresist is applied. Most of these specialty adhesion promoters are applications composed of hexamethyldisilazane, or HMDS, manufactured especially for semiconductor applications.
The Evolution of Die Attach for Electronic Materials
The die attach has two main functions: to mechanically attach the die to the substrate, and to dissipate the heat generated in the die. The die generates heat then cools in a cyclical way through out the lifetime of the electronic material it forms an integral part of, and so any die attach material must be able to dissipate the heat and withstand it over time. In high power applications, because the heat density generated is so high, some conventional die attach materials are not suitable. As the trends towards thinner and thinner die continues, the techniques for all aspects of die attach must continue to evolve as well. Die pick up, dispensing of epoxy, or other adhesion material, greater placement accuracy, and bonding processes need to be fine-tuned to meet the need of industry.