Traditional Packaging (Wire Bonding and Die Attach)

Methods of Wire Bonding

There are three main methods for connecting metal wires to pads:

1. **Thermo-Compression Method** (Medium to High Bonding Strength)  
2. **Ultrasonic Method** (Low Bonding Strength)  
3. **Thermosonic Method** (High Bonding Strength)  

When performing chip bonding, alloys made of gold or silver (or nickel) can be used, especially for large sealed packages. Connections can also be made using solder or metal-containing pastes (Power Tr), or through chip bonding with polymer-polyimide (Polymer, Polyimide). Among polymer materials, silver-containing paste or liquid epoxy resin is relatively easy to use and frequently employed.

When using epoxy resin for chip bonding, a very small amount of epoxy can be precisely placed on the substrate. After placing the chip on the substrate, the epoxy is cured through reflow or curing at temperatures between 150°C and 250°C to bond the chip and substrate together. At this point, if the thickness of the epoxy used is not uniform, warpage may occur due to differences in thermal expansion coefficients, leading to bending or deformation. Therefore, while using a small amount of epoxy is advantageous, any use of epoxy can result in various forms of warpage.

For this reason, an advanced bonding method using Die Attach Film (DAF) has become the preferred choice in recent years. Although DAF has the disadvantages of being expensive and difficult to handle, it allows for easier control of the amount used and simplifies the process, leading to an increasing adoption rate.

DAF is a film that adheres to the bottom of the die. Compared to polymer materials, DAF allows for thickness adjustments to a very small and consistent level. DAF is not only used for bonding between the chip and the substrate but is also widely applied for bonding between chips, thereby forming Multi-Chip Packages (MCP).

From the perspective of the structure of the diced chip, the DAF located at the bottom of the chip supports the chip, while the dicing tape exerts a weak adhesive force that pulls on the DAF beneath it. During the bonding process, after removing the chip and DAF from the dicing tape, the die is immediately placed on the substrate without the need for epoxy resin, skipping the dispensing step. This simplifies the process and improves thickness uniformity, thereby reducing defect rates and increasing productivity.