Die Attachment Oven

Die Attachment Oven we carry

What is a die attach oven?

The die attach process involves attaching a semiconductor die sourced from a silicon wafer to a given package through substrates or lead frames using a die attach oven and adhesives. There are two types of die-attach ovens; the cold-chamber machine and the hot chamber machine. Let’s discuss each of them.

Hot-chamber die casting oven

Hot-chamber die casting can also be referred to as a gooseneck machine. It uses molten metal to supply the die.

One of its advantages is that it has fast cycle times and a very convenient casting machine for melting metals.

However, it can only use the low-melting-point metals, which means that metals like aluminium cannot be used.

Cold-chamber die casting oven

The Cold-chamber die casting oven is purposely used for casting alloys that cannot be used in the hot-chamber machines—for example, the Zinc and Aluminum alloys since they have high melting temperatures.

The metal is first melted in a separate melting furnace, usually positioned in a different oven. The molten metal is then conveyed to the cold-chamber machine, which has an unheated shot chamber.

The shot is then transported into the die through a mechanical piston. Cold-chamber die casting ovens usually have a slower cycle since the molten metal must be transferred from a furnace and fed into a cold-chamber machine.

How does the die attach process work?

There are four common die-attach process methods used to form different bond properties. Each process uses a distinct workflow procedure and materials. These processes are Adhesive Bonding, Solder attach, Eutectic Bonding and Flip Chip.

Epoxy is currently the most preferred type of die-attach; about 70 to 80 percent of current manufacturers use it today. Let’s discuss the two most used die attachment processes used today.

Adhesive Die Attach Method

As the name suggests, the Adhesive die attach method utilizes adhesives such the silver-filled glass, epoxy and polyimide as the primary die to attach materials when mounting a die on a given die cavity or die pad.

First, the adhesive is dispensed on the cavity or die pad in a regulated quantity. The die mounting is then compelled from the primary wafer using one or multiple ejector needles.

At the same time as ejection, a collet (pick and place gear) picks the die from a wafer tape and places it on the adhesive.

These steps are performed using a piece of special die-attach equipment or the die bonders.

Die attach filet is the mass of epoxy that has climbed on the die edges. Too much die attach filet may contaminate the die attach surface.

Similarly, too little die attach may result in die cracking or die lifting.

Ejection of the die originating from the wafer tape at the pick and place system is another critical feature of an adhesive die attachment.

Slight use of a worn-out or inappropriate ejector needle and inaccurate ejection parameter control can result in die backslide micro-cracks or took marks that eventually result in die cracking.

Eutectic Die Attach

Eutectic Bonding involves attaching a die to a substrate or a package using a low melting metal alloy as the intermediate layer that forms an even and a continuous bond.

An eutectic bond is usually created by melting a metal alloy to form atomic contact with the substrate and the die.

The Eutectic die attach method is commonly used in hermetic packages and uses a eutectic alloy when attaching a die to a cavity.

Ideally, the eutectic alloy has the lowest melting point for the total metals combined in a given alloy. In most cases, the Au-Si eutectic alloy is the most opted die-attach alloy for semiconductor packaging.

During heating, a gold preform is positioned on the upper side of the cavity. Once the die has been mounted over the gold preform, Si from the backside of the die diffuses into the upper gold preform, thus combining to form an Au-Si alloy.

With more Si diffusing into the upper gold preform, the ideal Si-to-Au proportion increases until the desired ratio is achieved. The AU-Si eutectic comprises about 2.86% of Si and a melting point of 363 degrees C.

For that very reason, the die attach temperature is considerably above this temperature to attain the eutectic melting point. At this temperature, the alloy will melt so that the die is attached to the cavity.

To ensure optimum die attachment, the machine controller scrubs the die directly to the eutectic alloy to ensure the even distribution of the die attachment to the alloy.

Gradually the silicon atoms diffusing into the top gold perform surpasses the eutectic limit, thus making the die attach start solidifying once again.

The package is given time to cool down and solidify completely to form the eutectic, thus concluding the die attach process.

Die attach machine uses and applications

Die bonding machines have various uses and applications in the packaging assembly environment.

These machines form a joint or a bond between a substrate and package to the die to its correct placement.

The die attach machine aims at achieving the following goals.

• Mechanically attaching a die onto a substrate, package or on a different die.
• Creating an even contact between a die and other material surfaces
• The die attach machine ensures ideal heat dissipation to ensure that the die can withstand extreme temperatures without getting damaged.
• Ensuring high thermal stability reduces mechanical stress arising from the extreme temperature in the joints between the package/ substrate and the die.

However, with the advancement of packaging technology and scope every day, you must consider using a die attach machine that meets your current die attachment work needs and the possibility of future changes.

The die attach oven machines that we carry at Trident Technologies adopt advanced technology with the ability to work on small dice (e.g. 300mm wafers), greater speed, handle a wide variety of substrate types, and precise accuracy.
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