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The Basic Die Bonding Process

1. Wafer Processing

1. Wafer Processing

Everything starts with a thin slice of material, usually silicon, but sometimes also Gallium Arsenide, Quartz, Glass, Lithium Tantalate, Lithium Niobate , etc. called wafer. Once you have received the so valuable tested wafer in your hand, you have been asked to return the packaged dice with an acceptable yield, we say 98%. Now, the game is on.
2. Frame Mounting

2. Frame Mounting

Prior to wafer sawing, the backside of the wafer is attached onto a flexible PVC sticky foil, held by a plastic ring or metallic frame.
3. Wafer Mounting

3. Wafer Mounting

Stored a few hours in ambient temperature or even placed in an oven to increase adhesion between wafer and foil. Different film material, featuring high tear strength and elongation, are proposed by the vendors from low tack for large die, high tack for small die or hard to cut material, to UV sensitive film which looses tack property after exposure to UV once the wafer is sawn. Manual or automatic wafer mounters are available, with or without front wafer surface contact. Adequate temperature and pressure control will result in bubble-free wafer attachment.
4. Wafer Sawing

4. Wafer Sawing

Metallic or resinoid diamond impregnated dicing blades are designed to cut through different substrate materials in different techniques : Single mode - the return trip is made over the wafer. Dual mode - where effective sawing takes place in both directions. Multiple steps -when several passes at different depths are necessary to cut through the wafer. Very accurate blade cooling must be monitored to avoid premature blade wear or worse consequences for the wafer in case of coolant shortage or poor jets alignment.
5. Wafer Rinsing / Cleaning

5. Wafer Rinsing / Cleaning

Many wafer sawing equipments are delivered today with a wafer cleaning unit incorporated into the system. Soon after sawing completion, the wafer is transferred to the cleaning station preventing silicon dust or any liquid droplet to dry on the wafer surface.
6. Die Picking

6. Die Picking

After sawing & cleaning, every individual die must be removed from the plastic foil and placed either in a intermediate carrier, like a waffle pack, gel pack, tape and reel, etc.. or directly on the substrate over the die attach material. Pick & place machines and die bonders are equipped with an ejector needle system that will push against the die back side to help break the adhesion force of the adhesive foil. A vacuum pick-up tool with coordinated z-axis movement holds the die before transfer to bond position.
7. Epoxy Dispensing

7. Epoxy Dispensing

Paste with appropriate viscosity (from higher range to lower) are applied by screen printing, needle dispensing, print stamping or through the less known process of fluid jetting.
8. Die Placing

8. Die Placing

The way the die is secured on the pick-up tool as well as the bonding parameters will determine the type and material of tool to be used. The tip of the pick-up tool may be replaceable or fixed to the shank and made of plastic, rubber or metal base material. A few of these solutions may be compatible with your application.

9. Epoxy Curing

9. Epoxy Curing

Adhesive polymerization or curing takes place in stand alone ovens, belt furnaces or under UV wave length exposure. Curing time ranges from a few minutes for fast (snap) cure adhesive formulation to a few hours to minimize the stress by applying low or non thermal energy. Depending on the type of die attach material, the weight loss during thermal treatment ranges from 0% to 80%.
10. Wire Bonding

10. Wire Bonding

 
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