Tell Me. What Is Die Bonding? – The Pros & Cons

What is die bonding?

DieBondChip2

Die bonding (often referred to as die attach) is the process of attaching a die/chip to a substrate or package. Die attach is accomplished by using one of the following processes:

  • Eutectic
  • Solder
  • Adhesive
  • Glass or Silver-Glass

For our purposes here we will focus on Eutectic, Adhesive and Silver-Glass.

 


 

Eutectic Bonding

A eutectic bond is formed by melting a preform consisting of a mixture or alloy of two or more dissimilar metals in the joint between the die and substrate. In some cases the die may have a eutectic alloy pre-plated on its back omitting the need for a preform. The preform has a melting point which is lower than the melting point of its base materials. Consider a typical preform composed of gold and silicon. The melting point of gold is 1640° C, and the melting point of silicon is 1414°C. However, when the materials are combined into a preform, the melting point becomes 363° C.

Some typical preform materials:

Materials

Melting Point

Au97-Si3 363°C
Au88-Sn12 350°C
Au80-Sn20 280°C
Pb63-35Sn-1.8Sb 230°C

In the eutectic process, the substrate is secured on a heated workstage which operates at a temperature just below the eutectic melting point. When the die and preform are placed on the substrate, the bonder initiates a light scrubbing action with the bond head. This scrubbing generates just enough energy to raise the temperature at the bond site above the eutectic melting point. When scrubbing ceases, the melted material solidifies, thereby creating the bond. Nitrogen is used as a cover gas in order to prevent oxidation due to the high heat.

Pros

Cons

Good thermal conductivity High processing temperature
Electrically conductive Requires use of inert gas to prevent oxidation
Good fatigue/creep resistance
Low contamination

 


 

Adhesive Bonding

An adhesive bond is formed by adhering the die to the substrate using some type of adhesive material. It can be electrically insulating or conductive depending on the adhesive material used. Adhesive bonds are conducted at room temperature.

Typical Adhesives

Acrylic thermoplastic resins
Epoxy Thermo-set resins
Silicone resins

In the adhesive bonding process, the substrate or package is secured to an unheated workstage. The adhesive material is contained in a reservoir and a small amount is metered out onto the substrate, usually in a pattern conforming to the shape and size of the die. The bonder then picks up the die and places it on the adhesive, making the bond. The bond process is complete once the adhesive dries.

Pros

Cons

Ease of automation Outgassing
Low curing temperatures Contamination/bleed
Reduced die stresses Voids in the bond (sometimes)
Low cost Inferior thermal/electrical conductivity
Wide range of die sizes Dimensional changes during processing and service life
Special plated surfaces are not required Sensitive to harsh environments
Rework is possible

 


 

Glass /Silver-Glass Bonding

A glass bond is formed by adhering the die to the substrate using glass in the form of a paste. The glass paste may also contain silver particles which enhance thermal and electrical conductivity (this is what is called Silver-Glass die bonding).

Typical glass die attach material

Lead borate based glass – 80%Ag

The Glass bonding process is similar to Adhesive bonding. The differences are the material used and the need for heat. Glass bonds are heated to 350-450°C which melts the glass into a low viscosity liquid. The glass hardens as it cools thereby making the bond.

Pros

Cons

Relatively insensitive to metallization High processing temperature
Low void content Heat during processing causes oxidation
Good thermal & electrical conductivity
Limited stress relaxation
Low contamination
High process/operating temperature resistance

YOP POLL
________________________

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Reference: Hybond

 

 

 

 

 

 

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