About Die Bonding

Local Time at Hybond: Tuesday, 21 October 2014, 6:30 PM

What is die bonding?

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 and that of Hybond products 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

    Hybond’s UDB-140A semi-automatic and UDB-206 manual eutectic die bonders can be used for these types of applications. For more information please contact us.

    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

    Hybond’s EDB-140A semi-automatic epoxy die bonder can be used for these types of applications. For more information please contact us.

    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

    Hybond’s EDB-140A semi-automatic epoxy die bonder can be fitted with a stirring mechanism (to maintain the silver particles in suspension while in the reservoir) and be used for Silver-Glass applications. For more information please contact us.