3 Uses of Silver Sintering in Electronics

In the domain of silicon-based technologies, silver sintering is a popular option for electronic packaging. Due to its ability to increase conductivity, reducing thermal resistance, and high reliability, it has become an alternative to soldering.

Now let’s us look some use cases of silver sintering:

1. Making silver sintering composite without adhesive resin

Micron-sized silver flakes and a fluxing agent is used to make a silver sintering composite without adhesive resin.

A fluxing agent, peroxide, or oxygenated solvent is chosen that is sufficiently volatile at the sintering temperature so that no residue of it remains in the composition after sintering.

This mixture sinters at temperatures of 250°C or less, and can form an intermetallic bond with a copper substrate without applying pressure.

For information refer to this patent.

2. Packaging of quartz crystals

Sintering silver paste can be used for packaging quartz crystals. The process involves:

  1. attaching ceramic surfaces to the quartz crystal by applying layers of silver paste,
  2. sintering the silver paste in an oxygen-free atmosphere at temperatures in the range of 225°C to 325°C. The sintering is done in a way that the quartz crystal exhibits a positive drift in resonance frequency of the quartz crystal over time.
  3. hermetically sealing the quartz crystal.

This process can also improve the frequency accuracy of the quartz crystal.

For information refer to this patent.

3. Sintering silver paste for bonding semiconductor chips

To bond semiconductor chips, a sintering silver paste is made of silver particles with an average particle size of 0.1 to 2.0 μm and an organic silver solution.

The organic silver solution is made by dissolving liquid or solid fatty acid silver salt in an organic solvent. The organic solvent has a boiling point of 150°C or above. The content of carbon, hydrogen and oxygen and silver present in the organic silver complex solution is 30 wt% or more.

Additionally, sintering paste may also contain a reducing agent like ascorbic acid or formamidin.

For information refer to this patent.

4. For making extended contact pads for LED

Extended contact pads made of sintered silver can increase the yield rate of LED packaging. This extended pad has a height/thickness of about 100 μm.

The LED flip chip with extended pads is produced at the wafer level. The wafer level process involves forming multiple flip chips on a wafer and dicing the wafer into individual flip chips. Each flip chip has extended cathode and anode contact pads made of sintered silver.

The sintering temperature is from about 180°C to 240°C depending on the characteristics of the sintering silver paste.

Finally, a phosphor layer is applied over the LED flip chip such that the LED emits white light.

For information refer to this patent.

Why silver alloy composite is preferred over pure silver for liquid-phase sintering?

Silver alloy composite is better than pure silver for liquid-phase sintering because it contains low molecular weight organic auxiliaries, a silver salt, silver particles and tin.

Using tin in the mixture helps to reduce the material cost of the sintering compound.

Furthermore, tin make it possible for lower processing temperatures to produce a dense sintered connection. Thus, significantly reducing the process cost of sintering.

Compounds produced this way have higher electrical and thermal conductivity than pure silver.

For information refer to this patent.

More articles on sintering