DCSIMG

Bonding the Future

SCHOTT Primoceler offers wafer scale and chip scale bonding to create reliable, fully hermetic glass packages without heat or added materials.

SCHOTT Primoceler Glass Micro Bonding – Reliable Hermetic Sealing Technology 

Glass – The Material of the Future

The use of glass wafers has increased in recent years and the growth is expected to continue.

There are two types of traditional bonding methods: bonding with additive materials, and bonding with heat. Examples of technologies based on additives include adhesives, metallic coatings, and absorbing layers. Additive materials can contribute to outgassing. Additionally, issues with temperature changes are common, and the gap between wafers is challenging to control. Poor gap control often leads to lower yield and a drop in device performance. Examples of bonding methods based on heat include fusion bonding, anodic bonding and eutectic bonding. Heat-based bonding is not suitable for heat-sensitive MEMS components. Furthermore, many coatings are sensitive by heat. Organic coatings and thin film coatings, for example, can be damaged due to heat.

Hermetic optical sensor package

 

X

Hermetic, Gas-tight Seal

7

Extremely Low Heat Load

SCHOTT Primoceler has developed a Glass Micro Bonding method based on laser technology.

The technology is suitable both for wafer level bonding and for chip scale bonding. Bonding is done without any additive materials and in room temperature.

Technology assessment by SCHOTT Primoceler presented below.

SCHOTT Primoceler Glass Micro Bonding Fusion bonding Anodic bonding Adhesives or Additives
Hermeticity High High High Medium
Heat load Low High High Medium / low (UV)
Outgassing Low Low Medium High
Gap control High High High Low
Miniaturization possibility High High High Low
Other One step process Ultra high purity needed Conductivity needed Glue or other additives needed

Laser and glass bonding have intriguing possibilities for optical device packaging, as well as other applications in high-reliability markets. The process has already shown its potential effectiveness in solving problems for which there has never been a practical solution.

Liam Murphy

Hybrids and Packaging Technologies, European Space Agency (ESA)

Bonding Principle

Perfect gap control

SCHOTT Primoceler’s glass-to-glass sealing is done with a laser at room temperature
without any additive materials.

Bonding is done only at the material interface, and all surfaces are untouched. The top material needs to be transparent to visible light. The bottom material can be non-transparent, such as silicon.

Suitable materials:  SCHOTT Primoceler’s laser bonding technology is suitable for most glass types, including SCHOTT BOROFLOAT® 33 Borosilicate Glass, SCHOTT D 263®, SCHOTT AF 32® eco, SCHOTT MEMpax® Ultra-Thin Borosilicate Glass as well as fused silica, quartz and soda lime glasses or silicon. Other glass types are available on request. Most glass substrates can be supplied with SCHOTT HermeS® TGV (Through Glass Via) technology or as SCHOTT FLEXINITY™.

Minimum bottom wafer / material thickness: 30 micrometers

Maximum bottom wafer / material thickness : 30 mm

Maximum top wafer / lid thickness: 3 mm

Minimum material thickness: 30 micrometers

Example hermetic sensor package

Proven technology: verified reliability in extreme conditions

SCHOTT Primoceler’s bonding technology has been tested by third parties.

Furthermore, performance in extreme conditions for aerospace and for medical implant applications has been verified.

An example device is shown in the picture on the left. The entire device package is manufactured from glass. Only the electrical feedthroughs and metallizations for die and wire bonding are non-glass. As the material variety in the package is kept minimal, issues due to temperature changes or outgassing are avoided.

The same principle can be used to design and manufacture using a silicon base. In this case, the base plate is replaced with silicon. The interface to the PCB can be designed according to customer specifications. In addition to ball grid arrays (BGA), other types of interfaces are possible. For example, a leadless chip carrier (LCC) -type of interface.

Example device – Process and reliability verification

Shar strength comparison

Shear force testing

The chart demonstrates shear force strength comparison between SCHOTT Primoceler’s Glass Micro Bonding and UV cured adhesive bonding.

Glue used in the experiment was Vitralit 7256, which is often used in glass to glass bonding.

The shear force test was done according to MIL STD-883, method 2019.7 at the Technical Research Center of Finland (VTT).

 

Test method Conditions Visual inspection Device performance
Temperature cycling MIL-STD-750, Method 1051.1 -55oC…+175oC 100 cycles Passed Passed
Moisture resistance MIL-STD-750, Method 1021 Temperatures: 65oC, 25oC, -10oC Humidity 80-100 Rh% Cycle duration 24h Total number of cycles 10 Passed Passed
Solderability and temperature cycling SnPb solder -55oC…+150oC, 100 cycles Passed Passed
Hermeticity Set rejection limit for fine leak 6,0x10-12atmcm3/s Kr-85 Passed Passed

Reliability verification using MIL testing

The unique bonding technology has been tested using MIL standard testing methods. A review on tests performed is presented on the left.

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