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Miniaturised Hermetic Packages in Glass and Sapphire Mark Fretz

Swissphotonics Workshop

Alpnach, 16.05.2017

Copyright 2017 CSEM | Miniaturized Hermetic Packages in Glass and Sapphire | Mark Fretz | Page 1

Outline What’s in the package?

• Challenges in miniaturized packaging

• State-of-the-art package sealing

• CSEM approach

• Laser assisted bonding

• Examples

• Hermeticity testing

• Volume production


Challenges in Miniaturized Packaging

• Transparency for RF and visible light and Laser assisted

bonding

• Limited number of materials which comply with

above requirements and are suitable for harsh

environments (e.g. space or implants)

• Solution

• Sapphire & glasses

• Laser assisted diffusion bonding



• Bonding of miniaturised packages

• New bonding materials for harsh environments

and medical applications have high melting

points (Pt, Ti, Pd, Au)

• Lid brazing or soldering of these materials

generates excessive heat

• Solution

• (Localised heat) + (bonding below melting point)

• (Laser assisted) (diffusion bonding)



• Stresses

• High temperature brazing or soldering lead to

stresses in the package

• Solution

• Localised heat keeps the package cool

• Diffusion bonding generates lower stresses at the

interface)

(Laser assisted) (diffusion bonding)



• Hermeticity Testing

• Small packages require lower leak rates down to 6*10-15 atm.cc/s(1)

• Current best helium leak rate detection: 5*10-12 atm.cc/s(1)

• New Approach

• Fourier transform infrared spectroscopy (FTIR)

(1)G. Jiang, D.D. Zhou, Implantable Neural Prostheses 2, Chapter 2: Technology Advances and Challenges in Hermetic Packaging for

Implantable Medical Devices, Springer, 1st Edition


State-of-the-Art Package Sealing

• Glass frit bonding

• High temperature bonding, not biocompatible

• Laser assisted soldering

• High temperature, not biocompatible

• Laser welding /Resistance welding

• Very high temperatures, not biocompatible


CSEM Approach: Laser Assisted Diffusion Bonding

Proper metallisation

Good surface roughness

Transparent lid


CSEM Approach: Laser Assisted Bonding: Examples

Cochlear Implant


CSEM Approach: Laser Assisted Bonding: Examples

Implantable pressure sensor

4 mm

Sapphire package

Commercial pressure sensor

LADB seal


CSEM Approach: Non Destructive FTIR Leak Testing

• Bombing with N2O high pressure

• 2 to 5 bars

• Not present in ambient

atmosphere (low background)

• Peaks at wavenumber 2237 & 2212

cm-1


CSEM Approach: Non Destructive FTIR Leak Testing

• Detection depends mainly on

• Concentration of N2O

• Duration of bombing

• Bombing pressure

• Length of light path through the package

• Detector sensitivity/resolution

1E-13

1E-12

1E-11

0 20 40 60

Det

ecti

on

lim

it

(atm

cm

3s-1

)

Bombing time (day)

3.6 mm3

1.4 mm3

1E-6

1E-5

1E-4

0 1 2 3 4 5 6 7 8

Larg

est

le

ak

ra

te(a

tm c

m3

s-1)

Cell volume (mm3)

30 min

10 min

3 min

2 bar bombing pressure


CSEM Approach: Volume Production

• Array level tested successfully

• Glass on silicon

• Chip size: 3.350 x 2.0 mm

• Array size : 13.4mm x 8.0mm

• Overall time for the array is 48 seconds

• Estimated on 200mm wafer: 75mins (~4’000 parts 1 sec/part)

• Estimated for 100mm wafer: 15 minutes (~1’000 parts)

• Further reduction by a factor of 4 seems feasible with further optimisation

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