Thin film ceramics microelectronic components

anufacturing microelectronic components offering solutions for optoelectronic, semiconductor, hybrid and microwave applications

Manufacturing microelectronic components offering solutions for optoelectronic, semiconductor, hybrid and microwave applications

AlN Laser Diode Carriers

Thin Film metallised Aluminium Nitride (AlN) submounts/carriers for mounting of laser diodes and associated components and devices for optical sub-assemblies.

Ceramic material:
The ceramic substrate material is Aluminium Nitride (AlN). Standard grade is 170W/m•K. 200W/m•K is also available. Typical properties are:

TC (W/m•K) ~170

CTE (ppm/°C) ~4.6

Dielectric constant ~8.8 @ 1MHz

Thickness, Flatness and Surface Finish:

The AlN substrate material is available with as-fired, lapped or polished surface finishes. Standard substrate thicknesses are 0.63mm and 1.0mm with as-fired finish. Non-standard thickness material can also be fabricated. Substrates can be lapped and polished from 0.25mm thick up to 1.5mm thick.

The flatness and surface finish of the substrate material affects conductor definition and adhesion and also the quality of the laser die attachment. Typical substrate properties are:

Surface Thickness Flatness Surface Finish Notes
As fired ± 15% 50µm/25mm ~1.6µm Ra Lowest cost
Lapped ± 0.02mm 5µm/25mm ~1.0µm Ra Better thickness and flatness control but poor surface integrity
Near polish " " ~0.15µm Ra Best for conductor and AuSn adhesion
Polished " " <0.05µm Ra Best for conductor definition and minimising epoxy bleedout

Mechanical Dimensions:
Small mounts are commonly used for individual chip-on-carrier assemblies, and large substrates with complex pattering for optical sub-assemblies. General size limits are:
Min. length and width 0.5mm x 0.5mm
Max. length and width 75mm x 75mm

Parts can be machined using diamond saws for the highest edge quality and dimensional control. Laser profiling/scribing are ued for complex shapes, holes, etc. Typical tolerances available:

Diamond sawing: Typical High
Length and width ±0.05mm ±0.02mm
Edge chipping <0.05mm <0.01mm
Pattern to edge ±0.05mm ±0.01mm

Laser profiling
Holes ±0.05mm ±0.025mm
Pattern to edge/feature ±0.05mm ±0.025mm

Metallisations:
Various metallisation schemes can be applied to form conductors, integral resistors, solder barriers, solder dams etc. Typical schemes include:

Conductors Notes
Ti/Pt/Au Best overall conductor scheme but highest cost
TiW/Pd/Au (+ Au) Pd barrier layer (plus electroplated Au) for standard low cost scheme
TiW/Au (+ Ni/Au) Ni barrier layer for extra protection when soldering with Sn and Pb based solders
TiW/Au (+ Au) For high temperature soldering. Suitable for Au bearing solders only

Resistors
Ta2N or NiCr Typical sheet resistivity of 50 ohms per sq, with a standard tolerance of 20% or 0.2% if laser trimmed

Dielectrics
Polyimide For conductor cross overs, solder dams and passivation protection

The Au and barrier layer thicknesses depend on the application. Generally for Au wire bonding 1µm minimum of Au is required. For Pt or Pd barrier layers a minimum of 0.5µm is usually specified.

Plated thru-holes (substrate vias)

Front and back faces of the component can be electrically interconnected using pre-drilled metallised thru-holes. Typical hole diameter is = substrate thickness.

Wrap around metallisation

Plain submounts can also be fabricated with metallisation that wraps around one or multiple sides walls to connect the top and bottom faces. Wrap around connections can also be accomplished on patterned mounts, with due consideration to process limitations and cost.

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