| CERAMIC MATERIAL |
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Wrap around PD mount
with 25° slope front face |
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| The ceramic substrate material is typically alumina (90%, 96% or >99%). |
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| Mechanical Dimensions |
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Parts are machined using diamond saws for the highest edge quality and
dimensional control, or using laser profiling or scribing for complex shapes,
holes etc. |
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| Diamond sawing: |
Min. |
Max. |
Typ. tol. |
Tight tol. |
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Length and width
Thickness
Pattern to edge gap |
1.0 x 1.0 mm
0.125 mm
0.025 mm |
75 x 10 mm
2.0 mm
n/a |
±0.05 mm
±0.05 mm
±0.05 mm |
±0.020 mm
±0.010 mm
±0.025 mm |
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| Laser profiling: |
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Hole diameter
Hole to hole
Pattern to edge gap |
0.15 mm
= thickness
n/a |
n/a
n/a
n/a |
±0.05 mm
±0.05 mm
±0.05 mm |
±0.025 mm
±0.025 mm
±0.025 mm |
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| Machined Features |
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| Slots, grooves, angles, holes, apertures, cut outs, chamfers, etc. can all be realized by precision diamond machining or laser drilling or profiling. |
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| Moulded Features |
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For special applications the ceramic body can be moulded and fired to shape before metallising, allowing for complex shapes not economically realizable by
machining. |
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| METALLISATION |
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| Thick Film Metallisations |
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| For lowest cost, thick film metallisations are screen printed with the required pattern directly onto the ceramics and then fired, usually in air at >800°C, to fix the metal to the ceramic. Special attention is paid to ensure a high reliability of connection where the conductors wrap over the edges of the ceramics. |
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| Thick Film Type |
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| Au (standard) |
Au wire bondable, epoxy attach or AuSn solderable. The most common metallisation system. |
| Au (special) |
Modified Au metallisation with excellent flux-free AuSn solderability (see flux-free AuSn solderability). |
| Pt/Au |
Platinum doped to improve leach resistance to PbSn and SnAg type solders. Au wirebondable. |
| Pt/Pd/Ag |
Doped silver based metallisation for lowest cost. Solderable with fluxed solders. Not wirebondable. |
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| The thick film metallisation schemes can be mixed on the same or adjoining faces to accommodate varied bonding and soldering processes. |
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Thick-film Au with
75µm track/gap |
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| Thin Film Metallisations |
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| For special applications wrap around conductors can be achieved using thin film type metallisations. Thin films are generally smoother, flatter and better defined than thick films but are usually more costly. |
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| Thin Film Type |
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TiW/Pd/Au
Ti/Pt/Au |
Au wire bondable, epoxy attach or solderable.
Best soldering performance but more costly. |
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| Patterning |
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THICK FILM
Typical |
High spec. |
THIN FILM
Typical |
High spec. |
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Minimum line width
Minimum gap width
Line tolerance
Line to feature
(e.g. hole) tolerance |
150µm
150µm
±50µm
±50µm |
50µm
50µm
±25µm
±25µm |
25 µm*
25 µm*
±20 µm*
±50 µm* |
10 µm*
10 µm*
±5 µm*
±25 µm* |
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| Alignment guides/fiducials can be incorporated into design for subsequent automated assembly.* |
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| * Dependent upon imaging method available (design dependent). |
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| Flux-free AuSn soldering |
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| Angled photodiode mounts |
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| Assemblies |
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| FLUX-FREE AU/SN SOLDERING - THICK AND THIN FILM |
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| Thin film materials usually provide very good surfaces for flux-free AuSn soldering. Obtaining good results using traditional thick film metallisations normally requires additional processing, but LEW Techniques offers a thick film Au that has exceptionally good flux-free wettability with AuSn. This provides the wettability performance of thin film with the cost benefits of thick film. |
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| PRE-DEPOSITED AU/SN |
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| For some applications it is possible to selectively pre-deposit AuSn solder onto the conductors. This removes the need to use a solder preform. Alignment, thickness and alloy control are dependent upon the underlying conductor metallisation and component geometry. |
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| ANGLED PHOTODIODE MOUNTS |
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| It is possible to produce conductors on an angled face to allow the photodiode to be located close to the rear facet of a laser diode without causing emitted light to be reflected back into the laser. This can reduce the real estate required and aid miniaturisation. |
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| ASSEMBLIES |
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| Metallised ceramics can be assembled to other ceramics or metal components to produce precision assemblies. Joints can be realized by several means, including soldering and glassing. |
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| For further details please contact us for datasheets about our thick and thin film microcircuit manufacturing capabilities, design guidelines and materials specifications, or find them on this website. |
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Images are not to scale |
