Precision Shims, Spacers, Washers and Submounts
Glass, quartz, ceramic and metal parts as thin as 25 microns, lapped or polished to micron tolerances
Valley Design laps and polishes precision shims, spacers, washers and submounts in glass, quartz, aluminum nitride, alumina and other materials, with accurate pitch tolerances, spacing sequenced to less than 1/4 micron, and flatness as precise as 1/4 wave.
Precision shims, spacers, washers and submounts are thin, flat, dimensionally controlled parts that set the exact distance between components, align them, spread loads, or carry a chip and move heat away from it. Valley Design fabricates them by lapping and polishing glass, fused silica, fused quartz, aluminum nitride, alumina and other materials, with thicknesses from 25 µm, thickness tolerances of ±1 µm, and lapped or polished mirror finishes. If a gap in your assembly has to be right to the micron, these are the parts that hold it.
What are precision shims, spacers, washers and submounts?
| Part |
What it does |
| Shim |
A thin, precisely cut piece of material that fills a small gap or adjusts spacing between parts. Made to tight thickness tolerances for optics, rotating equipment and high-performance assemblies. |
| Spacer |
Separates and locates components, sets clearance, or holds a fixed distance between parts. Precision spacers add tight control of thickness, parallelism and flatness. |
| Washer |
A flat ring with a center hole that spreads the load from a screw or bolt. Precision washers can also act as spacers. |
| Submount |
A platform that supports an optoelectronic or electronic device such as a laser diode. It gives mechanical stability, conducts heat away from the device, and often carries metallized pads for electrical connections. |
A note on “glass spacers”: on this page the term means precision lapped or polished glass and quartz parts for optics, photonics and microelectronics. It does not mean the spacer strips used between panes in insulated window units.
Precision shim and spacer capabilities
| Smallest blocks |
250 µm square |
| Thinnest parts |
25 µm |
| Rings and washers |
Up to 450 mm diameter |
| Thickness tolerance |
As tight as ±1 µm |
| Spacing between parts in a sequence |
Less than 1/4 µm |
| Flatness |
As precise as 1/4 wave |
| Surface finish |
Lapped or polished mirror finish |
| Shapes |
Any flat shape, with or without cavities or holes; custom edge profiles, steps and cavities |
Parts can be arranged sequentially, so that a set of shims or spacers shares one thickness within a very small spread. Flatness describes how far a surface departs from a perfect plane, here in fractions of a wavelength of light. Surface finish (Ra) is the fine-scale roughness of the surface. They are separate specifications.
Need shims or spacers to a specific thickness?
Reach out to our Technical Team Request a Quote
Materials for precision shims and spacers
We fabricate precision shims, spacers, rings, washers, submounts and blocks from a wide range of materials. Many glass, quartz and aluminum nitride sizes are available from stock (see the stock tables below).
| Material family |
Examples |
| Ceramics |
Aluminum nitride, alumina, silicon carbide |
| Glass and quartz |
Borosilicate glass, soda lime glass, fused silica, fused quartz, sapphire |
| Metals |
Stainless steel, tool steel, copper, brass, aluminum, tungsten, nickel-plated or hard-coated metals |
| Polymers |
Teflon and other polymers |
Not sure which to choose? See our full materials list. In general, fused silica and fused quartz suit optical and low-expansion applications, borosilicate and soda lime glass are economical glass choices, and aluminum nitride suits parts that must conduct heat while staying electrically insulating.
Aluminum nitride and ceramic spacers and submounts
Aluminum nitride (AlN) is widely used for submounts and heat-spreading spacers because it conducts heat well and is an electrical insulator. Typical AlN grades run from about 170 W/mK upward; the AlN we lap and polish is rated 170–185 W/mK. Its thermal expansion, roughly 4.5 ppm/K, is close to silicon and many optoelectronic chips, which reduces stress during temperature cycling.
Valley Design does not make the AlN. We lap and polish it into precision shims, spacers and submounts:
| Thermal conductivity (typical) |
170–185 W/mK |
| Standard lapped finish |
25 µin Ra (about 635 nm), lapped both sides |
| Polished finish |
2 µin Ra (about 51 nm), one or two sides |
| Tighter tolerances |
As low as ±1 µm |
Learn more about aluminum nitride and our ultra-thin ceramics. For laser-diode and optoelectronic mounting parts, see submounts, spacers and carriers.
Precision glass and quartz spacers
Soda lime glass, borosilicate glass, fused silica and fused quartz spacers are lapped to a 25 µin Ra finish (about 635 nm), or optically polished on request. They are used to set precise gaps between optical elements, in fiber optic components, and in microelectronic and photonic assemblies. Larger and smaller sizes with tighter tolerances are also available. See also ultra-thin glass and lapping and polishing.
Stock precision shims and spacers
These are the configurations we list as stock. Stock levels fluctuate and are subject to change. Please call 978-425-3030 or email us to confirm current pricing and availability. Finish “LBS” means lapped both sides.
Aluminum nitride (AlN) stock
| Geometry (square) |
Thicknesses available |
Finish |
| 1 mm ± 0.05 mm |
0.127, 0.25, 0.381, 0.5, 1, 1.5, 2 and 2.5 mm, each ± 0.01 mm |
LBS |
| 2 mm ± 0.05 mm |
| 3 mm ± 0.05 mm |
| 4 mm ± 0.05 mm |
Glass and quartz stock
| Geometry |
Thicknesses available |
Finish |
| 1 mm × 0.5 mm rectangle (each ± 0.05 mm) |
0.05, 0.075, 0.1, 0.127, 0.15, 0.2, 0.25, 0.381, 0.5, 1, 1.5 and 2 mm, each ± 0.01 mm |
LBS |
| 1 mm square ± 0.05 mm |
| 2 mm square ± 0.05 mm |
| 3 mm square ± 0.05 mm |
| 4 mm square ± 0.05 mm |
Need a different size, thickness or tolerance? Custom shims, spacers, rings and washers are routine work. Send us your drawing.
Frequently asked questions about precision shims and spacers
What is a precision shim?
A precision shim is a thin, flat piece of material, cut and lapped or polished to a tight thickness tolerance, used to fill a small gap or adjust the spacing between parts. Valley Design makes shims from glass, quartz, ceramics and metals as thin as 25 µm with thickness tolerances as tight as ±1 µm.
What is the difference between a shim, a spacer and a washer?
A shim adjusts or fills a small gap, usually in a very thin, tightly controlled thickness. A spacer separates and locates parts to hold a fixed distance. A washer is a ring that spreads the load from a fastener, and can also act as a spacer. The categories overlap, and precision versions of all three are available.
What is a precision glass spacer?
A precision glass spacer is a lapped or polished glass, fused silica or quartz part that holds an exact distance between optical or electronic components. It is not the same as the spacer strip used between panes in an insulated window unit.
What is a submount?
A submount is a platform that supports an optoelectronic or electronic device, such as a laser diode, between the device and a heat sink. It gives mechanical stability, conducts heat away, and often carries metallized pads for electrical connections. Its thermal expansion should be close to the device’s so temperature cycling does not stress the chip.
Why use aluminum nitride for spacers and submounts?
Aluminum nitride conducts heat well (typically 170 W/mK or higher; our parts are rated 170–185 W/mK), is an electrical insulator, and has a thermal expansion of roughly 4.5 ppm/K, close to silicon and many optoelectronic materials. That combination makes it a common choice for heat-spreading spacers and submounts.
How small and how thin can you make precision shims and spacers?
Blocks as small as 250 µm square, parts as thin as 25 µm, and rings up to 450 mm in diameter, with custom edge profiles, steps and cavities. Results depend on the material and shape, so ask us about your part.
What finishes and tolerances are available?
Lapped finishes of 25 µin Ra (about 635 nm) and polished mirror finishes, including 2 µin Ra (about 51 nm) on aluminum nitride. Thickness tolerances are as tight as ±1 µm, with flatness as precise as 1/4 wave and spacing within a sequence of less than 1/4 µm.
Which materials can precision shims and spacers be made from?
Aluminum nitride, alumina, silicon carbide, borosilicate glass, soda lime glass, fused silica, fused quartz and sapphire, plus metals such as stainless steel, tool steel, copper, brass, aluminum and tungsten, and polymers such as Teflon.
Which shims and spacers are in stock?
Aluminum nitride squares of 1, 2, 3 and 4 mm in thicknesses from 0.127 to 2.5 mm, and glass and quartz parts of 1 × 0.5 mm and 1 to 4 mm squares in thicknesses from 0.05 to 2 mm. Stock fluctuates, so call 978-425-3030 to confirm.
Related resources
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