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Topics Covered
Introduction
Production to Thick-Film Alumina Substrates by Roll Compaction
As-Fired Substrates Design Guidelines
A. Materials
B. Dimensional Criteria
C. Design Criteria
D. Thicknesses and Standard Sizes
Laser Services
A. Laser Scribing
B. Laser Machining
C. Annealing
D. Lasered Edge Treatments
E. Tolerances
This publication is designed to provide engineers with design guidelines, material property information, inspection methods and quality standards for CoorsTek thick-film alumina substrates. These guidelines will aid in optimizing substrate design and material selection in order to meet technical requirements cost-effectively.
If a substrate design does not comply with these guidelines, CoorsTek may still be able to offer options to specific design requirements. It is our practice to indicate exceptions to customer prints and specifications should they differ from these guidelines, for the purpose of offering alternatives and possible cost reduction.
Roll compaction is a method of fabricating continuous thin sheets of ceramic materials by compacting flowable ceramic powders in a rolling mill. This fabrication technology allows parts to be manufactured to precise dimensional specifications, yields two identical working surfaces and tighter thickness control. CoorsTek roll compaction substrate technology incorporates three basic steps: spray dried powder preparation, tape fabrication by roll compaction and sintering.
Initially, the raw materials (which consist of high purity ceramic powders) are ball-milled with dispersants, organic binders and plasticizers to achieve proper particle size distribution and slurry rheology. The slurry is then spray dried to form a flowable powder that can be fabricated into a tape when roll compacted.
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Roll Compaction Process
The roll compaction process is related to dry pressing in that it uses spray dried alumina powders as feedstock. However, the process differs in the type and amount of binders and plasticizers used in order to fabricate a flexible, continuous sheet of tape.
The process consists of a powderfeed system, which continuously replenishes a reservoir above the metal rolls. The powder is controllably presented to the rolls where it is subsequently compacted to form a continuous sheet of tape. This tape is then edge trimmed, cleaned and collected on a take-up reel.
Tungsten carbide tooling is used to mechanically punch the tape, producing parts of the desired green size and shape. Following the tape punching process, the parts are sintered by passing them through a high-temperature tunnel kiln. The sintering process brings about several significant changes in the ceramic part: total surface area is reduced, bulk volume is reduced and strength is increased. The process produces polycrystalline, homogeneous parts having the desired physical and electrical properties.
Green scored substrates are produced in the same tape manufacturing process with reliance on specialized tooling to form the score lines in the unfired substrate. As the tool produces the substrate shape, score blades in the tooling penetrate the part surface to a controlled depth. The substrate can then be singulated by the customer at the appropriate time. Dimensional and design criteria discussed in this specification generally apply for green scoring with some exceptions. It is suggested that the customer's design department discuss specific requirements during the design phase to minimize costs. Green scoring can be an economical alternative to laser scribing. However, there is usually a tolerance trade-off due to shrinkage of the tape.
The following design standards represent factors that should be considered to ensure optimal substrate design and material selection. Material samples are available on request so that the design or process engineer can determine, by proof test, the product specifications that best fit the process needs.
- ADS-96R Thick-Film substrates are engineered to minimize as-fired resistor variations and maximize aged adhesion values. Superior resistor stability is achieved by controlling the substrates' effects on the temperature coefficient of resistance. ADS-96R is particularly well suited for small geometry, high resistor value circuitry.
- ADSR-96R Thick-Film DuraStrate™ substrates are a fine-grained material which offers over a 20% increase in strength over the standard ADS-96R. DuraStrate material is primarily used in applications requiring substrates 0.020" thick or less.
- ADOS-90R (opaque) is the alumina substrate material of choice for light-sensitive semiconductor device applications.
- ADS-995R Mid-Film™ substrates are compatible with etchable ink and photo-formed systems, have higher flexural strength, higher thermal conductivity, higher dielectric constant with lower loss, uniform density and grain size.
| 1 |
Length/Width Tolerances |
|
| |
Economy |
± 11.5% NLT ± 0.010" (±0.254 mm) |
| |
Standard |
± 1% NLT ± 0.004" (± 0.102 mm) |
| |
Premium |
± 0.5% NLT ± 0.003" (± 0.076 mm) |
| 2 |
Thickness Tolerances |
| |
Applies to thicknesses from 0.010" (0.254 mm) to 0.140" (3.556 mm) |
| |
Standard |
± 10% NLT ± 0.002" (± 0.0508 mm) |
| |
Lapping services are available for tighter tolerances. |
| 3 |
Camber Tolerances |
|
| |
Standard |
= 0.003 in./in. (= 0.003 mm/mm) |
| |
Premium |
= 0.002 in./in. (= 0.002 mm/mm) |
| |
Tighter tolerances available upon request. Lapping services are also available. |
| 4 |
Hole Diameter Tolerances |
|
| |
Hole Diameter |
Tolerance |
| |
0.015" (0.381 mm) - 0.029" (1.737 mm) |
± 0.002" (± 0.051 mm) |
| |
0.030" (0.762 mm) - 0.099" (2.515 mm) |
± 0.003" (± 0.076 mm) |
| |
= 0.100" (2.540 mm) |
± 0.005" (± 0.127 mm) or ± 1%, whichever is greater |
| 5 |
Hole-to-Hole Tolerance |
|
| |
Standard |
± 1% NLT ± 0.004" (± 0.102 mm) |
| |
Premium |
± 0.5% NLT ± 0.003" (± 0.076 mm) |
Note: NLT=not less than
| 1 |
Hole-to-hole and Hole-to-edge spacing |
| |
Under no circumstances should the resulting wall
between two holes be less than 1.5 times the thickness of the substrate. |
| 2 |
Minimum Hole Diameters |
|
| |
Substrate Thickness |
Minimum Hole Diameter |
| |
0.025" (0.635 mm) - 0.035" (0.889 mm) |
0.015" (0.381 mm) |
| |
0.036" (0.914 mm) - 0.060" (1.524 mm) |
0.020" (0.508 mm) |
| |
0.061" (1.549 mm) - 0.080" (2.032 mm) |
0.025" (0.635 mm) |
| 3 |
Tooled Corner Radius |
| |
Minimum 0.125" (3.175 mm) Radius recommended to maximize yields. |
CoorsTek offers thicknesses from 0.010" (0.254 mm) to 0.140" (3.556 mm).
The most economical thickness range is 0.025" (0.635 mm) to 0.040" (1.016 mm).
| Standard Sizes: |
| 3.5" x 3.5" (88.9mm x 88.9mm) |
| 4.5" x 4.5" (114.3mm x 114.3mm) |
| 4.5" x 6.5" (114.3mm x 165.2mm) |
| 5.0" x 7.0" (127.0mm x 177.8mm) |
| 5.5" x 6.5" (139.7mm x 165.2mm) |
The following are designed to provide engineers with design guidelines, inspection methods, and quality standards for laser machining/profiling, drilling, and scribing of CoorsTek thick-film alumina substrates. These guidelines will aid in optimizing lasered substrate design in order to meet your technical requirements cost-effectively. The illustration below depicts some of our laser capabilities.
If a lasered substrate design does not comply with these guidelines, we may still be able to offer options to your specific design requirements. CoorsTek will indicate exceptions to customer drawings and specifications should they differ from these guidelines, for the purpose of offering alternatives and possible cost reduction. We offer services in design consultation, rapid prototyping and expedited deliveries for laser scribing, machining and annealing.
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CoorsTek offers special differential scribing to enhance preferential singulation. By varying the laser pulse spacing and depth in the (x) and (y) scribe directions, the sequence of singulation may be controlled more precisely. Enhanced laser scribing helps to prevent hooking, chipping and premature breakage, which improves process yields.
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Coorstek offers machining surface for precise hole location edge definition, and to produce custom shapes and sizes.
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Annealing treatments are also available. CoorsTek offers annealing treatments to modify the microstructure of the heat affected zone (HAZ) in a laser drilled hole (reference photos immediately below) and/or to relieve any residual substrate stresses. The annealed microstructure provides an enhanced surface for metallization, thus improving via metal adhesion. The annealing process also increases the breaking force required for singulation of laser scribed substrates. Laser scribing parameters will be adjusted to result in desired singulation.
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CoorsTek offers a variety of edge finishing treatments: laser scribed, laser scribed and brushed, SilkEdge¢â substrates, SmoothEdge¢â substrates, and laser-machined substrates.
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These specifications are based on the application of statistical process control methods to determine multibeam equipment capability to a Cpk of = 1.33. Dimensional tolerances should be specified as close as necessary to facilitate process requirements and minimize cost.
Source: CoorsTek
For more information on this source please visit CoorsTek.