Operating temperature of 800°c+, high frequency and harsh environments
Ceramic Circuits
Choosing a ceramic substrate for a PCB design is becoming more popular. High maximum operating temperatures of 800°C+ allows for the much higher operating temperatures Silicon Carbide and Gallium Nitride Semiconductors can now operate at. The new DPC (Direct Plated Copper) method of production also allows for through hole plating, miniaturisation and microelectronics not possible with other methods. Ceramics are UV resistant and their inert nature also makes these substrates ideal when a hermetic package is required when no outgassing or moisture can be tolerated.
Low signal loss makes ceramics ideal for high frequency applications but the superior thermal conductivity of up to 180W/mK is often why designers are turning to ceramics.
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Advantages Over Other Technologies
Other PCB substrates such as FR4 and Metal Clad PCBs simply do not have the same heat dissipation properties of ceramics. With no isolation layer necessary components are mounted directly onto the boards making the flow of heat through the circuit much more efficient. Depending on substrate choice ceramics offer Thermal Conductivity values ranging from 24-180W/mK. This is matched by excellent CTE (Coefficient of Thermal Expansion) values.
Advantages include:
Thermal Conductivity up to 180W/mK
Hermetic packages - 0% water absorption
Excellent Coefficient of Thermal Expansion (CTE)
Low signal loss - ideal for high-frequency applications
Al2O3 (Alumina Oxide) - The most popular material is the 96% variant. This is the most cost-effective substrate and has a Thermal Conductivity of around 24W/mK. A 99.6% option is also available.
AlN (Aluminium Nitride) - When Thermal Conductivity is important this is the material to consider with a TC of around 180W/mK.
SiN (Silicon Nitride) - A choice for many automotive applications as it is more resistant to shock than other materials. It has a good bending strength and a higher fracture resistance making it ideal when structural reliability is key design factor.
Ceramic Material Specifications
Property
Unit
Al2O3 (96%)
Al2O3 (99.6%)
AlN
SiN
Thermal Conductivity
W/mK
24
29
180
85
Maximum Operating Temperature (MOT)
°C
>800
>800
>800
>800
Coefficient of Thermal Expansion (CTE)
x 10¯6/K
6.7
6.8
4.6
2.6
Dielectric Constant
-
9.8
9.9
9
9
Signal Loss
x 10¯3
0.2
0.2
0.2
0.2
Light Reflectivity
%
70/85
75
35
-
Dielectric Strength
KV/mm
≥15
≥15
≥15
≥15
Rupture Strength
Mpa
400
550
450
800
Alumina PCB (96% & 99.6%)
Alumina Oxide (Al2O3) PCB (96% & 99.6%)
The most popular ceramic with a Thermal Conductivity in the region of 24W/mK, a higher figure than the best performing Metal Clad PCB materials.
Available in two different, the 96% being the most cost effective and popular. The 99.6% variant has a higher Thermal Conductivity, in the region of 29W/mK.
Advantages
High values of Thermal Conductivity (24-29W/mK)
High operating temperatures to over 800°C
Low CTE
Suitable for high frequency applications due to low signal loss
High light reflectivity
Possibility for Hermetic packages with 0% water absorption
Technical Specifications
Download our complete design rules below. If you have different requirements, or have any questions please contact us.
If the driver in a design is high thermal conductivity then Aluminium Nitride (AlN) will be the right choice. AlN has a superior thermal conductivity of upto 180W/mK.
With its high temperature and a very low CTE makes AlN suitable for a variety of applications including Semiconductors, High power LEDs, testing and sensors.
Advantages
Superior values of Thermal Conductivity (Up to 180W/mK)
High operating temperatures to over 800°C
Very low CTE
Suitable for high frequency applications due to low signal loss
Possibility for Hermetic packages with 0% water absorption
Technical Specifications
Download our complete design rules below. If you have different requirements, or have any questions please contact us.
SiN has a high rupture strength - making it a more attractive solution for environments with high levels of vibration such as automotive.
The Thermal Conductivity value of 85-90W/mK sits between Al2O3 and AlN
High operating temperatures of over 800°C
Very low CTE
Suitable for high frequency applications due to low signal loss
Possibility for Hermetic packages with 0% water absorption
Active Metal Brazing (AMB)
Active Metal Brazing (AMB) - Ceramic PCBs
A new production method of manufacturing ceramics without metallisation is known as Active Metal Brazing (AMB)
In a vacuum, using high temperatures AMB 'brazes' the copper direct to the ceramic substrate.
AMB produces an extremely reliable substrate with unique heat dissipation properties.
The brazing method enables copper weights of up to 800µm to be produced on very thin ceramic substrates making it ideal for Power Electronics applications.
AMB Single Sided
The table below shows the copper weights that are available with the corresponding substrate thicknesses. For mechanical stability it is always recommended the copper thickness is no more than half the ceramic thickness.
AMB Double Sided
With copper both sides a higher stability and mechanical strength is achieved enabling Heavy Copper to be offered on thin ceramic substrates. The following is a guide on double sided material availability although during the etching process original copper weights can be reduced.
Active Metal Brazing Double Sided Panels
200µm
250µm
300µm
400µm
500µm
800µm
0.25mm
SiN AlN
SiN AlN
SiN
SiN
SiN
SiN
0.32mm
SiN
SiN
SiN
SiN
SiN
SiN
0.38mm
AlN
AlN
AlN
0.63mm
AlN
AlN
AlN
AlN
AlN
1.00mm
AlN
AlN
AlN
AlN
AlN
AlN
Copper Thickness
Ceramic Thickness
Ceramics - Process Methods & Capabilities
Ceramic - Thick Film
Thick Film technology involves the addition of layers of conductor (Copper or Silver) onto a Ceramic substrate via screen printing processes.
Suitable for use with Al2O3/AlN and Sapphire substrates.
A cost-effective solution with fewer manufacturing processes than other methods.
With a conductor thickness between 7-20µm it is not well suited to power electronics requiring high current capacity.
Due to conductor application it is also unsuitable for designs requiring fine tracks and/or plated/filled vias.
Ceramics - DBC (Direct Bonded Copper)
Direct Bonded Copper (DBC) is used when a high copper thickness is required - 140um (4oz)-350um (10oz). Heavy Copper.
The copper is bonded to the Ceramic substrate on one or both sides using a high-temperature oxidation process.
The copper and substrate are heated in an atmosphere of nitrogen containing about 30 ppm of oxygen; under these conditions, a copper-oxygen eutectic forms which bonds successfully both to copper and the oxides used as substrates.
The copper layers can then be etched using standard PCB technology to form an electrical circuit.
Laser drilling is then used for any through hole requirements and profile machining.
Disadvantages:
Due to the Oxidisation bonding process there can be a slight reduction in Thermal Conductivity created by a void between the Copper and Ceramic layers.
Applications:
Main applications are high power modules, like IGBT, CPV, or any other wide bandgap device modules.
IGBT
High-Frequency Switching Power Supply
Automotive
Aerospace
Solar Cell Component
Power Supply for Telecommunication
Laser Systems
Ceramics - DPC (Direct Plated Copper)
Direct Plated Copper (DPC) is the newest development in the field of Ceramic Substrate PCBs.
It involves plating the copper conductor layer to the copper substrate under high temperature and pressure conditions.
The addition of a thin titanium layer acts as a bonding interface between the copper and Ceramic layers.
A very thin layer of Copper is deposited at this stage coating the Ceramic substrate and any pre-drilled holes.
Track printing and etching is then performed with the thin Copper allowing for very fine tracks and reduced undercutting.
The panels are then plated up to the required end copper thickness.
Using this method can result in copper thickness' ranging from 10um (≈ 1/3oz) to 140um (4oz).
It also allows for the possibility of plated or filled vias. Something not possible with Thick Film or DBC technology.
Applications:
HBLED
Substrates for solar concentrator cells
Power semiconductor packaging including automotive motor control
Hybrid and electric automobile power management electronics
Packages for RF
Microwave devices
Ceramics - DPC vs DBC
Both DBC and DPC have the same advantages for high power applications, due to the use of a direct bond between Copper and the Ceramic substrate, therefore, the same key attributes for both of them are:
Outstanding Thermal Conductivity
High operating temperatures
Good mechanical strength; mechanically stable shape, good adhesion.
Excellent electrical insulation
Very good thermal conductivity
Superb thermal cycling stability
Good heat spreading
The differences come when looking at the design considerations and applications. DBC being suited to high current capacity, however limited on circuit design. DPC allowing for finer tracks and through hole connection.
Some of the surface finishes common with standard substrates such as FR4 are not suitable for ceramics. The finishes we offer are shown below. We would be happy to discuss with you further what might be a suitable finish for your boards.
Usual thickness : 0.20-0.65µm Shelf Life : 6 months
Unprotected copper will quickly oxidise which can cause soldering issues. OSP is a popular, low cost, environmentally friendly finish to prevent that oxidisation and provide an improved surface for solderability.
With PCB designs incorporating finer lines and micro vias the flatness issue of Hot Air Solder Levelling (HASL) can be an issue. ENIG is a popular alternative finish for small components, fine pitch and BGA. ENIG is also wire bondable.
Usual thickness :Nickel 3 – 6µm, Palladium is 0.05 – 0.3µm, Gold 0.05 – 0.125µm Shelf Life : 12 months
ENIG can give ‘Black Pad’ concerns on BGA. Black Pad refers to nickel corrosion on electroless nickel and gold immersion, (ENIG). It can occur when joints come under pressure and break to leave behind exposed corroded nickel, hence the name Black Pad.
ENEPIG is an upgraded version of ENIG and can defeat the Black Pad issue.
Palladium is added between the electroless nickel and immersion gold, ENEPIG results in containing a thin layer for resistance whose thickness usually falls in the range from 0.05μm to 0.1μm. The Palladium layer helps stop the immersion gold from corroding the nickel layer.
ENEPIG also has excellent wire bonding capability and reflow soldering capability.
EPAG - Electroless Palladium Autocatalytic Gold
Shelf Life : 12 months
EPAG Electroless Palladium Autocatalytic Gold is a new direct palladium surface finish process with an optional gold layer. It uses Auto-Catalytic Gold enabling a higher Gold thickness on the Electroless Palladium – so it can be used for more assembly techniques such as gold wire bonding as well as soldering therefore it is a more universal finish.
With no Nickel it is suitable for magnetic applications.
Features and benefits include:
Capable of high-density circuitry
Low temperature active steps to accommodate high frequency materials
Offers planar surface for soldering
Suitable for wire bonding of Au, Cu-Pd, Cu, Al, Ag
Used with conductive adhesives
Suitable for ceramics
Thermo compression bonding
Supports flex applications
Improved high frequency performance
Thickness < 0.2 µm allowing very fine L/S
Immersion Tin
Usual thickness :≥ 1.0µm Shelf Life : 6 months
Immersion Tin offers excellent flatness making it ideal for small components, fine pitch and BGA. The process offers good solderability and a mid-range cost.
The main area of concern with the process are ‘tin whiskers’ and it is a aggressive to soldermasks meaning a larger than normal soldermask dam is needed. It is also is very sensitive to handling meaning gloves must be used.
Immersion Silver
Usual thickness :0.12 – 0.4µm Shelf Life : 6 months
Silver has excellent conductivity and surface of silver is smooth and solderable, beneficial to signal transmission integrity. Like Tin, the flatness makes it ideal for small components, fine pitch and BGA. However, it is very sensitive to handling and can tarnish quickly meaning special packaging required and unused boards resealed quickly.
Frequently Asked Questions
Why should I consider a Ceramic PCB?
The main benefits of using ceramics is heat management. Ceramics are also specified for high frequency applications due to the low signal loss. Many high-power packages require substrates that can sustain high operating temperatures. Ceramic substrates from TCL feature high Thermal Conductivity values of up to 180W/mK and a maximum working temperature of over 800°C. They also offer advantages for hermetic applications because of their 0% water absorption and extremely low CTE (Coefficient of Thermal Expansion).
What Thermal Conductivity can I expect from a Ceramic substrate?
Depending on the ceramic substrate you choose thermal conductivity is available between 24-180W/mK
What type of ceramic substrate is most common?
Al2O3 (Alumina Oxide) - 96% is the most common substrate and a very cost-effective option and has a Thermal Conductivity of around 24W/mK.
What advantages does AlN (Aluminium Nitride) offer?
When Thermal Conductivity is the main consideration, AlN (Aluminium Nitride) is frequently chosen. It is the ideal choice for systems with high thermal demands because of its Thermal Conductivity of 180W/mK.
Why is SiN (Silicon Nitride) often used in automotive applications?
SiN (Silicon Nitride) is more shock-resistant than other substrates due to its increased fracture toughness and bending strength. As a result, it is an excellent option for automotive applications where structural durability is crucial.
What distinguishes the DBC and DPC ceramic production method?
DPC. The most recent advancement in the field of Ceramic Substrate PCBs is Direct Plated Copper (DPC). This production technique can produce copper thicknesses ranging from 10µm ( 1/3oz) to 140µm (4oz). After a procedure known as vacuum sputtering bonds a thin layer of copper on the substrate, the copper is plated up to the desired thickness and the PCBs are then etched. With this method we can produce fine tracks, excellent tolerances and through hole plated holes.
DBC. The traditional method of ceramic circuit production is Direct Bonded Copper (DBC). It is often used when a high copper thickness is required, often between 140µm (4 oz) and 350µm (10oz). A high-temperature oxidation method is used to bond the copper to the ceramic substrate on either one or both sides. The copper circuit is achieved by conventional PCB fabrication techniques to etch away unwanted copper. However, depending on the required copper weight, this production method may limit track widths and gaps due to etch tolerances. Through hole plating is not available with DBC.
Is there a size restriction for ceramic circuits?
Standard production panel sizes are 115 x 115mm but special panels can be used up to 170 x 250mm. After allowing for tooling the usable area from these panels is 105 x 105mm and 160 x 240mm.
What copper surface finishes are available for ceramic circuits?
HASL is not suitable, so the finishes available are: ENIG/ENEPIG/EPIG/Immersion Silver/Immersion Tin and OSP.
What are the main reasons PCB engineers are specifying Ceramic PCBs?
High Thermal Conductivity of up to 180W/mK, operating temperatures of the substrates of over 800°C, low CTE (Coefficient of Thermal Expansion) low signal loss for high frequency applications and 0% water absorption for Hermetic packages.
What is the production method Active Metal Brazing (AMB) for Ceramic circuits?
AMB uses a unique production method where the copper is directly attached (brazed) to the ceramic substrate in a high temperature vacuum. AMB enables copper weights of up to 800µm on thin ceramic substrates. It is ideal for Power Electronics applications.
What copper thickness can be achieved on ceramic circuits?
Using traditional DBC substrates copper to 350µm is available. With DPC we have manufactured panels to 1100µm.
If I specify a standard Solder Resist on ceramics, what temperatures will they tolerate?
For standard solder resists 130°C is maximum long-term exposure. For assembly, as a minimum, all Solder Resists used pass IPC thermal stress test; 3 times, 288°, 10 seconds.
Can a high temperature Solder Resist be used on ceramics?
We can offer a Glass Glaze Solder Mask that can be used at temperatures of up to 500°C. However, this resist is only suitable for silver paste on Alumina (Al2O3). It is not suitable for DBC or DPC construction.
I normally buy PCBs in a panel form and de-panel them after assembly? Can I do the same for ceramic circuits?
We can supply a panel of ceramic circuits, but the vast majority of our customers ordered singles. The reason for this is ceramics are more brittle than other substrates such as FR4. If required, we can supply laser cut v-score panels for careful manual break-out of the circuits after assembly. If you require non scored panels, then a laser or depaneling machine with a diamond blade should be used.
What is the lowest temperature a Ceramic PCB can be subject to?
Ceramic PCBs can be used at a very low temperature. We have manufactured boards without a solder resist or ident for use in a cryogenic chamber at -223°C.
I need different copper thicknesses on a ceramic circuit, can this be achieved?
It can. The DPC method of production can be utilised to produce different thicknesses of copper in selected areas. This can be useful if you need thin copper for a control section and thick copper for a power section on the same layer.
Rather than use an ident, can I have laser scribed information on a ceramic circuit?
A laser is used for drilling and routing ceramic circuits so this can be used for scribing. This is useful if outgassing is a consideration and conventional idents cannot be used.
In my DPC ceramic circuits can I have plated and filled vias that are flat and dome free?
No, the production method is irrelevant. This is because the roughness of the copper surface is determined by the polishing process after plating. For some products with strict requirements on surface roughness (such as LED, Ra< 0.3µm and Rz< 2µm), our factory will use polishing equipment to treat the copper surface after plating to reach the requirements of low roughness. Therefore, the same roughness requirements can be achieved for both DPC and DBC processes.
Populated with LEDs
Silver Paste Conductor with ENIG Surface Treatment
Populated with LEDs
Silver Paste Conductor with ENIG Surface Treatment
Immersion Tin Panel
Alumina Oxide Al203
Direct Bonded Copper
Alumina Oxide Al203
AIN Used For LED Products
Saphire Alumina 0.4mm 2 Layer Silver Conductor
Alumina 0.5mm Silver Fin
