What is a Ceramic PCB?
A ceramic printed circuit board is a PCB manufactured with copper directly on a ceramic substrate rather than a common alternative such as FR4. Ceramic substrate choices include Al2O3 (Alumina Oxide), AlN (Aluminium Nitride) and SiN (Silicon Nitride).
Why use ceramic PCB?
Heat management and high frequency applications due to low signal loss are the main advantages of using ceramics. For heat consideration, many high-power packages have the need for substrates that are capable of withstanding high operating temperatures. Ceramic substrates from DK-Daleba have a maximum operating temperature of over 800°C together with high Thermal Conductivity values of up to 180W/mK. They also have a very low CTE (Coefficient of Thermal Expansion) and offer advantages for Hermetic packages with their 0% water absorption.
What is the Thermal Conductivity of Ceramic substrates?
24-180W/mK - depending on the material chosen.
What is the most popular Ceramic substrate?
Al2O3 (Alumina Oxide) - the 96% is the most common substrate and a very cost-effective option and has a Thermal Conductivity of around 24W/mK. A 99.6% option is also available.
What are the advantages of AlN (Aluminium Nitride)?
AlN (Aluminium Nitride) is often the choice when Thermal Conductivity is the driver. With a Thermal Conductivity of around 170W/mK it is the best option for highly demanding systems.
What are the advantages of SiN (Silicon Nitride) for automotive applications?
SiN (Silicon Nitride) has a higher fracture toughness and bending strength than other substrates making it more resistant to shock. It is therefore a good choice for automotive applications where structural reliability is key.
What is the difference between DBC and DPC ceramics?
Direct Bonded Copper (DBC) is normally used when a high copper thickness is required - 140um (4oz)-350um (10oz). The copper is bonded to the Ceramic substrate on one or both sides using a high-temperature oxidation process. Traditional PCB production methods are used to etch away the unnecessary Copper. Due to etch tolerances however this can put a limitation on track widths and gaps depending on the copper weight required. through hole plating is not available with DBC.
Direct Plated Copper (DPC) is the newest development in the field of Ceramic Substrate PCBs and using this method can result in copper thickness' ranging from 10um (≈ 1/3oz) to 140um (4oz). This method involves plating up the copper to the final thickness. The PCBs are etched after a process called Vacuum Sputtering deposits a thin layer of Copper on the substrate. Due to the copper being thin at this stage we can achieve tight tracks and good tolerances with this method regardless of the finished copper weight. After etching, the boards are plated up to the final required copper thickness. DPC allows for plated through-holes to be included in the design.
What panel sizes are offered for ceramic circuits?
Master panel sizes are 115 x 115mm but special panels can be used up to 170 x 250mm.
After allowing for tooling the usable areas are 105 x 105mm and 160 x 240mm respectively.
What finish options are offered for ceramic circuits?
For ceramics ENIG/ENEPIG/EPIG/Immersion Silver/Immersion Tin and OSP finishes can be applied.
What are the main advantages of a Ceramic PCB?
Maximum operating temperatures of the substrates of over 800°C, high Thermal Conductivity of up to 180W/mK, very low CTE (Coefficient of Thermal Expansion), 0% water absorption for Hermetic packages, low signal loss and fine microcircuit applications with the DPC production method.
What is Ceramic Active Metal Brazing (AMB)?
Unlike other methods of substrate manufacturing DBC Active Metal Brazing (AMB) forms the substrates without any metallisation. Instead under a high temperature vacuum the copper is joined (brazed) direct to the ceramic base.
What copper thickness is available for ceramic circuits?
Using traditional DBC substrates copper to 350µm is available. The new Active Metal Brazing (AMB) substrates enables copper weights of up to 800µm on ceramics as thin as 0.25mm. DPC allows different copper thicknesses on selected areas of a single layer. We have manufactured a DPC panel with 1100µm copper.
What temperatures will standard Solder Resists tolerate?
130°C is maximum long-term exposure for solder resists. For assembly, as a minimum, all Solder Resists used pass IPC thermal stress test; 3 times, 288°, 10 seconds.
Is a high temperature Solder Resist available?
We can offer a Glass Solder Mask that can be used at temperatures of up to 500°C. At such a high temperature copper conductors will quickly oxidise unless the product is to be used in a vacuum making glass masks only suitable for silver paste or other high temperature conductors.
Can you supply whole a panel of ceramic circuits which we could then depanel ourselves after assembly?
Yes, but most customers choose to purchase single circuits. This is because ceramics are more brittle than other substrates such as FR4. However, we can supply laser cut v-score panels for careful manual break-out of the circuits after assembly. If non scored panels are required, then a depaneling machine with a diamond blade should be used.
What is the minimum temperature that Ceramic PCBs can be subject to?
Low temperatures have little effect on ceramic PCBs but we would always recommend specific environmental tests prior to order. A Daleba customer has been using Al2O3 at minus 269°C. Extreme low temperatures are not suitable for boards with Solder Resist or Ident.
Can you produce a ceramic circuit with different thicknesses of copper?
Yes. With the DPC production method a circuit can be manufactured with different thicknesses of copper in selected areas. You could therefore have a control section and a power section on the same layer.
Can you laser scribe an ident in a ceramic circuit?
Yes. If outgassing is a consideration customers will request no ident is used on the ceramic panels. In those circumstances we have laser scribed ident information into the non-copper areas of the ceramic panels.
Can you offer plated and filled vias for ceramic circuits that are flat and dome free?
Yes, using DPC we can offer plated and filled vias with a flat and dome free finish. The design rule for the plating process to succeed is the thickness of the surface copper should be equal or greater than the radius of the via that needs to be filled. As an example, a 0.2mm via will need 0.1mm (100µm) of copper, so in this case the conductor copper weight needs to be, equal to or greater that, 100µm. We would use 3oz (105µm) copper in this example.
For ceramics, is it true the surface roughness can be different between DBC and DPC?
No. 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< 0.3um and Rz< 2um), 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.
Can a surface finish be selectively applied?
We can selectively add a PCB surface finish to specific areas of the copper. This would be achieved using a dry film mask. ENIG is the recommended finish for selective plating as Silver and other finishes containing Palladium can react with the dry film.