FAQ

Our MCPCBs (Metal Clad Printed Circuit Boards) are comprised of a number of core processes/materials

  • Aluminium alloy – for 1mm and thinner we use 6061-T6 and for 1.5mm and thicker 6082-T6. (For the aluminium and copper we use numbers from MatWeb.com in our thermal models)
  • Nanotherm ceramic – Aluminium oxide dielectric formed on surface of Al alloy to provide a highly thermally-efficient dielectric
  • “RCC” (resin-coated Cu) – this is the Cu tracking metal layer (1oz – 35um) with extremely thin epoxy adhesive layer (see Q x below). Eloctroplating Cu can be added for thicker tracks
  • Solder mask – typically Tayio LEW-3 or Electropolymers EMP110.  However other options are possible.The manufacturer should be able to provide numbers for your thermal model
  • Pad Finish – a number of options available including ENIG, IAg, ENPIG, OSP, HASL dependant upon your soldering/performance requirements.

Certain combinations of MCPCB “stack” are UL approved and carry our UL approval mark. Please check with us directly for your specific combination.

The adhesive is used to attach the copper foil to the surface of the Nanoceramic.  In a conventional MCPCB, the epoxy is the dielectric, which is why it needs to be thick and consequently acts as a barrier to heat transport.  In a Nanotherm LC MCPCB the Nanoceramic is the dielectric and the epoxy is just and extremely thin glued joint.

The Nanoceramic dielectric is typically around 22um thick.

The thermal resistance value for Nanotherm LC that we quote (0.31C.cm2/W) is from the top side of the copper to the underside of the aluminium, so includes all interfaces in the stack.  This value is verified by laser flash (NPL), T3ster (Mentor Graphics) and Searle’s bar methods and agrees with finite element models (LISA). 

The parallel plate capacitor formed between the copper trace and the aluminium plate in both Nanotherm DM and LC can result in significant current flow with AC applied or high slew rate DC waveforms.  The capacitor current must be taken in to account in the circuit design and test method used.

Current carrying abilities of copper traces on Nanotherm DM and LC can be obtained from standard first principles formulae and a good fit is obtained.  However, the easiest method is to use a calculator for surface tracks on FR4 (20C permitted rise) and multiply the result x30 for Nanotherm LC and x50 for Nanotherm DM.

No. Due to the nanocrystalline structure of the ceramic, the ceramic is actually flexible and can therefore withstand both a bending stress and being held in compression indefinitely.

Using aluminium alloy for the substrate is 6082-T6 (1.5mm and thicker) or 6061-T6 (1mm and thinner), is best because they allow for excellent stiffness and are readily available in sheet form.  Our process will work with most wrought aluminium alloys, including 1000 series, should the thermal requirement override the mechanical properties.  Casting alloys can also be coated, but we have to be circumspect on the exact permutation and concentration of alloying elements that are allowable, so requires consideration on a case-by-case basis.

Aluminium metal is an excellent thermal conductor.  Furthermore, it is relatively low cost, lightweight, easily machined and readily available in sheet form.  For truly demanding applications, it is possible to purchase MMCs with copper cores, but the performance gain is small and price premium eyewatering.

The unconstrained surface expansivity of a Nanotherm MCPCB is 22ppm/k.  The value does not change significantly over the normal temperature range for which electronic components are specified for assembly and operation.

The adhesive used in the construction of Nanotherm MCPCB does not exhibit a classic Tg; it is flexible even at room temperature.  The recommended maximum sustained operating temperature in service is 130C.

The elastic modulus of the Nanoceramic dielectric is in the region of 210GPa (+/-60GPa) with around 20-25% elastic recovery.  The modulus of the adhesive has not been measured directly.  Applying the Hashim-Shtrikman model and average of bounds criteria for the constituents, 50GPa is obtained.  Both values are for room temperature, and the dependency on temperature has not been measured.

Nanotherm MCPCB materials are fabricated using RoHS compliant materials. Our proprietary electro chemical process for converting the aluminium into an alumina oxide uses a chemical formulation which is safe to the environment being no more impactful than the waste water from a dishwasher cycle.  

Our electro chemical process can be adapted to other aluminium alloys, but our standard  offerings are 6000,5000 and 1000(DM only) series.  The process can also be used with the so called “valve” materials such as magnesium.

Yes.  Nanotherm’s core process and product applications are protected by an intellectual property portfolio with coverage in all major international markets. 

Values are generally needed for thermal conductivity, expansivity and modulus.  These are quite a challenge to measure because the nanoceramic only exists as a thin film attached to a thick aluminium plate.  Thus far we have not been able to obtain a value for the CTE since, when attached to the aluminium, it is totally dominated by the metal.  The unconstrained surface expansivity is 22ppm/k.  For the film itself, a value of 8ppm/k is probably a good a guess as any.  Initial results, which are likely to be revised, are that the elastic modulus is in the region of 210GPa (+/-60GPa) with around 20-25% elastic recovery (Nano indentation method).  The thermal conductivity is 7.3 W/mK (laser flash method) and isotropic; this figure was derived by back-calculation and therefore includes the thermal interface resistance between the nanoceramic and base aluminium.  Typical nanoceramic thickness is 22+/-1um (eddy current method – by SEM its better expressed as 22um with Ra 0.7um, Rz 3-4um).

A feature of Nanotherm’s electro chemical process, is that it is a true 3D process, as the form ed oxide layer follows the surface features of the core material. Further the process is “self levelling” so all the aluminium exposed to the process will be coated evenly, ensuring that there are no uncoated areas in any axis of the part. 

Nanoceramic is not a true dielectric, but closer to a semiconductor.  Application of any potential will cause current to flow, albeit a very small one.  The relationship between potential and current is non-linear.  When the potential is sufficiently high the current avalanches and breakdown occurs.  When attempting to measure the intrinsic resistance of the dielectric, care must be taken to exclude the capacitor charge current, due to the parallel plate capacitor existing between the copper net and the aluminium substrate.