AlSiC Hermetic Packaging

CPS AlSiC-9 Hermetic Packaging in production

AlSiC at about 63 volume percent SiC (CPS AlSiC-9) provides similar thermal management to traditional thermal management materials like Copper Molybdenum (CuMo) and Copper Tungsten (CuW).  All these materials have thermal conductivities (measured at room temperature) of about 200 W/mK and instantaneous thermal expansion coefficients of about 7 -8 as measured at room temperature.   

CoMo and CuW are traditionally used in military applications, these materials we an answer to Kovar that has a low CTE, but is not a good thermal dissipation material as it has a low thermal conductivity (~ 20 w/mK).   These applications include radar Tx/Rx modules, optical communications and also power conversion modules.  Application of these materials is primarily for reliability, and are used to enclose the electronics from the outside environment  and are hermetic to 10x 10^8 cc/sec He Leak up rate or better (MIL STD-883, method 1014).  Also the AlSiC HP is compliant with MIL-PRF-38534 subgroups 1-4 and 6. To get signals into and out of the package there are glass or ceramic isolated pins that are also hermetically sealed in the wall.  As a result Hermeticity requirement these packages are typically referred to as "Hermetic Packages" (HP).

The difference between the traditional HP materials is that AlSiC has a very low density of 3 g/cc and Kovar, CuMo and CuW have densities around values of 9, 16 and 18 g/cc respectively.  AlSiC is therefore more appropriate in weight sensitive or shock and vibration applications as compared to the traditional HP materials.

CPS AlSiC-9 base alloy 49 sealring with brazed ceramic feedthrus

The solution to use AlSiC in these applications, and make it transparent to the customer's down stream processing, is to make a composite package consisting of an AlSiC base with an Alloy 48 seal ring.  In this configuration, the AlSiC package can be conservatively 40 to 60% the weight of the traditional package.   

Alloy 48 seal ring is an Iron Ni Alloy that is similar to Kovar.  It can be integrated with either brazed ceramic feedthroughs or sealed with glass feed throughs, and can be plated using standard plating processes.  Additionally the Alloy 48 seal ring can be sealed by solder, brazing or laser welding processes used today with standard hermetic packaging. 

CPS AlSiC-9 Material Properties

Another advantage is over traditional HP materials is that that AlSiC can be provided in traditional HP sheet stock thicknesses at a lower cost.  Thickness is not a limit with AlSiC and the manufacturing casting process can provide thicker functional shapes, pedestals, cavities walls and without costly machining as is necessary with the traditional HP materials. 


For more information on AlSiC please visit AlSiC-Hermetic-Packages, and for a summary on AlSiC Hermetic Packaging capabilities please see the Data Sheet.  Also CPS manufactures standard Hermetic Packaging too.  If you need to speak to someone on this subject pleas call Cheryl Oliveira at 508-222-0614 x247 or e-mail coliveira@alsic.com.

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