The Unique Capabilities and Advantages of Pressure Infiltrated Casting
AFT's Composites Division
has been making great strides in metal composites development and manufacturing—especially in the Pressure Infiltrated Casting™ (PIC) process. Able to deliver products with tight tolerances, high thermal conductivity, tailored coefficient expansion, reduced weight and high stiffness, PIC's current core capabilities include net-shaped reinforced components—mainly AlSiC (Silicon Carbide Reinforced Aluminum). Other materials, such as graphite reinforced aluminum and diamond reinforced aluminum, which are used in applications where very high heat dissipation is required, have also recently been developed.
Net-Shape Casting
The ability for net-shape thin plate casting is one of the fundamental advantages of the PICmanufacturing process.
AlSiC
base plates from 0.050" thin to 0.2" thick and as large as 11"x7" have been produced for a variety of applications. Net-shaped parts are produced by infiltrating pre-forms which contain all the details of the finished part within a casting mold system. The casting molds are designed not only to contain the pre-forms, but to form the desired thickness of the aluminum skin and all the dimensions of the final part. As-cast parts can easily meet +/- 0.003" in length and width.
Plating and Coating
Metal skin on a finished product is a characteristic of the PIC process. The pure metal skin allows the part to be plated or finished as though it were an aluminum metal part. Cast parts fabricated using the PIC process can be plated using traditional aluminum plating techniques and coated with various specialized coatings. Ni and Ni/Au plating are utilized when AlSiC parts are soldered to other electronic components. Cu base thermal spray coatings are also suitable for specific solder alloys. Chemical film coatings are suitable for epoxy bonding. Since the coatings cost less than the Ni plating, these coatings easily replace Ni plating in applications where the parts will be exposed to mildly corrosive environments. Furthermore, skinless parts can also be produced with PIC.
In Situ Bonding
Another advantage of the PIC process is the ability to bond a variety of formerly un-bondable materials. Titanium, iron-based alloys and ceramics have all been cast in situ using the PIC process. The figure below shows a hermetically sealed AlSiC electronic package with a Ti seal ring that was bonded in situ during the PIC process. An optical micrograph from a polished section of an in-situ formed AlSiC/Ti seal ring interface and welded Ti lid/Ti seal ring interface are also illustrated. The aluminum alloy in the joint is similar in chemical composition to the AlSiC matrix and the aluminum skin covering the composite. There is no discontinuity such as cracks or porosity at the aluminum/AlSiC interface and the aluminum/Ti interface.
Figure 3. Laser sealed AlSiC package, (left) and an optical micrograph
illustrating an AlSiC-Titanium joint and a Ti lid/Ti seal ring weld.
Due to the matched CTE of AlSiC and titanium, a Ti seal ring can be joined to AlSiC composites with minimal post-fabrication stress. A Ti lid can then be welded to the Ti seal ring utilizing laser welding. The high thermal conductivity of AlSiC makes it necessary that the interface temperature remains below the melting temperature of aluminum alloy during laser welding process. As a result, there is no change expected in this interface during the welding process. Laser sealed AlSiC packages produced with Ti seal rings maintain the hermetic integrity after 1,100 thermal cycles between -55 and 125ºC.
Let Your Design Ideas Run Wild
Exceptional design flexibility is a major benefit of the PICprocess. Pressure Infiltrated Casting by AFT Composites gives engineers the freedom to explore new opportunities in the design of thermal management solutions.
Pressure Infiltrated Casting offers manufacturers a broader range of options than ever before. For more information about PIC and
AFT's Composites Division, contact Matt Napier, PCC-AFT Composites Sales and Marketing Manager, at 303-833-6155 or via e-mail at mattn@pcc-aft.com.
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