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| Tiny ceramic caps, each as thin and as small as a fingernail, provide critical protection for sensitive electronic components in the radio frequency (RF) and microwave industries. |
Tiny ceramic caps, each as thin and as small as a fingernail, provide critical protection for sensitive electronic components in the radio frequency (RF) and microwave industries, creating a sealed enclosure that protects components from dust, moisture and other contaminants. The protective caps, also called “lids,” are constructed of high purity Alumina ceramic from the GBC Materials business of Morgan Advanced Ceramics (MAC) located in Latrobe, PA.
“The cap is actually an assembly, consisting of a ceramic lid and an epoxy preform,” explains Ed Dougert, the Director of Operations at North Penn Technology, Inc., (NPT) of Hatfield, PA, which provides epoxy film for this application. “We take epoxy in sheet form and die cut it, then we apply the epoxy preform to the lip of the ceramic cap. Our customers take the ceramic/epoxy assembly and bond it to the semiconductor package, creating a robust enclosure surrounding their sensitive components such as gold-metalized, silicon power transistors.”
Ceramic Armor
NPT utilizes GBC-96% Alumina, a formulation of aluminum oxide (Al2O3) from GBC Materials that is 96% pure. GBC-96% Alumina is ideally suited for the ceramic caps application because it is mechanically strong and dimensionally stable. GBC Materials fires the material at a high temperature to ensure that it is fully sintered, ensuring 0.0% porosity, to provide an air-tight seal.
The caps themselves are quite small, with dimensions ranging from 0.160 to about 0.500 inches. The width of the lip ranges from only 0.020 to 0.040 inches, depending on the customer’s specific design. To ensure proper alignment with the epoxy preforms, the ceramic caps need to be manufactured to tolerances of ±0.005 inch.
“One of the advantages of GBC-96% Alumina is the extremely smooth, hard surface,” explains Dougert. “We cannot have chipped edges and small cracks on the thin lip. The strong, smooth surface and consistent dimensions enable a robust bond and a tight seal, using epoxy film that is only 0.003 or 0.005 inches thick.”
Specialized Epoxy
NPT offers epoxy film which closely matches the coefficient of thermal expansion of the Alumina ceramic caps. Die cutting the soft and thin epoxy material is no easy challenge, especially for the small sizes and the large quantities required.
The specially developed MEG-150 and MEG -165 Epoxy Film from NPT provides excellent adhesion to metal, glass and plastics, with high shear, peal and cleavage strength over a wide temperature range.
Creating a Permanent Bond
The final step is to bond the ceramic/epoxy assembly to the semiconductor package. The epoxy is cured in a seal and bake over, or a sealing machine. For example, Polyfet RF Devices, of Los Angeles, CA, purchases the ceramic/epoxy assemblies from NPT, and bonds them to its RF devices in an Isotherm System (ITS).
The ceramic/epoxy caps typically require curing time of 60 minutes at 165-175°C, under 5 to 50 PSI. Polyfet claims to have a 99.9% success rate with proper alignment and Fine/Gross leak testing. When applications require hermetic seals, pressure die absorption tests are used for seal verification (by customers).
Customers Can’t Wait
NPT has been supplying the ceramic/epoxy caps since 1999, when it acquired MEG Products, Inc., with its competence in epoxy film die cutting. The ceramic/epoxy caps complement NPT’s expertise in providing mechanical services and parts required for robust semiconductor packages utilized in aircraft, missiles and satellites, for companies such as BAE Systems and Bell Helicopter.
In addition to Polyfet, NPT also supplies the ceramic/epoxy caps to Microwave Technology Inc., Microsemi Power Products Group, Semelab plc, and Hittite Microwave Corporation. The caps protect components used in medical, avionics, radar, and telecommunications equipment.
“We supply the premiere players in our industry,” explains Leslie Northcut, the NPT sales manager. “They demand high quality, rugged products for their military and aerospace customers. We need to work closely with GBC Materials to quickly delivery the ceramic/epoxy caps, sometimes with as little as a week lead time. With our expertise in handling epoxy film, and GBC Materials’ expertise in precisely manufacturing tiny ceramic caps, we continue to be the company that our industry relies on for this highly specialized component.”
This special expertise of North Penn Technology and GBC Materials will become increasingly critical to the RF and microwave industries, as these companies design and deploy ever smaller and more powerful semiconductor packages, driven in part by the migration to LDMOS (laterally diffused metal oxide semiconductor) transistors.